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Linkage and crossing over - class-XII

Description: linkage and crossing over
Number of Questions: 79
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Tags: inherited changes genetics and evolution biology botany chromosomal basis of inheritance
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Genes on same chromosome can be

  1. Linked

  2. Homologous

  3. Autosomes

  4. Identical alleles


Correct Option: A
Explanation:
  • When two genes are close together on the same chromosome, they do not assort independently and are said to be linked and will segregate together during meiosis, producing only two kinds of gametes. Whereas genes located on different chromosomes assort independently and have a recombination frequency of 50%, linked genes have a recombination frequency that is less than 50%.
  • Hence Genes on the same chromosome can be Linked.
  • So, the correct answer is 'Linked'.

The number of linkage groups in a cell having 10 pairs of chromosomes are

  1. 5

  2. 10

  3. 15

  4. 20


Correct Option: B
Explanation:

The total number of linkage groups in an organism equals to the number of autosomes in its haploid cell. The cell has ten pairs of chromosomes which means that the number of autosomes in its haploid cell is 10. Hence, total number of linkage groups will be 10 provided all the genes are mapped. Correct answer is B.

Linked gene are separated by

  1. Crossing over

  2. Mutation

  3. Both A and B

  4. Mitosis


Correct Option: A
Explanation:

Recombination can occur between any two genes on a chromosome, the amount of crossing over is a function of how close the genes are to each other on the chromosome. If two genes are far apart, for example at opposite ends of the chromosome, crossover and non-crossover events will occur in equal frequency. Genes that are closer together undergo fewer crossing over events and non-crossover gametes will exceed than the number of crossover gametes.

Maize has $10$ pairs of chromosomes. How many linkage groups does it have?

  1. $20$

  2. $10$

  3. $5$

  4. $40$


Correct Option: B
Explanation:
The total number of Linkage groups in an individual is equal to their total number of haploid sets of chromosomes.
Haploid number of chromosome = Linkage groups
In Maize there are 10 linkage groups, since 10 haploid chromosomes.
So, the correct answer is '10'.

A linkage group is defined as

  1. All the linked genes of a chromosomal pair

  2. Different groups of genes present on different chromosomes

  3. All the genes located on the same chromosome

  4. None of the above


Correct Option: A
Explanation:
Linkage group, in genetics, all of the genes on a single chromosome. They are inherited as a group; that is, during cell division they act and move as a unit rather than independently.
So, the correct answer is 'All the linked genes of a chromosomal pair'.

The blue green algae and bacteria contain.

  1. One linkage group

  2. Two linkage groups

  3. Three linkage groups

  4. None of the above


Correct Option: A
Explanation:

All the genes which are located on a single chromosome form one linkage group. The total number of linkage groups in an organism corresponds to the haploid number of chromosomes, i.e., to the number of chromosome pairs.

  • Most bacteria have a genome that consists of a single DNA molecule (i.e., one chromosome).
  • The blue-green algae is a cyanobacterium that possesses one chromosome.

So, the correct answer is 'One linkage group'.

Which of the following statements is not true of two genes that show 50% recombination frequency ?

  1. The genes may be on different chromosomes

  2. The genes are tightly linked

  3. The genes show independent assortment

  4. If the genes are present on the same chromosome, they undergo more than one crossovers in every meiosis.


Correct Option: B
Explanation:

The genes that are not tightly linked to each other do not show 50% of recombination frequency. Genetic linkage is the process in which genes are located close to each other on chromosomes are inherited together. When 2 genes are located far from each other or are located on different chromosomes have 50% of recombination rates.

So, option B is the correct answer.

What is not true of two genes that show $50\%$ recombination frequency?

  1. They undergo more than one crossovers in every meiosis

  2. The genes are present on different chromosomes

  3. The genes are tightly linked

  4. The genes show independent assortment


Correct Option: C
Explanation:
The tightly linked genes on chromosomes show 100% parental types and 0% recombinants. Two genes that undergo independent assortment indicated by a recombination frequency of 50% are either on non-homologous chromosomes are located far apart on a single chromosome. As the distance between two genes increases, crossover frequency increases. More recombinant gametes, fever parental gametes.

So, the correct answer is 'The genes are tightly linked'.

Which of the following will not result in variations among siblings? 

  1. Independent assortment of genes

  2. Crossing over

  3. Linkage

  4. Mutation


Correct Option: C
Explanation:

Independent assortment leads to separation of genes and is a violation of genetic linkage. Crossing over leads to exchange of fragments between two homologous chromosomes and results in the formation of chiasmata. The mutation is sudden lethal changes in a chromosome or genetic material that is often lethal. SO, all of these result in variations in genetic material.

Linkage means forming a group of genes together. So, option C is the correct answer.

All genes located on the same chromosome:

  1. From different groups depending upon their relative distance.

  2. Form one linkage group.

  3. Will not from any linkage groups.

  4. Form interactive groups that affect the phenotype.


Correct Option: B
Explanation:

 Linkage group is a group of a linked gene on the same chromosome and corresponds to the genome of an organism.

So, the correct option is 'Form one linkage group'.

A condition where an individual heterozygous for two pairs of linked genes (AaBb) possesses the two dominant genes on one homologous chromosome pair and two recessive on the other, it is said to be

  1. Cis-arrangement

  2. Trans-arrangement

  3. Partly cis partly trans

  4. More than one option is correct


Correct Option: A
Explanation:

A.cis – arrangement - two dominant alleles linked on one chromosome is called cis arrangement of genes.

B.Trans arrangement – two dominant alleles present on different chromosomes is called trans arrangement of genes

C.Partly cis partly trans – dominant alleles partly present on same chromosomes and partly present on different chromosomes.

So, the correct option is ‘cis arrangement’.

The presence of continuous phenotypic variation in an $F _2$-generation suggests that a character is inherited by?

  1. Gene linkage

  2. Epistasis

  3. Polygenic inheritance

  4. Recombination


Correct Option: A

Number of linkage groups in Pisum sativum is 

  1. 2

  2. 4

  3. 7

  4. 8


Correct Option: C
Explanation:

The garden pea, Pisum sativum was the model system used by Gregor Mendel to formulate his famous Mendel's laws. But the characters used by Mendel have been since shown to be controlled by genes belonging to different linkage groups or to distant parts of the same linkage group. Thus, Mendel failed to observe the phenomenon of linkage. Instead, linkage was first described and interpreted by Thomas Morgan in his works with Drosophila. Linkage in pea was first described in 1912 by Vilmorin and Bateson. Thus if the history of pea genetics begins with the Gregor Mendel, the history of the pea linkage map begins much later. There are seven linkage groups in pea; present on chromosomes 1, 6, 5, 7, 3, 2 and 4 respectively. So, the correct answer is '7'.

Number of linkage groups in Drosophila are

  1. 4

  2. 8

  3. 6

  4. 10


Correct Option: A
Explanation:

Linkage: Tendency of the genes located on the same chromosome, to stay together in hereditary transmission is known as linkage. The genes located on the same chromosome are called as linked genes. The principle of linkage was discovered by Bateson and Punnet in 1906 in the sweat pea plant, Lathyrus odoratus. However, linkage as a concept was put forth by Thomas Hunt Morgan in 1910 based on his experiment on Drosophila melanogaster. It has 4 linkage groups.

Coupling and repulsion hypothesis was given by

  1. Bateson and Morgan

  2. Morgan and Punnet

  3. Bateson and Punnet

  4. Morgan and Miller


Correct Option: C
Explanation:

Bateson explained the lack of independent assortment by means of a hypothesis known as coupling and repulsion hypothesis. Although coupling and repulsion were discovered later to be the aspects of same phenomenon. It is called as linkage, the terms coupling phase and repulsion phase are still considered to be useful terms in scientific literature. Bateson and Punnet proposed that the F$ _{1}$ had actually produced more dominant and recessive gametes in sweet pea cross than would be produced by Mendelian independent assortment. Because these genotypes were the gametic types in the original pure lines, the researchers thought that physical coupling between the dominant alleles P and L and between the recessive alleles p and l might have prevented their independent assortment in the F$ _{1}$. However, they did not know what the nature of this coupling could be.

Mendel failed to discover linkage because seven characters chosen by him were

  1. On 4 chromosomes on which they were closely placed

  2. On 4 chromosomes far apart

  3. On different seven chromosomes

  4. On different two chromosomes


Correct Option: B
Explanation:

Mendel studied 7 characters in pea plant. The genes for these characters were located on 4 chromosomes. Mendel was lucky enough as none of the genes showed linkage and assorted independently. This is because the genes studied were located far apart on the same chromosome and thus, expressed independently. 

Which statement is incorrect about linkage?

  1. It helps in maintaining the valuable traits of new varieties.

  2. It helps in forming new recombinants.

  3. Knowledge of linkage helps the breeder to combine all desirable traits in a single variety.

  4. It helps in locating genes on chromosome.


Correct Option: B
Explanation:

Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together. Linkage of genes in animals and plants is seen as deviations from independent segregation; recombination seen as deviation from complete linkage.
More linkage between genes, lesser will be the recombination frequency.

Mendel did not include in his laws

  1. Segregation

  2. Dominance

  3. Purity of gametes

  4. Linkage


Correct Option: D
Explanation:

Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together.

When a cluster of genes show linkage behavior, they

  1. Do not show a chromosome map

  2. Show recombination during meiosis

  3. Do not show independent assortment

  4. Induce cell division


Correct Option: C
Explanation:

Linkage is referred to the phenomenon wherein alleles located close together on a chromosome show tendency to be inherited together during meiosis. Genes present near to each other have less probability of being separated onto different chromatids during chromosomal crossover. Therefore, when a cluster of genes show linkage behaviour they do not show independent assortment. Genes showing linkage behaviour do not assort independently and hence, do not show recombination during meiosis. Linkage map shows relative position of genes on the chromosomes based on recombination frequency between them; the map show both linked and independently assorted genes. 

Thus, the correct answer is option C.

With increasing age the linkage becomes

  1. Strong

  2. Weak

  3. Terminated

  4. Remains unchanged


Correct Option: A
Explanation:

When the genes are present on the same chromosomes they are said to be linked. When gene remains together for two or more generation they are said to have complete or perfect linkage. Thus the bond between them becomes strong. Thus, the correct answer is option A.

Linkage discovered in Drosophila by

  1. Bateson

  2. Morgan

  3. Muller

  4. Correns


Correct Option: B
Explanation:

Thomas Hunt Morgan was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.
Following the rediscovery of Mendelian inheritance in 1900, Morgan's research moved to the study of mutation in the fruit fly Drosophila melanogaster. Morgan demonstrated that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics. As a result of his work, Drosophila became a major model organism in contemporary genetics.

Linked gene shows

  1. Always parental combination.

  2. Sometimes new combinations.

  3. Always new combination.

  4. None of the above


Correct Option: B
Explanation:

Linkage is the tendency of alleles present close to each other to be inherited together during meiosis and hence they show parental combinations. But since complete linkage occurs rarely, sometimes the linked genes separate during meiosis and new combinations are formed. Hence, option B is correct.

The association of parental characters combinations in the offsprings of a dihybrid in excess to non-parental combinations is said to be due to

  1. Co-dominance

  2. Blending inheritance

  3. Linkage

  4. Duplicate genes


Correct Option: C
Explanation:

Linkage is the tendency of genes present close on the chromosomes to be inherited together and not to assort independently in the offspring. It gives only parental combinations in the offspring. Since, complete linkage is a rare phenomenon, the linked genes sometimes show tendency of independent assortment and results in production of new combinations in offspring in lower percentage. Hence, production of parental characters combinations in the offsprings of a dihybrid in excess to non-parental combinations is due to "linkage". Option "C" is correct.

Genes when close together on a chromosome, it is called as

  1. Mutation

  2. Linkage

  3. Translation

  4. Transcription


Correct Option: B
Explanation:

Sudden inheritable changes in genetic material are called as mutations. Translation is the process of synthesis of polypeptides by polymerization of amino acids on ribosomes using the mRNA triplets as template. Transcription is the process of synthesis of RNA by RNA polymerase using DNA template strand. Thus mutation, translation and transcription are independent of distance between the genes on chromosomes which makes options A, C, and D wrong. Linkage is the tendency of closely placed genes on a chromosome to stay together during inheritance; it produces more parental combination and less/no new combinations of gene. Genes present together on a chromosome show linkage and do not follow independent assortment resulting in more parental types and less recombinants in progeny. Correct answer is B.

Which phenomenon is responsible for the association of deafness with white coat colour in cats such that cats with white coat colour often show deafness?

  1. Gene linkage

  2. Sex linkage

  3. Crossing over

  4. Independent assortment

  5. Recombination


Correct Option: A
Explanation:

The frequent occurrence of the phenomenon leading to the trait 'deafness' in
cats being associated with cats with 'white coat color' is possible only in the case when the alleles for these traits are so close together on a chromosome that they are inherited together during the meiosis phase. This tendency of the alleles to be inherited together is known as genetic linkage or gene linkage. Thus, the correct answer is option A.

When closely placed genes on the same chromosome are inherited together, the phenomenon is known as

  1. Qualitative inheritance

  2. Crossing over

  3. Gene interaction

  4. Multiple allelism

  5. Linkage


Correct Option: E
Explanation:

Tendency of genes located on the same chromosome, to stay together in hereditary transmission, is known as linkage. The genes located on the same chromosome are called as linked genes.

Mendel observed that some characters did not assort independently. Later researchers found it to be due to

  1. Crossing over

  2. Linkage

  3. Dominance of one trait over the other

  4. Amitosis


Correct Option: B
Explanation:

Mendel's law of independent assortment is not applicable for the genes which reside on the same chromosome. He was able to interpret the results and give out the laws because the 7 pair of contrasting characters which he chose in pea were residing on different chromosomes. 

The number of linkage group in E.coli is/are

  1. 4

  2. 2

  3. 1

  4. 5


Correct Option: C
Explanation:

The number of linkage groups equals the number of chromosomes in the basic set. The number of linkage groups in an organism is equal to the haploid number of its chromosomes. Example - In Drosophila, the haploid number is n = 4, so linkage group is 4. But the number of linkage group is prokaryotes (bacteria, like E. coli) is one. This is because bacteria being prokaryotes have only a single circular chromosome.

So, the correct answer is '1'.

Which enzyme is responsible for linking the fragments of DNA?

  1. DNA polymerase III

  2. Endonuclease

  3. DNA polymerase I

  4. DNA ligase


Correct Option: D
Explanation:

DNA Ligase is the enzyme which helps in joining the fragments of DNA, basically, it acts as a glue. In the given options endonuclease helps in cutting the DNA into fragments it cleaves the polynucleotide chain by acting on the nucleotides by breaking the hydrogen bonds between them, whereas DNA polymerases synthesize the DNA molecule from deoxyribonucleotides. So, the correct answer is "DNA ligase".

Drosophila has four homologous pairs of chromosomes. What is the number of linkage groups (homologous) in this animal?

  1. Four

  2. Two

  3. Eight

  4. Uncertain


Correct Option: A
Explanation:
In the diploid nucleus, each chromosome is represented twice: by a homologous pair and there are same genes on homologous chromosomes.
In Drosophila, there are four pair of chromosomes: 2 pairs of large autosomes, (one slightly smaller than the other pair), 1 pair of very small autosomes, and a pair of sex chromosomes. Genes present on one chromosome form a linkage group. Homologous chromosomes carry same set of genes (the alleles may differ), hence same linkage group.
So, the correct answer is 'Four'.

Suppose that out of $1000$ offspring in the $F _2$ generation of a dihybrid cross, $748$ are tall and hairy, $6$ are tall and smooth, $4$ are short and hairy, $242$ are short and smooth. The reason is that the genes controlling these characters are.

  1. Lethal genes

  2. Complementary genes

  3. Linked genes

  4. Epistatic genes


Correct Option: C

Association of parental combination of characters in offspring in excess of dihybrid cross is due to.

  1. Pseudoalleles

  2. Linkage

  3. Polygeny

  4. Codominance


Correct Option: B
Explanation:
Linkage is the tendency of genes present close on the chromosomes to be inherited together and not to assort independently in the offspring. It gives only parental combinations in the offspring. Since, complete linkage is a rare phenomenon, the linked genes sometimes show tendency of independent assortment and results in production of new combinations in offspring in lower percentage. Hence, production of parental characters combinations in the offsprings of a dihybrid in excess to non-parental combinations is due to "linkage".

So, the correct answer is 'Linkage'.

Read (i) to (v) and find the correct option
(i) Nitrogen base is linked to pentose sugar through N-glycosidic linkage
(ii) Phosphate group is linked to 5 - OH of a nucleoside through phosphoester linkage
(iii) Two nucleosides are linked through 3' -5' N-glycosidic linkage
(iv) Negatively charged DNA is wrapped around positively charged histone octamer to form nucleosome
(v) Chromatin that is more densely packed and stains dark is called euchromatin

  1. i, ii, iii wrong

  2. iv alone is wrong

  3. iii and v are wrong

  4. i alone is wrong

  5. i, ii and iv are wrong


Correct Option: C

Number of linkage in a polynucleotide would be __________________.

  1. Same as number of nucleotides

  2. Twice the number of nucleotides

  3. One less than the number of nucleotides

  4. One


Correct Option: D

Which of the following is suitable for experiment on linkage ?

  1. aaBB $\times$ aaBB

  2. AABB $\times$ aabb

  3. AaBb $\times$ AaBb

  4. AAbb $\times$ AaBB


Correct Option: B
Explanation:
AABB x aabb is suitable for the experiment on the linkage. Linkage is the tendency for certain genes tend to be inherited together because they are on the same chromosome. Thus, parental combinations of characters are found more frequently in offspring than non-parental.

So, the correct answer is 'AABB × aabb'.

Linkage decreases frequency of.

  1. Recessive allele

  2. Dominant allele

  3. Hybridisation

  4. Both B and C


Correct Option: C
Explanation:
Distance between the linked genes is the major factor which controls the frequency of crossing over. Hence, greater is the linkage lesser will be the chances of crossing over or Hybridisation.

So, the correct answer is 'Hybridisation'.

Determination of percentage of crossing over between two linked genes is important in

  1. Maintaining heterozygosity in population

  2. Indicating relative position of genes in chromosomes

  3. Fixation of heterosis in organisms

  4. Explaining the phenomenon of coupling and repulsion


Correct Option: B
Explanation:
If the distance between two linked genes is more then the frequency of crossing over will be more and vice versa.
Hence, percentage of crossing over may indicate the relative position of genes in chromosomes.
So, the correct answer is 'Indicating the relative position of genes in chromosomes'.

In a dihybrid cross between two heterozygotes, AaBb $\times$ AaBb, if we get a 3 : 1 ratio among offspring, the reason would be ___________.

  1. Polygenes

  2. Linked genes

  3. PIeiotropic genes

  4. Hypostatic genes.


Correct Option: B
Explanation:

A.Polygenes – Inheritance is controlled by two or more genes in which the dominant alleles have cumulative effect, with each dominant allele expressing a part of functional polypeptide and full trait is shown when all the dominant alleles are present, is called Polygenic or Quantitative inheritance.

B.Linked genes – The tendency of some genes to inherit together is known as linkage, and the genes are linked genes.

C. Pseduoalleles - Genes are present together side by side and they produce related phenotypes are called pseudoalleles. These are distinguished from true alleles through rare crossing over.

D. Hypostatic gene – A gene whose effect are masked is by another gene is called Hypostatic gene. In the F2 generation 12:3:1 ratio.

In a dihybrid cross between two heterozygotes, AaBb x AaBb, if we get a 3:1 ratio among offspring, the reason would be Linked genes.

So, the correct option is ‘Linked genes’.

An exception to Mendel's principle/ Mendel did not include in his discoveries

  1. Dominance

  2. Purity of gametes/segregation

  3. Linkage

  4. Independent assortment


Correct Option: C
Explanation:

A.Dominance - When two contrasting alleles for a character come together in an organism, only one is expressed and another one is not expressed. Expressed character is called Dominant character and the character which is not expressed is called Recessive character. It is the Mendel’s first principle.

B.Purity of gametes/segregation - In the living organisms, two alleles controlling each character maintains identity in the organism, but during the formation of gametes or spores, by meiosis move apart due to separation of the homologous chromosomes which bear them, so that each gametes or spore receives only one allele of each character on random basis. It is called Law of segregation. It is the Mendel’s second principle.

C.Linkage – The physical association of genes in a chromosome is called Linkgage. It is not the Mendel’s principle.

D.Indepedent assortment - When a cross is made between two individuals different from each other in two or more characters, then the inheritance of one character is independence of the inheritance of another character.

So, the correct option is ‘Linkage’.

The phenomenon of closely placed genes being inherited together is

  1. Linkage

  2. Crossing over

  3. Gene interaction

  4. Qualitative inheritance


Correct Option: A
Explanation:

  • Linkage refers to the presence of two different genes on the same chromosome. Two genes that occur on the same chromosome are said to be linked, and those that occur very close together are tightly linked.
  •  Crossing over is the exchange of chromosome segments between non-sister chromatids during the production of gametes.
  • When the expression of one gene depends on the presence or absence of another gene in an individual, it is known as gene interaction.
  • The pattern of inheritance for a qualitative trait is typically monogenetic, which means that the trait is only influenced by a single gene. Inherited diseases caused by single mutations are good examples of qualitative traits.

So, the correct answer is 'Linkage'.

Number of linkage groups in Pisum sativum is?

  1. $4$

  2. $5$

  3. $7$

  4. $10$


Correct Option: C
Explanation:
Number of linkage groups is equal to its haploid number.
Since haploid number of Pisum sativum is 7, it has 7 linkage groups.

So, the correct answer is '7'.

The cross-over percentage between linked genes is (a) J and M- $20\%$ (b) J and L - $35\%$ (c) J and N - $20\%$ (d) L and K - $15\%$ (e) M- N - $50\%$ (f) M and L - $15\%$. The sequence of genes on the chromosomes is?

  1. J, N, M, L, K

  2. J, M, L, N, K

  3. J, M, L, K, N

  4. M, J, L, K, N


Correct Option: C

Consider the following statements regarding linkage of genes.
a. Two genes are said to be linked when they fail to show independent assortment.
b. The strength of the linkage is determined by the distance between the two genes in question.
c. The strength of the linkage is directly proportional to the distance between the two genes.
Of these statements.

  1. $1, 2$ and $3$ are correct

  2. $1$ and $2$ are correct

  3. $2$ and $3$ are correct

  4. $1$ and $3$ are correct


Correct Option: A

If, in Macrospore, the progenies of the cross between an Orange colonial strain and Albino spreading strain segregated into $1:1:1:1$ ratio of Albino spreading: Orange colonial : Normal Albino colonial, then the inference is that the traits are controlled by.

  1. Single gene

  2. Two genes

  3. Three genes

  4. Four genes


Correct Option: A

Assuming that genes x and y are linked and exhibit 20% recombination. If ++/++ individuals are crossed with xy/xy, then types and percentage proportion of gametes in $F 1$ will be _____________.

  1. ++80%: xy 20%

  2. ++40%: xy 40%: +x10%: y 10%

  3. +x40%: xy 40%: ++20%

  4. +x20%: ++ 40%: xy 20%


Correct Option: A

Distance between 2 linked genes is measured in map units that depict:

  1. ratio of crossing over between them

  2. cross-over value

  3. number of gene

  4. both b and c


Correct Option: A
Explanation:

The methods used to identify the locus of a gene and the distances between genes is called gene mapping. It indicates the % of crossing over occurs between the linked genes. The essence of all genome mapping is to place a collection of molecular markers onto their respective positions on the genome. Recombination between linked genes can be used to map their distance apart on the chromosome. The distance between the two linked genes is measured by centimorgans or map units.

So, the correct option is ‘ratio of crossing over between them’.

How many linkage groups would be revealed by careful analysis of human genetics?

  1. 23

  2. 4

  3. 3

  4. 1


Correct Option: A
Explanation:
Linkage group, in genetics, all of the genes on the single chromosome, they are inherited in groups and move as a unit rather than independently. In human beings have 23 linkage groups.
So, the correct option is '23'.

The number of linkage groups is greater in Drosophila than in human beings.

  1. True

  2. False


Correct Option: B
Explanation:

The number of linkage groups is four in number which is less than humans. Fruit-fly Drosophila melanogaster has four linkage groups (4 pairs of chromosomes), human beings 23 linkage groups (23 pairs of chromosomes) So, the correct option is 'False'.

All genes located on the same chromosome

  1. Form different groups depending upon their relative distance

  2. Form one linkage group

  3. Will not from any linkage groups

  4. Form interactive groups that affect the phenotype


Correct Option: B
Explanation:

All the genes located on a single chromosome, are inherited together. So, they constitute a linkage group. They don't move independently during the process of cell division. They always in a group. They form a set of genes on different loci in a single chromosome. But the chromosome should not be a cross over one.

So, option B is the correct answer.

Gametic maps of chromosomes are based on

  1. Non disunction

  2. Tranlocation

  3. Dominance

  4. Genetic recombination

  5. Chromosomal aberrations.


Correct Option: D
Explanation:

A linkage or genetic chromosome map is a linear graphic representation of the sequence and relative distance of the various things present in a chromosome. A chromosome app is also called a linkage map or the genetic map. The percent of crossing over between two genes is directly proportional to the distance. The unit of crossing over has been termed as centiMorgan.


So, the correct option is 'Genetic recombination'.

Out of three characters on chromosome no. 4, two characters indicate linkage and not mentioned by Mendel. These characters were

  1. Pod form - stem length

  2. Pod form - pod position

  3. Pod form - pod colour

  4. Pod position - stem length


Correct Option: A
Explanation:

The chromosome no. 4 of pea plant carries genes for flower position, pod form and plant height. Out of these three genes, the two genes namely the gene for pod form and the one for plant height are closely placed on the chromosome that they show linkage. However, the gene for flower position is located far apart from the other two genes and do not show linkage. Hence, option A is correct. 

How many linkage groups are present in human male?

  1. 24

  2. 23

  3. 46

  4. 22


Correct Option: A
Explanation:
Humans can have 2 linkage groups based on gender. 
Male have 22 pairs of autosomes and 1X and 1Y. So, in all 24 linkage groups. 
While females have 22 pairs autosomes and 1X pair. So, total 23 linkage groups
Thus, the correct answer is '24'.

Lack of independent assortment between two genes A and B would be due to

  1. Crossing over

  2. Linkage

  3. Recombination

  4. None of the above


Correct Option: B
Explanation:
Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes to produce new genetics combinations or variations; it does not interfere with an independent assortment of genes. Option A is incorrect. The linkage is the tendency of closely placed genes on a chromosome to stay together during inheritance and do not assort independently; it produces more parental combination and less/no new combinations of the gene. The linkage is indirectly proportional to the distance between genes; the less the distance between the genes, the more linkage due to lack of independent assortment between them. Option B is correct. Recombination is new arrangements of genes on chromosomes which is carried out by independent assortment and crossing over; thus recombination is the result of independent assortment which makes option D is incorrect. Option B is correct.

Number of linkage groups in Pisum sativum is 

  1. 4

  2. 5

  3. 7

  4. 10


Correct Option: C
Explanation:

The total number of linkage groups in an organism equals to the number of autosomes in its haploid cell. Pisum sativum has seven pairs of chromosomes which mean that the number of autosomes in its haploid cell is 7. Hence, a total number of linkage groups will be 7 provided all the genes are mapped. So, the correct answer is option C.

Linkage was first observed in

  1. Field pea

  2. Sweet pea

  3. Pea

  4. Grass pea


Correct Option: B
Explanation:

The phenomenon of linkage was first observed by Bateson and Punnet in 1906 in sweet pea (Lathyrus odoratus). Linkage describes the way in which two genes that are located close to each other on a chromosome are often inherited together. Hence option B is correct.

In a long-term study of a population of a self-pollinated plant, it was observed that an allele, which significantly enhanced vegetative growth and production of flowers in the plant, did not expand in distribuation over subsequent generations in the population. This could be because the allele is

  1. Dominant lethal in nature

  2. Tightly linked to a gene that allows formation to large number of seeds in each plant

  3. Linked to a gene that suppresses development of axillary branches

  4. Tightly linked to a gene that suppresses development of pollen mother cells in the plant


Correct Option: D
Explanation:

In the case of self pollinated plants, the self pollen pollinates on the stigma. The allele involved in the production of pollen affects the progeny plants in the subsequent generations. The allele for the formation of pollen from pollen mother cells and the allele for vegetative growth and production of flowers are tightly linked. So, when the plants did not show enhanced growth and flowering, it can be said that this gene also suppresses development of pollen mother cells which will thereby affect the distribution in the next generations. 

Thus, the correct answer is option D.  

Linkage gene do not show

  1. independent assortment

  2. 9:3:3:1

  3. segregation

  4. All of the above


Correct Option: D
Explanation:

Linked gene do not show :

Correct option is (D) All of the above .
Linked gene violates independent assortment , having the phenotype ratio 9;3;3;1. Linked gene is also influenced by the segregation.
Hence, option D is correct.

Genes located very close to one another on same chromosome tend to be transmitted together and are called as

  1. Allomorphs

  2. identical genes

  3. Linked genes

  4. recessive genes


Correct Option: C
Explanation:

Genes that are sufficiently close together on a chromosome will tend to "stick together," and the alleles of those genes that are together on a chromosome will tend to be inherited as a pair more often than not. This phenomenon is called genetic linkage. These genes are called as linked genes that are likely to be inherited together because they are physically close to one another on the same chromosome.

So, the correct answer is 'Linked genes'.

The primary biological importance of sex in organisms is that it

  1. Is essential for organismic reproduction

  2. Is essential for cellular reproduction

  3. Causes new mutations to occur in offspring

  4. Promotes genetic variability in offspring


Correct Option: D

P is the daughter of Q. R has only two children - P and S. T is the brother of U. S is married to V. R has only two daughters. X is the father of Q. T is married to P. W is married to X. R is the son of Y. Who among the following is the mother of Q?

  1. W

  2. Y

  3. R

  4. X


Correct Option: A

A DNA molecule measures 204 nm in length; 35% of the molecule has AT base pairs. Find out the number of H-bonds existing between the two strands of DNA.

  1. 1590

  2. 159

  3. 1410

  4. 141


Correct Option: A

What is the probability of three daughters to a couple in three children?

  1. $\dfrac{1}{4}$

  2. $\dfrac{1}{8}$

  3. $\dfrac{1}{16}$

  4. $\dfrac{3}{8}$


Correct Option: A

A family has five girls and no son, the probability of the occurrence of son in $6^{th}$ child is?

  1. $1/2$

  2. $1/5$

  3. $1$

  4. No chance


Correct Option: A

Find out the frequency of AabbCcDdee if parents are AabbCCddEe and AabbccDdee.

  1. $0.78\%$

  2. $12.5\%$

  3. $25\%$

  4. $50\%$


Correct Option: A

A family of five daughter only is excepting sixth issue. The change of its beings a son is?

  1. $0\%$

  2. $25\%$

  3. $50\%$

  4. $100\%$


Correct Option: C
Explanation:

If you have five girls and expect a sixth child, then there is a  chance that it will be a boy slightly more than 50%.

So, the correct option is '50%'.

A human male is heterozygous for two autosomal genes A & B and homozygous dominant for 3rd autosomal gene C. The individual is having sry gene (S) on its Y-chromosome. What will be the probability of sperms to carry abcS condition? 

  1. $\frac{1}{4}$

  2. $\frac{1}{8}$

  3. $0$

  4. $\frac{1}{16}$


Correct Option: A

Assume that the occurrence of nitrogen bases in adjacent positions in a DNA strand is random. Identify the minimum number of nucleotides in a DNA strand where GAAT can occur once on the basis of probability

  1. 512

  2. 256

  3. 4096

  4. 1024


Correct Option: B

Assume that the occurrence of nitrogen bases in adjacent positions in a DNA strand is random. Identify the minimum number of nucleotides in a DNA strand where GAAT can occur on the basis of probability.

  1. $512$

  2. $256$

  3. $4096$

  4. $1024$


Correct Option: A

Probability of getting fairly light and light progeny from mulattoe and albino parents in

  1. $\cfrac{15}{64}$ and $\cfrac{6}{64}$

  2. $\cfrac{20}{64}$ and $\cfrac{15}{64}$

  3. $\cfrac{3}{8}$ and $\cfrac{1}{8}$

  4. $\cfrac{3}{8}$ and $\cfrac{3}{8}$


Correct Option: A

In an organism punk is a sex-linked recessive trait and black hair heterozygous female is mated to white male which is not spotted, the phenotypic ratio of the offspring would be :

  1. 1/4 spotted black; 1/4 pink spotted white; 1/4 unspotted black; 1/4 uspotted white

  2. 1/2 spotted black; 1/2 pink spotted white

  3. 3/4 pink spotted black; 1/4 pink spotted white

  4. 3/4 unspotted black; 1/4 pink spotted white


Correct Option: A

A man with pure blue eyes and pure black hair marries a woman with black eyes and red hair. (Black eyes are dominant over blue eyes and black hair over red hair). What will be the probabilities of phenotypes of the children?

  1. $50$% with black eyes and black hair, and $50$% blue eyes and black hair

  2. All will be with black eyes and black hair

  3. Both the above cases are possible

  4. $1 : 1 : 1 : 1$


Correct Option: A

A dithered tall plant bearing yellow flowers(Tt\cdot Yy)$ was crossed with a dwarf plant bearing white flowers(tt, yy). What percentage of the progeny is expected to be homozygous tall bearing yellow flowers?

  1. $75$

  2. $50$

  3. $25$

  4. Zero


Correct Option: A

If one chain of a DNP molecule has the base order $5$' ATTGACGT $3$'. Then the base order of its complementary chain will be.

  1. $3'$ATTGACGT$5'$

  2. $5'$TGCAGTTA$3'$

  3. $5'$TUUCTGCU$3'$

  4. $3'$TAACTGCA$5'$


Correct Option: A

Mr. Kapoor has $Bb$ autosomal gene pair and $d$ allele sex-lined. What shall be proportion of $Bd$ in sperms.

  1. Zero

  2. $1/2$

  3. $1/4$

  4. $1/8$


Correct Option: A

If both parents are bald and their first female child is normal, then chances of bald ness is second male child are ________________.

  1. $100$%

  2. $50$%

  3. $25$%

  4. $0$%


Correct Option: A

Choose the correct answer from the alternatives given.
If you had two guinea pigs of opposite sex, both homozygous, one black and one brown, but you didnt know which was the dominant characteristic, how would you find out the dominant colour?

  1. Mate them together and see what colour the offspring arethat will be the dominant colour

  2. Mate them together and see what colour the offspring arethe other will be the dominant colour

  3. Mate them together, then mate their offspring to see what colour the grandchildren arethat will be the dominant colour

  4. Mate them together, then mate their offspring to see what colour the grandchildren arethe other colour will be the dominant colour


Correct Option: A
Explanation:

Since both the guinea pigs are homozygous mating them will result in a heterozygous genotype in the offspring. In the heterozygous condition, the dominant allele has the ability to mask the effect of the recessive allele. Therefore, the phenotypic character that will be expressed will be the phenotype of the dominant character and the F1 progeny color will be the dominant color. So, the correct option is 'Mate them together and see what color the offspring are that will be the dominant color'.

The vascular cambium of a stem does not produce _____.

  1. Cork

  2. Wood

  3. secondary phloem

  4. secondary xylem


Correct Option: A
Explanation:

Cork is produced by cork cambium which is a lateral meristem responsible for secondary growth that replaces epidermis of root and stems. The vascular cambium of a stem is responsible for the formation of secondary phloem and secondary xylem while wood is mainly composed of secondary xylem element it is also a derivative of vascular cambium.

So, the correct option is 'Cork'.


A heterozygote has a .......... for the trait being studied.

  1. haploid condition, in genetic terms

  2. pair of non-identical alleles

  3. pair of identical alleles

  4. both (a) and (c)


Correct Option: B
Explanation:

An individual having two different alleles of a particular gene or genes, and so giving rise to varying offspring.

So, the correct option is 'pair of non-identical alleles'.

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