Layering method is used for the propagation (or reproduction) of plants like hibiscus.

This is the correct option. 

Yes, a pair of contrasting characteristics is called an allele.

Some plants like potato, ginger and sweet potato develop into new plants from the ‘eye’ of that plant, i.e. they undergo vegetative propagation.

 Feathers help in providing insulation.

Formation of gamete is essential for sexual reproduction as gametes from two different individuals fuse together for the production of a new individual. 

 Adenine, thymine, guanine, cytosine are groups of nitrogen bases present in a DNA molecule.

 Genetic drift describes random fluctuations in the numbers of gene variants in a population.

Mendel’s law of segregation is based on separation of alleles during gamete formation.

 7 pairs of contrasting traits were considered by Mendel in pea plant.

Homozygous means that both alleles are the same. Dominant traits are symbolised by capital letters and dihybrid condition means that two traits are discussed at a time.

 In peas, tall plant trait is dominant over dwarf. If a heterozygous for tall is crossed with one homozygous for dwarf, there will be 50% tall and 50% dwarf appearance of the offspring of a cross of F1.

If the frequency of a dominant phenotype in a stable population is 75%, then the frequency of recessive allele will be 25%.

It provides the fluid which makes the sperm transport easier. 

We know that a mother, being female (XX), can contribute only X chromosome to the progeny. If a child inherits X chromosome from the father, then its genetic makeup will contain a pair of X chromosomes, i.e. XX state, and the child will develop into a girl.