CBSE Class 12 - Biology solved questions with answers

Answer: Option [A]

Organisms phenotypically similar but genotypically different are said to be heterozygous. The presence of two different alleles at a particular gene locus. A heterozygous genotype may include one normal allele and one mutated allele or two different mutated alleles (compound heterozygote).

Answer: Option [C]

A crtoss used to ascertain whether a dominant is homozygous or heterozygous is termed Test cross. In genetics, a test cross, first introduced by Gregor Mendel, involves the breeding of a phenotypically dominant individual with a phenotypically recessive individual, in order to determine the zygosity of the former by analyzing proportions of offspring phenotypes. Zygosity can either be heterozygous or homozygous. Those that are heterozygous have one dominant and one recessive allele. Individuals that are homozygous dominant have two dominant alleles, and those that are homozygous recessive have two recessive alleles.

Answer: Option [B]

An individual receiving like genes for the same characters from its two parents, is known as homozygous. The homozygous parent carries two copies of the same allele of a gene, for example, TT or tt. Owing to the presence of a single type of allele, it forms all same gametes carrying the same type of allele (for example, T or t). Hemizygous condition refers to the presence of single copy on a gene rather than two as are present for mendelian traits. For example, XY pair in human males. Owing to the presence of two different chromosomes, it produces two types of gametes, half with X and half with Y. The term “homologous” refers to the members of a pair of identical chromosomes that synapse during meiosis.

Answer: Option [B]

When dominant and recessive alleles express themselves together, it is called co-dominanace. A condition in which both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other. Codominance is a relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent.

Answer: Option [D]

The correct answer is Homozygote. An organism with identical pairs of genes for a specific trait. If both of the two gametes that fuse during fertilization carry the same form of the gene for a specific trait, the organism is said to be homozygous for that trait.