The genes, which remain confined to differential region of Y-chromosome, are:
Correct answer: B. Holandric genes
- A. Autosomal genes
- B. Holandric genes
- C. Completely sex-linked genes
- D. Mutant genes
Explanation
Despite differences in morphology, the XY chromosomes are homologous and synapse during zygotene. It is because they have two parts, homologous and differential. Homologous regions of the two help in pairing. They carry the same genes which may have different alleles. The differential region of Y-chromosome carries only Y-linked or holandric genes, e.g., testis determining factor (TDF). It is perhaps the smallest gene occupying only 14 base pairs. Other holandric genes are hypertrichosis (excessive hairiness) on pinna, porcupine skin, keratoderma dissipatum (thickened skin of hands and feet) and webbed toes. Holandric genes are directly inherited by a son from his father. Chromosomes which control most of the morphophysiological characters other than sex, are called autosomes. Sex-linked genes are those which are found on the sex chromosomes. Mutant genes are formed by a change in the nucleotide type and sequence of a DNA segment representing a gene or a cistron.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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