Question

Holandric gene is made of
A. 14 bp
B. 1400 bp
C. 14000 bp
D. 140,000 bp

Answer 1

Hint: Genes are the physical and functional unit of inheritance. Genes are the segments of DNA which carries hereditary information that is passed from parents to offspring. Since DNA is double-stranded, the size of a gene is measured in terms of base pairs (bp). The base pairing is the chemical bond formed between a purine and pyrimidine.

Complete answer:
Holandric gene is a gene that exclusively occurs only in Y-chromosomes. In XX-XY type of sex determination which is found in mammals and in some insects (e.g., Drosophila); the female is homomorphic and has two similar set of chromosomes XX. The male is heteromorphic and has an XY chromosome. In the XY chromosome of human males, the X-chromosome is similar to that of a female, whereas, Y-chromosome is shorter and morphologically different. Regardless of difference in morphology, the X and Y chromosomes contain homologous regions (similar genes), which synapse during zygotene. The region which does not synapse is known as differential region. The genes present in this differential region are known as Y-linked or Holandric genes (e.g., SRY, hypertrichosis of pinna, porcupine skin, ZFY, keratoderma dissipatum, PQ 2V, webbed toes). It is the smallest gene with 14 base pairs only. Gene SRY (sex determining region) produces TDF or testis determining factor. Sperm formation is controlled by the ZFY gene.

Hence, the correct answer is option (A).

Note: The homologous part of X and Y chromosomes possess similar genes in two chromosomes which are called as XY-linked genes, e.g., genes of xeroderma pigmentosum. Holandric genes are transmitted directly from father to son. The traits exhibited by Y-linked genes have not been known to appear in females.