Question

1)Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

A)XⁿXⁿ and XⁿY

B)X^NX^N and X^NY

C)X^NXⁿ and X^NY

D)X^NX^N and XⁿY

2)A poison interferes with the action of RNA polymerase II, but not RNA polymerase I or III. Which of the following is likely to be true of a cell exposed to the poison?

A)production of tRNA would be stopped but not rRNA or mRNA.

B)production of mRNA would be stopped but not rRNA or tRNA.

C)A cell could perform transcription but not translation

D)The cell would ignore the G1 checkpoint and eventually become cancerous.

Answer 1

Ans

1-X^NXⁿ and X^NY

Colour blindness is a sex linked recessive trait , so in males presence of even one copy of color blindness allele on X chromosome will make the male colour blind . In females to be colour blind , both X chromosome must carry a copy of the recessive color blindness allele each.  

In this case since the son is color blind its understood the mother is carrier , since son's i gerit X chromosome from mother's ,so if mother is a carrier then 50% chance son will be normal and 50% chance son will be color blind. Father cannot be carrier as fathers have only one X chromosome , and if that chromosome carries the recessive allele father will be color blind .

So N is normal dominant allele

And n = revessive vision for color blindness.

So mother is carrier and hence Heterozygous , where dominant alelle supresses the color blindness allele and she appears normal .

2-B) production of mRNA would be stopped and not tRNA or rRNA.

RNA polymerase l transcribes rRNA and RNA pol lll transcribes tRNA

RNA polymerase ll synthesises mRNA , it would inhibit RNA polymerase ll , since mRNA is not synthesised the cell will not undergo transcription and translation for protein synthesis and the cell will die being unable to synthesise necessary proteins .

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