CHALLENGE QUESTIONS Sex Linkage: Red-green colorblindness is a sex-linked, reces
ID: 202389 • Letter: C
Question
CHALLENGE QUESTIONS Sex Linkage: Red-green colorblindness is a sex-linked, recessive trait. Cliff and Clair Huxtable both have normal color vision. Clair's father, however, was red-green color-blind. 4. a. b. c. d. What is the Cliff's genotype? What is the Clair's genotype? What is the probability that their daughters will be color blind? What is the probability that their sons will be color blind? Incomplete Dominance: Hair curl is a trait that shows incomplete dominance (see table 10.2 above). Mr, and Mrs. Cunningham (Howard and Marion) both have wavy hair 5. a. What is Howard's genotype? b. What is Marion's genotype? c. Determine the predicted genotype and phenotype frequencies of their offspringExplanation / Answer
Red-Green Colour blindness is an X linked Recessive Trait. Let us represent the colour blind allele as 'b' ( Lower case b)and the normal allele as 'B' ( upper case B). It is linked to the X chromosome. So, the possible genotypes for male and female can be as follows :
Female Male
XBXB - Normal female XBY - Normal male
XBXb - Carrier female XbY - Colour blind male
XbXb - Colour Blind female
That is there is only 2 genotypes possible for a male and in case of female 3 genotypes are possible ( an extra carrier condition).
4 a) Here, as the question says both Cliff and Clair are normal persons, It is sure that Cliff ( male) has the genotype XBY.
b) Clair ( female) is normal. But, her father was a colour blind which shows the genotype for clair's father as XbY. Since clair is female she has two X chromosomes ie, one from father and one from mother. Since Clair is normal, she might have got a nomal allele (XB) from her mother, while there a complete chance (100%) of getting a recessive allele Xb from her father (because father has only the diseased Xb allele to transfer to clair).
Hence genotype of Clair is XBXb ( Carrier female)
c) There is No probability that their daughters get Colour blindness. The disease is recessive in nature. So, only if the daughter gets two recessive alleles (ie, genotype XbXb), she gets disease. This condition is not possibe as Cliff (father) is normal (XBY) and he always provide normal allele XB to daughters.
d) There is 1/2 or 0.5 chance for their sons to get diseased. It is because their father is normal. But he provides only Y chromosome to their son and X chromosome is provided only by mother. Since mother is a carrier, She can transer either XB (normal) or Xb ( recessive) to their son ( Half chance for either one to get inherited).
The cross can be represented as follows :
XBY X XBXb
Cliff (male) Clair( female)
XbY
(Colour blind son)
So, the probability to get colour blind son is 0.5