In: Biology
In human beings, the gene for red green colorblindness (r) is sex linked and recessive to its allele for normal vision (R), while the gene for freckles (F) is autosomal and dominant over its allele for nonfreckled (f). A nonfreckled, normal visioned woman whose father was freckled and colorblind, marries a freckled, colorblind man whose mother was nonfreckled.
a. What is the genotype of the woman's father? b. What is the probability that the couple's first child will be a non-freckled, normal visioned girl c. What is the probability that the first two children born to the couple will be freckled and colorblind girls? d. What is the probability that the first child born to the couple will either be a freckled, colorblind boy or a non freckled, normal visioned girl or a non-freckled, normal visioned boy e. What is the probability that the first four children born to the couple will be freckled and normal visioned girls?
colorblindness is a sex-linked recessive trait.
let the alleles be XR- normal vision, Xr- colorblindness
F-freckles, f- non-freckled.
a) woman`s father is freckled and colorblind.
the woman is non-freckled so her genotype is ff, so she has inherited f allele from both parents, so the genotype of the father is FfXrY, since the man is colorblind his genotype is XrY.
the genotype of a woman`s Father is FfXrY.
b) since the Woman`s father is the colorblind woman has inherited Xr allele from the father, so her genotype is ffXRXr.
Man is colorblind and has freckles, but his mother has no freckles so her genotype is ff, she has passed f allele to her son. he has freckles so his genotype is FfXrY.
ffXRXr * FfXrY
let`s divide this into 2 different crosses.
Ff * ff
F | f | |
f | Ff | ff |
probability of getting non-freckled (ff) progeny = number of ff/total number=1/2
XRXr * XrY
XR | Xr | |
Xr | XRXr (normal vision female) | XrXr (colorblind female) |
Y | XRY ( male, normal vision) | XrY (colorblind male) |
probability of getting girl with normal vision= number of girls with normal vision/total number=1/4
probability of getting a non-freckled girl with normal vision= probability of getting non-freckled progeny probability of getting girl with normal vision=1/21/4=1/8.
c)
probability of getting freckled child= number of Ff/total number=1/2
probability of getting colorblind female= number of colorblind female/total number=1/4
probability of getting a colorblind female child with freckles= (probability of getting freckled child probability of getting colorblind female=1/21/4=1/8.
probability of getting first two girls with colorblindness and freckles= (probability of getting a colorblind female child with freckles)^2=(1/8)^2=1/64
d) probability of getting colorblind boy= number of colorblind boys/total number=1/4
probability of getting girl with normal vision= number of girls with normal vision/total number=1/4
probability of getting normal vision boy= number of progeny with normal vision/total number=1/4
probability of getting freckled child=number of Ff/total number=1/2
probability of getting non-freckled (ff) progeny= number of ff/2=1/2
the probability that the first child born to the couple will be a freckled, colorblind boy = probability of getting colorblind boy probability of getting freckled child=1/21/4=1/8.
the probability that the first child born to the couple will be a nonfreckled, normal visioned girl = probability of getting non-freckled child probability of getting normal visioned girl= 1/21/4=1/8.
the probability that the first child born to the couple will be a non-freckled, normal visioned boy = probability of getting non-freckled child probability of getting non visioned boy= 1/21/4=1/8.
probability that the first child born to the couple will either be a freckled, colorblind boy or a non freckled, normal visioned girl or a non-freckled, normal visioned boy e = the probability that the first child born to the couple will be a nonfreckled, normal visioned girl + probability that the first child born to the couple will be a non-freckled, normal visioned boy+ the probability that the first child born to the couple will be a freckled, colorblind bo= 1/8 +1/8+1/8=3/8.
d) probability of getting freckles= ( number of ff/total number)=1/2
probability of getting a girl with normal vision= number of girls with normal vision/total number=1/4
probability of getting a freckled girl with normal vision= probability of getting non-freckled progeny probability of getting girl with normal vision=1/21/4=1/8.
probability that the first four children born to the couple will be freckled and normal visioned girls = ( probability of getting a freckled girl with normal vision)^4=(1/8)^4=1/4096