First of all, we must check if the allele for the red-green color blindness is dominant or recessive.
Father transfers his mutant X allele to all his daughters. Since not all of his daughters are color blind, the allele cant be dominant. So the allele for the color blindness is recessive.
Let's symbolize X
R the dominant (wild) allele and X
r the recessive (mutant) allele.
Father is color-blind so his genotype is: X
rY. (
I-1 is XrY)
Let's check
II-7 now. She is color blind, so she must be:
XrXr (since X
r is recessive).
II-7 inherited a X
r from her father
and a Xr from her mother. Since the mother is not color-blind. she also has one dominant X
R allele. So her genotype is:
I-2 XRXr.
As we said earlier, all daughters inherited a X
r gene from their father. Since II-4 is not color blind, she also has one dominant X
R allele. So she is:
II-4 XRXrNow, let's check III-1. As we said earlier, II-7 is X
rX
r. So, III-1 inherited a X
r allele from her mother (II-7). But she is not color blind (and her father is not color blind either) so, she also inherited a dominant X
R allele from her father. So,
III-1 is XRXrFrom the above:
Write the following genotypes for individuals I -1 I-2 II-4 and III-1
I-1 is XrYI-2 is XRXrII-4 is XRXrIII-1 is XRXrIf II-1 and II-2 have a son what is the possibility that the son will have redgreen color blindness ?
As we said earlier, all daughters inherited a X
r allele from their fathers. Since II-2 is not color blind, she also has a dominant X
R (genotype: X
RX
r). I-1 is male and not color blind, so he can only be: X
RY.
If I-1 and I-2 make a son, then:
The son will inherit the Y chromosome from his father, and a X chromosome from his mother. So, it all depends from the allele that the son will inherit from his mother. If he inherits the X
R allele, then he will be normal (X
RY). If he inherits the X
r allele, he will be color-blind (X
rY). There is 50% possibility for the son to inherit X
R, and 50% to inherit X
r. So, the possibility we need is 50%.
If couples II-7 and II-8 have a son what is the probability that the son will have red green color blindness ?
Likewise, the son will inherit a Y chromosome from his father, and a X from his mother. Again, all depends on his mother. Since his mother is X
rX
r, the son will surely inherit a X
r allele, and he will be color-blind (genotype X
rY). Therefore, the son has 100% possibility to be color-blind.
Quick Reply
