Sex-linked traits?

1. Color blindness is a sex-linked trait in humans. A normal woman whose father was color-blind marries a normal man. What will be the proportion of color-blind children?





2. A blue-eyed woman whose father was colorblind marries a normal brown-eyed man whose mother was blue-eyed. What proportion of sons would be blue-eyed and color blind?





3. In cats the genotype BB is black. Bb is tortoise shell, and bb is yellow. The gene is on the X-chromosome. A tortoise shell female is crossed with a black male. What offspring will be expected?

Sex-linked traits?
1)


N=normal n=colour blindness





woman = XN Xn (one from mother-N and one from colourblind father-n)


man= XN Y





possible gametes (sex cells) =


man- 1/2 Y 1/2 XN


woman- 1/2 XN 1/2 Xn





Punnet Square:


.....................XN..........Y


XN...........XN.XN.....XN.Y


Xn............XN.Xn......Xn.Y





children= 1/4 XN XN, 1/4 XN Xn, 1/4 Xn Y, 1/4 XN Y


1/4 chance of having child with colourblindness


(the boy is colourblind as he has the genotype: Xn Y)








3)


BB=black Bb=tortoise shell bb=yellow





tortoise shell female= XB Xb


black male= XB Y





possible gametes (sex cells)


female= 1/2 XB 1/2 Xb


male= 1/2 XB 1/2 Y





punnet square:


...................XB..............Y


XB............XB XB......XB Y


Xb............XB Xb.......Xb Y





children: 1/4 XB XB, 1/4 XB Xb, 1/4 XB Y, 1/4 Xb Y


1/4 black girl, 1/4 tortoise shell girl, 1/4 black boy, 1/4 yellow boy
Reply:you should do your own homework
Reply:1 Xx colorblind gene 50% of the boys 0% of the girls 25% total





2


xx recessive blue woman


Xx colorblind gene


Xx heterozygous brown male


100% blue * 50% blue = 50% blue


males are still 50% colorblind since the x only comes from the mother


so .50*.50 = .25 so 25%





3


males only get 1 x so they can't be tortoise shell.


so its Bb X b


so bb, Bb, B, and b


so 25% yellow females 25% tortoise shell females, 25% black males and 25% yellow males
Reply:100% blue * 50% blue = 50% blue

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