5. Below are the karyotypes of two individuals What is the difference?

6. Below are two additional karyotypes. What is the difference?

7. What We Have Learned If you are female, the 23rd pair of chromosomes are homozygous XX If you are male, the 23rd pair of chromosomes are heterozygous XY

8. Based on what you know about the determination of sex in humans, Which parent determines the sex of the offspring?

9. The offspring of any mating between humans will have a 50:50 chance of having 2 X chromosomes, XX, which is female, or having one X and one Y chromosome, XY, which is male.

10. Drosophila (fruit flies), inherit sex chromosomes in the same way as humans. Some traits are controlled by genes located on sex chromosomes and are called sex-linked traits. The alleles for sex linked traits are written as superscripts of the X ? and Y ? chromosomes.

11. Because the X and Y chromosomes are not homologous, the Y chromosome has no corresponding allele to the one on the X chromosome. Remember that any recessive allele on the X chromosome of a male will not be masked by a corresponding dominant allele on the Y chromosome.

12. Since the Y chromosome has no corresponding allele to the one on the X chromosome any trait carried on the X chromosome will be expressed in males. In fruit flies red eyes (R) are dominant to white eyes (r). XRXRXRXRXRXRXRXR XRXrXRXrXRXrXRXr XRYXRYXRYXRY XrYXrYXrYXrY

13. X? X?X? X?X? X?X? X? Based on what we know about sex linked inheritance of eye color in fruit flies, what would be the genotype of the female fruit fly below?

14. Create a Punnet Square that shows the cross of a male fruit fly with white eyes with a homozygous dominant red eyed female.

15. X R X r XRXR XrXr Y XRXR X R Y

16. Color blindness in humans is also a sex linked trait that is carried on the X chromosome. X XX XX XX X Normal Vision XC XXC XXC XXC X but a carrier for color blindness XC XCXC XCXC XCXC XC Color Blind For Women there are three possibilities

17. Normal Vision X YX YX YX Y... But for males there are only 2 possibilities XC YXC YXC YXC Y Color Blind Remember that since the Y chromosome has no corresponding allele to the one on the X chromosome any trait carried on the X chromosome will be expressed in males.

18. If a color blind man marries a women with normal vision, what are the chances of one of their children being color blind? X C X XX X YX Y Y XCXC X YX Y

19. Woman who is a carrier for color blindness marries a normal vision man, what are the chances of one of their children being color blind? X C X XCXC X X C Y Y X X X YX Y