<p> Sex Linkage in Humans</p><p>A little back ground information It all started with Thomas Morgan in 1866. He was studying fruit flies. Fruit flies have only 8 chromosomes and reproduce very quickly. </p><p>In males the last 2 chromosomes are different. We call them X and Y chromosomes. In females the last 2 chromosomes are the same. We call them X and X chromosomes.</p><p>These hormones determine the sex of the individual.</p><p>Human Male  46 chromosomes, 23 pairs, one XY chromosomes  the Y chromosome is very small</p><p>Human Female  XX chromosomes</p><p> All of the chromosomes produced in the human body will have an X chromosome.</p><p> Only ½ of the males sperm will contain an X, the other half contain a Y chromosome</p><p> Therefore the sex of the offspring depends on which chromosome it gets from the father! Not the mother</p><p>Some traits are only past on my male or female sex chromosomes. This is called sex-linkage. For example red/green colour blindness. The gene for this blindness is located on the X chromosome. Females have 2 copies of the X chromosomes and males only have 1 copy. </p><p>Here is how it works:</p><p>Regular vision is dominant, red/green colour blindness is recessive. </p><p>For the female to be colour blind she needs to have the gene on BOTH of her X chromosomes. If only 1 X chromosome has the gene for colour blindness, then the other gene has the normal colour vision and it will be expressed because it is dominant.</p><p>If the male carries he WILL BE colour blind because his Y chromosome does not carry the corresponding full color vision gene to give him normal vision Example 1;</p><p>Red eye color (R) is dominant, and white (r) is recessive. The alleles are XR, Xr, x. </p><p>Draw a Punnett square for mating a female with white eyes and a male with red eyes. </p><p>Possible gametes from male Parent XR Y</p><p> r R r r Possible X X X X Y gametes from Female Parent Xr XRXr XrY</p><p>So the female will have Red eyes and the males will have white eyes. </p><p>Example 2;</p><p>Draw a Punnett square for mating a female with 2 alleles for red eyes and a male with white eyes Possible gametes from male Parent XR Y</p><p>XR XRXR XRY Possible gametes from Female Parent XR XRXR XRY</p><p>1. What percent of the offspring will have: White eyes ______Red eyes ______</p><p>1. a) 0% will have white eyes. b) 100% will have red eyes. 2. Are the male offspring able to pass on the trait for white eyes on to the next generation? </p><p>2. None of the male offspring have the white-eye allele so they cannot pass on the white-eye trait.</p><p>3. Are the female offspring able to pass on the trait for white eyes on to the next generation? </p><p>3. All of the female offspring have the white-eye allele so they can pass on the white eye trait.</p><p>4a. If having white eyes resulted in reduced vision in a fly, would any of the offspring also have reduced vision?</p><p>4. a) None of the offspring have the white-eye trait so none have reduced vision.</p><p>4b. Would any of the offspring be carriers of the reduced-vision trait?</p><p> b) The female offspring all carry one white-eye allele so they are all carriers.</p><p>4c. When any of the offspring be genetically free of the reduced vision trait?</p><p> c) The male offspring do not carry the white-eye allele so they are free of the trait. Sex Linkage in Humans</p><p>A little back ground information It all started with Thomas Morgan in 1866. He was studying fruit flies. Fruit flies have only 8 chromosomes and reproduce very quickly. </p><p>In males the last 2 chromosomes are different. We call them ____ and ____ chromosomes. In females the last 2 chromosomes are the same. We call them ___ and ____ chromosomes.</p><p>These hormones determine the ______of the individual.</p><p>Human Male  46 chromosomes, 23 pairs, one ______chromosomes  the Y chromosome is very small</p><p>Human Female  ______chromosomes</p><p> All of the chromosomes produced in the human body will have an X chromosome.</p><p> Only ½ of the males sperm will contain an X, the other half contain a Y chromosome</p><p> Therefore the sex of the offspring depends on which chromosome it gets from the ______! Not the mother</p><p>Some traits are only past on my male or female sex chromosomes. This is called ______. For example red/green colour blindness. The gene for this blindness is located on the X chromosome. Females have 2 copies of the X chromosomes and males only have 1 copy. </p><p>Here is how it works:</p><p>Regular vision is dominant, red/green colour blindness is recessive. </p><p>For the female to be colour blind she needs to have the gene on ______chromosomes. If only 1 X chromosome has the gene for colour blindness, then the other gene has the normal colour vision and it will be expressed because it is dominant.</p><p>If the male carries he ______colour blind because his Y chromosome does not carry the corresponding full color vision gene to give him normal vision Example 1;</p><p>Red eye color (R) is dominant, and white (r) is recessive. The alleles are XR, Xr, x. </p><p>Draw a Punnett square for mating a female with white eyes and a male with red eyes. </p><p>Possible gametes from male Parent</p><p>Possible gametes from Female Parent</p><p>So the female will have Red eyes and the males will have white eyes. </p><p>Example 2;</p><p>Draw a Punnett square for mating a female with 2 alleles for red eyes and a male with white eyes Possible gametes from male Parent</p><p>Possible gametes from Female Parent</p><p>1. What percent of the offspring will have: White eyes ______Red eyes ______2. Are the male offspring able to pass on the trait for white eyes on to the next generation? </p><p>3. Are the female offspring able to pass on the trait for white eyes on to the next generation? </p><p>4a. If having white eyes resulted in reduced vision in a fly, would any of the offspring also have reduced vision?</p><p>4b. Would any of the offspring be carriers of the reduced-vision trait?</p><p>4c. When any of the offspring be genetically free of the reduced vision trait?</p>