Sex Linked Gene is the phenotypic expression of an allele that is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on non-sex chromosomes, where both sexes have the same probability of expressing the trait. Since, in humans, there are many more genes on the X than there are on the Y, there are many more X-linked traits than there are Y-linked traits.
A particularly important category of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked.
Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes.I think in males if one gene is recessive, it will be expressed in his phenotype, while in females, it will only be expressed if two of her genes are affected.
*Examples of Abnormal Conditions Caused by Sex Linkage…
1. Hemophilia
2. Color Blindness
3. Muscular Dystrophy
4. Fragile X-Syndrome
Queen Victoria’s Pedigree on Hemophilia…
I’m wondering from where Queen Victoria got the hemophilia allele. Her mother and father have normal alleles. I think,mutation occured in that allele on one of Queen Victoria’s X chromosomes.
Sex-Linked Gene
-The disease in X-linked gene is more common in males than in females because females have two X chromosomes while males only have one. This means, females can only inherit the disease if both of her parents are inflicted. While in males, if their mother is inflicted, surely, they will also be inflicted.
*Example:The father is normal and the mother is a carrier. Will they have a hemophiliac son?”H”
Female XHXh x Male XHYH
XH YH
XH XHXH XHYH
Xh XhXH XhYH
Genotypic Ratio: 1:1:1:1
Genotype: FEMALE(XHXH, XhXH) MALE(XHYH, XhYH)
Phenotype: F normal, carrier M normal, inflicted
Phenotypic Ratio: 2:1:1
Answer: There will be a 25% possibility for them to have a hemophiliac son.
Note:
-If a woman is a carrier of and her partner is normal, their sons will have a 50% chance in inheriting the disorder, none of their daughters will have it, but 50% of them are likely to be a carrier
-If a man is inflicted and his partner is normal, since the girls will be the only one to receive the X chromosome from the father, none of the boys will inherit the disorder but the girls would be carriers.
Y-Linked Gene
-It refers to a trait carried by Y chromosome. Because only males have Y chromosome, the genes are simply passed from father to son.
*Example of Y-linked Gene
1. Hypertrichosis- it is a condition where there is an excessive body hair found in the ears.
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