Question

In humans (and most animals), sex is determined using the X-Y system. The basis of this system is that the number of X chromosomes and Y chromosomes determines whether the individual will be male or female. A male will contain one X and one Y chromosome, while a female will contain two X chromosomes.

For this discussion, consider how the number of X chromosomes affects the inheritance of traits that are carried on the X chromosome. Does this make one sex more likely to display certain characteristics? Why or why not?

• Clearly explain how the number of alleles for sex-linked genes varies in males and females.
• Include how this affects the genotypes of each sex. In other words, are these terms applicable: homozygous, heterozygous, carriers, etc.?
• Considering a recessive genetic disorder that is carried on the X-chromosome, should a male child be more concerned if his mother has the disorder or his father has the disorder? Explain your reasoning. How might this differ for a female child?

Answer 1

1. Sex-linked is a trait that comprises of the gene is located on a sex chromosome. The traits generally affected by genes on the X chromosome.
2. The number of X chromosomes affects the inheritance of traits because the X chromosome is large in size with many genes thanas compared to the Y chromosome.
3. Yes, make one sex more likely to display certain characteristics. The characteristic of X chromosome for the phenotype is always expressed in males than females. This is because the male has only one X chromosome whereas females two X chromosomes.
4. The number of alleles for sex-linked genes is different in males and females. Male has only one allele abut female has two alleles.
5. Males are heterozygous and have two different allele X and Y but females are homozygous and have one X allele. If one of the X alleles is mutated than females are termed as a carrier of that allele
6. In the case of X-linked recessive disorder, a mutation in a gene on the X chromosome can lead to a change in phenotype of males.
7. The male should be more concern about the X-linked recessive disorder because they have single X allele that sufficient for the phenotypic change and development of the disorder in males.
8. If the mother is affected by an X-linked recessive disorder then it is a 100% chance of a male child getting affected because both the X chromosome of the mother are mutated.
9. If the father has a defect in X chromosome / affected then there are 0% chances of a male child getting affected. Hence if a mother is affected than a male child should be a concern.
10. In the case of female if the father is affected then there are 100% chances of daughters as a carrier of the disease. Even if the mother is affected there are 100% of daughter being a carrier of the disorder. Daughter is only affected if both parents have an inherent disorder.