Sex inherited traits can be carried on the X or Y chromosomes, but they usually appear on the X chromosome. This is because the Y chromosome is small and has fewer genes than the X chromosome. There are three variations of how sex can influence traits. The first is X linked and X linked traits typically develop in males rather than females. This is because males only have one X chromosome while females have two. This matters because females have that second X chromosome that can combat a recessive trait in the other chromosome, while males only have one X so if that X is recessive they have the trait or disorder. That means that males cannot be a carrier and can only express the trait if present, but females are the carriers because it is more likely for them to receive one recessive X than two recessive X’s. The second variation is the sex influenced inheritance which are influenced by a person’s sex. For example if a male has one recessive allele he will express the trait, but females must have two recessive alleles in order to express the trait. This means that the same genotype will have differing manifestations in both sexes. The third variation is the sex limited inheritance and that is where a trait is expressed genetically in both sexes, but only appears in the anatomically correct sex. For example prostate cancer can only appear in a male, while ovarian cancer can only appear in a female. All three have differences and similarities. For example, in both sex influenced and sex limited inheritance a person can have have the same genotype as another person, but at the same time express a different phenotype. Sex influenced and sex linked inheritance are similar because in sex linked the female and male will both have one recessive X except the male will express the trait, while the female will only be a carrier. A good example of something that is caused by X linked is color blindness, which is typically found in males because they will have the one recessive X. A similar sex influenced trait is baldness, which like color blindness, is almost often seen in males for the same reason, because females require two recessive X’s, while males only require one. The differences between the three different types of inheritance occur mostly between the sex limited inheritance and the other two. For example, Sex limited causes different traits depending on the sex, while a sex linked trait, such as sickle cell, can appear in both sexes. Looking at all three variations of sex inheritance give me insight on some information I knew and also new information. For example, I never really knew much about sex limited traits before writing this blog.
Goldberg, D., & Goldberg, D. (2010). AP biology (3rd ed., p. 168). Hauppauge, N.Y.: Barron’s Educational Series.
Sex-Limited, Linked, and Influenced Traits. (n.d.). Retrieved May 22, 2015, from http://www.animalgenome.org/edu/blue_genes/sexlim.html
X linked Genteic Disorders. (2005, July 1). Retrieved May 25, 2015, from http://www.geneticalliance.org.uk/docs/translations/english/23-x-linked-t.pdf