Pedigrees: Sex-Linked or Autosomal?

In this class, we went over pedigrees. We learned what each of the symbols mean, how to read a pedigree chart, and how to interpret the data from it:

From these types of charts, we can determine who is a female and male (female circle, male square), who shows the phenotype for the particular trait (colored vs. non-colored), and if it is not provided, we can make educated guesses on which of the other members of each generations must be carriers for the trait.

These types of trais help us determine whether a trait is sex-linked or autosomal.

A sex linked trait refers to the phenotypic expression of an allele that is related to the chromosomal sex of the individual involved.

In sex linked traits, if it is located on the Y-chromosome, it is a Y-linked gene. In this case, it is only inherited by males, because in most cases, males are born with the XY genotype (as shown on the right)

If it is found on the X chromosome, it is an X-linked gene. These genes can be inherited by both males and females. Since genes for a trait can have two alleles, one allele is usually dominant over the other one, the recessive. But in this case, since the chromosome for the male is somewhat "incomplete", the it has nothing to mask or cover the trait of the female. So regardless of the type of gene, the females trait will show in her sons, and possibly her daughters.





Autosomal traits are traits that are carried on the chromosomes that aren't the sex chromosomes (X and Y).