Solving Pedigree Problems

If you're behind a web filter, please make sure that the domains *.and *.are unblocked.- [Instructor] What you see depicted here is known as a pedigree.

Here is an example pedigree: One trick for identifying a recessive trait is that if a trait skips a generation in a pedigree, it is often an autosomal recessive trait (although a trait can be autosomal recessive and not skip generations).

These traits appear with equal frequency in both sexes.

And the trait of this particular pedigree is for is the trait of freckles. Although we might be able to infer some ideas about the genotype by seeing how the phenotype patterns spread from generation to generation.

And whether or not we're colored in, that is a phenotype. You just look at the person and say do they have freckles or not. But just going back to understanding the pedigree itself.

But let's just break it down, so we understand all of the different parts of a pedigree.

So big picture, a circle represents a female in the family. If either the circle or the square is colored in, like we see right over here, or we see right over here, that means that that person exhibits the trait. But once again, this phenotype, that's the observed characteristic, we don't know exactly the genotype just from this.When you have a horizontal line connecting a male and a female, it's called a marriage line.And it means that they are coupling up and they are reproducing. And then this vertical line that goes from that horizontal line, that's known as the line of descent.Because male offspring receive only one copy of the X chromosome, the trait is expressed phenotypically in all men with the X-linked recessive allele.Female offspring can also express an X-linked recessive trait although only if they inherit two X-linked chromosomes (one from each parent) containing the recessive allele.Autosomal recessive traits require two copies of the recessive allele to be expressed.Autosomal Recessive Autosomal recessive pedigrees can look differently based on the genotype of the parents.Instead, use the tables to test your understanding of the inheritance mechanisms.If you understand the mechanisms well, you should be able to generate the ratios quickly on test day. Many intro biology classes will expect you to be able to identify different patterns of inheritance and parental genotypes based on either a pedigree or the rates of a given phenotype in the offspring.It is helpful to be familiar with the phenotype ratios, pedigree charts, and the specifics of the inheritance mechanisms to solve those kinds of problems.