Can someone help me tell when a trait is reccessive or dominant for a Autosomal chromosome for Pedigree tree?

Question

Can someone also please explain how to get it?

like examples of when the trait is recessive for autosomal

and when the trait is dominant for autosomal

thanks

Answer 1

What's important for you to remember is that for a dominant trait, only one gene for that trait needs to be present for the trait to be expressed.  For a recessive trait, both parents would have to have at least one copy of the gene.

In a pedigree chart, the square or circle should be colored in if the trait is present to help you keep track.

If the trait shows up in every generation, it's most likely a dominant trait.  Remember also that if you cross a person who is even heterozygous for the dominant trait (say Dd) and their spouse is recessive (dd) when you figure the probability of the offspring in a Punnett square, about 1/2 of the children will have the dominant trait as a heterogygous genotype (Dd).

If the parent was homozygous dominant (DD) and the spouse was homozygous recessive, ALL the children would be heterozygous (Dd) and show the trait.

For a recessive trait, BOTH genes would have to be for the trait for it to be expressed (dd).  So if the other parent was homozygous dominant (DD) all offspring would be heterozygous (Dd) and none of the children would have the trait.  If the other parent was heterozygous (Dd) 1/2 of the children could show the trait.

So the best way to look for if the trait is dominant or recessive is that if dominant, it will show up in most generations (rows across on the pedigree: http://www.biology.arizona.edu/human_bio... ).  If it's recessive, it will often skip generations (rows).