Chapter 14 Notes

Pedigrees

 

What is a pedigree?

A chart that shows relationships within a family that is used to show inheritance of traits.

      Square indicates male.

      Circle indicates female.

      Shaded square or circle indicates the individual expresses the trait.

      Unshaded square or circle indicates the individual does not express  the trait or has the normal phenotype.

      Ĺ shaded square or circle indicates a carrier (heterozygous) individual.

      Horizontal line connecting circle to square indicates a marriage.

      Vertical line with a bracket connecting circles or squares to a marriage line indicates siblings (oldest child first)

      Roman numerals or capital letters indicate generations.

 

Autosomal Pedigree

In humans, cystic fibrous is an autosomal trait. Normal mucus formation is dominant to cystic fibrous.

 

In humans, cystic fibrous is caused be a recessive allele (ff) that causes over production of mucus in the lungs and digestive tract.  Suppose you are male #5 in generation III of the pedigree below. You have just married a young lady (#6) and she tells you that her mother had cystic fibrous.  You are now afraid that your children will inherit this awful disease so you have a pedigree of your family done.

 

HINT:

anytime parents donít have a trait but the child(ren) does, the parents are carriers (heterozygous).

 

HINT:

anytime one of the parents has a trait but the child(ren) doesnít, the child is carrier

(heterozygous).

 

 

NOTE: This is an autosomal trait because the males and females are affected equally.

 

Sex-linked Pedigree

In humans, hemophilia is a sex-linked trait. Normal blood clotting is dominant to hemophilia.

 

 

HINT: the child has it but the parent doesnít, the parent is a carrier (heterozygous).

 

NOTE: If a female has 3 or more SONS that do not have a sex-linked trait, she is very likely homozygous dominant.

 

NOTE: This is a sex-linked trait because more males are affected than females.