Human Genetics It’s all in the…

Inheritance Parents and offspring often share observable traits. Grandparents and grandchildren may share traits not seen in parents. Why do traits disappear in one generation and reappear in another?

A pedigree is a chart that shows how a trait and the genes that control it are inherited within a family.

Genetic predictions Ellen and Michael’s parents must be carriers. Ellen’s brother Michael has sickle cell anemia, an autosomal recessive disease. A a A a AA Aa aa Ellen is not affected and cannot carry aa genotype What is the chance that Ellen’s child has a sickle cell anemia allele (a)? Ellen Michael ? Chance Ellen is a carrier = 2/3 Chance child inherits sickle cell allele = 1/2 Overall chance child carries sickle cell allele from Ellen = 2/3 x 1/2 = 1/3

Autosomal recessive inheritance Heterozygous individuals carry the recessive allele but exhibit the dominant phenotype. Males and females are equally affected and may transmit the trait. May skip generations.

Sex chromosomes determine gender Human males are the have two different sex chromosomes, (XY). Human females only have one (XX).

What determines gender? Number of X chromosomes, or presence of Y chromosome? X0 Female with Turner syndrome XXY Male with Klinefelter syndrome

X-linked traits Males One X chromosome Inherited from mother Two possible genotypes XNY XnY Have trait or do not have trait- they can’t be a carrier! Females Two X chromosomes Inherited from both parents Three possible genotypes XNXN XNXn XnXn Heterozygous individuals are carriers of recessive traits- they can pass it down to their offspring- especially their male children!

X-linked recessive traits Always expressed in males if the male inherits the recessive gene from the mother. Affected males: Inherited from mother Females need to be homozygous recessive to show the trait Affected females : Fathers affected or mother had the trait or carried it!

X-linked dominant inheritance Expressed in females with one copy. Males are often more severely affected. Typically associated with miscarriage or lethality in males.

BLOOD TYPE Human blood type genes are an example of a codominant trait- meaning a trait with more than one set of alleles. Phenotype : A B AB O Genotype : AO, AA BO, BB AB OO