Mendelian Genetics in People

Objectives

• Explain multiple allele traits
• Distinguish autosomal from X-linked traits

Genes like blood type have more than two alleles.

Polygenic traits are controlled by more than one gene.

Polygenic Traits

• May be on same chromosome...
• Or on nonhomologous chromosomes
• Thus, inheritance is very complicated.
• E.g., skin color and height

Environmental Effects

• Poor nutrition may prevent one from reaching full height
• UV light can increase skin pigmentation

Earlobe attachment is an autosomal trait. The allele for free-hanging (F) earlobes is dominant over attached (f).

Other autosomal traits

• Widow's peak
• Hitchhiker's thumb

Because males only have one X chromosome, a recessive x-linked trait is always expressed in males.

Females have two X chromosomes and thus must inherit two copies of the recessive allele to exhibit the recessive trait.

X-linked traits

• Red-green color blindness
• Hemophilia A