12d

There are some important exceptions to Mendel’s principles

Incomplete dominance is when one allele is not completely dominant over another

Heterozygous phenotype is somewhere in between the two homozygous

One plant is homozygous for red flowers and the other is heterozygous for pink flowers. What are the possible offspring?

Similar to incomplete except both phenotypes are expressed

In certain chickens one allele codes for either black or white feathers

Combination is not grey but feathers that are speckled with black and white

A and B are codominant in blood, O is recessive

Phenotypes Genotypes

Homozygous A AA

Heterozygous A AO

Homozygous B BB

Heterozygous B BO

AB AB

O OO

A father is homozygous for A blood type and a mother is heterozygous for B blood type. What are the possible blood types of their child?

Most genes in nature code for more than 2 alleles

Example is fur color in rabbits. One gene codes for fur color but there are 4 possibilities

Pedigrees show the patterns of inheritance in a family

Squares are males

Circles are females

Shaded means presence of trait

Unshaded means absence of trait

• Shows a trait caused by a recessive allele

• Some examples are tay sachs disease and cystic fibrosis

Shows traits that are dominant passed from at least one parent

Examples are Huntington’s disease and cleft chin

Disease in which the body’s ability to control blood clotting is impaired

X-linked recessive disorder, meaning that men are more likely to get the disease because they only have one X