Dominance and Multiple Allele Notes

Mendel’s Principles – A Review Inheritance of traits is determined by genes. Genes are passed from parents to offspring. Alleles can be dominant or recessive. In sexually reproducing organisms – each adult has two copies of each gene – one from each parent.

Exceptions to Mendel’s Work Some alleles are neither dominant or recessive. Many traits are controlled by multiple alleles or multiple genes.

Genetic Interactions Incomplete dominance – When the alleles are blended and the offspring have a mix of their parent traits.  ex. Snap Dragons R = red W = white Offspring can be pink! white

Genetic Interactions Codominance – in this case both alleles are expressed. BB= black corn YY= yellow corn BY = black and yellow corn Heterozygous genotype

Incomplete Dominance or Codominance?

Incomplete Dominance or Codominance?

Incomplete or Codominance?

Polygenic Traits A polygenic trait is determined by multiple genes. (poly=many, genic=genes) Example: eye color and height Skin color is controlled by more than four genes

Multiple Alleles Homologous chromosomes - Chromosomes occur in pairs. (homologous means “same”)   - The different alleles of a gene occupy the same positions on each chromosome

Multiple Alleles So far each gene we have discussed has been made of two possible alleles.   Ex. B = blue b= yellow R = red r = white

Multiple Alleles However, it is possible to have several different allele possibilities for one gene.  Multiple alleles is when there are more than two allele possibilities for a gene. Coat color in rabbits is determined by a single gene with 4 possible alleles.

The gene for blood type has 3 possible alleles. Multiple Alleles In traits with multiple alleles, each individual can carry any two of the several possible alleles.   Ex. BLOOD TYPE The gene for blood type has 3 possible alleles. IA, IB, and i

Blood Type In this case both A and B are dominant to O (recessive). A and B are codominant (both expressed)   So... there are four human blood types Genotype Phenotype IAIA, IAi Blood type A IBIB, IBi Blood type B IAIB Blood type AB ii Blood Type O

Multiple Alleles Alleles for blood type are: -IA (dominant) -IB (dominant) -i (recessive)

Blood Type Practice Problems: 1. A mother is AB and a father is O. Draw the punnett square. IA IB i   What is the probability their offspring will have A type blood? ____ Can they have an offspring with O blood? ____

Blood Type 2. A mother is IAi and a father is IB IB. Draw the punnett square.   What is the probability their offspring will have B type blood? Can they have an offspring with O blood?

Blood Type 3. If a child has AB blood which of the following could NOT be the parents? a) ii, IAIB b) IAi, IBIB c) IBIB, IAIA d) IAi, IBi