Dominance and Multiple Allele Notes Mendels Principles A

Mendel’s Principles – A Review • Inheritance of traits is determined by genes. •

Exceptions to Mendel’s Work • Some alleles are neither dominant or recessive. • Many

Incomplete dominance – When the alleles are blended and the offspring have a mix

Heterozygous genotype Codominance – in this case both alleles are expressed. BB= black corn

Polygenic Traits • A polygenic trait is determined by multiple genes. (poly=many, genic=genes) Example:

Homologous chromosomes - Chromosomes occur in pairs. (homologous means “same”) - The different alleles

So far each gene we have discussed has been made of two possible alleles.

However, it is possible to have several different allele possibilities for one gene. Multiple

In traits with multiple alleles, each individual can carry any two of the several

In this case both A and B are dominant to O (recessive). A and

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

Practice Problems: 1. A mother is AB and a father is O. Draw the

2. A mother is IAi and a father is IB IB. Draw the punnett

3. If a child has AB blood which of the following could NOT be

Slides: 18

Download presentation

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.

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!

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

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

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

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

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.

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

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

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

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

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?

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