Genetic Crosses

Incomplete Dominance

• One allele for a trait is not dominant over the other

• Heterozygous condition produces a phenotype that is intermediate of the two alleles

• Use capital form of two different letters

Incomplete DominanceRed Snaps White Snaps

RR WW

RWAll Pink

RW X RW

Codominance

• One allele for a trait is not dominant over the other

• The heterozygous condition produces a phenotype in which both variations appear

Codominance

Try these two1) In cats when a long tailed cat is bred with a no

tailed cats short tailed cats are produced. If a short tailed cat was bred with a no tailed cat, what is the likelihood that a short tailed cat would be produced? Is this incomplete or codominance?

2) Also in cats a black haired cat and a white haired cat produce a tuxedo (mix of black and white). If a two tuxedo cats were bred, what would be the likelihood of producing a white cat? Is this incomplete or codominance.

Sex-Linked Traits Activity

Genotype Phenotype Group Total Overall Total

XHXH Normal Female

XHXh Carrier Female

XhXh Hemophiliac Female

XHY Normal Male

XhY Hemophiliac Male

Sex Linked Traits• Traits that have a gene (allele) located

on a sex-chromosome. Most traits the gene is located on the X chromosome

• Since males have only one of two X chromosomes they only need one recessive gene to carry the trait.

• Must include sex chromosome in cross

• Examples are colorblindness and hemophilia

Colorblindness Test

Sex-linked Trait example• Normal vision is dominant to

colorblindness. A heterozygous (carrier) female marries a normal male.

3-2-1 Think about

• List 3 human traits that seem to have a range of possible variations (rather than simply 2 or even 3 distinct variations)

• Describe 2 reasons why you think traits could have a range of variations

• Give one definition for the word POLYGENIC

Polygenic Traits• Traits controlled by more than one

gene.

• Usually creates a range of variations possible

• Examples: Eye color, skin color, hair color, height

• See Child/Grandchild lab for examples

Answer the following

• How similar or different does your child look compared to you in terms of hair, eye, or skin color?

• How could the genotypes of the child change to make them look more/less similar than you?

Multiple Alleles

• More than two alleles (gene variations) for a trait.

• Example A B O blood types

Blood Type

Blood Type

Genotype Antigen on Blood

Antibody for:

Donate /Receive

A IAIA IAi

B IBIB IBi

AB IAIB

O ii

Blood Type Examples

• A woman with O blood and man with A blood marry. Could they have a child with O blood? Could it be possible that there is no chance of having children with O blood?

• A man with B blood marries a woman with AB blood. They have a child with A blood. What has to be dads genotype? Prove it.

• A man with A blood (IAIA) and woman with B blood (IBIB) have a child. The child needs a blood transfusion. Do they need to worry about the child getting the wrong type of blood? Why or why not?