Genetic Crosses
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?