Beyond Dominant and Recessive

1
Beyond Dominant and Recessive
2
Dihybrid Cross

• Describes the simultaneous inheritance of two or
  more traits in the same organism
• The male gives four types of allele combinations
  and the female gives four types of allele
  combinations
• The resulting ratio is 9331

3
Law of Independent Assortment

• Random distribution of alleles occurs during
  gamete formation
• Genes on separate chromosomes sort independently
  during meiosis.
• Each allele combination is equally likely to
  occur.

4
Dominant or Recessive?

• Some alleles are neither dominant nor recessive,
  and many traits are controlled by multiple
  alleles or multiple genes.
• BB, Bb, bb

5
Incomplete Dominance

• The heterozygous phenotype is somewhere in
  between the two homozygous phenotypes.
• Blending
• Ex. Snapdragons and Four Oclock plants red,
  white, pink

6
Incomplete Dominance
7
Codominance

• Both alleles contribute to the phenotype of the
  organism.
• Ex. Cattle red hair is codominant with the allele
  for white hair. Cattle with both alleles are
  roan (pinkish brown).
• Ex. Chickens with speckled feathers.

8
Multiple Alleles

• When genes have 3 or more alleles.
• Ex. Coat color in rabbits.
• Ex. Human blood types.

9
Blood Types and Codominance
10
Blood type problem

• Charlie Brown and Peppermint Patty got married.
  What possible genotypes will the children have if
  Patty has type A blood (IAIO) and Charlie has
  type AB
• (IAIB) ?

11
Polygenic Traits

• Traits controlled by 2 or more genes.
• Ex. Eye color in fruit flies (3 genes).
• Ex. Human skin color. Wide range of skin colors
  because 4 genes control color.

12
Sex- Linked Genes

• X Y chromosome determine sex, genes located on
  these are sex-linked.
• Colorblindness, hemophilia, Muscular Dystrophy
  located on the X chromosome.

13
X-Linked Alleles

• Males have only one X chromosome.
• All X-linked alleles are expressed.
• Females- both of the recessive alleles have to be
  present to have colorblindness.
• Men pass their X chromosome along to their
  daughters.
• X-linked genes ?father?daughter?son.

14
Colorblindness

• A man with normal XC Y
• vision XCY marries
• a woman with XC
• normal vision XCXc.
• This woman is a Xc
• Carrier of the gene.

15

• What is the probability that a daughter will be
  colorblind?
• O chance of colorblind daughters
• What is the probability that a son will be
  colorblind?
• 50 chance of colorblind son