Transcript Beyond Dominant and Recessive Alleles

Beyond Dominant
and Recessive
Alleles
The Principle of Independent
Assortment= that genes for
different traits segregate
independently during the formation
of gametes.
Dominant or Recessive?
 Some alleles are
neither dominant nor
recessive, and many
traits are controlled
by multiple alleles or
multiple genes.
 BB, Bb, bb
Incomplete Dominance
 The heterozygous
phenotype is
somewhere in
between the two
homozygous
phenotypes.
 Blending
 Ex. Snapdragons
and Four O’clock
plants: red, white,
pink
Incomplete Dominance
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.
Multiple Alleles
 When genes
have 3 or more
alleles.
 Ex. Coat color in
rabbits.
 Ex. Human blood
types.
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.
Blood Types and
Codominance
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) ?
Sex- Linked Genes
 X &Y chromosome
determine sex,
genes located on
these are sex-linked.
 Colorblindness,
hemophilia, Muscular
Dystrophy located on
the X chromosome.
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.
COLORBLINDNESS
 A man with normal
XC
vision XCY marries
a woman with
XC XCXC
normal vision XCXc.
This woman is a
Xc XCXc
Carrier of the gene.
Y
XCY
XcY
 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