Download (dominant) -i

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 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
IA IA, IAi
Blood type A
IB IB, 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