Download Patterns of Inheritance

Patterns of Inheritance
Biology
Vocabulary
 Homozygous- The offspring are homozygous
if the alleles from each parent are the same.
 Heterozygous- The offspring are
heterozygous if the alleles from each parent
are different.
 Gamete- A haploid reproductive cell, such as
an egg or sperm. Two gametes make an
offspring.
Predicting the Outcome of a
Cross
These punnet squares show a variety of
crosses between homozygous or
heterozygous purple plants and
homozygous white plants.
The purple plant is homozygous
dominant:WW. Each gamete it produces has
a W allele.
W
w
w
W
Genotype: Ww
heterozygous
Genotype: Ww
heterozygous
Phenotype:Purple
Phenotype:Purple
Genotype: Ww
heterozygous
Genotype: Ww
heterozygous
Phenotype:Purple
Phenotype:Purple
The white plant is homozygous recessive:ww. Each
gamete it produces has a w allele.
Both plants are purple. They are
heterozygous: Ww. They produce gametes
with either a W or w allele.
W
W
w
w
Genotype: WW
homozygous
Genotype: Ww
heterozygous
Phenotype:Purple
Phenotype:Purple
Genotype: Ww
heterozygous
Genotype: ww
homozygous
Phenotype:Purple
Phenotype: White
The purple plant is heterozygous: Ww. It
produces gametes with either a W or w allele.
W
w
w
w
Genotype: Ww
heterozygous
Genotype: ww
homozygous
Phenotype:Purple
Phenotype:White
Genotype: Ww
heterozygous
Genotype: ww
homozygous
Phenotype:Purple
Phenotype: White
The white plant is homozygous recessive: ww. Each
gamete it produces has a w allele.
Incomplete Dominance
 Offspring appears to a blending of its parents
traits.
 Ex: white snapdragons + red snapdragons=
pink snapdragons
 The red and white snapdragons are both
homozygous, but neither are dominant over
the other.
 The pink snapdragons are heterozygous.
Codominance
 Sometimes both genes in a heterozygote
offspring are fully expressed.
 Ex: Coat color in horses. A red horse
(homozygous) + a white horse
(homozygous)= a roan horse (heterozygous).
 Roan means that the horse’s coat is made
up of both red and white individual hairs.
Multiple Alleles Can Control
One Trait
Some traits are controlled by genes that
have more than two alleles.
Combinations of any two of these
alleles can produce different
phenotypes.
Ex: human ABO blood groups
Human ABO Blood Groups
The four human blood groups are
controlled by three different alleles; IA,
IB, and i. But a person can have only 2
alleles for any gene.
Phenotype
Genotype
A
B
IAIA or IAi
IBIB or IBi
AB
I AI B
O
ii
Polygenic
A trait that is controlled by more than
one pair of genes.
The genes for a polygenic trait could be
scattered along the same chromosome
or located on different chromosomes.
Ex: height, weight, body build, hair and
skin color.
Environmental Factors
Phenotype often depends on the
environment.
Ex: arctic fox are white in the winter and
brown in the summer because of
enzymes that manufacture pigments.
What other examples can you think of?