Transcript Genetics Beyond Mendel Incomplete Dominance Phenotype is a blend of the alleles An intermediate is seen Four o’clocks Homozygous Red Heterozygous Homozygous White Sometimes written: C and C1 Incomplete.

Genetics Beyond Mendel
Incomplete Dominance
Phenotype is a blend of the alleles
An intermediate is seen
Four o’clocks
Homozygous Red
Heterozygous
Homozygous White
Sometimes written: C and C1
Incomplete Dominance - Humans
Hair Follicles
– Curly hair is homozygous recessive
– Straight hair is homozygous
dominant
– Heterozygous individuals have
wavy hair
Incomplete Dominance - Humans
Cholesterol Gene
– Homozygous
dominant – Very
high cholesterol
– Heterozygous –
high cholesterol
– Homozygous
recessive – normal
cholesterol
Multiple Allele Traits
More than two alleles for a trait
Only two forms are inherited
Can have co-dominance
Can have a hierarchy of dominance
– hair color in mice determined by a single gene
with alleles for black, brown, agouti, gray,
albino
agouti > black > brown > albino.
Codominance
Both alleles are expressed
at the same time
Roan horse appears
grey but has a mixture
of white and black
hairs
Hybrid camellia
Blood Types
Multiple Alleles (3) and Co dominant
A, B, O alleles produce:
AA = A
AO = A
AB = AB
BB = B
BO = B
OO = O
Four blood type phenotypes
Sometimes written IA IB i
Polygenic Inheritance
More than one set of
alleles controls a trait
Skin color has three
different sets
Effect is additive
Environment and Inheritance
Gene expression is influenced by the
environment
Chemicals, temperature, pH levels, radiation,
nutrition can all be factors
Himalayan rabbits – fur changes color with exposure to cold
Environment and Inheritance
Turtles
– Sex determined by temperature of eggs
– Males produced at lower incubation
temperatures than females
– At temperatures around 30 degrees Celsius
only female turtles arise
Lizards and crocodilians
– Females produced at lower temperatures,
males at higher temperatures
Gender Inheritance
Due to one set of
chromosomes in
humans
XX = female
XY = Male
One X must come from
mother
Sperm can donate an X
or Y
Sex is determined at
fertilization
Sex-linked Inheritance
Sex linked traits:
– Genes that are carried by either sex chromosome
– Y linked genes appear on Y chromosome
– X linked genes appear on the X chromosome
Only men inherit Y chromosomes
– Only ones to inherit Y-linked traits
Men and women both inherit X chromosomes
– Both can get the X-linked traits
Sex-linked Inheritance
Males –
Genes on the X chromosome
that do not code for gender are
expressed
Even recessive genes
No corresponding gene on the
Y chromosome.
Sex-linked Inheritance
Females –
Recessive allele on one X
chromosome is masked by a
dominant allele on the other
Women are frequently
carriers of X-linked traits but
rarely have them expressed
in their own phenotypes.
Sex-linked Inheritance
X chromosome
carries coat
pigment genes
One X chromosome
randomly becomes
deactivated.
The active X
chromosome
determines the
color in that
particular cell
Sex-linked Inheritance
A human female "carrier“ heterozygous for sexlinked trait causing red-green color blindness
(recessive) marries a normal male
What proportion of their male progeny will have
red-green color blindness?
Genotype of parents
Mother:
heterozygous for red
green color blindness
½ of the
daughters
are carriers
½ of the
daughters
are normal
Father:
homozygous dominant
on X no allele on Y
½ of the
sons are
color blind
½ of the
sons are
normal
The two most
noted X linked
genetic disorders
are hemophilia
and color
blindness
Pedigree Diagram
Visual chart of a family’s genetic history
Pedigree Diagram
Pedigree Diagram
Pedigree Diagram