Download Complex Patterns of Inheritance

Complex Patterns of Inheritance
Complex Patterns of Inheritance
1. Incomplete dominance
2. Codominance
3. Multiple alleles
4. Sex linked inheritance
5. Polygenic inheritance
Incomplete Dominance
Inheritance pattern where the phenotype of a
heterozygote is intermediate between those of the two
homozygotes
Homozygous Red
Flower
RR
X
Homozygous
White Flower
rr
Heterozygous
Pink Flower
Rr
Incomplete Dominance
Parent
Offspring
Parent
Codominance
Inheritance pattern where phenotypes of both
homozygote parents are equally expressed in the
heterozygous offspring
Black Feathered Chickens
Homozygous Dominant
BB
X
White Feathered Chickens
Homozygous Recessive
bb
Codominance
Inheritance pattern where phenotypes of both
homozygote parents are equally expressed in the
heterozygous offspring
Black Feathered Chickens
Homozygous Dominant
X
BB
White Feathered Chickens
Homozygous Recessive
bb
Checkered Feathered Chickens
Bb
BB
bb
Bb
Codominance: phenotypes of both homozygote parents are equally
expressed in the heterozygous offspring
Multiple Alleles
-Although an offspring can only inherit two alleles for
one trait, sometimes more than two alleles exist for
that one trait
-Traits controlled by more than two alleles are said
to have multiple alleles.
Examples of a gene that has multiple
alleles:
Polygenic Inheritance
The inheritance pattern of a trait that is controlled by
two or more genes
-Polygenic inheritance causes wide variation among a
single trait.
Polygenic Inheritance
-In polygenic inheritance, a dominant allele contributes
a small but equal portion to the trait being expressed.
Examples of traits that are controlled
by polygenic inheritance:
Polygenic Inheritance
Example:
-Stem length in a plant is controlled by three different
genes: A, B, and C
-Each gene is on a different chromosome and has two
alleles, so each diploid plant has six total alleles for
stem length
-A plant that is homozygous for short alleles at all
three locations (aabbcc) will be 4 in tall, while a plant
homozygous for tall alleles (AABBCC) will be 16 in tall
-The existence of each tall gene gives the plant 2 inches in
height
Polygenic Inheritance
Sex-linked Inheritance
(-Sex determination:
-Autosomes: The 1st- 22nd pairs of homologous
chromosomes in somatic cells
-Sex chromosomes: the 23rd pair of chromosomes which
determine the sex of the individual
-Sex chromosomes found in females: XX
-Sex chromosomes found in males: XY)
Sex-linked Inheritance
-Sex linked traits: traits controlled by genes found
on sex chromosomes
-The alleles for sex-linked traits are written as
superscripts of the X or Y chromosome:
XRXr or XRY
-Just like normal alleles, each parent will pass on
one of two possible sex chromosomes to the
offspring.
R
r
Mom can pass on X or X
Dad can pass on XR or Y
Complex Patterns of Inheritance
1. Incomplete dominance
2. Codominance
3. Multiple alleles
4. Sex linked inheritance
5. Polygenic inheritance
Environmental Influences of Gene
Expression
-External environmental influences (temperature,
nutrition, light, chemicals) can affect gene expression
-Internal environmental influences (hormones) also
affect gene expression
Complex Inheritance of Human
Traits
1. Codominance in humans
Sickle-Cell Anemia
2. Multiple Alleles in humans
Blood type
3. Sex linked Traits in Humans
Color Blindness
Hemophilia
4. Polygenic Inheritance in humans
Skin color
5. Changes in Chromosome Numbers
Down Syndrome
Codominance in Humans
Example: Sickle Cell Anemia
-If you cross a homozygous
normal with a homozygous
sickle cell, the offspring will
have both normal and sickle
celled red blood cells
-The offspring will exemplify
codominance because it will
express the phenotypes of both
parents equally
Multiple Alleles in Humans
Example: Blood typing
-Possible blood types:
A, B, AB, O
-The I gene determines
blood type
-There are three alleles for
the I gene:
IA, IB, i
IAIA or IAi = Type A blood
IBIB or IBi = Type B blood
IAIB = Type AB blood
ii = Type O blood
Sex-linked Traits in Humans
Example: Hemophilia
-Much more frequent in males
than females
-Men need to inherit only one
recessive hemophilia allele for
them to express the disease
-Women need to inherit two
recessive hemophilia alleles to
express the disease
*SIMILAR TO HEMOPHILIA: COLOR BLINDNESS
Polygenic Inheritance in Humans
Example: Skin Pigmentation
-Skin pigmentation in humans
is controlled by four genes
-The range of possible skin
shades can be shown in a bell
shaped curve
Changes in Chromosome Numbers:
Example: Down Syndrome:
(Trisomy 21)
-Occurs as the result of the
presence of an extra 21st
chromosome
Changes in Chromosome Numbers:
Example: Down Syndrome:
(Trisomy 21)
-Occurs as the result of the
presence of an extra 21st
chromosome
-Karyotype: a chart of
chromosome pairs
valuable in identifying
unusual chromosome
numbers in cells
Complex Patterns of Inheritance
1. Incomplete dominance
2. Codominance
3. Multiple alleles
4. Sex linked inheritance
5. Polygenic inheritance