Transcript Autosomal Dominance

Types of Inheritance:
Autosomal Dominance (A.D.):
If the genotype contains a dominant allele, the
phenotype will show the dominant trait.
If it does not contain a dominant allele, it will
show the recessive trait.
A.D. occurs on your autosomes, which are the 44
chromosomes that are not your sex
chromosomes.
This is the rule that Mendel came up with after
studying pea plants!
Examples of Autosomal Dominance
1.
2.
3.
4.
5.
Earlobe attachment
Hitchhiker’s thumb
Widow’s peak
Eye dominance
Mid-digital hair
Side note
• Genetic conditions may be referred to as
“autosomal dominant” or “autosomal
recessive”.
• AD – the trait is dominant
• AR – the trait is recessive
• Autosomal means it is not on a sex
chromosome (X or Y)
• These are always “either or” traits!
There are exceptions to this rule!
• Some traits are not “one way or the other” or
they do not have just one dominant form.
• We know several exceptions to this rule!
Co-Dominance:
A heterozygous genotype shows BOTH
phenotypes.
Both of the alleles present will show up
separately, they are equally dominant
Examples:
Red horse and white horse  roan coat
(both red and white hair)
Human blood types
Roan Coat Horses
Blood Types (Co-Dominance)
• Humans have different types of blood. You can
have A, B, AB, or O.
• Types of blood indicate what antigens are present
(or absent) on your red blood cells
• You have 2 alleles (one from each parent) for
blood type, making your genotype one of the
following: AO, AA, BO, BB, AB, or OO.
• A and B are both dominant, O means you do not
have any antigens!
Side note: You also have a + or • The positive and negative symbols represent
the presence or absence of the Rh factor (a
protein found in your blood).
• + means you have it
• – means you do not
+ can only donate to +
- can donate to – and +
Incomplete Dominance:
A heterozygous genotype displays a mix of the 2
traits in its phenotype.
The dominant does not fully cover up the
recessive – the recessive shows through
Examples:
Red roses and white roses  pink roses
Brown hair with red color tints
Black fur and white fur  gray fur
Polygenic:
Means “many genes”
The trait is controlled by more than one gene.
Examples:
Skin color
Eye color
Wheat kernel color
Hair color
Epistasis:
“Epi” means… top!
One gene suppresses or masks the effects of
another gene. (1 phenotype controlled by 2
genes)
Examples:
Square chin – masked if the person does not
have a prominent chin
Deafness – deafness gene can be masked with
a healthy gene
Sex-Linked (or X-Linked)
– An X-linked gene means the gene is carried on the sex
chromosome (the X chromosome)
– You have 2 sex chromosomes (XX = girl or XY = boy) in
addition to your 44 autosomes
– You get the X from your mom and either an X or a Y
from your dad
– Usually, these show up in men but they get it from
their mom!
– Examples:
• Color blindness
• Hemophilia
How sex-linked (or X-linked) disorders are
passed to offspring:
– X from mom, X or Y from dad = XX is a girl and XY
is a boy
– Sex linked disorders are found on genes that are
carried on the X chromosome
– They are usually recessive
– Men usually have these but they get them from
their mother because she contributes the X
chromosome that it is carried on…
Color Blindness
The picture shown above is the
Creamer Colorblindness test. A
colorblind individual can see the circle,
but not the star.
About Color Blindness
Example:
This red
band is the
color
blindness
recessive
gene
This is a
different
way of
looking at it,
but this is a
Punnett
Square!
Trisomy/Trisomies
(Extra chromosomes)
• Trisomy 21 – Down Syndrome
– 3 chromosomes on the 21st pair of autosomes
– Associated with older men and women (over 35)
becoming parents…
• At age 30 a woman has less than a 1 in 1,000 chance of
conceiving a child with DS. Those odds increase to 1 in 400
by age 35. By 42, it jumps to about 1 in 60.
– Symptoms: flat facial profile, low set small ears,
upward slant to the eyes, hyper-flexibility, cognitive
and physical delays, mental retardation… the extent
of these symptoms can vary from child to child.
Other Trisomy Disorders…
• Trisomy 18: Edward’s Syndrome
– 90% die within the first year
• Trisomy 13: Patau’s Syndrome
– 82% die within the first year
• Trisomy 16:
– The most common trisomy in humans, occurring in more
than 1% of pregnancies. This condition results in
spontaneous miscarriage in the first trimester.
• Trisomy involving sex chromosomes in humans
includes:
– XXX (Triple X syndrome)
– XXY (Klinefelter's syndrome)
– XYY (XYY syndrome)
Missing Chromosomes/Mosaics
• Turner’s Syndrome – Missing one of the 2 X
chrom. in a female (X instead of XX)
• Cri du chat – Missing part of chrom. #5
• Many others… but not common
• Mosaics: The abnormality is only found in
some (not all) cells in the body.
Other abnormalities
(Other ways chromosomes can “mess up” during meiosis
and fertilization)
• Deletion - loss of part of a chromosome
• Duplication - extra copies of a part of a
chromosome
• Inversion - reverse the direction of a part of a
chromosome
• Translocation - part of a chromosome breaks off
and attaches to another chromosome