Download NonMendelian Inheritance PPT

Genome references
• Ch “X and Y”: Conflict (sexual
antagonism)
• Ch 9: Disease (Blood Type/ Disease)
• Ch 15: Sex (Genetic Imprinting)
• Ch 4: Fate (Huntingtons)
Where do we get genetic
variability in a population?
1. Random Mating
--Sexual Reproduction
--Meiosis
--crossing over
2. Mutation
NonMendelian Inheritance Patterns
There are other patterns of inheritance that
do not follow Mendel’s Principles.
Be sure you recognize what is different or
what Law is violated by these different
patterns.
1. Co-dominance=when two alleles
are both expressed (neither masks
the other)
• Ex = human blood type
• 3 different alleles = IA, IB, and i that code
for A, B, and “o” blood types.
• IAIB  Type AB blood (Co-dominant)
(genotype)
(phenotype)
Why the different blood types?
• Because there is a connection between
blood type and susceptibility to disease.
• Genome Chapter 9 (“Disease”)
--AB nearly completely resistant to
Vibrio cholera (a diarrheal) disease
--O slightly more resistant to malaria
2. Incomplete Dominance
• Also known as “blending” b/c neither
allele in a pair is fully expressed
• Example seen in Shorthorn Cattle
C = color gene with
alleles possible = CR (red), CW (white)
• Cross a red bull with a white cow (Punnett
Square)
Shorthorn Cattle
CR CW (Roan)

3. Linked genes = found on the
same chromosome
• Ex: the genes for petal shape & color are
linked (C=curved or c=straight / W=white
or w=blue); C & w are linked, c & W are
linked
• Cross two heterozygotes (Punnett Square)
• What Mendelian law do these results
violate?
Crossing over switches linked genes
Recombination Frequency
• Linkage map can be determined by using
recombination frequency calculations
• See p. 293-5
Nondisjunction
4. Epistasis (“stopping”)
• A gene at one locus alters (usu. inhibits)
the phenotypic expression of a gene at
another location.
• Ex: Fig 14.12 on p. 273 ( labradors)
5. Sex-linked Traits
• Also known as “X-linked”
• Example = Color blindness in humans /
normal color seeing is dominant to color
blindness but the gene that codes for this
trait is linked (found on) the X
chromosome
• X-C codes for normal color vision
• X-c codes for color blindness
• y doesn’t code for color-seeing
What # do you see?
• Light-sensitive opsin
proteins made in the eye
& necessary for color
vision, are encoded by a
cluster of genes on the X
chromosome.
• Mutations in these genes
can lead to an
insensitivity to certain
colors (like red and
green) when seen
together.
Eye Color in Fruit Flies
6. X Inactivation
• The phenomenon in a female by which one X chromosome
(either Mom’s or Dad’s) is randomly inactivated in an early
embryonic cell, with fixed inactivation of that same X in all
cells descended from that cell. Ex: Tortoise Shell Cat
• X inactivation is not restricted to females. It also occurs in males
with Klinefelter syndrome who have more than one X
chromosome. The phenomenon is also called lyonization after
geneticist Mary Lyon who first described it.
7. Sex-influenced Traits
• Aka, Gender-influenced
• Usually influenced by sex hormones like
estrogen, testosterone
• Examples include baldness in humans,
plumage in birds, horns on cattle
8. Multiple Alleles (vs. just two)
• Sometimes a trait is coded for by more
than just two alleles
• Example = human blood type has 3 alleles
A, B, or O
@ 9q34
9. Polygenic Traits
• More than one set of genes coding for a
trait (NOT the same as multiple alleles)
• Eye color is influenced by many genes
coding for different kinds of pigment as
well as where in the iris those pigments
are found (some have been located on
chromosomes 15 & 19)
10. Environmentally-influenced
• Color of the Hydrangea flower determined
by the pH of the soil
• Acidic soilblue flower
• Basic soilpink flower
• How about “intelligence” in humans?
11. Transposons (Jumping Genes)
& Their Effect On The Kernel Color
Of Indian Corn
• The explanation?
Involves "jumping
genes" or
transposons, and
earned Dr. Barbara
McClintock the
Nobel Prize in
Medicine (1983).
Grains of Indian corn
come in
different colors like purple
or yellow. But what
happens when they
appear mottled (have
streaks)?
• This mottling effect defies Mendel's basic
principles of genetics b/c individual grains
may be multicolored rather than just one
single color or another (purple vs. yellow).
How do Jumping Genes Work?
• Transposons are genes that move from
one location to another within or between
chromosomes. In the pigmented layer of
corn grains, the position of transposons
may inhibit or block pigment production in
some cells.
• Examples (from “DNA’s New Twists”):
-- “Air gene” in Volvox when cold
-- P element betw. Drosphilia species
via mite gut infection
Transposons move
directly from one
position to another
within the genome
using a transposase
enzyme to "cut and
paste" them within
the genome.
12. Genomic Imprinting
• A fundamental belief of Mendelian
principles of inheritance is that a
gene's parent of origin does not
influence its dominance or
recessiveness in determining
phenotype. (Ex: if you inherit a
dominant allele from either parent, the
offspring will express it, right?)
• However, in sexually reproductive
organisms, the parental origin of genetic
alleles often determines their fates. For
these imprinted genes, the diploid
offspring distinguishes between
maternally-inherited and paternallyinherited alleles, and selectively expresses
only one of them while inactivating the
other.
• In recent years it has become
apparent that the parental origin of
genetic material DOES have an
impact on gene expression and this
effect has become known as
genomic (genetic) imprinting.
Who’s your Daddy?
See http://epigenome.eu/en/2,5,126 on how ligers created by male
lions mating with female tigers are much larger than tigons created
by a male tiger with a female lion.
Genetic Cause of PWS
• In Prader-Willi
syndrome, these
critical genes are
missing (deleted) from
the father’s
chromosome 15,
functioning improperly
because of an
imprinting defect.
Who gave me the defects now?
• When a deletion of chromosome
15q11-q13 region is found on the
mother’s chromosome 15, the result
is an entirely different = Angelman
syndrome.
• Because the genetic errors happen in
the same section of chromosome 15,
PWS and AS are sometimes called
“sister” syndromes even though the
disorders have few features in
common.
• The two syndromes are not
at the same genetic locus,
but are controlled by genes
that are within a small region
of chromosome 15 leading to
very different phenotypes:
• Prader-Willi  Severe
obesity, hyperactivity &
severe mental retardation.
• Angelman  Absence of
speech, mild to moderate
mental retardation, small
hands/feet, laugh a lot,
dancing gait so called
“Happy Puppet syndrome.”
Treatment for Angelmann’s?
• Science News 1/28/2012 (p. 8)
• Class of chemotherapy drugs turns on the
inactive gene of Dad’s chromosome in the
brain cells of mice.
Evolutionary Significance?
• A widely accepted hypothesis for genomic
imprinting is the "parental conflict
hypothesis" (Moore and Haig 1991) = the
inequality between parental genomes due
to imprinting is a result of the differing
interests of each parent in terms of the
evolutionary fitness of their genes. (Read
Genome “X/Y Conflict.” )
• The father is more 'interested' in the
growth of his offspring, at the expense of
the mother. The mother's interest is to
conserve resources for her own survival
while providing sufficient nourishment to
current and subsequent litters.
Accordingly, paternally expressed genes
tend to be growth promoting whereas
maternally expressed genes tend to be
growth limiting. (mouse study)
The Legacy of Solid Gold
• Scientists have pinpointed the genetic
mutation on chromosome 18 that causes
lambs to develop large and muscular
rumps--a trait known as callipyge, from the
Greek for 'beautiful buttocks.’
• Only lambs that inherit the callipyge
mutation from their father but not their
mother develop the trait.
Crespi & Babcock: Our minds,
too, are shaped by conflict
between our parents’ genes.
Mothers: want offspring w/ moderate demands.
Fathers: want behaviors that get more resources
from mom; nurse, demand more attention.
Angelman & Prader-Willi syndromes arise
from mutations to imprinted genes
• In Angelman, the
• In Prader-Willi,
same segment of
mom’s genes are
silenced, allowing
genes is deleted so
these offspring
Dad’s genes to act
w/out constraint.
make few
They nurse a lot,
demands of
they smile, laugh
mother—do not
gaining attention.
nurse
More on Parental Tug-of-War
• Children w/ autism show signs of father-imprinting
(aggressive growth of placentas).
• Children w/ schizophrenia appear to be influenced by
mother-dominated genes (low birth weight & slow growth
benefit mom).
• Autistic: difficult time figuring out what people are feeling
paternal genes may reduce such distractions so they get
more resources from Mom.
• Schizophrenic: too concerned about others (too much
empathy, even believe inanimate objects are talking to
them) maternal genes boost our abilities to be in-tune
w/others.
Crespi & Badcock
Pedigree Analysis
Autosomal Recessive
Sex-linked Recessive
Autosomal Dominat