Download Heredity not following the Rules

Heredity
not following
the Rules
Learning Goal:
predict possible outcomes of
various genetic combinations such
as non-Mendelian inheritance
Incomplete dominance=Blending

A heterozygous condition in which both alleles are
partially expressed, often producing an
intermediate or blended phenotype (which is
different than either of the homozygous forms).
Snapdragons
Incomplete dominance
Snapdragons
Incomplete dominance
RR
R’R’
RR’
RR RR’ RR’ R’R’
Incomplete dominance


Palomino horses are a cross between a
chestnut horse and a cremello (white) color
horse.
Practice the cross using a Punnett Square.
H’
H’
H
HH’
HH’
H
HH’
HH’
Codominance=Both Show

Codominance –Both phenotypes are dominant.
Instead, the heterozygous individual expresses both
phenotypes.
Co – both are dominant enough to be expressed!!
Dominique chickens
Codominance
BB - Black
WW - White
BW - Black and White
Cross a black
chicken with a
white chicken and
what to you get if
the traits are
CODOMINANT?
W
W
B
BW
BW
B
BW
BW
Predict the
outcome if BOTH
chickens are
dominique
(black and white)
????
Codominance
BB - Black
WW - White
BW - Black and White
B
B
W
BB
BW
W BW WW
BB=1
BW=2
WW=1
Codominance

Another example of codominance is ABO blood
typing. The blood types A and B are codominant
to each other; however, type O is actually
recessive to A and B.
Codominance
IBIB or IBi
ii
IAIB
IAIA or IAi
When both alleles exist,
both are present!
Codominance
Blood
Group
Antibodies
Can give
blood to…
Can
receive
blood from
AB
None
AB
A, B, AB,
and O
A
B
A and AB
A and O
B
A
B and AB
B and O
O
A and B
A, B, AB,
and O
O
Practicing Blood Types

A man of blood type IAIA marries a woman
with blood type IAIB. What is the chance they
will have a child with type IAIB blood?
IA
IB
IA
IAIA
IAIB
IA
IAIA
IAIB
Practicing Blood Types #2

O?
A man of blood type B marries a woman with
blood type O. What is the chance they will
have a child with type O blood?
i
i
IB
IBi
IBi
IB
IBi
IBi
i
i
IB
IBi
IBi
i
ii
ii
Multiple Alleles

Each individual can only have 2
homologous chromosomes thus 2 alleles
for a trait, but there could be more than 2
alleles present in a population. This type of
inheritance is known as multiple alleles.
Why can you only have 2
genes for each trait?
Because… you only have 2 of
each type of chromosome!!
Multiple Alleles - examples


Blood Type is an example of a trait that has
multiple alleles. There are 3 possible alleles
that could be inherited – A, B, and O, but you
can only inherit 2 of them.
Coat color in rabbits is inherited as a series
of multiple alleles.
Multiple Alleles - examples
Multiple Alleles - examples
What are all of the possible genotypes for a
1. dark-gray coated rabbit? (4)
CC Ccch Cch Cc
2. chinchilla rabbit (3)
cchcch
cchch
cchc
3. Himilayan rabbit(2)
c hc h c hc
4. White rabbit (1)
cc
Multiple Alleles - examples
Predict the phenotype for a rabbit with a cchch.
Chinchilla
Is it possible to obtain a white rabbit if one parent is white and
the other is chinchilla?
Yes. Only if the chichilla is cchc
Polygenic Inheritance

Polygenic inheritance is the inheritance
pattern of a trait that is controlled by two or
more genes. The genes may be on the
same chromosome or on different
chromosomes.


Height in humans
Skin color
Polygenic Inheritance
Gametes
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc
ABC
6
5
5
4
5
4
4
3
ABc
5
4
4
3
4
3
3
2
AbC
5
4
4
3
4
3
3
2
Abc
4
3
3
2
3
2
2
1
aBC
5
4
4
3
4
3
3
2
aBc
4
3
3
2
3
2
2
1
abC
4
3
3
2
3
2
2
1
abc
3
2
2
1
2
1
1
0
Polygenic inheritance in people showing a cross between two bi-racial parents (AaBbCc x
AaBbCc). Skin color is controlled by 3 different genes. The offspring contain seven different
shades of skin color based on the number of capital letters in each genotype.
Sex-Linked Inheritance
X and Y Chromosomes
are sex chromosomes
 Remember that genes
are located on
chromosomes
 XX are female and XY
are male
Sex-Linked Inheritance
X and Y Chromosomes
 The X and Y chromosome carry different
genes, so they are NOT homologous.
Sex-Linked Inheritance
How Sex is Determined
 Treat the cross the same as a monohybrid
 Father has genotype XY
 Mother has genotype XX
X
X
X
XX
XX
Y
XY
XY
Sex-Linked Inheritance



Traits found only on the X chromosome only
are called sex-linked
Males will only have one copy of this gene,
either the dominant or recessive form
Females will have two copies, and can be
homozygous dominant, heterozygous, or
homozygous recessive
Sex-Linked Inheritance
Sex-linked genes



The Y chromosome is missing
this portion of the X
chromosome
X chromosome contains over
2300 genes
Y chromosome contains only
25 genes, including the sexdetermining gene SRY

SRY directs the formation of male
anatomy
Sex-Linked Inheritance
Sex-Linked Crosses
 Write alleles so X is shown with a superscript
for the trait (XH Xh)
 Y has no superscript (Y)
 Females who are heterozygous for a
recessive trait are called carriers – they will
not show the trait, but can pass it to offspring
Sex-Linked Inheritance
Sex-linked crosses Practice Problem
 Hemophilia, a disease where blood does
not clot properly, is caused by a
recessive sex-linked allele. A female,
who is a carrier for hemophilia and a
normal male have a child. What is the
probability that the child will be born with
hemophilia?
XH
Xh
XH XHXH XHXh
Y
XH Y
XhY
Hemophilia inheritance
POPQUIZ!! (Just kidding)

A roan cow is the product of a red cow and
a white cow. What type of inheritance is
exhibited?
A.
B.
C.
D.
E.
F.
Complete dominance
Codominance
Incomplete dominance
Sex-linked
Multiple alleles
Polygenic
POPQUIZ!!

Curly haired people have the genotype HH, while
straight haired people have the genotype hh. A
wavy haired person is heterozygous. What type of
inheritance does this exhibit?
A. Complete dominance
B. Codominance
C. Incomplete dominance
D. Sex-linked
E. Multiple alleles
F. Polygenic
POPQUIZ!!

How well a person performs on an IQ test is
controlled by multiple genes. Which of the
following types of inheritance does this
exhibit?
A.
B.
C.
D.
E.
F.
Complete dominance
Codominance
Incomplete dominance
Sex-linked
Multiple alleles
Polygenic
POPQUIZ!!

Hair loss is a trait caused by a gene located
on the X chromosome. This trait would be
considered A.
B.
C.
D.
E.
F.
Complete dominance
Codominance
Incomplete dominance
Sex-linked
Multiple alleles
Polygenic
BTW
POPQUIZ!!

Kim has always wondered why her 2nd toe is
longer than her first. She recently
discovered that it is a dominant trait. This
trait is considered to exhibit A.
B.
C.
D.
E.
F.
Complete dominance
Codominance
Incomplete dominance
Sex-linked
Multiple alleles
Polygenic
POPQUIZ!!

Here is an easy one! Blood types fall under
the category of which type of inheritance?
A.
B.
C.
D.
E.
F.
Complete dominance
Codominance
Incomplete dominance
Sex-linked
Multiple alleles
Polygenic