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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
RRR’R’
In Incomplete DOMINANCE, use the SAME letters since they both are weak!
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.
HH’ HH’
HH’ HH’
H
H
H’ H’
Codominance=Both Show
Codominance –Both phenotypes are dominant. Instead, the heterozygous individual expresses both phenotypes.
Co – bothboth are dominant enough to be expressed!!
Dominique chickens
Codominance
BB - Black WW - White BW - Black and White
BW BW
BW BW
B
B
W WCross a black Cross a black chicken with a chicken with a
white chicken and white chicken and what to you get if what to you get if
the traits are the traits are CODOMINANT?CODOMINANT?
Predict the Predict the outcome if BOTH outcome if BOTH
chickens are chickens are dominique dominique
(black and white) (black and white) ????????
In CODOMINANCE, use DIFFERENT letters since they both are strong!
Codominance
BB - Black WW - White BW - Black and White
BB BW
BW WW
B
W
B W
BB=1
BW=2WW=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
IAIA or IAiIAIB
ii
When both alleles exist, both are present!
Codominance
Blood Group
AntibodiesCan give
blood to…
Can receive
blood from
AB None ABA, B, AB,
and O
A B A and AB A and O
B A B and AB B and O
O A and BA, B, AB,
and OO
Which group is the universal donor?Which group is the
universal recipient?
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?
IAIA IAIB
IAIA IAIB
IA
IA
IA IB
AB?
Practicing Blood Types #2
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?
IBi IBi
IBi IBi
IB
IB
i i
O?
IBi IBi
ii ii
IB
i
i i
There could be 2 genotypes for the man: BB or BO
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
How many alleles
are there for
rabbit coat color?
Multiple Alleles - examples
What are all of the possible genotypes for a 1. dark-gray coated rabbit? (4)
CC Ccch Cch Cc2. chinchilla rabbit (3)
cchcch cchch cchc3. Himilayan rabbit(2)
chch chc4. White rabbit (1)
cc
Why is dark gray
a capital C?
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
XX XX
XY XY
X
Y
X XThe chance of
each sex being
born is 50%
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
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 sex-determining gene SRY SRY directs the formation of male
anatomy
Sex-linked genes
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?
XHXH XHXh
XH Y XhY
XH
Y
XH Xh
25%
chance
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. Complete dominance
B. Codominance
C. Incomplete dominance
D. Sex-linked
E. Multiple alleles
F. 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 dominanceB. CodominanceC. Incomplete dominanceD. Sex-linkedE. Multiple allelesF. 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. Complete dominanceB. CodominanceC. Incomplete dominanceD. Sex-linkedE. Multiple allelesF. Polygenic
POPQUIZ!!
Hair loss is a trait caused by a gene located on the X chromosome. This trait would be considered -
A. Complete dominance
B. Codominance
C. Incomplete dominance
D. Sex-linked
E. Multiple alleles
F. 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. Complete dominanceB. CodominanceC. Incomplete dominanceD. Sex-linkedE. Multiple allelesF. Polygenic
POPQUIZ!!
Here is an easy one! Blood types fall under the category of which type of inheritance?
A. Complete dominance
B. Codominance
C. Incomplete dominance
D. Sex-linked
E. Multiple alleles
F. Polygenic
HEE HEE