Transcript Use sex chromosomes and alleles.

Unit 5 – Genetics
Other forms of inheritance
Not all traits are simply dominant or recessive, with only
2 possible alleles.
Incomplete Dominance =
BLENDING in heterozygotes
Neither allele is dominant over the other, so
individuals with a heterozygous genotype
show a blended phenotype somewhere in
the middle. (i.e. red + white=pink)
 Use different letters to represent each
possible allele (instead of Rr use RW since
there is not dominant or recessive allele)
 Examples Beta fish, flower color such as
roses or snapdragons.


EXAMPLE:
◦ Red flowers x White Flowers = Pink
flowers
Choose letters to represent each
phenotype
Red = RR White = WW Pink = RW
 Cross a red parent with a white parent &
give phenotype and genotype ratios of
offspring.

Phenotype ratio: 100% Pink
Genotype ratio: 100% heterozygous
You Practice

Cross 2 pink flowers
R
R
W
W
RR
RW
RW
WW
Phenotype: 25% Red, 25% White, 50% Pink
Genotype: 25% Homozygous Red, 25% Homozygous White, 50%
Heterozygous
Co-dominance = TOGETHER or
SPOTTED – both traits are FULLY
and SEPARATELY expressed
 Co means together, and BOTH alleles are
dominant so they show up together. Ex:
hair color in humans, fur color in cattle.
 Use different letters to represent each
possible allele (instead of Bb use BW
since there is not dominant or recessive
alleles)

Sample
cross…black and
white fur in cows.
BB = Black
WW = White
BW = Black AND
White hairs
together
Cross a cow and a
bull that have black
and white hairs.
B
B
W
W
BB
BW
BW
WW
Phenotype: 25% Black, 25% white, 50% black and white
Genotype: 25% homozygous black, 25% homozygous white,
50% Hetero
You Practice

Cross a white cow with a black bull.
W
B
B
W
BW
BW
BW
BW
Phenotype: 100% Black and White Hairs
Genotype: 100% Heterozygous
Human Blood Types: Use both codominance and regular
dominant/recessive.
 A and B are co-dominant. O is recessive.
 Use the chart to help with crosses.
Cross a person who is homozygous for type A
blood with a person who has type AB blood.
A
A
A
AA
AA
B
AB
AB
Phenotype Ratio: 50% Type A, 50% Type AB
Genotype Ratio: 50% Homozygous AA, 50% Heterozygous AB
You Practice

Cross type O blood, with heterozygous
type B blood.
i
B
i
i
Bi
Bi
ii
ii
Phenotype: 50% Type B, 50% Type O
Genotype: 50% Heterozygous Bi, 50% Homozygous Recessive
Sex-Linked: Use sex
chromosomes and alleles.

Some disorders are carried on the X
chromosome. Examples of these
disorders are color blindness, and
hemophilia.
Some disorders are carried on the X
chromosome. Examples of these
disorders are color blindness, and
hemophilia.
 Only females can be carriers
(heterozygous) because they have two X
chromosomes
 Males either have the allele (and hence
show the trait) or they don’t. Males only
get 1 X, so whatever they inherit on that
1 X is what you see.


When doing Punnett Squares, you must first use sex chromosomes
(XX for female, XY for male) then assign letters to the trait and
put them as superscripts on the sex chromosomes.
B = normal vision, b = color blind.
Cross a heterozygous normal vision female
with a normal vision male. (First cross sex
chromosomes, then put on alleles and cross
them).

Phenotype:
50% Normal vision females
25% Normal vision males
25% Color Blind males
Genotype: 25% XBXb
(Carrier)
25% XbY
25% XBXB
25% XBY
You Practice

Cross a carrier female with a colorblind
male and give the genotype and
phenotype %.
XB
Xb
Y
Xb
XB Xb
XbXb
XBY
XbY
Phenotype: 25% Normal Vision Carrier Female
25% Colorblind Female
25% Normal Vision Male
25% Colorblind Male
Genotype: 25% XBXb, 25% XbXb, 25% XBY, 25% XbY
Sex-Linked Pedigree
Multiple Alleles

Multiple alleles are when there are more
than 2 forms of a gene. Ex: human blood
type (ABO), human hair colors.

HBr = brown

The possible genotypes and phenotypes: HBdHBd or HBdhbk =
blonde HBdHBr = mousy brown HBdhR = strawberry blonde
HBrHBr or HBr hbk = brown HBrhR = auburn hRhR or hRhbk
= red hbkhbk = black
HBd = blonde
hR = red
hbk = black
You Practice

Cross a black hair parent with a blond
hair parent whose mother had black hair.

P = hbk hbk x HBdhbk
hbk
HBd
hbk
hbk
HBdhbk
HBdhbk
hbkhbk
hbkhbk
Phenotype: 50% Blond, 50% Black
Genotype: 50% HBdhbk, 50% hbkhbk
Polygenic
Polygenic traits are the result of the interaction
of several genes (2 or more genes) Poly = many,
Genic = “genes”
 Examples: human skin color, human eye color

Sex-Influenced
Sex influenced traits are also
autosomal, meaning that their genes are
not carried on the sex chromosomes.
 These traits are influenced by gender.
They can be influenced by hormone
production.
 Example: pattern baldness due to
testosterone.

Sex-Influenced
What is the probability that you will be bald if your father is
homozygous and balding, and your mother is homozygous and not
balding?
Father = BB x Mother = B’B’

All offspring are BB’

If you are male, then you will
be bald.

If you are female, then you will not be bald.
X-Inactivation
In mammals, males receive one copy of the X
chromosome while females receive two copies. To
prevent female cells from having twice as many gene
products from the X chromosomes as males, one copy
of the X chromosome in each female cell is inactivated
randomly in each cell.