Transcript Use sex chromosomes and alleles.

Unit 5 – Other forms of inheritance
Non-Medelian 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: feather color in chickens, 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
Phenotype:
 25% Red
 25% White
 50% Pink


Genotype:
◦ 25% Homo Red
◦ 25% Homo White
◦ 50% Hetero.
R
R
W
W
RR
RW
RW
WW
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
Human Blood Types: Use both codominance and regular
dominant/recessive.
 A and B are co-dominant. O is recessive.
 Multiple alleles: when more than two
alleles for the trait exist in the population.
 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 Type A, 50% AB
Heterozygous Type AB
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
Sex-Influenced Traits
Sex influenced traits are also
autosomal, meaning that their genes are
not carried on the sex chromosomes.
 What makes these traits unusual is the
way they are expressed differently
phenotypically in the two genders (can be
influenced by things like hormones).
 Example: pattern baldness

Polygenic Traits

Traits produced by two or more genes.
◦ Example: Human skin color
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
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.
https://www.youtube.com/watch?v=Y9vXhmI5FXM