More Punnett squares

Complete Dominance

•Involves dominant and recessive alleles•dominant allele always overpowers the recessive allele in appearance

Incomplete Dominance

• Neither allele is dominant or recessive• Organisms with two different phenotypes

produces offspring with a third phenotype that is a blending of the parents

Incomplete Dominance

• Ex: Cross a red flower (RR) with a white flower (WW) and the offspring will be pink (RW)!

Incomplete Dominance

• In another flower, if red ____ and blue ____ flowers are crossed, they produce a 3rd purple ____ flower

• What would be the genotypic ratio and phenotypic ratio if you crossed two purple flowers?

(RR)

(RB)(BB)

Incomplete Dominance

• Cross of two purple flowers_RB_ X _RB_

• What are gamete possibilities?• genotypic ratio 1RR : 2RB : 1BB1RR : 2RB : 1BB• phenotypic ratio 1red : 2 purple : 1 blue1red : 2 purple : 1 blue

RRred

RBpurple

RBpurple

BBblue

R

B

B

R

Codominance

• Neither allele is dominant or recessive• Parents with different phenotypes produce an

offspring with a third phenotype– Third phenotype will show both parental

phenotypes simultaneously (at the same time)

Codominance• In cattle and horses, if you cross

a pure red (RR) with a pure white (WW), you get (RW) which produces the color roan.

Codominance• These cattle or horses actually have both red

and white hairs intermixed, or are spotted. Roan is a third phenotype.

• If you cross a roan with a white… • RW X WW

RWroan

WWwhite

RWroan

WWwhite

R

W

W

W

What is it?!

+ =

+ =

Multiple alleles

• two or more possible alleles for the same gene within a population

• Thus multiple alleles• However, individuals within the population

are only able to hold two of them

• Non-human examples: rabbit fur color, mice skin color, eye color in flies, wing size in flies

Multiple Alleles

• Blood type in humans• The _four_ different

blood types: – A, B, O, and AB

• Blood types are produced by three_ different alleles: – A, B and O

Phenotype Genotype

A AA or AO

B BB or BO

AB AB only

O OO only

Genotype for Blood Type

I and i used in genotypeI used with A and Bi used with O

A and B are dominant over O: A and B are codominant

Ex: Genotype: AA is IAIA

Blood type chart

PHENOTYPE GENOTYPEA AA, IAIA

A AO, IAiB BB, IBIB

B BO, IBiAB AB, IAIB

O OO, ii

Blood type AB is an example of codominance in humans

Blood Type Punnett Square

• Draw a Punnett square showing all the possible genotypes for the offspring produced by a type “O” mother and an a Type “AB” father.

Cross: ii x IAIBIAi IAi

IBi IBi

ii

IA

IB

Blood Type Punnett Square

• Cross a female with blood type A and a male with heterozygous B blood type.

• Complete ratios (phenotypic and genotypic)

• A male with blood type B has a child with a woman who has blood type A. The child is blood type O. What is the genotype of the male and female? Show your work.

How does blood type work?

Blood transfusions

Rh factor: Rh for Rhesus Monkey• Positive vs Negative Blood types

• Positive: protein is present• Dominant trait

• Negative: protein is absent• Recessive trait

Polygenic traits

• Traits controlled by two or more genes (one gene has two alleles)

• Show a wide range of phenotypes• Phenotype is produced by the interaction of

more than one pair of alleles

Examples of polygenic traits in humans

Example of polygenic traits in humans

Examples of polygenic traits in humans

Sex-linked traits

• Every new born has a 50% chance of being female and a 50% chance being male– DAD: X Y

• Sperm contains either:

– MOM: X X• Eggs all contain:

YX

X

or

XX XY

XX XY

X

X

X

Y

Sex-Linked traits

• The X chromosome contains many genes, whereas the Y chromosome contains only a few genes

• sex-linked genes: genes located on one of the sex chromosomes (X or Y) but not the other

• most sex-linked genes are X-linked genes

Examples of sex-linked traits: X-linked

• Colorblindness: more common in males than females

• Hemophilia: more common in males than females

Both colorblindness and Hemophilia are recessive traits

Colorblindness

Do any of these pictures look the same?!

Test time!

Colorblind: X-linked trait• C- normal vision• c- colorblind• You must incorporate XX (mom) and XY (dad)• This is how to set it up:

• (remember colorblindness is X-linked!)

Normal vision Heterozygous(carrier) Colorblind

Female: XX

Male: XY

Punnett Square

• Cross a female who is a carrier for colorblindness with a normal vision man.

• Cross a normal vision woman (homozygous) with a colorblind man.

Hemophilia: X-linked recessive trait

• Hemophilia is the inability for blood to clot– Your blood clots every time you get a papercut

–H: normal clotting– h: hemophilia

– Make a key for hemophilia:• Normal female: Normal Male:• Female Carrier: Can a man be a carrier? • Female with hemophilia: Male with: