Fnord babies ~ will be collected ~

In Fnords, orange (O) skin is dominant over blue skin (o). An orange fnord and a blue fnord mate, and

produce 314 orange offspring and 307 blue offspring.

A. What is the genotype of the orange parent?

B. Two of the orange F1 fnords mate, and they produce both orange and blue offspring. If they have 98 blue babies in the F2 generation, about how many orange

ones are there?

C. Describe a cross you could make to figure out if one of the orange fnords from the F2 is homozygous

dominant or heterozygous.

FNORDS!

A. Oo

B. about 300

C. cross with a blue fnord. If all offspring are orange, must have been a homozygote.

O o

O OO Oo

o Oo oo

Codominance

For a trait that is codominant, both alleles affect the phenotype, and the result is offspring that have BOTH phenotypes.

Look at the example of horses

RR = Red fur

rr = White fur

Rr = Red AND White fur (roan)

Codominance – Roan Horses

Incomplete Dominance

RR RR’ R’R’

For a trait that shows incomplete dominance, one allele has an effect, and the other does not. If there are two copies, the

organism gets a “double dose” of the effect (red flower on left)

Pink flowers = RR’

• Since one allele isn’t really dominant, the non-functional allele (white in this example) is written with a capital letter and an apostrophe (i.e. R’, Q’, etc.)

Flower Power

• If you crossed two of the pink flowers on the previous slide,– What % would be pink?– What % would be red?– What % would be white?

• What is the phenotype ratio?

Shh! Don’t say a word!

Write down what numbers (if

any) you can read in each circle

Are you color blind?

• 4 Sex-Linked Traits:

• 1. Normal Color Vision: A: 29,  B: 45,  C: --,  D: 26  

• 2. Red-Green Color-Blind: A: 70,  B: --,  C: 5,  D: --  

• 3. Red Color-blind: A: 70,  B: --,  C: 5,  D: 6  

• 4. Green Color-Blind: A: 70,  B: --,  C: 5,  D: 2

There are a LOT more color blind men than women!

Try One – on the back of your drill• A female with normal vision that has 1 copy of a

colorblindness gene (genotype X+ Xo) has children with a normal male (X+ Y).

A. What % of their male children will be colorblind?

B. What % of their female children will be colorblind?

C. Do all colorblind women have a colorblind father? Explain

Use Punnett squares to support each answer!

3 Different Alleles: Multiple Allele Traits

• The three alleles that determine blood type are represented as IA, IB, and i.

Phenotype Genotypes

A IAIA, IAi

B IBIB, IBi

AB IAIB

O ii

Crosses

• A woman with blood type A has a baby with blood type O. The man she believes to be the father has the blood type AB. Is it possible the man is the father of the baby?

He isn’t the Father!

mom

Possible dad

IA

IB

IA

IAIA

(A)IAIB

(AB)

i

IAi(A)

IBi(B)

Multiple Allelic Traits

• Traits for which there are 3 or more alleles are said to be multiple allele traits, or multiple allelic.

• Try the example cross on your notes

Wrap up• Alleles can react in different ways, for

different genes:– Codominance: both alleles expressed (roan

horses)– Incomplete: heterozygote has blended

phenotype (pink flowers)– Sex-linkage: males only get 1 copy!

(colorblindness)– Multiple alleles: 3 or more alleles for 1 gene.

(blood type)