3-11-11

IN What are the probabilities of a monohybrid

cross between two heterozygous parents? Flower color R=red r=white

3-11-11

Through Quiz Part B page 434 Notes

OUTBunny/Meiosis

worksheet

QUIZ!!!

Two Mendelian Traits: Pea Pod color and Shape

Dihybrid cross -- A genetic cross between individuals differing in two alleles

In garden peas, the genes for the traits of pod color and pod shape are on different chromosomes.

Pod color Green = G Yellow = g

Pod shape Expanded = E Constricted= e

Peas that are homozygous for both green and expanded are crossed with peas that have yellow, constricted pods

Parent 1 Phenotype=Green, Expanded Genotype= GGEE

Parent 2 Phenotype= Yellow, Constricted Genotype= ggee

Through Meiosis, what are all the possible gametes produced by the parents?

Parent 1 G G E E

GE GE GE GE

Parent 2 g g e e

ge ge ge ge To do a Dihybrid cross

1. Find possible gametes 2. Create a 4X4 table 3. Plug in gametes

4. Find offspring possibilities

Dihybrid crossF1 Generation

GE GE GE GE

ge

ge

GgEe GgEe GgEe GgEe

GgEe GgEe GgEe GgEe

GgEe GgEe GgEe GgEe

GgEe GgEe GgEe GgEe

ge

ge

Results for possible offspring for F1 generation

16 / 16 100%:

Phenotype- Green, Expanded

Genotype- GgEe

Carriers

To find a F2 generation, take two offspring and cross them.

What are possible gametes for the F2 generation for each parent?

Parent 1---- GE, Ge, gE, geParent 2---- GE, Ge, gE, ge

Complete the cross of the F2 Generation

GGEE GGEe GgEE GgEe

GGEe GGee GgEe Ggee

GgEE GgEe ggEE ggEe

GgEe Ggee ggEe ggee

GE Ge gE ge

GE

Ge

gE

ge

3. From the F2 generation, what fraction would you predict to have each of the following phenotypes?

A. The dominant phenotype for pod color and pod shape.

9 / 16 B. The dominant phenotype for pod color

and recessive phenotype for pod shape.3 / 16

C. The recessive phenotype for pod color and the dominant phenotype for pod shape.

3 / 16 D. The recessive phenotype for pod

color and pod shape.1 / 16

4. If there were 288 offspring, how many would you predict to be:

Green, Expanded?162Green, Constricted?54Yellow, Expanded?54Yellow, Constricted?18

Actual Results

Green, expanded=165Green, constricted= 51Yellow, expanded=56Yellow, constricted=16A. Do the results match your

predictions?B. Explain why they don’t match.

Short hair is a dominant trait for guinea pigs. Both parents are heterozygous.

Complete a monohybrid cross for F1 generation.

What is the probability that their offspring will have long hair?

SS Ss

Ss ss

S s

S

s

Part C Linked-Traits

Many different genes are located on the same chromosome.

When gametes are formed, alleles of genes that are located on the same chromosome end up together in the same gamete.

Notes:Linkage - genes that are on the same

chromosome end up together in the same gamete.

1. Suppose the genes for pod color and pod shape are on the same chromosome.

G= green pod g=yellow podE= Expanded pod e=constricted podParent 1 GGEE

Gametes GE/ GE/Parent 2 ggee

Gametes ge/ ge/

In this case, the green, expanded produce only GE/ gametes and the yellow constricted produce only ge/ gametes.

The slash represents the linkage

GE/ge GE/ge

GE/ge GE/ge

GE/ GE/

ge/

ge/

F1

Combine the gametes of two from the F1 generation to find the F2 generation.

GE/GE GE/ge

GE/ge ge/ge

GE/ ge/

GE/

ge/

F2

Using linkage, what would be the predicted phenotypes of the F2 generation?

75% green,expanded25% yellow, constricted

Notes:

Crossing-over - During meiosis, it is the breakage and exchange of corresponding segments of chromosome pairs.

Watch DVD “Crossing-over”Describe the effect that crossing over

might have on results.

PART D X-Linked Traits

In fruit fly, Drosophilia melanogaster, red eye color is dominant over white eye color. R-red r-white

Predict the genotypes and phenotypes you would expect in the F1 generation when a homozygous red-eyed female fly is mated with a white-eyed male fly.

Homozygous red-eyed female RR genotype

White-eyed male rr genotype

Predictions:100% Rr genotype100% Red-eyed offspring

Rr Rr

Rr Rr

R R

r

r

2. Actual resultsBased on 139 offspring, all had red eyes3. Next, you mated a red-eyed male flies with

white-eyed female flies.(reciprocal cross) Would you expect similar results?

4. In the early 1900’s, biologist Thomas Hunt Morgan performed a similar cross. But, instead of getting all red-eyed flies, he got half red-eyed flies and half white-eyed flies. However, all the red-eyed flies were females, and all the white-eyed flies were males. How might you explain these seemingly unexpected results?

Read Need to know on page 436

5. A. A superscript letter designates the allele. Often it is used with the chromosome symbol to diagram a cross of a trait that is carried on the X chromosome. For example, the allele for white eyes might be represented by Xr, and the allele for red eyes by XR. The symbol Y can represent the Y chromosome and does not carry a gene for eye color. Using these symbols, diagram the cross described in Step 3. Show the expected genotype and phenotype fractions.

Male --- red-eyedXRYFemale --- white-eyedXrXr

Predictions:Phenotypes 50% male 50% female100% red-eyed female100% white-eyed male

XRXr XRXr

XrY XrY

Xr Xr

XR

Y

Diagram the cross that would result if the F1 offspring were mated to create the F2 generation. Show the genotypes and phenotypes of the new offspring.

Male ---- XrYFemale ---- XRXr

Predicted outcomes:Genotypes 25% XRXr, 25% XrXr,

25% XRY, 25% XrYPhenotypes 50% females red-eyed,

50% females white-eyed, 50% males red-eyed, 50% males white-eyed

XRXr XRY

XrXr XrY

Xr Y

XR

Xr