•Genetics quiz Monday, January 26

Dihybrid CrossTtRr x TtRr

Dihybrid CrossesMendel noticed how one trait is inherited does not affect how the other trait is inherited is independent assortment

• Dihybrid cross have two separate traits • Make a key (genotypes and phenotypes): RR:red, Tt:Tall• Determine what alleles each parent can put into each

gamete• Foil method is an easy way (TtRr)• Put the genotype for each parent across the top and side• Keep alleles of the same trait together• Put dominant allele first for dihybrid when filling in the

cross/square

Dihybrid Crosses.• Consider all possible gametes for an individual, then

perform the cross.• Practice: cross two heterozygotes for pea color and

flower color.• PpYy x PpYy• Take a minute and figure out the possible gametes.

PY Py pY py

Dihybrid Crosses.• In order to accomplish this you must consider all possible

gametes for an individual, then perform the cross.• Let’s try crossing two heterozygotes for pea color and

flower color.• PpYy x PpYy… Conduct the cross, calculate

probabilities.

PY Py pY py

PY

Py

pY

py

Dihybrid Cross

BbRr x BbRr

Fur Color:B: Black b: White

Coat Texture:R: Roughr: Smooth

Dihybrid CrossBbRr x BbRr

Possible gametes:BRBrbRbr

Dihybrid Crosses:a cross that shows the possible offspring for two traits

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

Br

BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have black, rough coat?

How many of the offspring would have a black, smooth coat?

How many of the offspring would have a white, rough coat?

How many of the offspring would have a white, smooth coat?

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

Phenotypic Ratio

9:3:3:1

• Sea world worksheet• Punnett Square Exercises

Homework

• Pearsonsuccessnet.com• Read section 11-3 Exploring Mendel Genetics

• In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r).

• Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

YyRr X yyrr

YR yR

yr

yr

yr

yr

yrYr

YyRr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

Yyrr