Two trait genetic crosses & pedigrees

Crossing Two Crossing Two TraitsTraits

Cross a Cross a heterozygous heterozygous purple, purple, heterozygous heterozygous smooth corn plant smooth corn plant with a corn plant with a corn plant that is yellow and that is yellow and wrinkled.wrinkled.

Purple = Purple = PP

Yellow = Yellow = p p

Smooth = Smooth = SS

Wrinkled = Wrinkled = ss

P = PpSs x P = PpSs x ppssppss

P = PpSs x P = PpSs x ppssppss

Step #1Step #1 Determine Determine genotypes of genotypes of parents.parents.

Step #2Step #2 Determine the Determine the gametes of gametes of each parent.each parent.

Step #3Step #3

Set up Punnett Set up Punnett SquaresSquares

PSPS

PsPs

pSpS

psps

psps

xx

pSpS

PSPS

PsPs

psps

psps ppssppss

PpSPpSssPpsPpsssppSsppSs

ppssppss

PpSsPpSs

25% Purple & 25% Purple & SmoothSmooth

25% Purple & 25% Purple & WrinkledWrinkled

25% Yellow & 25% Yellow & SmoothSmooth

25% Yellow & Wrinkled25% Yellow & Wrinkled

What is a dihybrid What is a dihybrid cross?cross?

P = TtAa x TtAaP = TtAa x TtAa

TATA

TaTa

tAtA

tata

TATA TaTa tAtA tata

TTAATTAA

TTAaTTAa

TtAATtAA

TtAaTtAa

TTaaTTaa

TtAaTtAa

TTAaTTAa

TtaaTtaa

TtAATtAA

TtAaTtAa

ttAAttAA

ttAattAa

TtAaTtAa

TtaaTtaa

ttAattAa

ttaattaa

3/16 Short & Axial 3/16 Short & Axial (Rec & Dom)(Rec & Dom)

3/16 Tall & Terminal 3/16 Tall & Terminal (Dom & Rec)(Dom & Rec)

1/16 Short & Terminal 1/16 Short & Terminal (Rec & Rec)(Rec & Rec)

Dihybrid Cross Dihybrid Cross RatioRatio

9/16 Tall & Axial (Dom 9/16 Tall & Axial (Dom & Dom)& Dom)

Pedigrees • A pedigree is a type of family tree that

shows the sex of the individuals and the phenotype of that individual for a single trait

• Circles are female ,squares are male

• Filled in has the ‘affected’ phenotype, open has the ‘unaffected’

• The trait examined can either be dominant or recessive

• A person who has the trait but does not express it is a “carrier”

• (heterozygous for a recessive trait)

Using Pedigrees • A pedigree can be used to determine the genotype of individuals in a family

• It can be used to track a, dominant, recessive , or sex-linked trait

• Pair share: is the trait dominant or receive? How do you know? If it is recessive are there any carriers?

What does this pedigree tell us?

White board Review

1. What are the 3 steps of determining a dihybrid cross?

2. What does “di” mean?

3. What is a pedigree?