INTRODUCTION TO GENETICSCHAPTER 6:

MEIOSIS AND MENDELD I H Y B R I D S A N D T E S T C R O S S E S

DIHYBRID CROSSES(Involves 2 Traits)

Another question Mendel proposed?

• Does the gene that determines if a

seed is round or wrinkled have anything to do with the gene for seed shape?• Must a seed that is yellow also

be round?

MAKING A CROSS WITH ___________________=____________________

A Punnett square for a DIHYBRID CROSS looks like this:

DIHYBRID CROSSTWO gene traits

Section 11-3

Figure 11-10 Independent Assortment in Peas

REVIEW: LAW OF SEGREGATION (MENDEL’S FIRST LAW OF GENETICS

• Organisms inherit two copies of each gene, one from each parent

• Organisms donate only one copy of each gene in their gametes.

• Thus, the two copies of each gene segregate, or separate, during gamete formation

• LAW OF ______________________the factors are distributed to gametes

independently of other factors• Mendel’s second law of

genetics

INDEPENDENT ASSORTMENT

Image modified from: http://anthro.palomar.edu/mendel/mendel_1.htm

1. ___________ what _________________ are2. ________correct__________ square __________3. ______ possible_______________________4. ______ boxes with _____________________5. Determine ____________of_____________& ____________

LET’S MAKE A DIHYBRID CROSSR – YELLOW Y - ROUND

r – green y - wrinkled

HOMOZYGOUS

YELLOW ROUND

rryy

HOMOZYGOUSGREEN WRINKLED

Figure out parent allelesChoose Punnett sizePut in parent gametesFill in offspring combinations probabilities phenotypes

genotypes

RRYY

R R Y Y

HOMOZYGOUS ROUND YELLOW

PRACTICE MAKING GAMETES

WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE?R-yellow, r-green Y-round, y-wrinkled

Each gamete shouldget one of each kindof gene

___________ ____________ _____________ _____________R Y R Y R Y R Y

r r y y

HOMOZYGOUSWRINKLED GREEN

PRACTICE MAKING GAMETES

WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE?R-yellow, r-green Y-round, y-wrinkled

Each gamete shouldget one of each kindof gene

___________ ____________ _____________ _____________r y r y r y r y

ry ry ry ry

RY

RY

RY

RY

100% of offspring = _______ genotype _______________________ phenotype

RrYyROUND YELLOW

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

R r Y y R r Y y

HETEROZYGOUSROUND YELLOW

HETEROZYGOUSROUND YELLOW

MAKE ANOTHER CROSSR-yellow, r-green Y-round, y-wrinkled

X

R r Y y

HETEROZYGOUSROUND YELLOW

PRACTICE MAKING GAMETES

WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE?R-yellow, r-green Y-round, y-wrinkled

Each gamete shouldget one of each kindof gene

___________ ____________ _____________ _____________R Y r y r Y R y

POSSIBLE PARENT GAMETES?

RY ry RyrY

RY Ry rY ry

RY

Ry

rY

ry

Sign of a ______________________ cross is a_____________ ratio in offspring.9:3:3:1

____ Round & Yellow

____ Round & green

____ Wrinkled & yellow

____ wrinkled & green

9

3

3

1

RRYY RRYy RrYY RrYy

RRYy RRyy RrYy Rryy

RrYY RrYy rrYY rrYy

RrYy Rryy rrYy rryy

heterozygous dihybrid

__________ratio is a clue that it’s a ____________________________cross

____ ____________ TRAIT 1 ; ____________ TRAIT 2 ____ ____________ TRAIT 1; _____________ TRAIT 2

____ ____________ TRAIT 1; _____________ TRAIT 2

____ ____________ TRAIT 1; _____________ TRAIT 2

9

3

3

1

9:3:3:1

HETEROZYGOUS TWO gene

dominant dominant

dominant recessive

recessive dominant

recessive recessive

PRACTICE MAKING GAMETESFOR DIHYBRID CROSSES

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html

pure round & pure tall = __________

____ ____ _____ ______

What gametes can it produce?

WHAT ARE THE POSSIBLE GAMETES?Round-R, Wrinkled-r Tall-T, Short-t

R R T T

R T R T

R T R T

Heterozygous Tall = __________

& pure round

____ ____ _____ ______

What gametes can it produce?

WHAT ARE THE POSSIBLE GAMETES?Round-R, Wrinkled-r Tall-T, Short-t

RRTt

RT Rt

Rt RT

Hybrid tall = __________

& pure wrinkled

____ ____ _____ ______

What gametes can it produce?

WHAT ARE THE POSSIBLE GAMETES?Round-R, Wrinkled-r Tall-T, Short-t

rrTt

rT rt

rT rt

Heterozygous tall = __________

& hybrid round

____ ____ _____ ______

What gametes can it produce?

WHAT ARE THE POSSIBLE GAMETES?Round-R, Wrinkled-r Tall-T, Short-t

RrTt

RT rT

rt Rt

DIHYBRID CROSS

Dihybrid Cross