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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