One allele from a female egg is joined with one allele from a male sperm Probability and predicting inheritance Since alleles for a trait separate during meiosis we can use the laws of probability to predict genetic outcomes ID: 934092
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Slide1
Punnett
squares
Slide2REVIEW
Monohybrid cross is the cross between two parent organisms and the inheritance patterns of only one trait are studied.
One allele from a female egg is joined with one allele from a male sperm.
Slide3Probability and predicting inheritance
Since alleles for a trait separate during meiosis, we can use the laws of probability to predict genetic outcomes.
Probability is the chance that a certain event will occur.
Slide4Punnett
Squares
A diagram that shows all possible gene combinations from a genetic cross.
Dominant alleles are capital letters
Recessive alleles are lowercase letters
Slide5Using
punnett
squares for Monohybrid crosses
Step 1: draw a
P
unnett
square with four compartments
Step 2: take the genotype for one parent and put one letter outside the
P
unnett
square to the left of each row
Step 3: take the genotype for the other parent and put one letter outside the
Punnett
square above each column.
Step 4: now you can fill in the grid. Take the letter over each column and copy it into the two squares below it
Step 5: Take the letter at the beginning of each row and copy it into the two squares to the right.
Slide6Math review
Description
Ratio
Fraction
Percent
One
to three or one out of four
1:3
1/4
25%
Two
to two or two out of four
2:2
1/2
50%
Three to one or three
out of four
3:1
3/4
75%
Four out of four
100%
Slide7Dihybrid
cross
Studying 2 traits crossed from parent organisms
When two traits are studied at a time the illustrate the Law of Independent Assortment.
This means that inheriting one trait doesn’t affect the inheritance of another trait.
Ex. Having brown eyes has nothing to do with having freckles.
Slide8Using
punnett
squares for
dihybrid
crosses
Step 1: Pick a parent.
The mother is heterozygous for both traits, (
RrFf
), so she has a dominant R gene and a recessive r gene. She also has a dominant F gene and a recessive f gene. She can pass on each of these traits independently to her children.
What are the four possible combinations of these traits?
Slide9continued
Step 2: Consider the father.
He is also heterozygous for both traits, so the combinations of traits are the same
RF,
Rf
,
rF
, and
rf
Slide10continued
Step 3: Now fill in a
Punnett
square with these combinations.
Since there are four combinations for each parent, the square is 4X4 instead of 2X2.
You fill it in the same way.
Slide11Punnett
Square
RF
Rf
rF
rf
RF
RRFF
RRFf
RrFF
RrFf
Rf
RRFf
RRff
RrFf
Rrff
rF
RrFF
RrFf
rrFF
rrFf
rfRrFfRrffrrFfrrff
Mother
Father