1. STUDYING HEREDITY
Punnett Squares – a diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross; named after its inventor, Reginald Punnett.

2. Monohybrid Cross - a cross that involves one pair of contrasting traits; Mendel’s studies looked at one contrasting trait at a time

3. Setting Up Punnett Squares:
The possible gametes that one parent can produce are written along the top of the square.
The possible gametes that the other parent can produce are written along the left side of the square.
Each box inside the square is filled in with two letters obtained by combining the allele along the top of the box with the allele along the side of the box.
The letters in the boxes indicate the possible genotypes of the offspring.

4. Punnett Squares

5. Probability – the likelihood that a specific event will occur; probability calculations can be used to predict the results of genetic crosses
probability = number of 1 kind of possible outcome
total number of all possible outcomes
(%)

6. Setting Up A Punnett Square
Red flowers are dominant to white flowers.
A homozygous red flower is crossed with a
white flower. What percentage will be red?
R R
100% r Rr Rr Rr Rr

7. Setting Up A Punnett Square
Red flowers are dominant to white flowers.
A heterozygous red is crossed with a homozygous red. What percentage will be white?
R r 0% RR Rr R RR Rr

8. Setting Up A Punnett Square
Black hair is dominant to brown hair.
Calculate the probability of heterozygous offspring from a cross between two homozygous dominant parents. 0%
B B BB BB B BB BB

9. Genotypic & Phenotypic Ratios
T t
Tall is dominant to short. T TT Tt t Tt tt
Genotypic Ratio –
Phenotypic Ratio –
1 TT:
2 Tt:
1 tt
3 tall:
1 short

10. Genotypic & Phenotypic Ratios
T t
Tall is dominant to short. t Tt tt t Tt tt
Genotypic Ratio –
Phenotypic Ratio –
2 Tt:
2 tt
2 tall:
2 short

11. Genotypic & Phenotypic Ratios
T T
Tall is dominant to short. T TT TT t Tt Tt
Genotypic Ratio –
Phenotypic Ratio –
2 TT:
2 Tt
4 tall

12. Determining Unknown Genotypes:
*Animal breeders, horticulturists, and others
involved in breeding organisms often need to
know whether an organism with a dominant
phenotype is heterozygous or homozygous for a
trait. In this case, they could perform a test
cross. In a test cross, an individual whose
phenotype is dominant, but whose genotype is
unknow is crossed with a homozygous
recessive individual.

13. What is a test cross? In a test cross, the unknown genotype
If the offspring
show that half are dominant and half
are recessive, then
the unknown parent
was heterozygous
for the trait.
In a test cross, the
unknown genotype
is crossed with a
known homozygous
recessive genotype. ?
If all offspring
show the dominant
trait, then the
unknown parent was
homozygous for
the trai.t