1. Heredity
Probability and Punnett Squares

2. Probability = # times event is expected to happen
Likelihood that a specific event will occur
Probability = # times event is expected to happen
# opportunities for event to happen
Decimal, %, fraction or ratio
Remember: The more trials you perform – the more likely you are to reach the expected probability

3. Punnett Squares
You can predict & compare genetic variations that will result in offspring by performing a cross using a punnett square M m MM Mm mm

4. Monohybrid cross Mono = 1 Inheritance of 1 trait Cross can be:
Homozygous-Homozygous
Heterozygous-Heterozygous
Heterozygous-Homozygous

5. Monohybrid cross T t TT Tt tt 2 heterozygous parents: Tt x Tt (F1)
T=dominant tall
t=recessive short
Genotypic ratio: 1:2:1
¼ (25%) = homozygous dominant
¼ (25%) = homozygous recessive
½ (50%) = heterozygous
Phenotypic ratio: 3:1
¾ (75%) = are tall
¼ (25%) = are short T t TT Tt tt

6. Dihybrid Cross
Di = 2
Inheritance
of 2 traits

7. Dihybrid cross R = dominant round r = recessive wrinkled
Y = dominant yellow y = recessive green
P generation: rryy x RRYY
F1 generation:
All offspring have same
Genotype (RrYy)
All have same Phenotype
(round and yellow)
16:16 or 100% ry RY
RrYy

8. Dihybrid cross
R = dominant round r = recessive wrinkled Y = dominant yellow y = recessive green
Cross 2 individuals from the F1 generation: RrYy x RrYy
Analysis of Punnett Square:
Genotypes Phenotypes
RRYY round, yellow
RRYy round, yellow
RrYY round, yellow
RrYy round, yellow
RRyy round, green
Rryy round, green
rrYY wrinkled, yellow
rrYy wrinkled, yellow
rryy wrinkled, green 9 3 1 RY Ry rY ry
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy

9. 1. How many guinea pigs will have black fur? _________________
2. How many guinea pigs will have brown fur? ________________
3. How many guinea pigs will have short fur? _________________
4. How many guinea pigs will have long fur? __________________
5. How many guinea pigs will have black short fur? ____________
6. How many guinea pigs will have black long fur? _____________
7. How many guinea pigs will have brown short fur? ____________
8. How many guinea pigs will have brown long fur? ____________

10. In dogs, there is a hereditary deafness caused by a recessive gene, “d
In dogs, there is a hereditary deafness caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breeding purposes. The dog also has a black tongue which he inherited from his mother, a Chow. The dog’s genotype is DDbb. (DD because he is not deaf; bb because the black tongue is recessive.) Suppose the dog mates with a dog who is deaf, but is heterozygous for the pink tongue (ddBb). Make a dihybrid Punnett square to illustrate this cross.
1. How many dogs will be deaf? _____________________________
2. How many dogs will be able to hear? _______________________
3. How many dogs will have black tongues? ____________________
4. How many dogs will have pink tongues? _____________________
5. How many dogs will be deaf and have black tongues? _________
6. How many dogs will be able to hear and have black tongues? ____
7. How many dogs will be deaf and have pink tongues? ___________
8. How many dogs will be able to hear and have pink tongues? _____