1. Probability in Genetics
The inheritance of a trait is by chance. Probability laws apply when calculating the chance of an offspring inheriting a specific genotype
The probability is the “likelihood” of an event to occur. A value of 1 means the event is certain to occur, and a value of 0 means the event is certain not to happen.
Punnett Square and probability laws are used to determine the probability.

2. Click to next slide to see solution
Punnett Square: visual of the possible genotype and phenotype of offspring; determine probability
Example:
Rules:
Write genotype of parents.
Determine the allele in the gamete cell produced by parent: “law of segregation” separates alleles when making gametes
Draw the Punnett square and solve. Write down the # & type of phenotypes and genotypes
Re-read question and then find the information from the Punnett square to answer it.
A woman who is heterozgyous for freckles and a man without freckles have children. What is the probability of having freckled and no freckled children. *Question tells you which is dominant because the heterozygous carried a dominant and recessive allele and shows only one trait. So freckles is dominant and no freckles is recessive.
Click to next slide to see solution

3. Two heterozygote parents for freckles have children
Two heterozygote parents for freckles have children. What is the probability of having freckled children? If they have 12 children, how many should be freckled and non freckled?

4. Genetic Cross Vocabulary
One trait cross – cross studying the inheritance of one trait
Hybrid organism – organism that carries two different alleles
True breeding organism – organism that carries two same alelles
Monohybrid cross – a cross between two heterozygote organisms for one trait
Phenotypic Ratio – comparison in # among the different phenotypes produced from crossing two individuals with specific traits
Genotypic Ratio – comparison in # among the different genotypes produced from crossing two individuals with specific traits
Expected outcome – results determined by following the laws of probability
Observed outcome – results that actually happened/visibly observed/ data collected

5. Can you think of any other questions?
Reading the Question is important to answering it correctly! Some examples of questions…
What are the possible phenotypes?
What are the possible genotypes?
What is the probability of having offspring with the recessive phenotype?
What is the probability of having offspring with the dominant phenotype?
In a litter of 8 puppies, how many could show the recessive trait?
How does the “expected” ratio compare to the “observed” ratio?
If the observed phenotypes for a litter of 21 offspring showed 14 brown fur and 7 white fur, what is the phenotypic ratio?
Write down the probable phenotypic ratio for this cross.
Can you think of any other questions?

6. What is the probability of your 4th Baby…
Having no dimples? Having wavy hair?
Being a boy? Having a large nose?
Show all work…

7. Probability is not affected by previous outcomes.
What size nose did baby #1, #2 and #3 have? What is the probability for having a large nose?
What can change the probility?

8. Compare the phenotypic & genotypic ratios for the two monohybrid cross with different gene interactions
Simple Dominance
Incomplete Dominance

9. Using the Punnett Square or Multiplication and the Addition Rules
Inheritance of More than One Trait Example: Cheek Dimple and Lip Thickness
Using the Punnett Square or Multiplication and the Addition Rules

10. Genotypes of Parents: DdNn and DdNn
Using the Punnett Square to solve a two trait cross: Two heterozygous parents for dimple and thick lips have children. What is the probability of having a dimple and thin lips child?
Genotypes of Parents: DdNn and DdNn
Both traits are controlled by simple dominance
Gametes for Male: DN, Dn, dN, dn.
Gametes for Female: DN, Dn, dN, dn.
Make the Punnett Square: Gametes go on the top and right side of the box.

11. Look for the questions and find the answers in the notes…
Question #1 “What’s the probability of having a child with dimple and thin lips?
Question #2 “What is the phenotypic ratio?
Question #3 “What phenotype has the greatest probability of appearing in the children?
Question #4 “How could the chance increase of having more dominant traits in the children?
Question #5 “Where is the product of meiosis located in the diagram?”

12. Genetics of ABO Blood Type
Phenotypes with corresponding genotypes:
Gene Interactions controlling blood type
IA and IB alleles are dominant over i. You only have to have one of the dominant alleles to produce either Type A and Type B blood cells. Unless..
If you inherit IA and IB together then both type of cells will be produced. This is codominance now.
If you inherit two recessives, you get type O cells. Look at the picture. Which genotype goes with each picture?
Type A – IAIA or IAi
Type B – IBIB or IBi
Type AB - IAIB
Type O - ii

13. Below is a punnett square predicting the phenotypes for a homozygous Type A woman and a heterozygous Type B man. Use the table to the left to help you interpret the children’s blood type.
Genotypes: Ibi and IAIA
Probable phenotypes: Type AB, and Type A
What is the probability for each blood type?

14. Using Math to Calculate Probability in Genetics Video