1. Probability & Heredity
A number that describes how likely it is that an event will occur.
The laws of probability predict what is likely to occur, not necessarily what will occur.
Probability is written as
The number of ways of getting a particular outcome to the total number of possible outcomes.
Can be expressed as a ratio, fraction, decimal or percent
Ex.) Getting heads when flipping a coin
1 to 2, ½, .50, or 50%

2. Independent versus Dependent events
Independent event
An event in which the outcome or the likelihood of an outcome is not affected by a 2nd event happening.
Ex.) Landing on heads after tossing a coin AND rolling a 5 on a single 6-sided die.
Ex.) Choosing a marble from a jar AND landing on heads after tossing a coin.
Dependent event
An event in which the outcome or the likelihood of an outcome is affected by the outcome of the 1st event.
Ex.) Picking 3 Aces in a row from a deck of cards without replacing the cards.

3. Punnett square Developed by Reginald Punnett, a British geneticist.
A chart that shows all the possible combinations of alleles that can result from a genetic cross for a specific trait.
Also called a monohybrid cross when trying to determine the possible allele combinations when dealing with 1 trait or dihybrid cross when dealing with 2 traits.

4. Completing a Punnett Square:
Start by drawing a box & dividing it into 4 squares.
Write the male parent’s alleles along the top of the square & the female parent’s alleles along the left side. R r

5. Copy the male parent’s alleles into the boxes beneath them.
Copy the female parent’s alleles into the boxes to their right. R r RR Rr rr

6. R r RR Rr rr In a Punnett square, each square is equal to ¼ or 25%.
The completed Punnett square shows all the possible allele combinations for the offspring.
In a Punnett square, each square is equal to ¼ or 25%.
To determine the total probability of a particular outcome, determine the number of times that outcome appears in the Punnett square & multiply by 25% or ¼.
Ex.) Rr = 2 squares  2 x 25% 50% or ½. R r RR Rr rr

7. Genotype An organisms specific allele combination for a trait
Seed color: YY, Yy, or yy
Seed shape: RR, Rr, rr
Categories of genotypes
Heterozygous
Having 2 different alleles for a trait
Also known as hybrids
Yy or Rr
Homozygous
Having the same 2 alleles for a trait
Also known as purebreds
YY or yy; RR or rr

8. Phenotype
The physical appearance or visible traits.
In human genetics heterozygotes are those who have a dominant and a recessive allele are called carriers.
This means they are carrying a recessive allele without expressing it physically.
Genotypes
Phenotypes YY
Homozygous
Yellow Yy
Heterozygous yy
Green

9. Codominance or “Incomplete dominance”
The alleles are neither dominant or recessive. As a result both alleles are expressed in the offspring.
Ex.) Roan cattle or Appaloosa horses
Ex.) Hazel or dual colored eyes in humans & animals
Huskies  1 white & 1 blue eye or 1 blue & 1 brown eye
Both alleles for the trait are written as superscripts for the trait.
Ex.) Feathers  FBFW Black & White Feathers
Ex.) Eye color  EBEg Hazel eyes