1. Probability & Heredity Page __

2. Probability & Heredity
A number that describes how likely it is that an event will occur.
The laws of probability predict was is likely to occur, not necessarily what will occur.

3. Probability & Heredity
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%

4. Independent vs 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.

5. Independent vs Dependent events
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.

6. 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.

7. 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

8. 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

9. The completed Punnett square shows all the possible allele combinations for the offspring.
In a Punnett square, each square is equally 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

10. Genotype An organisms specific allele combination for a trait
Seed color: YY, Yy, or yy
Seed shape: RR, Rr, rr
There are TWO 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

11. Phenotype
The physical appearance or visible traits.
In human genetics heterozygotes; 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

12. 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