Probability & Heredity Page __

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.

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%

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.

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.

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.

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

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

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

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

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

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