# Probability and Inheritance. ►T►T►T►The likelihood that a particular event will occur. Probability.

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Probability and Inheritance

►T►T►T►The likelihood that a particular event will occur. Probability

Percentages  One way you can express a probability is as a percentage.  Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you can calculate what percent of the coins landed with heads up: 1.Write the comparison as a fraction. Specific events vs possible events 3 out of 5 = 3/5 2. Multiply the fraction by 100% to express it as a percentage. 3/5 x 100%/1 = 60%

How is probability associated with genetics? ►M►M►M►Much like the flipping of a quarter, the likelihood of alleles is completely random.

What is a PUNNETT SQUARE ? ► predict the probability ► A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine ► phenotype genotype ► A way to show phenotype (the trait) & genotype (the alleles) ► ► A chart that shows all the possible combinations of alleles that can result when genes are crossed

Genotype and Phenotype ► Genotype refers to genetic makeup, or what alleles the organism has ► Phenotype refers to the physical appearance of an organism  Organisms with the same phenotype may not have the same genotype

Dominant and Recessive Traits ► When making Punnett squares, capital letters are used to represent dominant traits  P= Purple Flower   always shows up when present ► Lower case letters are used to represent recessive traits  p= white flower   hidden when dominant allele is present

Homozygous & Heterozygous ► Organisms that have two identical alleles for a particular trait (TT or tt) are said to be homozygous homozygous  True-breeding ► Organisms that have two different alleles for the same trait Tt are heterozygous  Hybrid

A Punnett Square In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.

Punnett Square #1: breeding 2 homozygous animals Bb BB b b Phenotype 100% All brown offspring Brown= BB white= bb Daddy Mommy What is the probability? Genotype 100% Bb = hybrid brown

Punnett Square #2: breeding 1 homozygous animal and 1 heterozygous animal Bbbb Bbbb Bb b b Phenotype 50% brown offspring 50% white offspring Brown= Bb white= bb Daddy Mommy What is the probability? Genotype 50% Bb = hybrid brown 50% bb= white

Punnett Square #3: breeding 2 heterozygous animals BBBb bb Bb B b Phenotype 75% brown offspring 25% white offspring Brown= Bb Daddy Mommy What is the probability? Genotype 25% BB= brown 50% Bb = hybrid brown 25% bb= white

Codominance In codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.

Incomplete Dominance When one allele is NOT completely over another (they blend) When one allele is NOT completely dominant over another (they blend) ► Example: In carnations the color red (R) is incompletely dominant over white (W). The hybrid color is pink.

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