ProbabilityProbability and and

Inheritance Inheritance

►The The likelihoodlikelihood that a that a particular event will occur.particular event will occur.

ProbabilityProbability

PercentagesPercentages 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 = 3/52. Multiply the fraction by 100% to express it

as a percentage. 3/5 x 100%/1 = 60%

How is probability associated How is probability associated with genetics?with genetics?

►Much like the flipping of a Much like the flipping of a quarter, the likelihood of quarter, the likelihood of alleles is is completely randomcompletely random..

What is aWhat is a PUNNETT SQUAREPUNNETT SQUARE??

►A tool to predict the probability predict the probability of certain traits in offspring that shows the different ways alleles can combine

►A way to show phenotypephenotype (the trait)

& genotypegenotype (the alleles)►A chart that shows all the possible

combinations of alleles that can result when genes are crossed

Genotype and PhenotypeGenotype and Phenotype

► GenotypeGenotype refers to genetic makeup, or refers to genetic makeup, or what alleles the organism haswhat alleles the organism has

► PhenotypePhenotype refers to the physical refers to the physical appearance of an organismappearance of an organism Organisms with the same phenotype may Organisms with the same phenotype may

not have the same genotypenot have the same genotype

Dominant and Recessive TraitsDominant and Recessive Traits►When making Punnett squares, When making Punnett squares, capitalcapital letters are letters are

used to represent used to represent dominant traitsdominant traitsP= Purple FlowerP= Purple Flower always shows up when present

►Lower caseLower case letters are used to represent letters are used to represent recessive traitsrecessive traits

pp== whitewhite flowerflowerhidden when dominant allele is present

Homozygous & HeterozygousHomozygous & Heterozygous

►Organisms that have two identical Organisms that have two identical alleles for a particular trait (alleles for a particular trait (TTTT or or tt) tt) are said to be are said to be homozygous True-breedingTrue-breeding

►Organisms that have two different Organisms that have two different alleles for the same trait alleles for the same trait TtTt are are heterozygousheterozygous HybridHybrid

A Punnett SquareA Punnett SquareIn this cross, both parents are In this cross, both parents are heterozygous for the trait of seed shape. heterozygous for the trait of seed shape. RR represents the dominant round allele, and represents the dominant round allele, and rr represents the recessive wrinkled allele. represents the recessive wrinkled allele.

Punnett Square #1: Punnett Square #1: breeding breeding 2 homozygous 2 homozygous animalsanimals

Bb Bb

Bb Bb

B B

b

b Phenotype

100% All brown offspring

BrownBrown= BB= BB

white= bbwhite= bb

Daddy

Mommy

What is the probability?

Genotype

100% Bb = hybrid brown

Punnett Square #2: Punnett Square #2: breeding 1 breeding 1 homozygous homozygous animal and animal and

1 1 heterozygousheterozygous animal animal

Bb bb

Bb bb

B b

b

b Phenotype

50% brown offspring

50% white offspring

BrownBrown= Bb= Bb

white= bbwhite= bb

Daddy

Mommy What is the probability?

Genotype

50% Bb = hybrid brown

50% bb= white50% bb= white

Punnett Square #3: Punnett Square #3: breeding 2 breeding 2 heterozygousheterozygous animals animals

BB Bb

Bb bb

B b

B

b Phenotype

75% brown offspring

25% white offspring

BrownBrown= Bb= Bb

BrownBrown= Bb= Bb

Daddy

Mommy What is the probability?

Genotype

25% BB= brown

50% Bb = hybrid brown

25% bb= white25% bb= white

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

Incomplete DominanceIncomplete Dominance• When one allele is When one allele is NOTNOT completely completely dominant

over another (they over another (they blendblend) ) ► Example: Example: In carnations the color red (R) is In carnations the color red (R) is

incompletely dominant over white (W). The incompletely dominant over white (W). The hybridhybrid color is color is pinkpink. .