Unit 4: Mendelian Genetics

Section 2- Mendelian Inheritance

I. Probability

a. The likelihood that a certain event will occur.b. Used to determine the pattern of inheritance

of a trait.c. Formula: (# of times it is expected to occur)

(# of times it could occur)a. Ex: Mendel got 705 purple plants and 224

white plants. What is the probability of getting a purple plant?

b. 705/929=76%

II. Punnett Squares

a. Used to find genotypes and predict outcomesb. Shows every possible combination of mother’s

alleles and father’s allelesc. Ex: P=purple allele p=white alleled. Purple is dominant-overpowers white allelee. 75% purple 25% white

III. Determining Genotypes

a. Testcross- if genotype is unknown, cross with the homozygous recessive individual.

b. RR x rr= Rr (Red x white=red)c. Rr X rr= 50%Rr(red) 50% rr (white)d. rr x rr= rr (white)

IV. Practice

A round pea is crossed with a wrinkled pea. Round is dominant. What are the genotypes of the F1 generation?

What are the genotypes of the F2 generation?

IV. Practice

Green is dominant to yellow in pea pods. Cross a heterozygous green with a yellow plant. Give the genotypic and phenotypic ratios.

V. Example

Mendel bred 7324 plants. He got 5474 round peas and 1850 wrinkled. Which is the dominant trait? What is the probability of getting the

dominant phenotype? What are the genotypes and phenotypes of

the parents?