PUNNETT SQUARES PART1

Unit 10 Lesson 2

REMEMBER? Gregor Mendel = Father of Genetics Used peas to study heredity Cross fertilization: he crossed two

parent plants (P) (purple X white) and got all purple in the first generation (F1)

Self fertilization: he allowed two purple flowers from the first generation (F1) to self-pollinate to produce the second generation (F2)

The end result = 3 purple and 1 white Purple is dominant and white is

recessive.

SO WHAT? Mendel concluded that each flower has

two alleles (genes) that determine the appearance.

One allele inherited from each parent. We use letters to represent the alleles:

Uppercase letter = dominantP = purple

Lowercase letter = recessivep = white

PP = purple Pp = purple pp = white

ALLELE COMBINATIONS homozygous: the alleles are the

same (identical)PP = purple pp = white Other examples: HH hh AA aa

heterozygous: two different alleles for a traitPp (in this case the dominant allele

P is expressed… so the flower is purple)

Other examples: Hh Tt Aa

ALLELES CONTINUED…

Alleles can be explained in two ways…genotype: the letters that are

used to show the genes. Examples: PP, Pp, pp

phenotype: what the organism looks like.

Examples: purple or white flowers

NOW YOU TRY!

PUNNETT SQUARES

T = tall plant t = short plantT T X Tt

T T

T

t

T T

T t

T T

T t

T = tall plant t = short plantT T X Tt

T T

T

t

T T

T t

T T

50% T T50% Tt

100% Tall

T t

PUNNETT SQUARES

aa