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Intro to Punnett SquaresMrs. MacWilliamsBiology

+ REVIEW

THE PARENTS CAN ONLY GIVE ONE OF EACH HOMOLOGOUS CHROMOSOME. BUT, THERE ARE 2 DIFFERENT CHROMOSOMES EACH CAN GIVE!

+ Punnett Squares – 7 Steps We will use 7 STEPS to complete punnett squares. Make

sure you complete ALL 7 STEPS for every assignment and test and quiz.

+Step 1List the type of cross (P, F1, F2)

Parental or Purebread P ALWAYS 2 homozygous individuals

First Filial or F1 generation Term used to describe the offspring obtained from

a P generation ALWAYS 2 heterozygous individuals

Second Filial or F2 generations Term used to describe the offspring obtained from

two individuals from the F1 generation Any other combination (hetero x homo)

+Step 2 List the gender of the parent

Symbol represents male

Symbol represents female

+Step 3 List the genotype of the parents

Genotype – the pair of alleles in the cells of an organism.

The actual GENES in the pair

+Step 4 List the phenotype of parents

Phenotype the organisms appearance of the expressed trait.

The Photo of what the organism looks like The Physical traits of what it looks like

+Step 5 Complete the Punnett Square

A grid that uses symbols to show the possible gene combination from a cross.

+Step 6 List Genotypic Ratio of cross

Homozygous Dominant: Heterozygous: Homozygous Recessive

YY: Yy: yy

+Step 7 List Phenotypic Ratio of cross

Dominant: Recessive

Yellow: green

+ Generation Ratios! KNOW THESE!!!!! Parent (P) generationMonohybrid cross: genotype 4:0phenotype 4:0Dihybrid cross: genotype 16:0

phenotype 16:0 First Filial (F1) generation

Monohybrid cross: genotype 1:2:1phenotype 3:1Dihybrid cross: genotype 1:2:2:4:1:2:1:2:1

phenotype 9:3:3:1Trihybrid cross: phenotype 27:9:9:9:3:3:3:1

Symbol represents female

+ Monohybrid Cross A cross that involve ONLY ONE trait

Ex: Seed color

We will now complete a P generation Punnett Square and an F1 generation Punnett Square

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