# Punnett Squares Step by step how to guide. Putting it together Alleles represented by letters –Capital letters = dominant (T) –Lowercase letters = recessive.

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Punnett Squares Step by step how to guide

Putting it together Alleles represented by letters –Capital letters = dominant (T) –Lowercase letters = recessive (t) Two letters combined = trait –TT, Tt, tt One from mom and one from dad Homozygous = both letters same –TT or tt Heterozygous = both letters differ –Tt

Punnett Squares A diagram that shows all possible outcomes of a genetic cross –Can be used to predict probabilities –Phenotype – an observable trait Tall or short –Genotype – genetic make-up or combination of alleles TT Tt tt

Initial Steps (for a monohybrid cross) 1. Identify the Parents being used in the cross –Homozygous or heterozygous –TT, Tt, tt? –Most important step! 2. Segregate the alleles in each set of genes for each parent –Show meiosis creating the haploid cells

Parent: (P) Segregation of alleles: Draw the Square: Place the parents: Heterozygous Tall crossed with Heterozygous Tall

What’s next? Ratio of allele combinations Ratio of traits

Examples for you to work out! 1.Tt x tt -be sure to show both types of ratios 2.Cross a homozygous tall plant with a short plant -be sure to show both types of ratios

Initial Steps (for a dihybrid cross) 1. Identify the Parents being used in the cross and figure out the combo of both traits. –Homozygous or heterozygous –TTGG, TTGg, TTgg, TtGG, TtGg, Ttgg, ttGG, ttGg, ttgg? –Most important step! 2. Segregate the alleles in each set of genes for each parent –Show meiosis creating the haploid cells

Heterozygous Tall, Heterozygous Green plant crossed with Heterozygous Tall, Heterozygous Green plant

Step 3 – Set up and complete the Punnett Square

Phenotypic Ratio Phenotypic Ratio:

Examples for you to work out! 1.Cross a heterozygous tall, yellow plant with a homozygous tall, heterozygous green plant. 2.Cross a heterozygous tall, yellow plant with a short, heterozygous green plant.

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