Punnett Squares

Gene – one set of instructions for an inherited trait

Allele – different forms of a gene Capital letter = dominant trait Lowercase letter = recessive trait Example: P = purple, p = white

Talk with a partner! When talking about alleles, what does the capital and lower case letter mean?

Phenotype – physical appearance of trait (brown, short, etc.) Genotype – (Pp, pp, TT, etc.)

TT, tt = homozygous Tt = heterozygous

EXAMPLE: T = tall, t = short TT = tall phenotype tt = short phenotype Tt = tall phenotype (****If there is at least one large letter it will always appear!)

https://www.youtube.com/watch?v=V_pl5lcSUFg

Punnett Squares: tool that predicts the traits in offspring Steps Examples Write down the genotypes for both parents. 2) Separate the genes into dad’s sperm and mom’s eggs. 3) Draw Punnett Square 4) Write the possible outcomes. Mom: Ff and Dad: Ff (freckles) 2) 3) 4) Freckles: ¾ = 75% No Freckles: ¼= 25%

Punnett Square Guided Practice Each square is worth 25%

Example #1 P = purple flower, p = white flower Cross Pp x Pp Offspring phenotype: _____% purple, _____% white

Example #2 B = black hair, b = blonde hair Cross BB x bb Offspring phenotype: _____% black hair, _____% blonde hair

Example #3 L = long fingers, l = short fingers Cross Ll x ll Offspring phenotype: _____% long fingers _____% short fingers

More Practice

2) R = round ears, r = pointy ears RR x Rr Practice Problems: Find the phenotype percentages using Punnett squares: 1) T = tall, t = short Tt x Tt 2) R = round ears, r = pointy ears RR x Rr 3) W = wavy hair, w = straight hair Ww x ww