1. Punnett Squares

2. Gene – one set of instructions for an inherited trait

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

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

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

6. TT, tt = homozygous
Tt = heterozygous

7. 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!)

9. 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%

10. Punnett Square Guided Practice Each square is worth 25%

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

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

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

14. More Practice

15. 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