1. Traits and Punnett Squares

2. Traits and Alleles
Traits are characteristics passed from your parents, ex) eye color
Each cell in your body has a complete set of DNA-46 chromosomes (23 from mom, 23 from dad)
Sex cells (sperm and egg) have 23 chromosomes each
Each trait is determined by a pair of genes, called alleles
For each trait, you have 1 allele from mom, 1 allele from dad.
Alleles are shown by using letters, ex) T for height
Alleles are considered dominant or recessive

3. Dominant Alleles An allele that masks a recessive alleles
Dominant alleles are shown in capital letters.
Presence of the dominant allele will mean the dominant trait is shown ex) Tt or TT
Dominant alleles are always listed first-so it would be Tt not tT.

4. Recessive Alleles An allele that is masked by a dominant allele
Recessive alleles are shown in lower case letters.
The only way that a recessive trait is shown is if there are 2 of them-1 from each parent
Ex) tt

5. Homozygous Traits or Alleles
Means that there are 2 of the same alleles ex) TT or tt
Pure is another word for homozygous

6. Heterozygous Traits or Alleles
Means that there are 2 different alleles ex) Tt
Hybrid is another term for heterozygous

7. Genotype
What 2 alleles are present
Ex) TT or Tt or tt

8. Phenotype What trait is shown-the characteristic that is shown
Ex) tall or short

9. Punnett Square
Used to determine the genotype and phenotype of offspring
Steps:
Draw square
Fill in parent genotypes
Complete offspring genotypes
Determine % of genotypes of offspring
Determine % of phenotypes of offspring

10. Punnett Square Example
Example 1) A brown (BB) rabbit is crossed with a white rabbit (bb). For their offspring, give the % of each genotype and each phenotype.
Steps:
Draw square

11. Punnett Square 2) Fill in parent genotypes B B b b
Example 1) A brown (BB) rabbit is crossed with a white rabbit (bb). For their offspring, give the % of each genotype and each phenotype. B B
2) Fill in parent genotypes b b

12. Punnett Square 3) Complete offspring genotypes Bb Bb Bb Bb B B b b
Example 1) A brown (BB) rabbit is crossed with a white rabbit (bb). For their offspring, give the % of each genotype and each phenotype. B B
3) Complete offspring genotypes Bb b Bb b Bb Bb

13. Punnett Square Determine % of genotypes of offspring: BB-0/4=0%
Example 1) A brown (BB) rabbit is crossed with a white rabbit (bb). For their offspring, give the % of each genotype and each phenotype. B B
Determine % of genotypes of offspring:
BB-0/4=0%
Bb-4/4=100%
bb-0/4=0% Bb b Bb b Bb Bb

14. Punnett Square 5) Determine % of phenotypes of offspring:
Example 1) A brown (BB) rabbit is crossed with a white rabbit (bb). For their offspring, give the % of each genotype and each phenotype. B B
5) Determine % of phenotypes of offspring:
Brown-4/4=100%
White-0/4=0 % Bb b Bb b Bb Bb

15. Punnett Square Fill in parent genotypes
Example 2) A cross is done between green (Gg) and yellow parent plants (gg) . For their offspring, give the % of each genotype and each phenotype. G g
Fill in parent genotypes g g

16. Punnett Square Complete square gg Gg Gg gg
Example 2) A cross is done between green (Gg) and yellow parent plants (gg) . For their offspring, give the % of each genotype and each phenotype. G g
Complete square gg Gg g g Gg gg

17. Punnett Square gg Gg Gg gg
Example 2) A cross is done between green (Gg) and yellow parent plants (gg) . For their offspring, give the % of each genotype and each phenotype. G g
Genotypes:
GG-0/4=0%
Gg-2/4=50%
gg-2/4=50% gg Gg g g Gg gg

18. Punnett Square Phenotypes: Green-2/4=50% Yellow-2/4=50% gg Gg Gg gg
Example 2) A cross is done between green (Gg) and yellow parent plants (gg) . For their offspring, give the % of each genotype and each phenotype. G g
Phenotypes:
Green-2/4=50%
Yellow-2/4=50% gg Gg g
More practice: g Gg gg