1. Punnet Square Notes

2. Phenotype & Genotype
Phenotype – the physical characteristics of an organism (example: blue eye color)

3. Phenotype & Genotype
Genotype – the alleles possessed by an organism (example: inheriting two blues alleles on from each parent)

4. Dominant & Recessive Allele
Dominant Allele – An allele that dominants over a recessive allele. Represented in genetics with a capital letter (example the capital letter B could represent the dominant allele for brown eyes).

5. Dominant & Recessive Allele
Recessive Allele - An allele that does NOT dominate over other traits. Represented in genetic by a lower case letter (example the lower case letter b could represent the allele for blue eyes)

6. Types of Genotypes
Homozygous Dominant: An organism having two identical dominant alleles. Represented in genetic by having two upper case letters. (example: BB represents a person that has two alleles for brown eyes)

7. Types of Genotypes
Homozygous Recessive: An organism having two identical recessive alleles. Represented in genetic by having two lower case letters. (example: bb represents a person that has two alleles for blue eyes)

8. Types of Genotypes
Heterozygous: An organism having two different alleles for a trait, one recessive and one dominant. Represented in genetic by having one upper case and one lower case letters. (example: Bb represents a person that has a dominant alleles for brown eyes and a recessive allele for blue eyes).

9. Punnet Square/ Grid
Punnet Square / Grid is a grid or table that shows all the possible outcomes between a cross between a male in female organisms

10. Example
Cross a __________________________ __pea plant with smooth seeds with a __________________________ ____plant with wrinkled seeds.
Select Symbols the alleles:
Write the cross (alleles parents can give):
Make a punnet square.
What percent are heterozygous?
What percent are smooth?
What percent are wrinkled?

11. P-square Practice Question #1
Let's say that in seals, the gene for the length of the whiskers has two alleles.  The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers. Cross two long-whiskered seals, one that is homozygous dominant and one that is heterozygous?
The Symbols (letters you will use) ______________________
The Cross (the parent’s genotypes)_________________________
The Punnett square:

12. P-square Practice Question #2
In purple people eaters, one-horn is dominant and no horns is recessive. Draw a Punnet Square showing the cross of a purple people eater that is heterozygous for horns with a purple people eater that does not have horns.
The Symbols (letters you will use) ______________________
The Cross (the parent’s genotypes)_________________________
The Punnett square:

13. Test Crosses
Problem:
When an organism has a shows a dominant phenotype (example: Brown Eyes) it is not always possible to know if this organism is has a heterozygote genotype (Bb) or Homozygote dominant genotype (BB) because the phenotype (physical appearance) it the same for both genotypes.

14. Test Cross
Solution:
To determine the genotype of an organism showing a dominant phenotype a test cross is used.

15. What is a test cross?:
In a test cross an individual that might be heterozygous or homozygous dominant is crossed with an individual that is homozygous recessive.

16. How it works?
If you cross a homozygous recessive organism with a homozygous dominant organism all (100%) the offspring will have the dominant phenotype.

17. Example: Black fur color is dominant to white fur color in sheep
Example: Black fur color is dominant to white fur color in sheep. A homozygous dominant black sheep is cross with a homozygous recessive white sheep.
The Symbols (letters you will use) ______________________
The Cross (the parent’s genotypes)_________________________
The Punnett square:

18. If you cross a homozygous recessive organism with a heterozygote 50% of the offspring will have the dominant phenotype and 50% will have the recessive phenotype.

19. Example: Black fur color is dominant to white fur color in sheep
Example: Black fur color is dominant to white fur color in sheep. A heterozygous black sheep is cross with a homozygous recessive white sheep.
The Symbols (letters you will use) ______________________
The Cross (the parent’s genotypes)_________________________
The Punnett square: