1. Punnett Square Notes

2. CCR Biology Objectives
I can use monohybrid and dihybrid crosses to predict the genotypes and phenotypes of off spring.
I can describe how genes determine who we are.

3. Punnett squares
Allele - one of two or more different forms of a gene that are found at the same place on a chromosome. They give us our traits.
Dominant – The allele that will show through on our phenotype.
Recessive – The allele that is the weaker of the two types
Genotype – Our actual genetic makeup. Ex. Bb
Phenotype – The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. Ex. Brown hair

4. Punnett Squares Homozygous dominant – Two dominant alleles
Homozygous recessive – Two recessive alleles
Heterozygous – A mixture of dominant and recessive alleles

5. B BB Bb b Bb bb Punnett Squares
The allele for brown hair (B) is dominant to red hair (b).
If you cross a man heterozygous for brown hair and a woman heterozygous for brown hair, what is their possibility of having a red headed child?
Genotypes:
BB Bb bb
Phenotypes:
Brown hair (3)
Red hair (1)
Ratio:
3:1
Red head probability:
25%

6. Dihybrid Cross
A dihybrid is an individual that is heterozygous at two genes (YyRr)
This means they show two different traits for two different alleles
We use dihybrid crosses to predict possible offspring genotypes and phenotypes with individuals like these

7. History of Medelian Genetics
Gregor Mendel did an experiment with pea plants and found…
Segregation - the separation of pairs of alleles at meiosis and their independent transmission via separate gametes
Independent Assortment - The process of random segregation and assortment of chromosomes during anaphase I of meiosis resulting in the production of genetically unique gametes.

8. Dihybrid Cross Genotypes:
YYRR YYRr YyRR
YyRr YYrr Yyrr
yyRR yyRr yyrr
Phenotypes:
Yellow and Round (9)
Yellow and Wrinkled (3)
Green and Round (3)
Green and Wrinkled (1)
Ratio:
9:3:3:1
In pea plants the alleles for pea color and shape are displayed. If you take a pea plant heterozygous for yellow, round seeds (YyRr) and cross it with another heterozygous yellow, round seeded plant (YyRr), what kinds of offspring would you have? (The recessive for color is green and the recessive for shape is wrinkled.)
YR Yr yR yr
YR YYRR YYRr YyRR YyRr
Yr YYRr YYrr YyRr Yyrr
yR YyRR YyRr yyRR yyRr
yr YyRr Yyrr yyRr yyrr