Lecture 40

1. Lecture 40 Mr. Sover 2 December 2009

2. Return Homework • Go over homework from yesterday

3. Let’s talk about PUNNETT SQUARES!

4. Punnett Squares • These are tools for you to help see the genetic combinations which can be created by various crosses. • Gametes are listed on top and to the left side of the square…

5. What if we crossed an F1 plant with a white plant?

6. Terminology • Inherited traits take different forms. • Each alternative form of a gene for a certain trait is called an allele.

7. Genotype vs. Phenotype • The combination of alleles for a given trait is referred to as the GENOTYPE (Ww). • The appearance of a trait as determined by a given genotype is called PHENOTYPE (purple)

8. Homozygous vs. Heterozygous • When each cell of an organism contains two of the same alleles for a given trait, the organism is HOMOZYGOUS for that trait. (WW and ww) • Homozygous dominant, homozygous recessive • When each cell of an organism contains two different alleles for a trait, such as Rr, the organism is heterozygous for that trait.

10. Mendelian Genetics

11. Two Traits • OMG Mr. Sover, what are we to do now??

12. Mendel crossed two plants. One had peas which were round and yellow (RRYY). The other had peas which were wrinkled and green (rryy). • The law of segregation states that each gamete must contain one allele for each trait. • What would be the possible genotypes for the zygotes created from this combination?

13. RrYy • Mendel wondered if the alleles segregate independently of each other during gamete formation. • Do they stay in the same combination of RY and ry? • He correctly hypothesized that they segregate independently and the possible gametes would be RY, Ry, rY and ry.

14. Homework • Read the rest of chapter 8. • Do 1, 4, 5, and 9 on page 222-226