1. If you have a dominant phenotype (like purple flowers) how would you determine if it was homozygous (PP) or heterozygous (Pp)? What experiment would you design?
Dominate alleles mask recessive ones
Dominant phenotype, unknown genotype: PP or Pp?
Recessive phenotype, known genotype: pp
What would your hypothesis be if the genotype was PP?
What would your hypothesis be if the genotype was Pp?
If PP, then all offspring purple:
If Pp, then ½ offspring purple and ½ offspring white: P p P p Pp Pp P p p p Pp Pp pp Pp Pp pp
This is called a test cross
Back to Mendel’s Conclusions

2. Review: Law of Segregation
Two alleles for each trait segregate (______________) during gamete production
separate
In what way does crossing over segregate alleles?
In what way does Meiosis I and Meiosis II segregate alleles?

3. Page 295
Discuss: Observe the images below. Explain to your group or seat partner the difference between linked genes and genes that are not linked. Use the image below to help you.

4. Law of Independent Assortment:
Page 296
Law of Independent Assortment:
Two different genes can separate independently from one another if they are on separate chromosomes and are not linked.
The law of segregation followed one single trait at a time, such as seed color.
What if two traits were followed, such as seed color and seed shape?
Are the genes for seed color and seed shape always inherited together? In other words, are yellow seeds always round and green seeds always wrinkled? To help you find out, answer questions 1-4 on page 296.

5. Page 296 Alleles for Seed Color: Yellow (Y) or green (y)
Alleles for Seed Texture: Round (R) or wrinkled (r)

6. Back to “Beyond Mendel”
Linked Genes
Genes that are linked, and found on the same chromosome will most likely be inherited together and will not undergo Mendel’s Law of
unless cross over segregates the linked genes
independent assortment g g G G W w W w
Back to “Beyond Mendel”

7. Circle which stages of Meiosis Creates the Law of Independent Assortment

8. YyRr YyRr x YyRr Law of Independent Assortment
What are the genotypes of the P Generation?
YYRR
yyrr
Law of Independent Assortment
What does the P Generation pass on to F1? YR yr
Gametes
F1 Phenotype?
YyRr
YyRr x YyRr
F1 Genotype?
What does the F1 Generation pass on to F2?
Ova
Sperm YR YR Yr
Combine the sperm and ova to produce the offspring in F2 Yr
YYRR yR yR
YYRr
YYRr yr yr
What do you expect the phenotype will be when YR and YR are combined?
YyRR
YYrr
YyRR
Phenotypic Ratios
YyRr
YyRr
YyRr
YyRr
9/16
Yellow & Round
What will the Genotype be when YR and YR are combined?
Yyrr
yyRR
Yyrr
3/16
Green & Round
yyRr
yyRr
3/16
Yellow & Wrinkled
yyrr
1/16
Green & Wrinkled

9. Page 298
How do I use statistics and probability to predict genotypic and phenotypic ratios?

10. White-board exercises
Two-trait cross
Following two traits:
Kernel shape: Plump vs. withered (P and p) and Kernel color Red vs. yellow (R and r)
Predict the cross between a homozygous recessive corn plant and a homozygous dominant corn plant.

11. Punnett Square Exercise
Two-trait cross
Now take the offspring from that cross, and self-pollinate that plant.
What is the phenotypic ratio of this cross?

12. Punnett Square Exercise
Two-trait cross
My pet guinea pigs (Joni and Chachi) are going to have little guinea pigs.
What is the possibility that their offspring will have long hair, if I know that Joni and Chachi are heterozygous for the following traits?
Black fur (B) White fur (b)
Long hair (L) Short hair (l)