1. Crosses and Chromosomes
Do Now (dihybrid cross)
In fruit flies, red eyes are dominant to white, and wings are dominant to no wings
Draw a Punnett square representing a cross between two flies heterozygous for both traits.
What is the probability of having a white-eyed wingless offspring?

2. Quiz Review 1: floppy completely dominant to pointy
2: yellow + orange = codominant
3: more common in men = sex-linkage
4: in between phenotype (blend) = incomplete dominance
5: 4 phenotypes = >2 alleles

3. 6: Sex-Linkage X+ Xo X+X+ X+Xo Y X+Y XoY Carrier f.
50% of males will be colorblind
50% of females will be colorblind, 50% will be carriers.
No females w/ disease
Normal m.

4. 7: multiple alleles G B O GO BO Green + Blue 1:1 green spots:blue
OO = no spots
No spots

5. Dihybrid Punnett Square
PY Py pY py
PY Py pY py
PP YY
PP Yy
Pp YY
Pp Yy
PP yy
Pp yy
pp YY
pp Yy
pp yy

6. Pedigree

7. TEST WEDNESDAY COME TO COACH CLASS TOMORROW! TOPICS: CHAPTER 9
Chromosomes, cell reproduction, crosses, + today’s topics (Mendel’s Laws + crossing over)
CHAPTER 9

8. Mendel’s Law of Segregation
A pair of factors is segregated (separated) during the formation of gametes (sex cells) Y y
For example:
50%
Of Gametes
50%
Of Gametes

9. Mendel’s Law of Independent Assortment
Factors (alleles) for different characteristics are distributed independently from one another. T T t t Y Y y y
For example:
25%
Of Gametes
25%
Of Gametes
25%
Of Gametes
25%
Of Gametes

10. Mendel’s “Laws” of Heredity
It is important to note that these “laws” work under certain conditions:
Each gene is on a different chromosome
The organisms are diploid

11. It’s all about the Chromosomes
In meiosis, the chromosome number is reduced by half (2nn; diploidhaploid)
50% of gametes get one allele, 50% get the other. b b B B

12. Dihybrid Gametes Pea plant cross: PpYy x PpYy
Gametes: reproductive haploid cells (sperm and egg)
One individual heterozygous for 2 traits can produce 4 (2n, where n= number of different genes)possible combinations of alleles. PY Py pY py

13. Dihybrid Punnett Square
PY Py pY py
PY Py pY py
PP YY
PP Yy
Pp YY
Pp Yy
PP yy
Pp yy
pp YY
pp Yy
pp yy

14. One More Twist a A
crossing over: when two homologous chromosomes exchange material during meiosis, leading to a new combination of alleles B b a A B b

15. Meiosis and Genetics
The 2 alleles a diploid organism has for a trait are located on 2 homologous chromosomes.
The separation of these chromosomes during meiosis leads to the 50/50 chance of a gamete having one version or the other.
Mendel’s Laws of heredity only work for alleles on different chromosomes.
Crossing over creates new combinations of alleles.