1. 10.4 Genes of Different Chromosomes Are Inherited Independently
A. Dihybrid Crosses Track the Inheritance of Two Genes at Once
P generation true-breeding for 2 traits
F1 crossed to yield F2
Four phenotypes in ratio 9:3:3:1
All possible combinations found
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RR YY rr yy

2. F1 generation rr yy Female gametes r y r y R Y Rr Yy Rr Yy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
F1 generation rr yy
Female gametes r y r y R Y Rr Yy Rr Yy
Male gametes R Y RR YY Rr Yy Rr Yy

3. F2 generation Rr Yy Female gametes R Y R y r Y r y R Y RR Y Y RR Yy Rr
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
F2 generation Rr Yy
Female gametes R Y R y r Y r y R Y RR Y Y RR Yy Rr YY Rr Yy
Phenotypic ratio 9:3:3:1 R y 9
Smooth, yellow RR Yy RR yy Rr Yy Rr yy 3
Smooth, green
Male gametes 3
Wrinkled, yellow 1
Wrinkled, green Rr Yy r Y Rr YY Rr Yy rr YY rr Yy r y Rr Yy Rr yy rr Yy rr yy

4. 10.4 Genes of Different Chromosomes Are Inherited Independently
B. Meiosis Explains Mendel’s Law of Independent Assortment
During gamete formation, segregation of alleles for one gene does not influence alleles for another gene
Provided genes are on different chromosomes

5. Figure 10.9 Mendel’s Law of Independent Assortment.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R R Y Y
MEIOSIS II R R R Y Y R Y Y r y
MEIOSIS I r y r y r y y
MEIOSIS II y
Alternative 1 r y R R r r r
Haploid
gametes y Y
Metaphase I
Metaphase II Y R y R
Diploid cell R y
MEIOSIS II R y R y y
MEIOSIS I R r Y r Y y r r Y
Alternative 2
MEIOSIS II Y r Y r Y
Figure 10.9 Mendel’s Law of Independent Assortment.

6. 10.4 Genes of Different Chromosomes Are Inherited Independently
B. Meiosis Explains Mendel’s Law of Independent Assortment
Punnet squares for more than 2 genes cumbersome
Product rule
Chance that two independent events will both occur equals the product of the individual chances that each event will occur

7. Probability that off spring is Rr Yy Tt = 1/8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R r Y y T t R RR Rr Y YY Yy T TT Tt r Rr rr y Yy yy t Tt tt
1/2 Rr ×
1/2 Yy ×
1/2 Tt
Probability that off spring is Rr Yy Tt = 1/8
Figure The Product Rule.

8. Explain how meiosis contributes to independent assortment of alleles.
10.4 Mastering Concepts
Explain how meiosis contributes to independent assortment of alleles.

9. 10.5 Genes on the Same Chromosome Many Be Inherited Together
A. Genes on the Same Chromosome Are Linked
Unlike genes on different chromosomes, they do not assort independently during meiosis
First noticed in early 1900s

10. Figure 10.11 Gene Linkage Changes the Results of a Dihybrid Cross.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Pp Ll self-cross, genes not linked
b. Pp Ll self-cross, genes linked P p P p × × P p P p L l L l L l L l
Male
Female
Male
Female
Crimson flowers,
long pollen
Crimson flowers,
Long pollen
Crimson flowers,
long pollen
Crimson flowers,
long pollen
Female gametes
Female gametes
P L
P l
P L
P l
P L
p l
P L
PP LL
PP Ll
Pp LL
Pp Ll 9
Crimson flowers,
long pollen
P L
PP LL
Pp Ll 3
Crimson flowers,
long pollen
P l
PP Ll
PP ll
Pp Ll
Pp ll 3
Crimson flowers,
round pollen
Male gametes
p l
Pp Ll
pp ll 1
Red flowers,
round pollen
Male gametes 3
Red flowers,
long pollen
p L
Pp LL
Pp Ll
pp LL
pp Ll 1
Red flowers,
round pollen
p l
Pp Ll
Pp ll
pp Ll
pp ll
Figure Gene Linkage Changes the Results of a Dihybrid Cross.

11. 10.5 Genes on the Same Chromosome May Be Inherited Together
A. Genes on the Same Chromosome Are Linked
Thomas Hunt Morgan
Drosophila melanogaster – fruit fly
Linkage groups are on the same chromosome

12. 10.5 Genes on the Same Chromosome Many Be Inherited Together
A. Genes on the Same Chromosome Are Linked
Sometimes did see combinations not found in parents
Due to crossing over
Parental chromatid- no crossing over
Recombinant chromatid

13. Homologous chromosomes cross over in prophase I
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Gametes P P p L L L
Parental
MEIOSIS II p L P p P p L L l
MEIOSIS I
Homologs part
Recombinant p l l P p l
Homologous chromosomes
cross over in prophase I
Parental
MEIOSIS II P l
Recombinant
Figure Crossing Over.

14. 10.5 Genes on the Same Chromosome Many Be Inherited Together
B. Studies of Linked Genes Have Yielded Chromosome Maps
Some crosses had a higher proportion of recombinant offspring
Alfred Sturtevant, Morgan’s undergraduate assistant, proposed linkage maps
Genetic markers used now

15. Figure 10.13 Breaking Linkage.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A a
Genes A and B are far apart; crossing over
is more likely to separate these alleles.
0 1.5
33.0
36.1
54.5 B b
Genes B and C are close together; crossing
over is less likely to separate these alleles. C c y w v m r a. b.
Figure Breaking Linkage.

16. Clicker Question
What is the order of genes on a chromosome if g and m are 4 units apart, k and h are 6 units apart and m and h are 2 units apart?
ghmk
gmkh
hkmg
g h m k
Correct answer is A