1. OUTLINE 15
E. Violation of independent assortment
1. Bateson and Punnet
2. Linkage
3. Crossing over
4. Chromosome mapping
5. Effects of linkage and crossing over on genotypic
and phenotypic ratios

2. Application of Mendel’s Rules assumes:
1. One allele completely dominates the other
2. All genes have 2 allelic forms
3. All traits are monogenic (affected by only one
locus)
4. All chromosomes occur in homologous pairs
5. All genes assort independently
6. An allele is completely expressed when either
dominant or homozygous
7. Each trait is controlled by a different set of factors

3. Bateson and Punnett also studied peas:
Flower Color: P = purple p = white
Pollen seed shape: L = long l = round
True Breeding lines: PPLL x ppll P
PpLl F1
Phenotype Number Exp Ratio Exp Number
Purple long
Purple round
White long
While round
What is going on????

4. Test cross F1 to double recessive:
Parents PpLl X ppll
Gametes PL pl Pl pL pl
Expect 1:1:1:1 ratio of phenotypes
Bateson and Punnett observed 7:1:1:7
Some gamete types more common that others…but why???

5. Independent loci
Linked loci
Hair Color
Eye Color
Hair Color
Eye Color

6. Test cross to determine if genes are linked in coupling or repulsion
PL//pl x pl//pl Pl//pL X pl//pl
Gametes 1/2 PL all pl 1/2 Pl all pl
1/2 pl 1/2 pL
F1 1/2 PL//pl (purple, long) 1/2 (purple, round)
1/2 pl//pl (white, round) 1/2 (white, long)
With independent assortment: PpLl x ppll expect 1:1:1:1

7. Thomas H. Morgan Linked genes sorted on chromosomes
Explained why linkage not perfect
Thomas H. Morgan

10. P: PL//PL X pl//pl
F1: (PL//pl) P p L l P p P p L L l l
= centrosome

11. Effects of crossing over on number of possible gamete types
With x-over
No x-over p P p P P P p p L L l l L L l l p P P p L l L l pL Pl PL pl

12. Alfred H. “Hot Dog” Sturtevant

13. Test cross F1 to double recessive:
Parents PpLl X ppll PL//pl X pl//pl
Gametes PL pl PL parental (7)
Pl pl parental (7)
pL pL recombinant (1)
pl Pl recombinant (1)
Expect 1:1:1:1 ratio of phenotypes
Bateson and Punnett observed 7:1:1: /16 = 12.5% recomb.

14. L P
12.5 map units
5 units A L
How do we know if it’s P- A - L , or P - L- A?
If x-over frequency between P and A is 7.5% then: P A L
7.5 map units
5 map units
If x-over frequency between P and A is 17.5% then: P L A
12.5 map units
5 map units

15. Fig 15.7 b cn vg
be (eye
color) sa
(antennae
mutation) 17 9
9.5