9.19-9.20 Warm-Up

• Explain what recombinant gametes are.
• What did Morgan and Sturtevant study?
• Differentiate wild type and mutant.
• Give a short answer on what we can use to map genes.

Crossing over produces new combinations of alleles

Section 9.19

A

B

a

b

Tetrad

Crossing over

A

B

a

b

a

B

A

b

Gametes

Breaking Linked Genes

Recombination Frequencies

• the number of recombinants divided by the total number of offspring
• this measures how often linked genes break due to crossing over

Geneticists use crossover data to map genes

Section 9.20

g

c

l

17%

9%

9.5%

Mapping Genes from Crossover Data

Thomas Morgan and Alfred Sturtevant Partying

Morgan and Sturtevant Working

(Experimenting with Flies)

Short�aristae

Black

body

(g)

Cinnabar

eyes

(c)

Vestigial

wings

(l)

Brown�eyes

Long aristae�(appendages�on head)

Gray

body

(G)

Red

eyes

(C)

Normal

wings

(L)

Red�eyes

Mutant phenotypes

Wild-type phenotypes

Homework:

• Read 9.21-9.23
• Packet Exercise 13