Housekeeping

1
Housekeeping

• Exam Friday ( 12-17 questions)
• Review tonight 6 pm Sc278
• Homeworks posted outside office
• Ch1,2,3
• Ch 4 through p. 125
• Ch 5 through p. 160
• Childrens book due 3/14
• Lab
• Need 3!!

2
The A and B loci are 35 map units apart on
chromosome 15 in humans. An Ab/aB woman marries
an AB/AB man. What is the probability that their
first child will be AB/AB?
3
Three recessive genes on the same chromosome in
the tomato plant have the following phenotypes a
produces the absence of anthocyanin pigment, hl
produces hairless plants, and j produces
jointless fruit stems. Among 3000 progeny from a
3-point testcross, the following phenotypes were
observed259 hairless 268 no pigment,
jointless, hairless40 jointless, hairless 941
no pigment, hairless931 jointless 32 no
pigment260 normal 269 no pigment,
jointless A.     Determine the genotypes of the
parents that were crossed based on the above
information. (what alleles are linked??) (2
points)B.      Plot the map distances for the
three genes. (2 points)
4
How does DNA carry genetic information?
How does DNA replicate to pass on to offspring?
How does the DNA change to allow for so much
diversity?
How does DNA encode for a phenotype?
5
DNA diversity?

• Crossing over/Homologous recombination
• Independent assortment
• Mutations

6
General rules of recombination

• Occurs between like chromosomes
• Exact exchange
• no base pairs lost or gained
• DNA doesnt break and rejoin at the same place on
  each piece of DNA
• Heteroduplex region

Figure 5.20a
7
Steps of recombination

• 1. DNA nick created
• 2. Whisker displacement
• 3. First strand invasion
• 4. Second strand invasion
• 5. Repair and ligation
• 6. Branch migration
• 7. Disengagement

8
Nicking

• Can be random or specific
• Enzymes endonucleases

Figure 5.21-Nicking
9
Whisker displacement

• DNA helicase unwinds DNA
• Single strand displaced whisker

Figure 5.21. Whisker displacement
10
First strand invasion

• Enzyme binds to whisker strand and double helix
• RecA in E. coli
• opens double helix
• Homologous region recognized
• H-bonds allow strands to bind
• S.S. binding protein keeps region open

Figure 5.21 1st strand invasion
11
Second strand invasion

• Leftover strands come together
• D-loop and original strand that was nicked

Figure 5.21 2nd strand invasion
12
Repair and ligation

• Leftover gap is repaired
• repair enzymes
• Repaired region is reconnected to strand
• DNA ligase

Figure 5.21 repair and ligation
13
Branch migration

• Lengthens the heteroduplex
• Unzip double helix
• Rezip with complementary strand

Figure 5.21 branch migration
14
Disengagement
Figure 5.21 disengagement
15
Disengagement
Figure 5.21 alternative resolutions
16
Recombination
movie
17
Gene conversion at the heteroduplex
Figure 5.20
18
How does DNA carry genetic information?
How does DNA replicate to pass on to offspring?
How does the DNA change to allow for so much
diversity?
How does DNA encode for a phenotype?
19
DNA diversity?

• Crossing over/Homologous recombination
• Independent assortment
• Mutations

20
What is a mutation?
21
Types of mutations

• Substitutions
• Deletions
• Insertions
• Inversions
• Translocations

22
Figure 6.2