Chapter 11 - Meiosis Overview and Comparison with Mitosis

12 Questions

During meiosis, which process leads to genetic variation by the exchange of DNA between homologous chromosomes?

Crossover (recombination)

What occurs during Prophase I of meiosis that contributes to genetic variability?

Homologs pair up and undergo crossing over

Which stage of meiosis involves the alignment of homologous chromosomes for separation?

Metaphase I

In Griffith's Transformation Principle experiment, what was observed when heat-killed S strain bacteria were mixed with live R strain bacteria?

Transformation of R strain into S strain occurred

Which scientist proved that DNA was the genetic material responsible for transformation in bacteria?

Avery

What is the role of DNase in Avery's experiments on the transformation principle?

It prevented transformation

What did Chargaff's Rules establish regarding DNA base pairing?

A=T and G=C

In DNA replication, what is the function of DNA polymerase?

Attaching free nucleotides to DNA

What is the role of telomeres in DNA replication?

Provide a buffer for DNA loss at chromosome ends

How does semiconservative DNA replication work according to Meselson and Stahl's experiment?

One strand of parental DNA is conserved in the daughter DNA

Which enzyme is responsible for producing an RNA primer during DNA replication?

DNA primase

What is the purpose of the sliding clamp in DNA replication?

Helping keep DNA polymerase attached for efficient synthesis

Study Notes

Meiosis

Gametes are haploid (one set of chromosomes), while zygotes are diploid (two sets)
Sexual life cycle: meiosis, gamete formation, and fertilization
Meiosis has two stages: meiosis I (homologs separate) and meiosis II (sisters separate)
DNA exchange occurs by crossing over, and random mixing of chromosomes produces variation
Prophase I: homologs pair up (synapses) and crossing over occurs, forming chiasmata
Metaphase I: homologs line up to separate
Metaphase II: sisters line up to separate
Stages of meiosis: interphase, meiosis I, and meiosis II
Variation is introduced through independent assortment of chromosomes (2^23 = 8 million), random fertilization (2^23 x 2^23 = 64 trillion), and crossover (recombination) with 2-3 crossovers per chromosome

Discovery of Genetic Material

Griffith (1928): discovered transformation principle, transforming R strain into S strain
Avery (1944): proved DNA is the genetic material, using protease and RNase treatments
Hershey and Chase (1952): proved DNA is the genetic material, using 32P-labeled DNA and 35S-labeled protein
Chargaff (1952): discovered Chargaff's rules (A=T, G=C, and A+T/G+C ratio is variable)
Watson and Crick (1953): solved the structure of DNA, a double helix with bases pairing in the center and backbones on the outside

Properties of DNA

Nucleotide structure: phosphate, sugar, and base
Nucleotides are strung together by phosphodiester bonds
Double helix formation through H-bonding of bases
Base pairing rules: complementation
Denaturation and renaturation of DNA
Antiparallel strands with 5' → 3' direction

DNA Replication

Daughter strand is made from a template
Semiconservative replication: Meselson and Stahl experiment shows half of DNA helix is a daughter, the other half is a template
Dehydration synthesis and phosphodiester bond formation
DNA polymerase is the enzyme, working in 5' → 3' direction
Addition of free nucleotides according to base pairing rules
Replication begins at a replication bubble, with each side being a replication fork
Helicase opens the double helix like a zipper
ssDNA binding protein helps keep DNA from base pairing
RNA primer is required for DNA polymerase to work
Sliding clamp helps keep DNA polymerase attached
Leading and lagging strand synthesis, with different mechanisms
Telomeres solve the "end replication problem" by providing a buffer zone for DNA loss