1.1 Nature of the Gene and the Genome

Question 1

Mendel to Morgan: a quick history of genetics

Answer 1

1860’s-Mendel’s proposes laws of inheritance
Law of Segregation
Law of Independent Assortment
1880’s-Chromosomes discovered
1887-Weismann proposes reduction division during meiosis (formation of gametes)
1903-Sutton-proposes chromosomes are carriers of genetic material
Morgan identifies linkage groups in Drosophila

Question 2

What did Mendel Find our?

Answer 2

• Heritable factors-two copies per parent
• Determine phenotype of plant
• May be dominant or recessive (alleles)
• One factor contributed from each parent to offspring
• The seven pea plant trains

Question 3

Law of Segregation

Answer 3

Only one of two copies of heritable factor (gene) contributed to offspring

Question 4

Law of Independent Assortment

Answer 4

• Segregation of one gene pair has no influence on segregation of other gene pair
• Revealed by dihybrid crosses

Question 5

Chromo Linkage Groups

Answer 5

•Sutton predicted existence of linkage groups
•Traits studied by Mendel were not linked
•Obey law of independent assortment
•Flower colour and pollen shape are linked
•Not reported by Mendel*
They are inherited as a group; that is, during cell division they act and move as a unit rather than independentl

Question 6

Genetic Recombination

Answer 6

• Genes on same chromosome do not always segregate together (Incomplete Linkage)
• Recombination (exchange) of genetic material between homologous chromosomes
• Frequency of recombination depends on distance apart on chromosome
• Genes on homologous chromosomes can be “shuffled” by exchanging genetic material

Question 7

middle part of recombination chromo called

Answer 7

Chiasma

Question 8

Genetic Mapping and the odds of Recombination

Answer 8

•Frequency of recombination directly related to distance apart on chromosome
•Wing Length and Body colour genes are far apart
(Frequent recombination events)
•Eye colour and body colour genes are close together
(Fewer recombination events)

Question 9

Giant Chromos Called

Answer 9

Polytene Chromosomes
(Dark staining bands correspond to areas where DNA is more tightly compacted
DNA is plied together to make “fat” chromosome)(Chromosome puff is site of RNA transcription)

Question 10

Griffith experiment with virulent and nonvirulent Pneumococcal strains

Answer 10

Griffith used two strains of Streptococcus pneumoniae. These bacteria infect mice. He used a type III-S (smooth) and type II-R (rough) strain. The III-S strain covers itself with a polysaccharide capsule that protects it from the host’s immune system. This means that the host will die. The II-R strain does not have that protective shield around it and is killed by the host’s immune system.

In this experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R strain bacteria. While neither harmed the mice on their own, the blend of the two was able to kill mice.

Griffith was also able to get both live II-R and live III-S strains of S. pneumoniae from the blood of these dead mice. He concluded that the type II-R had been “transformed” into the lethal III-S strain by a “transforming principle” that was somehow part of the dead III-S strain bacteria.[3]

Today, we know that the “transforming principle” Griffith saw was the DNA of the III-S strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the II-R strain bacteria. The III-S strain DNA contains the genes that form the shielding polysaccharide part from attack. Armed with this gene, the former II-R strain bacteria were now protected from the host’s immune system and could kill the host

Question 11

Hershey-Chase Experiment

Answer 11

Hershey and Chase used T4 phage, a bacteriophage. The phage infects a bacterium by attaching to it and injecting its genetic material into it.

They put labels on phage DNA with radioactive Phosphorus-32. They then followed the phages while they infected E. coli. They found that the radioactive element left on the phage’s DNA was only in the bacterium, and not in the phage, meaning that the DNA had entered the bacterium.

In a second experiment, they put labels on the phage protein with radioactive Sulfur-35. After the phage was attached to the bacterium, the radioactive element was found in the phage, but not in the bacterium, meaning that the phage’s proteins stayed on the outside of the bacterium. This showed them that genetic material which infects the bacteria is DNA.

Question 12

Watson-Crick Proposal used what 2 things to come up with the structure of DNA?

Answer 12

• Used chemical knowledge

* X-ray crystallography

Question 13

3 Requirements for Genetic Material

Answer 13

• Storage of information: heritable instructions
• Self-duplication and inheritance: transmission from cell to daughter cells
• Expression of genetic message

Watson and Cric anserwed:
•Storage:Proposed that base sequence encoded genes
•Replication: Proposed that strands could separate and serve as templates for new synthesis

Question 14

Supercoiling

Answer 14

• Supercoiled DNA is more tightly compacted
• Travels faster in gel less volume
• negative supercoilled is when its underwound (greater number of base pairs per turn)
• plays role in DNA replication and transcription

Question 15

DNA Topoisomerases Types

Answer 15

• DNA Topo I-cuts one strand and permits relaxation

* DNA Topo II- cuts both strands and passes other region of DNA through break

Question 16

Topo I

Answer 16

• cleaves one strand and lets the other intact complementary strand to undergo a controlled rotation that relaxes the supercoiled molecule
• TP1 NB for transcription and replication by preventing supercoiling buildup

Question 17

Topo II

Answer 17

• cuts both strands and passes other region of DNA through break
• is needed to disentangle DNA before duplication chromo can be operated in mitosis

Question 18

3 Reactions Catalyzed by Topoisomerases

Answer 18

1) Supercoiling relaxation
2) Knotting/Unknotting
3) Catenation of DNA molecules (and decatenation)