Session 4

Question 1

At which stage of the cell cycle does cell content replication occur?

Answer 1

Growth phase 1 (G1)

Question 2

At which stage of the cell cycle does DNA replication occur?

Answer 2

Synthesis phase (S phase)

Question 3

What direction does the DNA chain grow in DNA replication?

Answer 3

5’ to 3’

Question 4

What drives the DNA replication reaction?

Answer 4

Pyrophosphate hydrolysis

Question 5

How is DNA replication initiated in prokaryotes.

Answer 5

Origin of replication is recognised.
DNA polymerase and other specific proteins are recruited.
Reaction kicked off by primase because DNA polymerase can only extend a 3’ end.

Question 6

On which strand of DNA is replication continuous?

Answer 6

Leading strand (strand where the original strand streches from 3’ to 5’)

Question 7

On which strand of DNA is replication not continuous, what is formed instead, and why?

Answer 7

Lagging strand (strand stretching from 5’ to 3’).
Forms Okazaki fragments.
DNA polymerase can only form DNA from 5’ to 3’ so it must work backwards on this strand to form many smaller fragments of complimentary DNA.

Question 8

How are Okazaki fragments joined?

Answer 8

Using DNA ligase.

Question 9

What is used to unzip DNA in replication?

Answer 9

DNA helicase.

Question 10

What is a replication fork in DNA replication?

Answer 10

The area on the DNA strand which is unwound and currently undergoing replication.

Question 11

How is DNA replication terminated?

Answer 11

Replication starts in several places along a chromosome when 2 regions of replicating DNA meet replication stops.
The DNA strands are joined by DNA ligase where they meet.

Question 12

What are metacentric chromosomes?

Answer 12

Chromosomes where the centromere is in the middle of the chromosome.
P and Q arms are similar lengths.

Question 13

What are submetacentric chromosomes?

Answer 13

Chromosomes where the centromere is towards the top of the chromosome.
P arm is shorter than the Q arm.

Question 14

What are acrocentric chromosomes?

Answer 14

Chromosomes where the centromere is very close to the top of the chromosome.
P arm is considerably shorter than the Q arm.

Question 15

What are telocentric chromosomes?

Answer 15

The chromatid is at the top of the chromosome.
No P arm only a Q arm.
Don’t occur in humans.

Question 16

After DNA replication does the chromosome number change? Why?

Answer 16

Chromosome number stays the same.

One replicated chromosome consists of two sister chromatids.

Question 17

What is mitosis?

Answer 17

Cell division of somatic cells.

Produces 2 identical daughter cells with the same chromosome content as the parental cell.

Question 18

In what order does mitosis occur?

Answer 18

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis.

Question 19

What occurs in prophase in mitosis?

Answer 19

Spindle fibres form from a pair of centrioles.

Chromosomes appear in the nucleosome.

Question 20

What occurs in prometaphase in mitosis?

Answer 20

Spindle fibres bind to the kinetocore of each chromosome.

Question 21

What occurs in metaphase of mitosis?

Answer 21

Centrioles of spindle fibres line up at the poles of the cell and chromosomes line up along the metaphase plate along the equator of the cell.

Question 22

What occurs in anaphase of mitosis?

Answer 22

Daughter chromosomes split up from the chromosome and migrate towards the poles attached to kinetocore spindle fibres.

Question 23

What occurs in telophase of mitosis?

Answer 23

The nuclear envelope reforms and delve age furrows appear.

Spindle fibres disappear.

Question 24

What occurs in cytokinesis of cell division?

Answer 24

The cytoplasm divides so the parent cell becomes 2 daughter cells.

Question 25

What is meiosis?

Answer 25

Cell division for germ line cells. Produces 4 non-identical cells with half the chromosome content of the parental cells. Occurs as a round of replication followed by 2 rounds of division.

Question 26

What creates variation in meiosis and how?

Answer 26

Crossing over: bivalent forms of chromosomes line up and cross over at chiasmata to exchange portions of DNA with each other. Random assortment: chromosomes are randomly assorted after division to produce a unique combination of chromosomes.

Question 27

What occurs in meiosis 1?

Answer 27

Cells divide to produce 2 diploid daughter cells. | Crossing over occurs so the genetic material in each daughter cell is not identical.

Question 28

What occurs in meiosis 2?

Answer 28

Daughter cells divide to create haploid gametes. | Random assortment occurs to give each gamete a unique combination of DNA.

Question 29

In spermatogenesis, how many sperm are produced from one spermatocyte.

Answer 29

4, all daughter cells go on to produce 2 gametes.

Question 30

In oogenesis, how many ovum a are produced from one oocyte?

Answer 30

1, 3 polar bodies are produced from the other gamete cells.

Question 31

Why must crossing over occur?

Answer 31

If crossing over didn't occur, meiosis couldn't occur because all genetic material in meiosis 1 would be passed on to one daughter cell. This would produce cells in meiosis 2 with diploid chromosomes so no gametes would form.

Question 32

What is genotype?

Answer 32

The genetic makeup of an individual. Can refer to the alleles of a particular gene that are present.

Question 33

What is phenotype?

Answer 33

The observable characteristics or traits of an individual.

Question 34

Define homozygous.

Answer 34

2 alleles of a gene are the same in an individual.

Question 35

Define heterozygous.

Answer 35

2 alleles of a gene are different in an individual.

Question 36

Define hemizygous.

Answer 36

Only one allele of a gene (on the X chromosome) is present. | Only occurs in males.

Question 37

What is a dominant allele?

Answer 37

The allele of a gene that determines the phenotype.

Question 38

What is a recessive allele?

Answer 38

The non-dominant allele of a gene.

Question 39

What is co-dominance in a gene?

Answer 39

More than one allele is dominant in the gene so multiple alleles can determine the phenotype.

Question 40

In blood type, which alleles are dominant over each other?

Answer 40

A and B are both dominant over O. | Neither A or B are dominant over each other.

Question 41

What are linked genes? What do they show?

Answer 41

Genes on the same chromosome. | They show no independent assortment in meiosis.

Question 42

What are non-linked genes? What do they show?

Answer 42

Genes on different chromosomes. | They show independent assortment in meiosis.

Question 43

Which enzyme catalysts DNA replication?

Answer 43

DNA polymerase