Genetics - Week 2

Question 1

What are alleles?

Answer 1

different versions of the same gene

Question 2

How might homologous chromosomes differ?

Answer 2

they may carry the same gene, but different alleles

Question 3

What happens to the alleles after replication?

Answer 3

sister chromatids have identical alleles

Question 4

What are genotypes?

Answer 4

combination of alleles in a single cell or single individual that relate to specific traits we are interested in

• alleles belonging to same gene are separated by a ‘/’
• alleles belonging to different genes are separated by a ‘;’

Question 5

The Cell Cycle

What is interphase?

Answer 5

G1/S/G2

Question 6

The Cell Cycle

When does DNA replication occur?

Answer 6

interphase

Question 7

What is the goal of mitosis?

Answer 7

• to produce daughter cells that are genetically identical to parent cell
• asexual reproduction (no gametes are produced)

Question 8

Mitosis

Describe the process.

Answer 8

prophase
metaphase
anaphase
telophase

Question 9

Mitosis

What occurs in metaphase?

Answer 9

allows splitting of sister chromatids to be shared between two daughter cells

Question 10

What happens go chromosomes after DNA replication?

Answer 10

the number of chromosomes do not change, but results in the formation of sister chromatids (which share one centromere)

Question 11

Mitosis

What happens in anaphase?

Answer 11

kinetochore microtubules pull the sister chromatids away from each other, breaking them into two individual chromosomes

number of chromosomes has doubled

Question 12

Mitosis

What happens in early telophase?

Answer 12

• chromosomes are still contained within ONE cell

Question 13

How is a cell replicated?

Answer 13

by undergoing several cell phases in the cell cycle

Question 14

What is the process of the cell cycle?

Answer 14

• Gap 1 (G1): phase for growth
• G0: resting phase - cell division ceases
• Synthesis (S): phase for DNA replication
• Gap 2 (G2): phase for more growth
• Mitosis and Cytokinesis

Question 15

The Cell Cycle

What are checkpoints?

Answer 15

ensure that everything is progressing normally before entering the next stage

Question 16

The Cell Cycle

Where are the checkpoints?

Answer 16

• one between G1/S
• one in G2
• one in mitosis

Question 17

The Cell Cycle

What happens if any mistakes are found in DNA?

Answer 17

it’s important to fix them before the cell divides in mitosis so that the errors aren’t present in the daughter cells

Question 18

The Cell Cycle

When will the cell still undergo mitosis even though there is some sort of defect?

Answer 18

in some cases, mutations occur that will allow the cell to undergo mitosis, despite such defects

Question 19

When can cancer occur?

Answer 19

when checkpoints fails to function properly, allowing the cell to divide uncontrollably

Question 20

What is a tumour (neoplasm)?

Answer 20

cluster of cells growing abnormally, but have not yet spread to other tissues

Question 21

What is metastasis?

Answer 21

occurs when abnormal cells break off and travel through the bloodstream, spreading to other tissues throughout the body

Question 22

Describe cancer cells.

Answer 22

• grow/divide when they aren’t supposed to
• don’t die when they are supposed to
• invade parts of the body they aren’t supposed to

Question 23

What can cancer be caused by?

Answer 23

an accumulation of mutations and/or nondisjunction events

Question 24

What are mutations?

Answer 24

permanent change in nucleotide sequence

Question 25

What are mutations caused by?

Answer 25

errors in: - DNA replication: incorrect bases are added to new DNA strand - DNA repair: ironically, sometimes when the DNA repair machinery is trying to fix a problem, it can make mistakes - if unchecked and isn’t corrected, it can lead to mutations as well

Question 26

When does nondisjunction occur?

Answer 26

when chromosomes don’t separate properly during mitosis or meiosis in anaphase, resulting in daughter cells with either too many (or missing) chromosomes

Question 27

What consequences does nondisjunction have on the genomes of the daughter cells?

Answer 27

one daughter cell is going to have more than the usual number of copies of a gene, while the other daughter cell is missing a copy - parent cell is diploid (2n=2) - one daughter cell is haploid (n=1) - one daughter cell is triploid (3n=3) this can have detrimental results on an organism

Question 28

What can nondisjunction cause in humans?

Answer 28

- down syndrome: experience physical growth and cognitive delay - turner syndrome: affects development in females and a common feature is short stature in affected individuals, some experience loss of ovarian function

Question 29

What are tumour suppressor genes?

Answer 29

act to slow down cell division, repair DNA replication errors, or start apoptosis (programmed cell death) if both tumor suppressor genes are affected by mutation or lost via nondisjunction, this results in an inability to prevent tumor growth

Question 30

Mitosis vs. Meiosis How many cell divisions are there?

Answer 30

MITOSIS: only one cell division (PMAT) MEIOSIS: two cell divisions (at end of meiosis I and meiosis II)

Question 31

Mitosis vs. Meiosis What are the ploidy levels of parent and daughter cells?

Answer 31

MITOSIS: ploidy level is the same between parent and daughter cells (ie. parents were diploid, so are the daughter cells) MEIOSIS: daughter cells have half of the chromosomes compared to the parents (ie. parents were diploid, daughter cells are haploid)

Question 32

Mitosis vs. Meiosis Describe the pairing of homologs.

Answer 32

MITOSIS: no pairing of homologs MEIOSIS: homologs pair up during prophase I (genetic recombination takes place)

Question 33

Mitosis vs. Meiosis Describe genetic recombination.

Answer 33

MITOSIS: no crossing over or genetic recombination occurs (parent and daughter genotypes are the same) MEIOSIS: homologs line up across one another during metaphase I, resulting in independent assortment of chromosomes, crossing over of homologs may occur in prophase I

Question 34

What is the result of meiosis?

Answer 34

daughter cells are not identical to parent cell, and allows for production of genetically variable offspring

Question 35

What is the process of meiosis?

Answer 35

chromosomes align and are split up in such a way that each daughter cell receives only half of all the genetic material in the parent cell

Question 36

What is the function of meiosis?

Answer 36

for the purposes of sexual reproduction, the diploid genome has to be split into two haploid genomes - if the gametes are not haploid with all genes properly represented, then when two gametes fuse the zygote will have an incorrect number of chromosomes/gene copies

Question 37

What are the two processes that allow for genetic variation?

Answer 37

independent assortment | crossing over

Question 38

When does crossing over occur?

Answer 38

prophase I (in meiosis I)

Question 39

How does crossing over occur?

Answer 39

- specialized proteins cause deliberate breakage of chromatids - during chromatid repair, non-sister chromatids from homologous chromosomes can cross over: if this occurs, then genetic recombination of chromosomes can result - if sister chromatids cross over, there is no genetic recombination as sister chromatids are replicates of one another

Question 40

What is a locus?

Answer 40

specific location of a gene on chromosome