Genetics: Genetic Diversity - Meiosis

Question 1

Does meiosis produce genetically identical or different daughter cells?

Answer 1

• Genetically different daughter cells

Question 2

How many daughter cells are produced in meiosis?

Answer 2

• 4

Question 3

How many chromosomes do cells produced from meiosis have?

Answer 3

• Daughter cells are haploids

- Have n number of chromosomes (half of 2n)

Question 4

What type of cells does meiosis produce?

Answer 4

• Gametes

Question 5

Where does meiosis occur?

Answer 5

• Occurs in reproductive organs

- Testes and ovaries in humans

Question 6

Outline the steps of meiosis

Answer 6

• Meiosis I

• Interphase
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

• Meiosis II

• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis

Question 7

What are sister chromatids?

Answer 7

• A chromatid is one strand of a replicated chromosome

- Sister chromatids are identical and joined by a centromere

Question 8

What is a chromosome?

Answer 8

• A thread like structure made up of one long DNA molecule

Question 9

What is a homologous pair of chromosomes?

Answer 9

• Aka bivalents
• Made of two chromosomes that:
- Carry the same genes in the same locus
- Are the same size
- Carry genes that may have different alleles

• One chromosome from mum, one from dad
- Not the same as sister chromatids (these are replications of each other)

Question 10

What happens during interphase?

Answer 10

• DNA unravels and replicates
• Produces two copies of each chromosome, called chromatids joined at a centromere
• Chromosomes are long and thin

Question 11

What happens during prophase I?

Answer 11

• Chromosomes condense and become visible
• Homologous pairs of chromosomes come together to form a bivalent: one from mum, one from dad
• Non-sister chromatids may exchange genes - crossing over
• Chiasma are sections that cross over, site of crossing over
• Chromatids now have different combination of alleles - called recombinants

Question 12

What happens during metaphase I?

Answer 12

• Nuclear membrane breaks
• Spindle fibres are made by the centrioles
• Bivalents move to the equator
• Centromeres attach to spindle
• Positioning of homologous pairs is random - independent segregation

Question 13

What happens during anaphase I?

Answer 13

• Spindle fibres contract

- Homologous chromosomes are pulled apart to opposite poles of cell

Question 14

What happens during telophase I?

Answer 14

• 2 chromosomes with 2 chromatids group together at each pole of cell
• Spindle disappears
• Nuclear envelope reforms
• Cytokinesis
• Cell cytoplasm divides producing 2 diploid cells

Question 15

What happens during prophase II?

Answer 15

• 2 diploid cells which will divide a second time

- New spindle begins to form in each cell

Question 16

What happens during metaphase II?

Answer 16

• Chromosomes, each comprised of 1 pair of sister chromatids line up on equator
• Sister chromatids may not be identical - recombinants

Question 17

What happens during anaphase II?

Answer 17

• Sister chromatids pulled apart by spindle

- Move to opposite poles of cell

Question 18

What happens during telophase II?

Answer 18

• Spindle fibres break down
• Nuclear envelope reforms around separated chromosomes
• Cytokinesis
• Produces 4 haploid cells, each with n chromosomes

Question 19

Which processes that occur during meiosis result in variation?

Answer 19

• Crossing over

- Independent segregation

Question 20

What is ‘crossing over’?

Answer 20

• Occurs during prophase I
• Process of non-sister chromatids in a homologous pair of chromosomes exchanging genes
• Chromatids have same genes but different combination of alleles
• Site of crossing over is at chiasmas

Question 21

What is independent segregation of chromosomes?

Answer 21

• Occurs during metaphase I
• Homologous pairs made of one chromosome from mum, one from dad
• Homologous pairs separated in metaphase I
• Random which chromosome from each pair ends up in which daughter cell

Question 22

What happens during meiosis I?

Answer 22

• Homologous chromosomes pair to form bivalents
• Crossing over occurs at chiasmata
• Independent segregation randomises which chromosome from each homologous pair goes into which cell
• Cell divides into 2

Question 23

What happens during meiosis II?

Answer 23

• Sister chromatids are separated
• 2 cells each divide again
• Four haploid cells are produced