Meiosis

Question 1

Why is meiosis important?

Answer 1

1. Produces haploid sex cells
2. During fertilisation the diploid number is restored which ensures that the diploid number remains the same after every generation
3. Meiosis produces genetic variation in offspring which increases the chance of species survival if the environment changes adversely

Question 2

What happens during Interphase and Prophase 1 of meiosis?

Answer 2

• bivalent forms
• chromosomes tangle (crossover)
• at the chiasma, sister chromatids break off, cross over and reattach

Question 3

What happens during Metaphase 1 of meiosis?

Answer 3

• centromeres attach to spindle fibres
• homologous chromosomes move to equator and line up in pairs

Question 4

What happens during Anaphase 1 of meiosis?

Answer 4

• each chromosome moves to opposite ends of the cell (random)
• independent assortment produces variation

Question 5

What happens during Telophase 1 of meiosis?

Answer 5

End of first division

Question 6

What happens during Metaphase 2 of meiosis?

Answer 6

• centromeres attach to spindle fibres
• chromosomes move to equator of cell

Question 7

What happens during Anaphase 2 of meiosis?

Answer 7

• spindle fibres contract and pull chromatids to opposite poles

Question 8

What happens during Telophase 2 of meiosis?

Answer 8

• haploid sex cells
• no pairs present
• all genetically unique
  —> 1. Crossover
  2. Independent assortment

Question 9

How does crossover result in genetic variance?

Answer 9

• bivalents form and homologous chromosomes twist around each other
• the point of crossover is called the chiasma
• a section of DNA with a block of alleles drops off, switches positions and reattaches creating a new combination of alleles

Question 10

How does independent segregation result in genetic variance?

Answer 10

• homologous chromosomes line up in pairs across the cell
• line up randomly in each pair
• producing different combinations of chromosomes
• thus creates different combinations of alleles

Question 11

How can non-disjunction of chromosomes occur?

Answer 11

1. Failure of a homologous pair of chromosomes to separate during the first division
2. Failure of a pair of sister chromatids to separate during the second division

Question 12

Describe how bacteria divide (binary fission).

Answer 12

1. Bacterial cell grows and becomes longer
2. The circulate DNA replicates to form genetically identical DNA
3. Plasmids replicate
4. A wall forms down the middle of the bacteria and the cytoplasm divides
5. The cell splits in two to from two genetically identical daughter cells

Question 13

Describe how viruses use host cells to replicate.

Answer 13

1. Virus antigen binds to specific receptor proteins in the host cell membrane
2. Reverse transcriptase is used to make single stranded DNA from the viral RNA
3. Viral DNA is made double stranded using host cells nucleotides and DNA polymerase
4. Viral DNA becomes a part of the hosts DNA
5. Viral DNA becomes activates causing transcription and translation, producing viral proteins
6. New viral particles are assembles and the viral particles burst out of the cell

Question 14

What is the key point to look out for when looking for meiosis on life cycles?

Answer 14

2n = n