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Biology A-level > Biology Chapter 9 > Flashcards

Biology Chapter 9 Flashcards

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1
Q

How many daughter cells does mitosis produce and what are the number of chromosomes of each daughter cell in relation to the parent cell?

A

2 daughter cells

Each daughter cell has the same number of chromosomes as the parent cell

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2
Q

How many daughter cells does meiosis produce and what are the number of chromosomes of each daughter cell in relation to the parent cell?

A

4 daughter cell

Each daughter cell has half the number of chromosomes as the parent cell

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3
Q

Why does the number of chromosomes halve during meiosis?

A

To keep the number of chromosomes constant through the generations/ so that when gametes fuse they have one complete set of chromosomes

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4
Q

What is the haploid number of chromosomes in a human?

A

23

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5
Q

How many nuclear division are involved in meiosis?

A

2

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6
Q

Besides halving the number of chromosomes, what is the function of meiosis?

A

To introduce genetic variation/diversity

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7
Q

What is the advantage of genetic diversity to an organism?

A

To adapt to changing environmental conditions

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8
Q

Give 2 ways in which meiosis brings about genetic variation

A
  1. Independent segregation (homologous chromosomes separated into different cells)
  2. Crossing over (recombination)
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9
Q

Explain how crossing over occurs

A

Homologous chromosomes pair up. Their chromatids wrap round one another and equivalent sections may be exchanged

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10
Q

When does crossing over happen?

A

During stage 1 of meiosis (first division)

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11
Q

What is meant by the ‘locus’ of a gene?

A

It’s position on a chromosome or DNA molecule

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12
Q

Explain how independent segregation of chromosomes occurs

A

In meiosis 1 the homologous pairs line up at random so the combinations of chromosomes that enters the 2 daughter cells is also random

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13
Q

How many homologous pairs are there in a human cell at the start of meiosis 1?

A

23

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14
Q

How many cells are formed by the end of meiosis 2?

A

4

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15
Q

Do the characteristics determined by the genes on the chromosome have to be the same in each of the chromosomes in a homologous pair?

A

Yes

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16
Q

Do the alleles have to be the same in each of the chromosomes in a homologous pair?

A

No

17
Q

What happens when chromosomes twist around each other?

A

Force is generated at the point of twisting and a part of the chromatid breaks off

18
Q

How does this result in recombination?

A

The broken parts of the chromatids re-join with their homologous partner chromatids

19
Q

how does this increase variety?

A

It means that each of the cells produced is genetically different

20
Q

Imagine a cell contained 21 chromosomes. Is it likely to be haploid or diploid?

A

Haploid- diploid cells usually have an even number of chromosomes as they occur in homologous pairs

21
Q

Variation between individuals in a species is due to:

A

Variation between alleles

22
Q

What is the advantage to a species of greater genetic diversity?

A

The species if more likely to survive a change in the environment

23
Q

Why is this?

A

They have a wider range of characteristics and so some individuals will be able to adapt to change

24
Q

Summarise the effect of both mutations on inheritance and allele frequency

A

The beneficial allele is inherited so will increase in frequency in the population, whereas the harmful allele is not inherited and will decrease in frequency in the population

25
Q

What affects the allele frequency in populations?

A

Differences between the reproductive success of individuals

26
Q

Why is there competition between members of a species to be the ones that survive?

A

More offspring are produced that can be supported by the supply of food, light, space etc.

27
Q

What makes certain individuals better able to survive in competition with others?

A

Those with combinations of alleles that make them fitter

28
Q

What is selection?

A

The process by which organisms that are better adapted to their environment survive and breed, while those that are less well adapted fail to do so

29
Q

What type of selection favours individuals that vary in one direction from the mean of the population?

A

Directional selection

30
Q

What type of selection favours average individuals?

A

Stabilising selection

31
Q

What type of curve describes the variation about the mean for a characteristic?

A

Normal distribution curve

Biology A-level (14 decks)

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