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cfe advanced higher biology - unit 2 > 2.3 VARIATION AND SEXUAL REPRODUCTION > Flashcards

2.3 VARIATION AND SEXUAL REPRODUCTION Flashcards

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1
Q

What is a benefit of sexual reproduction?

A

Huge genetic variability amongst offspring and therefore in population

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2
Q

What is a cost of sexual reproduction?

A

Only half of each parent’s genome is passed onto offspring disrupting successful parental genome

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3
Q

What is the term given to half of the population not being able to reproduce?

A

The paradox of the existence of males

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4
Q

Is sexual reproduction worth the cost?

A

The benefits far outweigh the disadvantages due to the increase in variation within the population

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5
Q

Genetic variation can be described as?

A

Essential raw material for natural selection (and the Red Queen’s arms race)

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6
Q

What are three benefits of asexual reproduction?

A

Rapid reproduction, lower metabolic costs, every member of population can reproduce

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7
Q

Where is asexual reproduction found?

A

In very narrow stable niches

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8
Q

When is asexual reproduction particularly useful?

A

In the recolonization of disturbed habitats

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9
Q

Give two examples of asexual reproduction in eukaryotes.

A

Vegetative cloning in plants, parthenogenesis in animals lacking fertilisation

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10
Q

What is vegetative cloning?

A

When a new plant grows from a fragment of the parent plant or from a specialised reproductive structure

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11
Q

What is the literal meaning of parthenogenesis?

A

Virgin creation

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12
Q

What is parthenogenesis?

A

Reproduction from an ovum without fertilisation - producing clones

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13
Q

Can males be produced by parthenogenesis?

A

Yes; through the deletion of a sex chromosome

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14
Q

Where is parthenogenesis most commonly found?

A

In cooler climates

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15
Q

Why is parthenogenesis more commonly found in cooler climates?

A

They are disadvantageous to parasites - regions of low parasite density

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16
Q

What are prokaryotes?

A

Microscopic single-celled organisms (eg bacteria, archaea)

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17
Q

Name a mechanism that prokaryotes use to move genes between individuals of the same generation.

A

Horizontal gene transfer

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18
Q

Give an example of horizontal gene transfer.

A

Plasmids of bacteria and yeast

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19
Q

What are homologous chromosomes?

A

Pairs of chromosomes of the same size, centromere position and genes at the same loci

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20
Q

How can two individuals produce a new combination of alleles?

A

Through production of haploid gametes

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21
Q

How are haploid gametes produced?

A

By meiosis in gamete mother cells

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22
Q

What is meiosis?

A

The process whereby one diploid gamete mother cell divides into four genetically dissimilar haploid gametes

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23
Q

What happens before meiosis begins?

A

Interphase

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24
Q

What are the three components of interphase?

A

Growth, DNA replication, general cell processes

25
Q

How can meiosis be described?

A

Reduction, division process

26
Q

How does sexual reproduction increase variation?

A

It involves crossing over, independent assortment and combining of two haploid genomes

27
Q

How many divisions take place during meiosis?

A

2 (Represented by I and II)

28
Q

What memory aid can be used to remember the process of meiosis (and also mitosis)

A

PMAT

29
Q

What does PMAT stand for?

A

Prophase, Metaphase, Anaphase, Telophase

30
Q

What happens during PI (Prophase I)?

A

Crossing over of chromosomes

31
Q

What is required for ‘crossing over’ to take place?

A

Chiasmata must form at random positions between homologous pairs

32
Q

What is the result of ‘crossing over’?

A

DNA is exchanged between the homologous pairs forming recombinant chromosomes

33
Q

What are linked genes?

A

Genes located on the same chromosome that usually travel together during meiosis

34
Q

How does ‘crossing over’ affect linked genes?

A

Linked genes can be separated and swapped

35
Q

What happens during MI (Metaphase I)?

A

Chromosomes line up in pairs on the metaphase plate and spindle fibres attach

36
Q

What is independent assortment?

A

The random orientation (left/right) in which the homologous pairs line up (irrespective of maternal and paternal origin)

37
Q

What happens during AI (Anaphase I)?

A

Microtubules of spindle fibres shorten, pulling chromosomes to opposite ends of the cell

38
Q

What happens during TI (Telophase I)?

A

Nuclear membrane forms around chromosomes and cytokinesis separates the two cells

39
Q

How does PII (Prophase II) begin?

A

Each cell is haploid with one copy of each homologous chromosome. Sister chromatids are non-identical

40
Q

What happens during MII (Metaphase II)?

A

Chromosomes line up on metaphase plate (in single file)

41
Q

What happens during AII (Anaphase II)?

A

Microtubules of spindle fibres shorten, separating and pulling the sister chromatids to opposite ends of the cell

42
Q

What happens during TII (Telophase II)?

A

Nuclear membrane forms around chromosomes and cytokinesis separates the cells

43
Q

What is the result of Meiosis II?

A

Four genetically different haploid cells have been produced

44
Q

Is meiosis the only way to produce gametes?

A

No; sometimes mitosis occurs after meiosis producing haploid organisms and gametes are formed later through differentiation

45
Q

What is a hermaphrodite?

A

An organism with both male and female reproductive organs

46
Q

What two factors can determine sex and sex ratio?

A

Genetic factors, environmental factors

47
Q

What environmental factor determines sex of some reptiles?

A

Environmental temperature of egg incubation

48
Q

Other than temperature, what other environmental factor can determine sex (ratio)

A

Resource availability

49
Q

What environmental stimulus could cause an individual to change their sex?

A

Size, competition, parasitic infection

50
Q

What is a live-bearing mammal?

A

A mammal which bears live young rather than laying eggs

51
Q

What determines maleness in most live-bearing mammals?

A

The SRY gene on the Y chromosome

52
Q

In mammals, what do males tend to be?

A

Heterogametic

53
Q

What does heterogametic mean?

A

(Male) has both a X and Y chromosome

54
Q

What is the result of being heterogametic?

A

Sex-linked traits are more common (in males)

55
Q

Why do males tend to be heterogametic?

A

They lack homologous alleles on the smaller (Y) chromosome

56
Q

Do sex-linked traits always affect females?

A

No; if trait is recessive then they can be carriers without symptoms

57
Q

How can females be carriers?

A

One X chromosome is randomly inactivated in each cell so half of all cells contain an active copy of gene

58
Q

Why are X chromosomes randomly inactivated in females?

A

To prevent a double-dose of gene products which could be harmful to cells

cfe advanced higher biology - unit 2 (3 decks)

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