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A/ AH Biology: Unit 2 > Key Area 3-Variation and Sexual Reproduction > Flashcards

Key Area 3-Variation and Sexual Reproduction Flashcards

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1
Q

What is sexual reproduction?

A

The formation of haploid gametes of 2 parents that fuse nuclei to form diploid zygotes

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2
Q

What are the two main disadvantages of sexual reproduction?

A
  • half of the population are unable to produce offspring (paradox of the existence of men)
  • by mixing the genetic information between two individual each parent disrupts a successful genome and only passes in half to each offspring
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3
Q

What is the main benefit of sexual reproduction?

A

It creates genetic diversity and variation therefore allows evolution

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4
Q

How does genetic variation link to the red queen hypothesis?

A

It’s essential that genetic variation occurs to allow constant running to stay in the same place

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5
Q

What is asexual reproduction?

A

The cloning of one single parent to form genetically identical offspring

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6
Q

Where does asexual reproduction occur?

A

Usually prokaryotes but some eukaryotes such as plants

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7
Q

Where is asexual reproduction particularly successful as a reproductive strategy?

A

Very narrow niches or when recolonising disturbed habitats

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8
Q

What is the name given to asexual reproduction in plants?

A

Vegetative propagation

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9
Q

Where is vegetative propagation a useful strategy?

A

Perennial weeds

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10
Q

What are two examples of eukaryotic organisms reproducing asexually?

A

Vegetative propagation

Parthenogenesis

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11
Q

What is parthenogenesis?

A

Where animals are capable of reproducing without fertilisation of eggs

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12
Q

What are the two conditions where parthenogenesis usually occurs?

A

Cooler climates

Where parasite diversity/density is low

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13
Q

Give two specific examples of parthenogenesis

A

Komodo dragons where females can reproduce alone in the absence of males and produce male offspring only
Stick insects can reproduce alone in the absence of males and produce female offspring only

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14
Q

What is mitosis?

A

The process of cell division that results in the formation of new diploid cells

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15
Q

What is meiosis?

A

The process of cell division that results in the formation of new haploid cells

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16
Q

What is a homologous chromosome?

A

Homologous chromosomes have the same:
Size
Centromeres in the same place
Carry the same genes at the same Loki

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17
Q

How does meiosis affect variation in organisms?

A

Increases variation

18
Q

What are the two divisions in meiosis and the products formed at each division?

A

Meiosis I - two haploid daughter cells with double the DNA

Meiosis II - four haploid gamete cells

19
Q

What cell begins meiosis?

A

A gamete mother cell (2n)

20
Q

What is the first stage in meiosis I?

A

Interphase where DNA replicates to form 2 sister chromatids

21
Q

What occurs in meiosis I after interphase?

A

Homologous chromosomes line up in pairs along the metaphase plate

22
Q

How do homologous chromosomes line up along the metaphase plate?

A

In an independent assortment

23
Q

What does an independent assortment assure in meiosis?

A

Further variation

24
Q

What occurs in meiosis I after homologous chromosomes line up?

A

The pairs touch at chiasmata and crossing over occurs which results in recombination of alleles (swapped DNA)

25
Q

What are linked genes?

A

All genes on one chromosome

26
Q

What occurs in meiosis I after crossing over?

A

Spindle fibres separate homologous chromosomes to form two haploid daughter cells that contain double copies of the DNA

27
Q

How are the two haploid daughter cells in meiosis I created?

A

Cytokinesis where the cleavage of the cytoplasm separates the cells

28
Q

What is the crossover frequency?

A

An indication of the likelihood that two genes will cross over

29
Q

How is cross over frequency determined?

A

The further apart the genes are on the chromosome, the greater the chance of crossover

30
Q

What are the three stages of meiosis II?

A
  • chromosomes line up singly along the metaphase plate
  • sister chromatids are separated by spindle fibres with random distribution in gametes
  • cleavage furrow develops and four haploid gametes are formed
31
Q

What happens in meiosis in algae?

A

Often haploid fells from meiosis divide by mitosis to form haploid individuals, rather than gametes fusing to form zygotes. These haploid individuals produce their gametes through mitosis. These can fuse so the next generation is diploid.

32
Q

What is a hermaphroditic species?

A

A species that contains both male and female reproductive systems and gametes

33
Q

What are two factors that that determine sex and sex ratio?

A

Genetics

Environmental conditions

34
Q

How does environmental conditions affect sex determination in crocodiles?

A

If nest temperature is lower then 31.7 or higher than 34.5 the offspring will be female

35
Q

Explain a sequential hermaphrodite

A

Some animals are sequential hermaphrodites which change their sex during their lives due to size, parasitic infection and/or competition

36
Q

What is the sex bearing chromosome in live-bearing mammals?

A

X and Y chromosomes

37
Q

What insect has X and Y sex chromosomes?

A

Drosophila

38
Q

Which chromosome has genes related to maleness?

A

Y chromosome

39
Q

Why do live-bearing mammals have males that lack some alleles?

A

Y chromosome lacks pair chromosome that features on X

40
Q

Why does sex-linked patterns of inheritance occur?

A

The male lacks homologous alleles for genes on X chromosome

41
Q

How is a lethal dose of the products of gene expression avoided in females?

A

To compensate for an extra dose of genes, the portions of the X chromosome that are lacking on the Y are randomly inactivated on one of the homologous X chromosomes in each cell

42
Q

Why are carries less likely to be affected by deleterious mutations?

A

Carriers are less likely to be affected by deleterious mutations on these X chromosomes as X chromosome inactivation is random so half of the cells in any tissue sample will have a working copy of the gene

A/ AH Biology: Unit 2 (5 decks)

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