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Advanced Higher Biology > UNIT 2 - variation and sexual reproduction > Flashcards

UNIT 2 - variation and sexual reproduction Flashcards

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1
Q

what are the costs of sexual reproduction?

A
  • males are unable to reproduce
  • only half of the parent’s genomes are passed on which disrupts successful parental genomes
  • metabolic costs are higher as energy is needed to mate and court
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2
Q

what are the costs of asexual reproduction?

A

populations have a LACK OF GENETIC VARIATION

may be more susceptible to parasites

unable to adapt to environmental changes/new selection pressures successfully.

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3
Q

what are the benefits of sexual reproduction?

A
  • Key benefit is GENETIC VARIATION.

This gives the raw materials for adaptation and increases survival chances under changing selection pressures.

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4
Q

what are the benefits of asexual reproduction?

A

Benefits include:

  • lower metabolic costs,
  • maintaining whole genomes from parent to offspting
  • reproduction at a rapid rate because every member of the population can reproduce.
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5
Q

what is the paradox of sex?

A

if asexual reproduction is so simple and cost effective, why is sexual reproduction the main strategy for almost all complex organisms?

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6
Q

what is used to justify sexual reproduction?

A

the Red Queen hypothesis and (in particular) co-evolutionary interactions between parasites and hosts are thought to explain the persistence of sexual reproduction.

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7
Q

why is the existence of males questioned in biology?

A

Needing males means only half the population breed and also combined genetic material can disrupt beneficial genomes.

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8
Q

what is parthenogenesis?

A

Parthenogenesis involves production of offspring without needing males or fertilisation.

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9
Q

where is parthenogenesis found?

A

Parthenogenesis is rare but is more commonly found in areas with lower parasitism such as cooler climates (which are disadvantageous to parasites) or other regions of low parasite density or diversity.

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10
Q

how do plants asexually reproduce?

A

Many plants can use methods of vegetative cloning to reproduce asexually (even if they also flower and reproduce sexually).

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11
Q

what is vegetative cloning?

A

a form of asexual reproduction occurring in plants where a new plant grows from a fragment of the parent plant or a specialised reproductive structure.

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12
Q

what does genetic variation provide?

A

Genetic variation provides the raw material required for adaptation, giving sexually reproducing
species a better chance of survival under changing selection pressures.

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13
Q

what are the positive effects of a co-evolutionary interaction between parasites and hosts?

A

Hosts that are better able to resist and tolerate parasitism have greater fitness and therefore parasites are better able to feed, reproduce and find new hosts and a have greater fitness.

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14
Q

why is it beneficial for hosts to reproduce sexually?

A

If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites.

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15
Q

when is maintaining a parents genome especially important?

A

Maintaining the genome of the parent is an advantage, particularly in very narrow, stable niches or when recolonising disturbed habitats.

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16
Q

what is a chiasmata?

A

a point at which paired chromosomes remain in contact during meiosis, and at which crossing over and exchange of genetic material occurs between the strands

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17
Q

what is crossing over?

A

the exchange of genetic material between non-sister chromatids of two homologous chromosomes that results in recombinant chromosomes during meiosis

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18
Q

what is cytokinesis?

A

the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells

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19
Q

what is a hermaphrodite?

A

species that have functioning male and female reproductive organs in each individual. The benefit to the individual hermaphrodite is that if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex.

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20
Q

heterogametic and homogametic meaning?

A

heterogametic - dissimilar sex chromosomes,

homogametic - sex chromosomes that do not differ in morphology, resulting in only one kind of gamete

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21
Q

what is a homologous pair?

A

Homologous pair - a pair of chromosomes of the same size, centromere position and same genes at the same loci

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22
Q

what is horizontal gene transfer?

A

inheritance of genetic material within a generation

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23
Q

what is independent assortment?

A

independent assortment is when homologous pairs of chromosomes line up opposite each other at the equator of the cell - regardless of parental origin.

These pairs are separated so one of each homologous pair ends up in the daughter cell.

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24
Q

what are linked genes?

A

genes located on the same chromosome

25
Q

meiosis definition?

A

the division of the nucleus that results in the formation of haploid gametes from a diploid Gametocyte

26
Q

what is recombination?

A

the establishment of new combinations of alleles following crossing over

27
Q

what are sex chromosomes?

A

a pair of chromosomes that can determine sex in some species

28
Q

what are sister chromatids?

A

the genetically identical strands of chromosomes

29
Q

what is X chromosome inactivation?

A

a process by which most of one X chromosome is randomly inactivated to prevent a double dose of gene products, which could be harmful to cells

30
Q

why do the pros of sexual reproduction overweigh the cons?

A

due to genetic variation

31
Q

what do organisms who reproduce asexually have to help with genetic variation?

A

Organisms that reproduce mainly by asexual reproduction often have mechanisms for horizontal gene transfer between individuals to increase variation

32
Q

how do prokaryotes exchange genetic material and how is this beneficial?

A

Prokaryotes can exchange genetic material horizontally, resulting in faster evolutionary change than inorganisms that only use vertical transfer.

33
Q

how do chromosomes appear in diploid cells?

A

In diploid cells, chromosomes typically appear as homologous pairs.

34
Q

what are homologous chromosomes and what traits do they have?

A

Homologous chromosomes are chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci

35
Q

what do the chromosomes that replicated prior to meiosis 1 have?

A

The chromosomes, which have replicated prior to meiosis I, each consist of two genetically identical sister chromatids attached at the centromere.

36
Q

what happens during meiosis I

A

At meiosis I, chromosomes condense, the homologous chromosomes pair up and chiasmata form at points of contact between the non-sister chromatids and sections of DNA are exchanged

37
Q

what does crossing-over produce (meiosis)?

A

Crossing over DNA is random and produces genetically different chromosomes through recombination.

38
Q

the function of spindle fibres? (meiosis)

A

Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle.

39
Q

what does meiosis I involve?

A

the pairing of homologous chromosomes and their separation into two cells.

40
Q

what does meiosis II involve?

A

the sister chromatids are separated and each new chromosome segregates into one of four haploid cells produced.

41
Q

how many cells are produced at the end of meiosis?

A

4 haploid cells

42
Q

what is the sex of some mammals, birds and insects decided by?

A

The sex of birds, mammals and some insects is determined by the presence of sex chromosomes

43
Q

what is the function of the SRY gene?

A

In most mammals the SRY gene on the Y chromosome encodes testes-determining factor (TDF)
and determines development of male characteristics.

44
Q

what do heterogametic males lack and what is the effect of this?

A

Heterogametic (XY) males lack most of the alleles corresponding to those on the X chromosome
on their shorter Y chromosome. The presence of the short Y chromosome can result in sex-linked patterns of inheritance.

45
Q

what occurs in homogametic females and what is the effect of this?

A

In homogametic females (XX), one of the two X chromosomes present in each cell is randomly
inactivated at an early stage of development. Carriers are less likely to be affected by deleterious mutations on one of their X chromosomes because of random inactivation.

46
Q

what does X chromosome inactivation do?

A

X chromosome inactivation prevents a double dose of gene products, which could be harmful to cells. Carriers are less likely to be affected by deleterious mutations on one of their X chromosomes because of random inactivation.

47
Q

how does sex determination work in reptiles?

A

Environmental sex determination in reptiles is controlled by environmental temperature of egg
incubation.

48
Q

what are some factors that can induce a change in sex?

A

Sex can change within individuals of some species because of size, competition or parasitic infection. In some species the sex ratio of offspring can be adjusted in response to resource availability.

49
Q

what two mechanisms in meiosis introduce variation?

A

independent assortment and crossing over

50
Q

what happens during crossing over?

A
  • crossing over happens at points called the chiasmata.
  • homologous pairs line up opposite each other at the equator in meiosis 1.
  • parts of the chromatids can become twisted around each other. this puts tension on the chromatids and causes them to break.
  • the broken parts recombine with another chromatid which results in the recombination of alleles of linked genes which produces a varied combination in gametes.
51
Q

what is the main difference between meiosis and mitosis?

A

meiosis - two nuclear divisions, haploid cells, introduce genetic variation

mitosis - one nuclear division, diploid cells and creates genetically identical cells

52
Q

explain why males are more likely to be affected by sex-linked conditions than females?

A

males only have one sex-linked allele for each gene; if it’s deleterious then they will show the condition. Females on the other hand have two sex-linked alleles and therefore can be carriers

53
Q

explain why females are less likely to be affected by a sex-linked condition even though they have a copy of the faulty allele?

A

X chromosome deactivation randomly inactivates an x chromosome in a cell meaning that in half of the cells the deleterious allele is not expressed.

54
Q

how is enough variation produced for natural and sexual selection to occur?

A

mutations cause genetic variation. some mutations may be advantageous and selected for.

55
Q

give an account of variation in meiosis

A
  • homologous chromosomes pair up in meiosis 1
  • pairs assort independently
  • separation after independent assortment occurs regardless of parental origin
  • chiasmata forms between non-sister chromatids in a homologous pair - leading to crossing over
  • recombination of linked alleles
  • final variation depends on separation of sister chromatids in meiosis 2
56
Q

how does the relationship between parasites and hosts (red queen hypothesis) be used to account for the benefits of sexual reproduction outweighing the negatives? (5)

A
  • variation is needed for evolution
  • evolution is needed for hosts to adapt to the increasing virulence of parasites
  • adaptations lead to resistance against parasites
  • parasite evolves and becomes more virulent towards the host
  • sexual reproduction produces the required variation and therefore this benefit outweighs the costs of sexual reproduction
57
Q

what is a bivalent?

A

homologous chromosomes pair up to form a bivalent

58
Q

what happens during meiosis? (essay)

A
  1. nuclear membrane breaks down and spindle forms
  2. homologous chromosomes pair up
  3. spindle fibres attach
  4. homologous pairs line up along equator
  5. homologous chromosomes segregate/pulled apart
  6. new nuclear membrane forms and cytoplasm divides
  7. to form2 cells with half the number of chromosomes
  8. two new spindles form, one in each cell
  9. chromosomes line up singly on equator
  10. chromatids are pulled apart
  11. new nuclear membranes form and cytoplasm divides
  12. to give 4 haploid cells

Advanced Higher Biology (11 decks)

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