2.3 - Variation and Sexual Reproduction Flashcards Preview

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Flashcards in 2.3 - Variation and Sexual Reproduction Deck (52)
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1
Q

what is sexual reproduction

A

the production of new living organisms by combining genetic information from two individuals of different types (sexes)

2
Q

what are the costs of sexual reproduction

A

males are unable to produce offspring

only half of each parent’s genome passed onto offspring, disrupting successful parental genomes

3
Q

why do the benefits of sexual reproduction outweigh the costs

A

due to an increase in genetic variation

4
Q

what does genetic variation provide

A

the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures

5
Q

how does the red queen hypothesis explain the persistence of sexual reproduction

A

the red queen hypothesis postulates that parasite pressure maintains sexual reproduction in the host population by selecting for the ability to reproduce rare genotypes that are resistant to infection

6
Q

hosts have greater fitness if

A

it is able to resist and tolerate parasitism

7
Q

parasites have greater fitness if

A

it is able to feed, reproduce and find new hosts

8
Q

if hosts reproduce sexually…

A

the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites

9
Q

what is asexual reproduction

A

a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes

10
Q

why can asexual reproduction be a successful reproductive strategy

A

whole genomes are passed on from parent to offspring

11
Q

when is maintaining the genome of the parent an advantage in asexual reproduction

A

in very narrow, stable niches or when re-colonising disturbed habitats

12
Q

examples of asexual reproduction in eukaryotes

A

vegetative cloning in plants

parthenogenesis in lower plants and animals that lack fertilisation

13
Q

what is parthenogenesis

A

asexual reproduction whereby embryos develop from an unfertilised egg

14
Q

where is parthenogenesis more common

A

in cooler climates which are disadvantageous to parasites, or regions of low parasite density or diversity

15
Q

asexually reproducing populations are not able to adapt easily to changes in their environment, what provides some degree of variation

A

mutations that can occur which enable some natural selection and evolution to occur

16
Q

what is vegetative progation/cloning

A

a form of asexual reproduction that takes place on some plants, resulting in offspring that are genetically identical to the parent plant e.g. bulbs and runners

17
Q

organisms that reproduce principally by asexual reproduction also often have mechanisms for…

A

horizontal gene transfer between individuals to increase variation, for example the plasmids of bacteria and yeasts

18
Q

what does prokaryotes exchanging genetic material horizontally result in

A

faster evolutionary change than in organisms that only use vertical transfer

19
Q

what is meiosis

A

a type of cell division where four haploid gametes are produced from one diploid gamete mother cell

20
Q

how do chromosomes appear in diploid cells

A

homologous

21
Q

what are homologous chromosomes

A

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

22
Q

which stages is meiosis split into

A

meiosis I

meiosis II

23
Q

where are reproductive organs produced in animals

A

ovaries and testes

24
Q

where are reproductive organs produced in plants

A

anthers and ovaries

25
Q

what is the first step of meiosis I

A

interphase - each undergoes DNA replication to become two identical chromatids

26
Q

what is the second step of meiosis I

A

homologous chromosomes pair up and line up along the equator of the cell

27
Q

what is the third step of meiosis I

A

crossing over occurs at points called chiasmata

28
Q

what does chiasmata mean

A

points of contact between non-sister chromatids of a homologous pair

29
Q

what does crossing over lead to

A

it shuffles sections of the DNA between the homologous pairs, allowing the recombination of alleles to occur thus increasing variation

30
Q

what are linked genes

A

genes that are on the same chromosome

31
Q

what is the fourth step of meiosis I

A

independent assortment - spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
the orientation of the pairs of homologous chromosomes at the equator is random
each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin

32
Q

what is the fifth step of meiosis I

A

the chromosomes of each homologous pair are separated and move towards opposite poles
cytokinesis occurs, the division of the parent cytoplasm, dividing the cell into two haploid daughter cells

33
Q

what happens in meiosis II

A

each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated
a total of four haploid cells are produced

34
Q

how is the sex of birds, mammals and some insects determined

A

the presence of sex chromosomes

35
Q

what is a sex chromosome

A

a type of chromosome that participated in sex determination

e.g. male - (XY) female - (XX)

36
Q

what determines the development of male characteristics

A

the SRY gene on the Y chromosome

37
Q

what does SRY stand for

A

sex determining region of the Y chromosome

38
Q

what do heterogametic (XY) males lack

A

most of the corresponding homologous alleles on the shorter Y chromosome

39
Q

what does heterogametic mean

A

dissimilar sex chromosomes e.g. mammalian males where the Y chromosome is much smaller than the X chromosome

40
Q

what does lacking most of the corresponding homologous alleles on the shorter Y chromosome lead to

A

sex-linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)

41
Q

what is sex linkage

A

when males have a greater chance of being affected by certain recessive conditions because females would need two copies of the recessive allele to be affected whereas males only need one

42
Q

what does homogametic mean

A

sex chromosomes which do not differ e.g. mammalian females have 2 X chromosomes (XX)

43
Q

what happens to one of the two X chromosomes present in each cell in females

A

it is randomly inactivated at an early stage of development

44
Q

what is X chromosome inactivation

A

the process by which most of one X chromosome is inactivated

45
Q

why is X chromosome inactivation important

A

prevents a double dose of gene products, which could be harmful to cells

46
Q

why are X carriers less likely to be affected by any deleterious mutations on these X chromosome

A

as the X chromosome inactivates in each cell is random, half of the cells in any tissue will have a working copy of the gene in question

47
Q

what are hermaphrodites

A

an organism with both functioning male and female reproductive organs

48
Q

what is the advantage of hermaphrodites

A

if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex

49
Q

other than genetic factors, what determines sex and sex ratio

A

environmental factors

50
Q

environmental sec determination in reptiles is controlled by…

A

environmental temperature of egg incubation

51
Q

how can the sex of an organism change

A

as a result of size, competition, or parasitic infection

52
Q

how can the sex ration of offspring be adjusted

A

in response to resource availability