UNIT 2 - KA3

Question 1

What are the costs of sexual reproduction

Answer 1

• males unable to produce offspring
• only half of each parents genome passed onto offspring distrusting successful parental genomes

Question 2

What are the benefits of sexual reproduction

Answer 2

Benefits outweigh costs due to an increase in genetic variation in the population

Question 3

What does genetic variation provide

Answer 3

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

Question 4

What may do evolutionary interactions between parasites and hosts select

Answer 4

Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts

Question 5

What hosts have greater fitness

Answer 5

Hosts better able to resist and tolerate parasitism have greater fitness.

Question 6

Which Parasites have greater fitness

Answer 6

Pasties better able to feed, reproduce and find new hosts have greater fitness

Question 7

What happens to hosts if they reproduce sexually

Answer 7

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

Question 8

Why can asexual reproduction be a successful reproduction strategy

Answer 8

Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring

Question 9

In asexual reproduction who can produce daughter cells

Answer 9

In asexual reproduction just one parent can produce daughter cells and establish a colony of virtually unlimited size over time

Question 10

When is maintaining the genome of the parent an advantage

Answer 10

Maintaining the genome of the parent is an advantage in very narrow, stable niches or when re-colonising disturbed habitats

Question 11

Examples of asexual reproduction in eukaryotes

Answer 11

Vegetative cloning in plants and
parthenogenesis in lower plants and animals that lack fertilisation are examples of asexual reproduction in eukaryotes

Question 12

Parthogenesis

Answer 12

Parthogenesis is reproduction from a female gamete without fertilisation

Question 13

How much offspring can be produced with asexual reproduction

Answer 13

Offspring can be reproduced more often and in larger numbers with asexual reproduction

Question 14

Where is parthenogenesis more common

Answer 14

Parthenogenesis is more common in cooler climates which are disadvantageous to parasites or regions of low parasite density or diversity.

Question 15

What are asexually reproducing populations not able to do

Answer 15

Asexually reproducing populations are not able to adapt easily to changes in their environment but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur

Question 16

What type of mechanisms do organisms that reproduce principally by asexual reproduction have

Answer 16

Organisms that reproduce principally by asexual reproduction also often have mechanisms for horizontal gene transfer between individuals to increase variation for example the plasmids of bacteria and yeasts

Question 17

How can prokaryotes exchange genetic material

Answer 17

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

Question 18

What is meiosis

Answer 18

Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte

Question 19

How do chromosomes appear in diploid cells

Answer 19

In diploid cells chromosomes typically appear as homologous pairs

Question 20

What are homologous chromosomes

Answer 20

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

Question 21

Stage 1 meiosis 1

Answer 21

The Chromosomes which have replicated prior to meiosis 1 each consist of two genetically identical chromatids attached at the centromere

Question 22

Stage 2 meiosis 1

Answer 22

• The chromosomes condense and homologous chromosomes pair up
• chiasmata form at points of contact between the non-sister chromatids of a homologous pair and selections of DNA are exchanged

Question 23

Stage 3 meiosis 1 -

Answer 23

• spindle fibres attach to the homologous pairs and line up at the equator of the spindle
• each pair of homologous chromosomes is positioned independently of the other pairs

Question 24

Stage 4 meiosis 1

Answer 24

• The Chromosome’s of each homologous pair are separated and move towards opposite poles. Cytokinesis occurs and two daughter cells form

Question 25

What are linked genes

Answer 25

Linked genes are those on the same chromosome

Question 26

What can crossing over result in

Answer 26

Crossing over can result in new combinations of the alleles of these genes

Question 27

What is the orientation of the pairs of homologous chromosomes at the equator

Answer 27

The orientation of the pairs of homologous chromosomes at the equator is random

Question 28

What is independent assortment

Answer 28

Each pair of homologous chromosomes in positioned independently of the other pairs, irrespective of their maternal and paternal origin

Question 29

Where do chiasmata form

Answer 29

Chiasmata form at a random position between the homologous pairs. Chiasmata never form between sister chromatids

Question 30

Where do non sister chromatids cross over

Answer 30

Non sister chromatids cross over at chiasmata

Question 31

What is crossing over

Answer 31

Chiasmata allow the shuffling of sections of DNA between homologous chromosomes a process called crossing over

Question 32

What happens to the DNA strands in relation to chiasmata

Answer 32

The DNA strands break and then rejoin at the chiasmata swapping a section of their genetic material resulting in the recombination of alleles

Question 33

What can crossing over result in

Answer 33

Crossing over can result in new combinations of the alleles of these genes

Question 34

What does crossing over of DNA produce

Answer 34

This crossing over of DNA is random and produces genetically different recombinant chromosomes

Question 35

Stage 1 of meiosis 2

Answer 35

The sister chromatids of each chromosome are no longer identical because of recombination

Question 36

Stage 2 of meiosis 2

Answer 36

Spindle fibres bind to the centromeres of each chromatid

Question 37

Stage 3 of meiosis 2

Answer 37

The sister chromatids separate to opposite sides of the cell and are now referred to as chromosomes

Question 38

Stage 4 of meiosis 2

Answer 38

Cytokinesis occurs and a total of four haploid cells are produced. The cells are all genetically different

Question 39

How is the sex of birds mammals and some insects determines

Answer 39

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

Question 40

What does the SRY chromosome determine the development of

Answer 40

In most animals the SRY gene on the Y chromosome determines development of male characteristics

Question 41

What do heterogametic males lack

Answer 41

Heterogametic (XY) males lack most of the corresponding homologous alleles on the shorter (Y) chromosome

Question 42

What can the lack of corresponding homologous alleles on Y chromosome result in

Answer 42

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

Question 43

What happens in homogametic females

Answer 43

In homogametic females (XX) one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development

Question 44

What is X chromosome inactivation

Answer 44

X chromosome inactivation is a process by which most of one X chromosome is inactivated

Question 45

What does C chromosome inactivation prevent

Answer 45

X chromosome inactivation prevents a double dose of gene products which could be harmful to cells

Question 46

What are carries less likely to be affected by

Answer 46

Carriers are less likely to be affected by any deleterious mutations on these X chromosomes

Question 47

What will half of the cells on any tissue have a copy of

Answer 47

As the C chromosome inactivated in each cell is random half of the cells in any tissue will have a working copy of the gene in question

Question 48

Hermaphrodites

Answer 48

Hermaphrodites are species that have functioning male and female reproductive organs in each individual

Question 49

What do hermaphrodites produce

Answer 49

They produce both male and female gametes and usually have a parter with which to exchange gametes

Question 50

What is the benefit to the individual organism

Answer 50

The benefit to the individual organism 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

Question 51

What determines sex and sex ration for other species

Answer 51

For other species environmental rather than genetic factors determine sex and sex ratio

Question 52

How is environmental sex determination on reptiles controlled

Answer 52

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

Question 53

What can change sex within individuals of some species

Answer 53

Sex can change within individuals of some species as a result of size, competition or parasitic infection

Question 54

How can the sex ratio of offspring be adjusted

Answer 54

In some species the sex ratio of offspring can be adjusted in response to resource availability