Variation and Reproduction

Question 1

What is meiosis?

Answer 1

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

Question 2

In diploid cells, what do chromosomes typically appear as?

Answer 2

homologous pairs.

Question 3

What are homologous chromosomes?

Answer 3

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

Question 4

What are the costs of sexual reproduction?

Answer 4

males unable to produce offspring; only half of each parent’s genome passed onto offspring, disrupting successful parental genomes

Question 5

Why do the benefits outweigh the costs?

Answer 5

due to an increase in genetic variation in the population

Question 6

What does genetic variation provide?

Answer 6

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

Question 7

Why do co-evolutionary interactions between parasites and hosts select for sexually reproducing hosts?

Answer 7

Hosts better able to resist and tolerate parasitism have greater fitness. Parasites better able to feed, reproduce and find new hosts have greater fitness.

Question 8

What happens to genetic variability if hosts reproduce sexually?

Answer 8

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

Question 9

What is asexual reproduction and why can it be successful?

Answer 9

In asexual reproduction, just one parent can produce daughter cells and establish a colony of virtually unlimited size over time. Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring.

Question 10

When is maintain the genome of a parent an advantage?

Answer 10

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

Question 11

What is an example 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

How is the sex of birds, mammals and some insects determined?

Answer 12

By the presence of sex chromosomes

Question 13

What determines the development of male characteristics?

Answer 13

In most mammals the SRY gene on the Y chromosome

Question 14

What do heterogametic(XY) males lack and what does this result in?

Answer 14

most of the corresponding homologous alleles on the shorter (Y) chromosome. This can result in sex-linked patterns of inheritance as seen with carrier females (XBXb ) and affected males (Xb Y).

Question 15

What happens in homogametic(XX) females?

Answer 15

One of the two X chromosomes present in each cell is randomly inactivated at an early stage of development

Question 16

What is X chromosome inactivation?

Answer 16

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

Question 17

Why are carriers less likely to be affected by any deleterious mutations on these X chromosomes?

Answer 17

As the X 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 18

What are hermaphrodites?

Answer 18

species that have functioning male and female reproductive organs in each individual. They produce both male and female gametes and usually have a partner with which to exchange gametes

Question 19

What is the benefit of being hermaphroditic?

Answer 19

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 20

What is an example of environmental sex determination?

Answer 20

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

Question 21

What can sex change be a result of?

Answer 21

size, competition, or parasitic infection