Unit 2 - section 3

Question 1

What are the advantages and disadvantages of sexual reproduction?

Answer 1

Disadvantages
Half pop unable to reproduce - paradox existence makes
Mixing genetic info of parents means only half of the successful genome passed on to offspring

Advantages
Creates genetic diversity and variation allowing evolution to take place
Genetic variation it creates essential for running in red queen hypothesis

Question 2

What are the advantages and disadvantages of asexual reproduction?

Answer 2

Disadvantages
Whole pop genetically identical so one disease could wipe out whole pop

Advantages
Successful for narrow stable niches
Faster so advantageous for recolonising disturbed habitats

Question 3

What are two eukaryotic organisms that carry out asexual reproduction?

Answer 3

Common in plants - perennial weeds
Rarely in animals - kimono dragon absence males females give birth to only males
Stick insects absence males females give birth all females

Question 4

What is asexual reproduction in plants called?

Answer 4

Vegetative propagation

Question 5

What is parthenogenesis?

Answer 5

Asexual reproduction in animals

Question 6

When does parthenogenesis occur?

Answer 6

When parasite diversity or density is low and in cooler climates

Question 7

What is meiosis?

Answer 7

Process of cell division that results in the formation of new haploid cells

Question 8

What are homologous chromosomes?

Answer 8

Chromosomes that are the same size and have their centromeres in the same place and carry the same genes at the same loci

Question 9

What effect does meiosis have on variation?

Answer 9

Increases variation in organisms because for each pair of homologous chromosomes there is two possible arrangements

Question 10

Process meiosis

Answer 10

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Question 11

What are the 2 divisions that occur in meiosis?

Answer 11

Meiosis I and meiosis ll

Question 12

What happens to gamete mother cells during meiosis?

Answer 12

Divide into 4 haploid sex cells

Question 13

What are the events of meiosis I?

Answer 13

Interphase - DNA replication occurs forming two sister chromatids

Homologous chromosomes pair up along the equator

Chromosomes can touch at chiasmata and crossing over can occur

Homologous chromosomes line up randomly (independent assortment) increasing variation

Spindle fibres separate homologous chromosomes forming two haploid daughter cells

Question 14

What increases the chances of two genes crossing over?

Answer 14

The further they are apart

Question 15

What are linked genes and what happens when you separate them?

Answer 15

All the genes on one chromosome are said to be linked

The separating of linked genes creates recombination

Question 16

What are the events of meiosis II?

Answer 16

Pairs of chromatids are separated by spindle fibres creating haploid gametes

Question 17

What forms gametes directly?

Answer 17

The cells that are produced by meiosis

Question 18

What is an alternative way of forming gametes? (From algae)

Answer 18

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

Question 19

What is a hermaphroditic species?

Answer 19

A species where an individual contains both male and female reproductive systems and gametes

Question 20

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

Answer 20

Environmental temperature-controls sex in reptiles 31.7°C< temperature<34.5°C offspring will be male

Female deer produce more male offspring when conditions favourable but produce less males when conditions harsher

Question 21

How can sex change in some species and what are theses species called?

Answer 21

Sequential hermaphrodites

Can be due to their size, a parasitic infection or competition

Question 22

What are the sex bearing chromosomes in live-bearing mammals and some insects?

Answer 22

X and Y chromosomes

Question 23

Which chromosome is responsible for characteristics related to maleness?

Answer 23

Y chromosome

Question 24

Does the X or Y chromosome have more genes?

Answer 24

The X has more

Question 25

Why do sex-linked patterns of inheritance occur?

Answer 25

Male lacks homologous alleles for genes on X chromosome which results in sex linked patterns of inheritance

Question 26

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

Answer 26

In order to compensate for an extra double dose of genes the portions of the X chromosome that are lacking on the Y are randomly inactivated on 1 of the homologous X chromosomes in each cell

Question 27

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

Answer 27

Because X chromosome inactivation is random so half of the cells in any tissue sample will have a working copy of the gene