Unit 2.3 - Variation and Sexual Reproduction

Question 1

Give three disadvantages of sexual reproduction

Answer 1

High metabolic cost, gametes are made by special type of cell division
Reproduction rate is much slower
Only half of the population can actually produce offspring

Question 2

Give two disadvantages of needing males for sexual reproduction

Answer 2

1. Males are unable to produce the offspring, so only half the population can reproduce
2. Only half of each parent’s genome is passed on so disrupts successful parental genomes

Question 3

Name a mechanism used by bacteria to allow the exchange of genetic material between generations

Answer 3

Horizontal Gene Transfer (HGT)

Question 4

Give examples of vegetative cloning methods in plants

Answer 4

Bulbs - Daffodils
Tubers - Potato
Rhizomes - Ginger
Spores - Fungi

Question 5

What is parthenogenesis?

Answer 5

Production of haploid offspring without needing males or fetilization

Question 6

Give conditions that parthenogenesis is common

Answer 6

Cooler Climates

Lower level of Parasitism

Question 7

In what conditions is asexual reproduction beneficial?

Answer 7

Very narrow and stable niche

Recolonising disrupted habitats

Question 8

Give an example of an area where asexual reproduction is beneficial

Answer 8

Butter cups using stolons to spread into flower beds with clear soil, gaining a competitive advantage

Question 9

What is the diploid number of chromosomes for humans?

Answer 9

46

Question 10

Give characteristics that are the same in homologous chromosomes

Answer 10

Same size
Same centromere position
Same genes at the same loci

Question 11

What is the first stage in meiosis?

Answer 11

Long uncoiled chromosomes replicate to form two identical chromatids
Chromosomes coil up and become visibile

Question 12

What is the site called where homologous chromosomes cross called?

Answer 12

Chiasma (plr. Chiasmata)

Question 13

What are seperated during Meiosis I?

Answer 13

Pairs of homologous chromosomes (Not actually any chromosomes, its the pairs)

Question 14

What is Independent Assortment?

Answer 14

A way of producing variation between daughter cells due to the fact there is no control over which chromosomes of each pair goes to which side of the cell

Question 15

How many different combinations of chromosomes is there in the resulting haploid cells where n is the number of homologous pairs?

Answer 15

2^n

Question 16

What does Chiasmata allow?

Answer 16

The chromosomes to exchange DNA with their homologous partner

Question 17

What happens during crossing over?

Answer 17

Chromosomes touch at chiasmata
Allows exchanging of DNA with homologous partner
Chromosomes in the gametes can have new combinations of alleles

Question 18

What is the process that allows chromosomes in the gametes to have new combinations of alleles?

Answer 18

Recombination

Question 19

The further apart genes are on a chromosome the more likely _____?

Answer 19

they are to have a chiasma form between them, leading to new allele combinations in the gametes

Question 20

What are the two types of factors that can influence the sex of individual?

Answer 20

Genetic Factors

Enviromental Factors

Question 21

What are hermaphordites?

Answer 21

Organisms which individually have both male and female reproductive structures

Question 22

What is the heterogametic sex in humans?

Answer 22

Male (XY)

Question 23

What causes embryos to develop as male?

Answer 23

SRY gene

Question 24

Describe the work of the SRY gene

Answer 24

Acts as a master switch which triggers a cascade to activate all male genes in the genome

Question 25

What is the default pathway for embryos?

Answer 25

To develop as a female

Question 26

What leads to sex linked patterns of inheritance?

Answer 26

The fact that X and Y chromosomes do not have homologous alleles

Question 27

What is X inactivation?

Answer 27

Most of the genes on one X chromosome are inactivated so that cells have a single working copy of the X chromosome genes

Question 28

What is X inactivation an example of?

Answer 28

Dosage Compensation

Question 29

What does dosage compensation ensure?

Answer 29

The female has exactly the same level of gene products as a male and do not get a double dose of gene products

Question 30

How many alleles are needed for a male to express the deleterious allele?

Answer 30

1

Question 31

How many alleles are needed for a female to express the deleterious allele?

Answer 31

2

Question 32

Who is less likely to express the effect of a deleterious allele carried on an X chromosome?

Answer 32

Female

Question 33

What environmental factors have an effect on sex or sex ratio?

Answer 33

Temperature
Size
Competition
Parasitic Infection

Question 34

Give an example of a species where temperature effects the sex ratio and explain how it does that

Answer 34

Hermann’s Tortoise
If eggs are incubated at less than 31 degrees - all males produced
If eggs are incubated at above 31 degrees - all females produced

Question 35

Give an example of a species where size effects the sex ratio and explain how it does that

Answer 35

Clown Fish
Live in groups, one large female and some smaller females
When the largest female is removed, the largest male becomes a female

Question 36

Give an example of a species where competition effects the sex ratio and explain how it does that

Answer 36

Lesser Mouse Lemur

If a solitary female detects urine of another female, she produces more male offspring

Question 37

Give an example of a species where parasite infection effects the sex ratio and explain how it does that

Answer 37

Insects infected by Wolbachia Bacteria

Bacterial infection of the eggs kills the males or feminises them

Question 38

What type of cell undergoes meosis?

Answer 38

Gamete mother cell