KA3 Variation and sexual reproduction

Question 1

What are some features of Homologous pairs of chromosomes

Answer 1

• Same centromere position
• Same size
• Same genes at same loci
• inherited from different parents

Question 2

What is meiosis

Answer 2

Meiosis is the division of the nucleus which results in the production of haploid gametes from a diploid gametocytes

Question 3

Explain the reason for meiosis

Answer 3

Meiosis increases genetic variation

Question 4

What occurs before the process of meiosis I

Answer 4

The chromosomes are replicated and each consist of two genetically identical chromatids attached to the centromere

Question 5

What are the 7 steps in the process of meiosis I

Answer 5

1) The chromosomes condense and the homologous chromosomes pair up
2) Chiasmata form at points of contact between the non-sister chromatids of a homologous pair - and sections of DNA are exchanged
3) This crossing over of DNA is random and produces genetically different recombinant chromosomes
4) Spindle fibres attach the the homologous pairs and line them up at the equator of the spindle
5) The orientation of the pairs of homologous chromosomes at the equator is random
6) The chromosomes of each homologous pairs are separated and move towards opposite poles
7) Cytokinesis occurs and two daughter cells form

Question 6

What occurs in the process of meiosis II

Answer 6

Each of the two cells produced in meiosis I undergo further division to which the sister chromatids of each chromosome are separated

Question 7

What does haploid mean

Answer 7

One set of chromosomes

Question 8

What does diploid mean

Answer 8

Two sets of chromosomes

Question 9

What could be a difference between homologous chromosomes

Answer 9

A difference could be the alleles of the genes

Question 10

What does independent assortment result in

Answer 10

Independent assortment results in new combinations of alleles and increases variation

Question 11

What is a chiasma

Answer 11

A chiasma is a point of contact between two chromatids which belong to homologous chromosomes

Question 12

How do linked genes arise

Answer 12

Genes on the same chromosome are said to be linked and the further apart the two linked genes are on a chromosome, higher the chance of a chiasma forming between them and greater frequency of recombination

Question 13

How does the crossing over of homologous pairs bring about increased variation

Answer 13

As the crossing over of DNA is random and produces genetically different recombinant chromosomes resulting in new combinations of alleles = increased genetic variation

Question 14

What does recombination frequency indicate and what is it used for

Answer 14

It indicates the distance between the linked genes on the same chromosome and is used to measure how close together linked genes are

Question 15

What is parthenogenesis

Answer 15

When an offspring is produced from a female gamete without fertilisation

Question 16

Give an example of parthenogenesis in animals

Answer 16

A species which carries out parthenogenesis is the whiptail lizard

Question 17

Where is parthenogenesis found

Answer 17

Parthenogenesis is found in areas with lower parasitism

Question 18

who is parthenogenesis disadvantageous to

Answer 18

It is disadvantageous to parasites as it occurs in cooler climates and regions where there is low parasite density or diversity

Question 19

What is horizontal gene transfer between individuals

Answer 19

Organisms that reproduce principally by asexual reproduction have mechanisms for horizontal gene transfer between indivuals to increase variation eg plasmids of bacteria and yeast

Question 20

What occurs through horizontal gene transfer of plasmids of bacteria and yeast

Answer 20

These allow for the exchange of genetic material and help to increase the rate of evolution

Question 21

What are hermaphrodites

Answer 21

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

Question 22

What are examples of hermaphroditism

Answer 22

An example of hermaphrodites are plants and land snails

Question 23

What does heterogametic mean

Answer 23

Males are heterogametic as they have two different chromosomes (XY)

Question 24

Give an example of a heterogametic animal

Answer 24

an example of a heterogametic animal would be ——————— idk

Question 25

How does a gene on the Y chromosome determine the development of maleness

Answer 25

The SRY gene on the Y chromosome determines the development of male characteristics

Question 26

Why can heterogamesis in males lead to sex-linked patterns of inheritance

Answer 26

As males have XY chromosomes resulting in the single X chromosome being affected by the recessive gene as the Y chromosome is not able to cover it up

Question 27

What are environmental factors that can influence sex and an example

Answer 27

• Temperature
• Size - eg clown fish
• Parasitic infection
• competition

Question 28

What does the random inactivation on X chromosomes in females prevent

Answer 28

The random inactivation on the X chromosome in females prevents a double dose of gene products

Question 29

Why does the random inactivation on X chromosomes in females prevent a double dose of gene products

Answer 29

As if both genes were to have a double dose of gene products it could be harmful, therefor one of the X chromosomes will inactivate and prevents a double dose of gene products