4b diversity and selection

Question 1

What are alleles?

Answer 1

These code for different versions of the same characteristic

Question 2

What is genetic diversity?

Answer 2

The number of different alleles of genes in a species or population

Question 3

How is genetic diversity in a population increased?

Answer 3

Mutations forming new advantageous alleles

Different alleles being introduced into a pop when individuals from another pop migrate and reproduce = gene flow

Question 4

What is a genetic bottleneck?

Answer 4

An event that causes a big reduction in a population which reduces the number of different alleles so reducing diversity

Question 5

What is the consequence of a genetic bottleneck?

Answer 5

The survivors reproducing and a larger pop being created from fewer individuals

Question 6

What is the founder effect?

Answer 6

When just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool

Question 7

What causes the founder effect?

Answer 7

Migration leading to geographical separation

New colony is separated from the original population for another reason

Question 8

What is natural selection?

Answer 8

When an allele codes for a characteristic that increases the chances of an organism surviving, its frequency within a pop increases

Question 9

What are the steps to natural selection?

Answer 9

1. Individuals that have an allele that increases chance of survival, reproduce and pass on their genes
2. The next generation have a greater proportion inheriting the allele
3. They survive, reproduce and pass on
4. Frequency of beneficial allele in the population increases from generation to generation
5. This leads to evolution as the advantageous alleles become more common in the pop

Question 10

What are the 3 types of adaptations?

Answer 10

1. Behavourial adaptations eg the way an organisms acts
2. Physiological adaptaions eg processes inside the body eg hibernation
3. Anatomical eg structural features of an organisms body that increases chance of survival eg blubber

Question 11

What are the types of selection and examples ?

Answer 11

Directional - individuals with alleles for certain characteristics of an extreme type are more likely to reproduce and survive eg antibiotioc resistance

Stabilising - Individuals with alleles in the middle of the range will survive and reproduce, this occurs when environment isnt changing eg birthweight

Question 12

What is the name of a chromosome mutation?

Answer 12

Chromosome non disjunction - failure of chromosomes to separate properly

Question 13

What is the difference between haploid and diploid?

Answer 13

Haploid cells have half the number of chromosomes as they only contain one copy of each chromosome in a homologous pair

-> in humans this is 23 (gametes)

Diploid cells have the full set as each cell contains two of each chromosome

-> in humans this is 46

Question 14

What is independant segregation?

Answer 14

When the homologous pair have been seperated, it is a random process for which chromosome ends up in which daughter cell

Question 15

What is crossing over?

Answer 15

The chromatids cross over each other and bits of chromatids swap over (the chromosomes contain the same genes but a different combination of alleles)

One chromosomes from each homologous pair ends up in each cell

The four daughter cells will contain chromatids with different alleles

Question 16

what is a substitution mutation?

Answer 16

This is when a base is swapped for another so it could code fro another amino acid

Question 17

What is a mutagenic agent? And examples?

Answer 17

This is something that increases the rate of mutations and the probability of a mutation occuring

• uv radiation
• ionising radiation
• chemicals
• viruses

Question 18

What is a deletion mutation?

Answer 18

This is when one base is deleted which causes a frame shift

Question 19

What is a chromosome mutation?

Answer 19

This is when there are variations in the number of whole chromosomes or parts of chromosomes

Question 20

What happens in the process of fertilisation?

Question 21

What happens in meiosis II?

Answer 21

The pair of sister chromatids seperate
Nuclei form around them
4 haploid cells that are genetically different from one another are produced

Question 22

What happens in meiosis I?

Answer 22

the dna unravels and replicates so there is two copies of each chromosome : CHROMATIDS

the dna condenses to form chromosomes made from SISTER CHROMATIDS joined by a CENTROMERE

The chromosomes arrange themselves into their homologous pair

The homologous pair then seperates which halves the chromosome number

Question 23

What are the 2 main events in meiosis that lead to genetic variation?

Answer 23

1. crossing over
2. independent segregation

Question 24

what are gene mutations?

Answer 24

this is a change in the dna base sequence of chromosomes

Question 25

state the differences between mitosis and meiosis?

Answer 25

Mitosis :
produces cells with the same number of chromosomes as the parent cell
genetically identical daughter cells
produces two daughter cells

Meiosis :

cells with half the number of chromosoemes as parent cell
genetically different
produces 4 daughter cells

Question 25

What is chromosome non dsyjunction

Answer 25

Failure to separate properly