9.Genetic diversity and adaptation

Question 1

Define a gene mutation

Answer 1

Any change to one or more nucleotide bases or sequence of bases in DNA

Question 2

Name 3 consequences of gene substitution

Answer 2

• One of the 3 stop codons are formed which prematurely stops the production of the polypeptide chain. This results in a significantly different protein that wouldn’t be able to function properly
• Another codon is formed, which codes for a different amino acid. This change in the polypeptide chain may cause a change in the proteins tertiary structure meaning the protein produce will be dysfunctional.
• The formation of different codon but codes for the same amino acid. This is because the genetic code is degenerate. It will have no effect on the overall protein shape/function

Question 3

What is substitution

Answer 3

A type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide

Question 4

What is deletion

Answer 4

A gene mutation arises when a nucleotide is lost from the normal DNA sequence

Question 5

What is the consequence of a deletion mutation

Answer 5

The deletion of a base causes a frameshift for every codon downstream of the mutation. This alters most triplets downstream meaning the amino acids coded for are different, significantly altering the proteins tertiary structure and therefore its dysfunction.

Question 6

What is a chromosomes mutation

Answer 6

A change in the structure or number of whole chromosomes

Question 7

Describe and explain the two forms chromosome mutations can take

Answer 7

• changes in whole sets of chromosomes (polyploid)

- changes in the number of individual chromosomes (non-disjunction)

Question 8

What is polyploid

Answer 8

Occurs when organisms have 3 or more sets or chromosomes rather than the usual two.

Question 9

What is non-disjunction

Answer 9

Sometimes individual homologous pairs fail to separate during meiosis. This results in a gamete having one more or one fewer chromosome. This produces an offspring with more or fewer chromosomes in their body cells

Question 10

Name two ways cell division occurs

Answer 10

• mitosis

- meiosis

Question 11

Why is meiosis important

Answer 11

The number of chromosomes must be lowered from diploid to haploid to maintain a constant number of chromosomes. This occurs during meiosis

Question 12

How many nuclear divisions occur in meiosis

Answer 12

2

Question 13

What occurs in the first division (meiosis I)

Answer 13

• homologous chromosomes pair up and their chromatids wrap around each other
• equivalent portions of these chromatids may be exchanged in the process (crossing over)
• the homologous pairs separate with one chromosome from each pair going into one of the two daughter cells

Question 14

What is crossing over

Answer 14

The process whereby a chromatid breaks during meiosis and re-joins to the chromatid of its homologous chromosome so that their alleles are exchanged

Question 15

What occurs in the second division (meiosis II)

Answer 15

• the chromatids separate and go into separate daughter cells
• this means there are 4 daughter cells at the end of this process

Question 16

In what two ways does meiosis bring about genetic variation

Answer 16

• independent segregation of homologous chromosomes

- crossing over

Question 17

What is independent segregation of homologous chromosomes

Answer 17

When homologous pairs line up, they do so randomly. This means the combination of chromosomes of maternal and paternal origin are up to chance

Question 18

How does independent segregation of homologous chromosomes bring out about genetic variation

Answer 18

Each member of a homologous pair of chromosomes have exactly the same genes and determine the same characteristics. However the genes of these alleles may be different therefore it produces new genetic combinations

Question 19

What is the calculation for the possible combinations of chromosomes for each daughter cell

Answer 19

2^n (where n is the number of homologous chromosomes)

Question 20

What is the calculation for the possible combinations of chromosomes of a zygote (after fertilisation)

Answer 20

(2^n)^2

Question 21

What is genetic diversity

Answer 21

The number of different alleles of genes in a population

Question 22

What is a population

Answer 22

A group of individuals of the same species that live in the same place and can interbreed

Question 23

Why are alleles of a population not equally likely to be passed on to the next generation

Answer 23

Only certain individuals are reproductively successful to pass on their alleles

Question 24

What is allele frequency

Answer 24

The number of times an allele occurs within the gene pool

Question 25

What is a gene pool

Answer 25

The total number of alleles in a particular population at a specific time

Question 26

How does differences of the reproductive success of individuals affect allele frequency

Answer 26

- within any population there is a gene pool - random mutation of alleles within this gene pool may result in a new allele of a gene (most cases is harmful) - in some environments this mutation has a selective advantage so more likely to survive/ live longer so have a better chance of successful breeding - only individuals that reproduce successfully pass on their alleles - offspring now have advantageous allele and are more likely to survive and reproduce successfully - over time this causes the frequency of the newer advantageous allele to increase

Question 27

Name the three types of selection and the individuals they favour

Answer 27

- directional (favour one extreme individuals) - stabilising (favour the average) - disruptive (doesn't favour the average)

Question 28

Using the example of the resistance of penicillin, explain directional selection

Answer 28

- spontaneous mutation occurred in the allele of a gene in a bacterium that enabled it to make a new protein that broke down the antibiotic for penicillin (penicillinase) - this happened in an individual being treated with penicillin - due to its advantageous mutation the bacterium survived and was able to reproduce - this increased the population of bacterium of the penicillin resistant bacteria - this shifts the normal distribution curve in one direction (towards the direction of a population of having a greater resistance)

Question 29

Using the example of human birth weights, explain stabilising selection

Answer 29

- most babies are born with average mass - babies that aren't (caused by its genes are less likely to survive - this means that these babies have an increased chance of successful reproduction and to pass on the gene for this baby weight - this means the average is favoured causing the normal distribution curve to steepen

Question 30

Name the 3 types of adaptations are there

Answer 30

- anatomical - physiological - behavioural