genetic diversity

Question 1

what is a mutation?

Answer 1

any change to the quantity or base sequence of the DNA of an organism.

Question 2

what is a gene mutation?

Answer 2

any change to one or more nucleotide bases, or a change in the sequence of bases in DNA.

Question 3

what is a substitution mutation?

Answer 3

a nucleotide in a DNA molecule is replaced by another nucleotide with a different base

Question 4

why do substitution reactions sometimes have a big effect?

Answer 4

missense substitution
the codon codes for a different amino acid.
change in the primary structure so polypeptide won’t function properly.

Question 5

why do substitution mutations sometimes not have a huge effect?

Answer 5

silent substitution.
the new triplet base may still code for the same amino acid due to the degenerate nature of the genetic code.
most amino acids have more than one codon.

Question 6

what is a deletion mutation?

Answer 6

a nucleotide is lost from the original DNA sequence.

Question 7

what is the effect of a deletion mutation?

Answer 7

the amino acid sequence of the sequence is different so the polypeptide can’t function properly.
the sequence of bases in DNA is read in triplets so one deleted nucleotide causes each triplet to be shifted to the left by one base.

Question 8

what are chromosome mutations?

Answer 8

changes in the structure or number of whole chromosomes.

Question 9

what does polyploidy mean?

Answer 9

changes in whole sets of chromosomes.
organisms have 3 or more sets of chromosomes rather than 2.

Question 10

what is the effect of a change in the number of individual chromosomes?

Answer 10

failure of separation during meiosis.
known as non-disjunction.
gamete has one more or one fewer chromosome.
eg down’s syndrome

Question 11

what can cause mutations?

Answer 11

ionising radiation - alpha, beta, gamma, x-ray, UV.
chemicals
carcinogens
viruses
drugs

Question 12

what does meiosis produce?

Answer 12

4 daughter cells with half the number of chromosomes as parent cells.

Question 13

what does mitosis produce?

Answer 13

2 daughter cells with the same number of chromosomes as each other and the parent cells.
haploid cells.

Question 14

how many nuclear divisions does meiosis involve?

Answer 14

2

Question 15

what happens in meiosis division 1?

Answer 15

1. homologous chromosomes pair up and chromatids wrap around each other.
2. crossing over occurs - chromatids exchanged.
3. homologous pairs separate and one chromosome from each pair goes to the chromosomes.

Question 16

what happens in meiosis division 2?

Answer 16

1. chromatids move apart
2. 4 cells form and contain 23 chromosomes each.

Question 17

what 2 ways allow meiosis to bring about genetic variation?

Answer 17

1. independent assortment
2. crossing over.

Question 18

what is a gene?

Answer 18

length of DNA that codes for a polypeptide.

Question 19

what is a locus?

Answer 19

position of a gene on a chromosome or a DNA molecule.

Question 20

what is an allele?

Answer 20

one of the different forms of a particular gene.

Question 21

what is a homologous chromosome?

Answer 21

pair of chromosomes, one maternal one paternal, that have the same gene loci.

Question 22

what is independent assortment?

Answer 22

-during meiosis 1, when chromosomes line up alongside their homologous partner, they do it randomly.
-one of each pair will go to a daughter cell.
-the combination of maternal and paternal chromosome entering the daughter cell is a matter of chance.

Question 23

how does genetic variation arise from independent assortment?

Answer 23

each member of a homologous pair has the same genes and characteristics, but the allele can differ, so the independent assortment of these chromosomes produces new genetic combinations.

Question 24

what is crossing over?

Answer 24

-chromatids of each pair become twisted around each other.
-tensions are created and portions of the chromatids break off.
-equivalent portions of the chromosomes are exchanged so genetic combinations form.

Question 25

what is the formula for number of pairs of homologous chromosomes?

Answer 25

2^n

Question 26

what is genetic diversity?

Answer 26

total number of different alleles in a population

Question 27

how does genetic diversity allow individuals to survive environmental changes?

Answer 27

wider range of alleles so wider range of characteristics.
greater probability that an individual will possess a characteristic that suits the new environment’s conditions.

Question 28

how does reproductive success link to allelic frequency?

Answer 28

1. within a population, there is a gene pool with a variety of alleles.
2. random mutations may result in a new allele which can give the possessor an advantage over individuals
3. these individuals will be able to survive and reproduce, passing on their alleles.
4. offspring will be more likely to survive and reproduce.
5. frequency of the advantageous allele will increase over time.

Question 29

what is selection?

Answer 29

the process by which organisms that are better adapted to their environment are more likely to breed and survive.

Question 30

what is stabilising selection?

Answer 30

individuals at extremes of a phenotype are at a disadvantage compared to the mid range.

Question 31

what is directional selection?

Answer 31

force for change.
extremes of a phenotype have an advantage.
causes a change in the genetically determined characteristics of next generation.