Genetic Diversity and Natural Selection

Question 1

what is a mutation

Answer 1

random change in a DNA base sequence

Question 2

explain how a mutation may lead to a non functioning protein

Answer 2

• mutation changes the primary structure
• this may change the position of the hydrogen, ionic and disulphide bonds
• this changes the tertiary structure of the protein

Question 3

what are the 3 different types of mutation

Answer 3

• substitution
• deletion
• addition

Question 4

what is a subsitition mutation

Answer 4

changing only one base in the DNA triplet

Question 5

expan why not all base substitutions cause a change in the primary structure

Answer 5

• the genetic code is degenerate
• a substitution may code for the original amino acid to be coded

Question 6

explain how a substitution mutation could effect the ploypeptide produced

Answer 6

• the substitution may result in the formation of a stop codon. This could make the polypeptide much shorter in length

Question 7

what are addition and deletion mutations

Answer 7

when DNA bases are added or deleted within the sequence

Question 8

addition and deletion mutation leads to a ……

Answer 8

frame shift

Question 9

what is a frame shift

Answer 9

the alteration of the base triplets and codons downstream from the mutation

Question 10

explain how deletetion and addition mutations affect the polypeptide produced

Answer 10

• frame shift
• chages the primary structure
• changes the tertiary structure

Question 11

what are mutagenic agents

Answer 11

increase the rate of gene mutations

Question 12

wat are 3 mutagenic agents and give examples

Answer 12

1. high energy radiation - x rays, uv light
2. carcinogens - nitrous acid converting cytosine to uracil
3. biological agents - viruses

Question 13

what does meiosis produce

Answer 13

daughter cells that are genetically different from each other

Question 14

1. how much DNA replications take place during meiosis
2. how much divisions take place during meiosis

Answer 14

1. 1
2. 2

Question 15

what are the 2 divisions in meisis referred to as

Answer 15

meiosis 1 and meiosis 2

Question 16

meosis produces ……… cells

Answer 16

4 haploid

Question 17

give two differences between mitosis and meiosis

Answer 17

• meiosis produces 4 geneticaly different cells, mitosis produces 2 genetically identical cells
• meiosis produces haploid cells, mitosis produces diploid
• meiosis involves 2 divisions, mitosis involves 1

Question 18

explain the process of meiosis one

Answer 18

• homologus chromosomes pair
• crossing over occurs at chiasmata
• cell divides into two. Homologus chromosomes seperate randomly (independant segregation)

Question 19

what are homologous chromosomes

Answer 19

pairs of chromosomes with the same genes at same loci

Question 20

what happens prior to meiosis

Answer 20

DNA replicates during interphase by semi conservative replication

Question 21

what are the 2 processes during meiosis one that lead to genetic variation

Answer 21

• independant segregation
• crossing over

Question 22

explain what happens during meiosis 2

Answer 22

• sister chromatids are pulled apart and move to opposite poles of the cell
• each cell divides, producing 4 haploid cells

Question 23

diagram of meosis

Answer 23

meiosis

Question 24

describe how the process of meiosis results in haploid cells

(4 marks)

Answer 24

• DNA replication
• Two divisions
• seperation of homologous chromosomes
• seperation of sister chromatids
• produces 4 halpoid cells

Question 25

give one way that genetic variation is increases which doesnt take place in meiosis

Answer 25

random gametes fuse during fertilisation

Question 26

explain the process of independant segregation

Answer 26

* during meiosis 1 * random assortment of homologous chromosomes * each pair of homologous chromosomes is seperated and the maternal and paternal move to opposite poles

Question 27

explain the process of crossing over

Answer 27

* homologous pairs of chromosomes associate * chiasmata forms * equal legths of non sister chromatids being exchanged * new combinatio of alleles

Question 28

how do mutations in chromosomes occur

Answer 28

non disjunction during meiosis

Question 29

how does non disjunction occur

Answer 29

when the homologous chromosomes or chromatids do not split equally

Question 30

give 3 sources of genetic diversity and variation

Answer 30

* random mutation * meiosis * random fusion of gametes

Question 31

explain the process of natural selection

Answer 31

* random mutations can produce new alleles of a gene * this creates variation in the phenotype * there is selection pressure present in the environment * oragnisms with phenotypes providing advantages are more likely to survive and reproduce * these organisms pass on their genes * the advantage allele frequency increases over many generations * the frequency of disadvantage alleles decreases

Question 32

what are the two types of selection

Answer 32

* stablising * directional

Question 33

explain the process of stablising selection

Answer 33

* occurs where the environment is stable * selected pressure at both ends of the distribution * individuals with extreme phenotype do not survive * favours the average and more common phenotype * more likely to survive, reproduce and pass on their favourable alleles * allele frequency increases * reduces variability * reduces opportunity for evolutionary change

Question 34

explain the process of directional selection

Answer 34

* environmental change may produce new selection pressures that favours an extreme phenotype * these organism are more likely to survive and reproduce * these organisms pass on their alleles for the extreme phenotype * the advtantageous allele frequency increases over many generations * over time selections means tis allele combination will predominate and the mean phenotype will shift towards the extreme phenotype