Chapter 9 - Genetic diversity

Question 1

what is a gene mutation?

Answer 1

any change to one or more nucleotide bases in the base sequence of DNA

Question 2

what can occur as a consequence of the deletion of bases?

Answer 2

frame shift

all subsequent bases are read in different triplets

Question 3

what are the two forms of chromosome mutation?

Answer 3

• change to whole sets of chromosomes such as having 3 known as polyploidy
• changes in individual number of chromosomes known as non-disjunction

Question 4

why must meiosis take place?

Answer 4

in order to ensure the same number of chromosomes in each adult, has to half the amount so when gametes fuse the chromosomes arent doubled

Question 5

outline meiosis 1

Answer 5

• homologous chromosomes pair up with chromatids and wrap around each other
• equilvalent portions of the chromatids can be exchanged by crossing over
• homologous pairs separate, with one chromosome from each pairing going into each daughters cell

Question 6

outline meiosis 2

Answer 6

• the chromatids move apart

- 4 daughter cells formed

Question 7

how does meiosis bring about genetic variation? (2)

Answer 7

• independent segragation of homologous chromosomes

- new combinations of maternal and paternal alleles through crossing over

Question 8

what is a gene

Answer 8

a length of DNA that codes for a polypeptide

Question 9

what is the locus

Answer 9

the position of the gene on a chromosome or DNA molecule

Question 10

what are homologous chromosomes

Answer 10

a pair of chromosomes, one from mother and one from father which each have the same gene loci

Question 11

how does genetic variation arise form independent segregation

Answer 11

the fact that which one of the homologous chromosomes goes into each daughter cell is totally random

Question 12

outline the process of genetic recombination by crossing over (3)

Answer 12

• chromatids each pair up ad become twisted around each other
• tensions are created by the twisting so portions break off
• broken portions might rejoin with the chromatids of the homologous partner, equivalent portions are therefore exchanged

Question 13

what is the formula for possible chromosome combinations following meiosis?

Answer 13

(2 to the power of n) squared

n being the number of homologous pairs of chromosomes

Question 14

define the term genetic diversity

Answer 14

the total number of different alleles in a population

Question 15

outline briefly the process of reproductive success and its effect on allele frequency (4)

Answer 15

• gene pool of species contains wide variety of alleles
• random mutations occasionally cause new alleles and very rarely are these advantageous
• individuals with new positive allele more likely to survive to reproduce and thus pass on allele
• over many generations number of new advantageous allele will increase

Question 16

what is directional selection?

Answer 16

selection which favours individuals which move in one direction from the mean, results in changes of characteristics

Question 17

what is stabilising selection?

Answer 17

selection which favours individuals closest to the mean, preserves the characteristics of the population

Question 18

how does the change appear on a graph for directional selection?

Answer 18

mean moves in one direction

Question 19

how does the change appear on a graph for stabalising selection

Answer 19

higher peak and narrower spread

Question 20

what are the 3 types of adaptation?

Answer 20

anatomical
physiological
behavioural