Mrs H bio 10 Genetic Diversity

Question 1

What is meiosis used by and for?

Answer 1

Used by diploid organisms to produce gametes for sexual reproduction

Question 2

What does meiosis produce?

Answer 2

4 genetically different daughter cells

Question 3

What occurs to do with the gametes during sexual reproduction?

Answer 3

Gametes fuse to form a zygote which then divided repeatedly by mitosis to form the adult organism

Question 4

How many chromosomes would the zygote have us it was diploid?

Answer 4

Double the number of chromosomes

Question 5

What occurs before meiosis?

Answer 5

The DNA is replicated in S phase (interphase) of the cell cycle. The chromosomes then go through 2 divisions. Each division has a prophase, metaphase, anaphase and telophase

Question 6

What happens in the first meiotic division?

Answer 6

The homologous chromosomes pair up. Crossing over occurs. By the end of the first division, the homologous pairs are seperated, with one chromosome from each pair going into one of the daughter cells

Question 7

What happens in the seconds division of meiosis?

Answer 7

The chromatids are separated. At the end of meiosis 2, four cells have usually been formed. In humans each of these cells contains 23 chromosomes

Question 8

what three processes in meiosis introduce variation between the daughter cells?

Answer 8

crossing over between sister chromatids during prophase one,
independent assortment of homologous chromosomes during metaphase one
both of these result in different combinations of alleles in gametes, thus creating genetic variation
also, random fertilisation

Question 9

what is crossing over?

Answer 9

during prophase the non-sister chromatids exchange alleles between homologous pairs forming a chiasmata

Question 10

what is the crossing points of two non-sister chromatids called?

Answer 10

chaismata

Question 11

how do chromatids swap alleles during crossing over?

Answer 11

entanglement places stress on the DNA molecules and as a result a section of chromatid from one chromosome may break and re-join with the chromatid from the other chromosome

Question 12

why is the swapping of alleles significant?

Answer 12

it can result in a new combination of alleles on the two chromosomes

Question 13

what is independent assortment?

Answer 13

the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle

Question 14

how is there a different combination of chromosomes in daughter cells through metaphase?

Answer 14

during metaphase, the homologous chromosomes attach to the spindle fibres and they line up side by side. it is entirely random which way they attach

Question 15

why is variation in the gametes important?

Answer 15

produces new combinations of characteristics which means the species is more likely to adapt to changes in the environment

Question 16

what happens if chromosomes fail to separate during meiosis?

Answer 16

a gamete may end up with two copies of a chromosome

Question 17

how and when does non-disjunction occur?

Answer 17

improper separation of the chromosomes during anaphase or telophase of meiosis

Question 18

what would happen to the gamete as a result of chromosome non-disjunction

Answer 18

the gamete would contain one more than the haploid number and would result in a chromosome mutation

Question 19

what is an example of a disease that results from chromosome non-disjunction?

Answer 19

Down’s syndrome

Question 20

where does variation exist and why?

Answer 20

between members of the same species (intra-specific) and between species (inter-specific) and may be due to genetic factors or environmental factors

Question 21

how does genetic diversity occur?

Answer 21

the differences in what genes are present in an organism and the different alleles of a gene

Question 22

what 4 things cause genetic variation?

Answer 22

-mutation: produces new alleles
-independent assortment- gives new combinations of existing alleles
-crossing over: gives new combinations of existing alleles
-random fusion of gametes: creates zygotes that will have a unique combination of alleles

Question 23

what is the formula to calculate the no. of combinations of chromosomes after the random fertilisation of two gametes?

Answer 23

(2 to the power of n) squared

n is the haploid number and the square is the no. of gametes

Question 24

what can mutations do?

Answer 24

-confer a selective advantage
-be neutral
-be disadvantageous

Question 25

what is natural selection?

Answer 25

process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within a population

Question 26

describe the process of natural selection

Answer 26

-genetic variation within a population result in differences in phenotype
-environmental factors affect the chance of survival of an organism, therefore acting as a selection pressure
-better adapted individuals more likely to survive and reproduce
-these organisms more likely to pass on their advantageous alleles
-as a result, over many generations, the new allele will increase in frequency in the population

Question 27

what is a selection pressure?

Answer 27

a factor which determines the spread of an allele within the gene pool

Question 28

what is a gene pool?

Answer 28

the total sum of all the alleles of all the genes in the population. in large populations, the gene pool will be large (high diversity) and so they have a strong ability to adapt to change

Question 29

what are the 2 different types of selection?

Answer 29

stabilising and directional

Question 30

when does stabilising selection occur?

Answer 30

all populations where the environment is stable

Question 31

what does stabilising selection mean?

Answer 31

there is selective pressure at both ends of distribution
favours the average
tends to eliminate extremes

Question 32

what does stabilising selection reduce?

Answer 32

variability ( the size of the range within population)
opportunity for evolutionary change

Question 33

when does directional selection occur?

Answer 33

when an environmental change may produce new selection pressure that favours an extreme characteristic
when conditions change optimum necessary for survival also changes

Question 34

what does directional selection mean?

Answer 34

mean in population represents optimum for existing conditions some organisms will possess the new optimum. over time selection selection means these will predominate and the mean will shift

Question 35

how can bacteria become resistant to an antibiotic?

Answer 35

some bactewria can replicate asexually as often as every 20 minutes, which means that their DNA is replicated regularly. As a result there is an increased chance of error during replication leading to mutation which may cause resistant bacteria

Question 36

how does the whole population of bacteria eventually become antibiotic resistant?

Answer 36

the resistant bacteria can continue to reproduce with less competition from the non-resistant bacteria, which are now dead so genes for antibiotic resistance are passed on with much greater frequency and over time the whole population will be resistant