Mechanisms of evolution

Question 1

define evolution

Answer 1

gradual change in the characteristics of a species

Question 2

population

Answer 2

group of organisms of the same species living together in a particular place at a particular time

Question 3

allele

Answer 3

alternate form of a gene

Question 4

gene pool

Answer 4

sum of alleles in a given population

Question 5

allele frequencies

Answer 5

how often each allele of a gene occurs in the gene pool of a population

Question 6

point mutations

Answer 6

change to a single nucleotide
- insertion
- substitution
- deletion
may result in a frameshift
eg sickle cell anemia

Question 7

define frameshift

Answer 7

mutation involving an insertion or deletion that results in a change in the way that the sequence is read

Question 8

gene mutation

Answer 8

changes in a single gene so traits normally produced by that gene are changed or destroyed
eg CF

Question 9

chromosomal mutations

Answer 9

part of or all of the chromosome is affected
- duplication
- deletion
- inversion
- translocation
- non-disjunction (aneuploidy)

Question 10

eg of chromosomal mutations

Answer 10

down syndrome (trisomy-21)
patau syndrome (trisomy-13)
klinefelter syndrome (XXY,XYY)
cri-du-chat syndrome (partial monosomy 5)
turner syndrome (X)
common symptoms: early death, intellectual disability etc

Question 11

mutagens

Answer 11

agents that increase rate of mutation, eg ionising radiation, formaldehyde, mustard gas

Question 12

how do mutagens cause changes to DNA

Answer 12

• resemble proteins and be incorporated into DNA
• chemically react with and modify DNA
• cause DNA breakages
• trigger replication errors

Question 13

somatic vs germline mutations

Answer 13

somatic: body cells that are not reproductive cells are affected, cannot be passed down, often cancerous
germline: reproductive cells affected, can be passed down
eg PKU, muscular dystrophy, CF, Tay-sachs

Question 14

effect on amino acids and protein

Answer 14

missense: change in amino acid and hence protein
nonsense: short protein
neutral: change in amino acid, not really protein produced
silent: no change in amino acid

Question 15

lethal recessive

Answer 15

recessive mutations that are lethal if not masked by the dominant allele

Question 16

genetic drift

Answer 16

random, non directional change in allele frequencies of a population between generation
- unlikely to have a significant impact on a large population, but more significant impact on small population
- random small sample of population not genetically representative of whole population

Question 17

why is random genetic drift more significant in small populations than large populations

Answer 17

less variation in small populations, less ability for small population to respond favourably to changing conditions

Question 18

founder effect

Answer 18

small group moves away from homeland and establishes a new population, with different allele frequencies compared to the original population
- decreased genetic variation in the population
- new population show a frequency of features not typical of the homeland population

Question 19

gene flow and migration

Answer 19

gene flow: movement of genetic material from 1 population to another
migration: movement of individuals between populations to enable gene flow
- will cause frequencies of alleles to be altered between the 2 populations, may even introduce new alleles into population

Question 20

advantage to blocking gene flow

Answer 20

high incidence of lethal recessive gene in a population, benefit to limit gene flow to not influence gene pools of other populations

Question 21

disadvantage to blocking gene flow

Answer 21

inbreeding occurs in isolated populations, frequencies of unusual characteristics much higher

Question 22

natural selection

Answer 22

• natural selection is the process by which the proportion of alleles producing favourable characterisitcs gradually increases in a population over several generations
  1) there is variation within a species
  2) overproduction of offspring that can possibly survive to maturity
  3) excessive birth rate, limited resources, there is a struggle for existence
  4) individuals with characteristics best suited for the environment have more chance of surviving and reproducing (survival of the fittest
  5) favourable characteristics are passed on to the next generation
  6) proportion of alleles that produce favourable characteristics gradually increase OVER SEVERAL GENERATIONS

Question 23

define selection pressure

Answer 23

environmental factor acting on population

Question 24

species

Answer 24

group of individuals that share many characteristics and are able to interbreed to produce fertile offspring

Question 25

describe speciation

Answer 25

1) varation
- range of varations exist within the population which shares a common gene pool
2) isolation
- barrier has formed, dividing the population into 2
- no interbreeding between the 2 populations, each population has a separate gene pool
3) selection
- different selection pressures act on each of the 2 populations OVER SEVERAL GENERATIONS
- change in allele frequencies of each gene pool, leading to evolution of subspecies
4) speciation
- over a long period of time, changes in gene frequency that when there is interbreeding between these 2 populations, fertile offspring can no longer be produced
- 2 species exist

Question 26

how does errors in DNA replication result in mutation?

Answer 26

replication: process where new strands of DNA are produced
- complementary strands are formed
- errors include subsitution, insertion, deletion, frameshift, alter DNA code
- DNA formed undergoes cell division to create a new cell
- new cells have the wrong DNA code

Question 27

how does errors in cell division result in mutation?

Answer 27

• homologous chromosomes line up
• genetic material swapped during crossing over
• however, errors during cell division alter chromosomes in daughter cells formed
• inversions, translocation, non disjunction
• gametes produced have faulty chromosomes or an incorrect chromosome number

Question 28

sickle cell anaemia pop cause symptoms

Answer 28

Black african populations, India
mutation of the gene responsible for haemoglobin production
- sickle shape RBC, reduced oxygen carrying ability of RBC, fatigue, shortness of breath, anaemia, inflammation of hands and feet

Question 29

sickle cell anaemia inheritance and effect on gene pool

Answer 29

recessive trait passed on from 2 carrier parents
homozygous : die from anaemia or malaria
heterozygous : have sickle trait, resistance to malaria, increase sickle cell allele freq. of population

Question 30

tay-sachs pop cause symptoms

Answer 30

Ashkenazi Jews, Cajun people
missing enzyme essential for fat metabolism
fatty tissue in nervous system, mental and physical disabilities like cannot swallow, paralytic, blind, deaf

Question 31

tay-sachs inheritance and effect on gene pool

Answer 31

homozygous: die because of Tay-sachs or TB
heterozygous: resistant to TB, increase tay-sachs allele freq. in population