selection

Question 1

what determines an organisms characteristics (phenotype)

Answer 1

the organisms genotype (all the alleles it has) and its interaction with the environment

Question 2

what is an allele

Answer 2

its a different version of the same gene

Question 3

what is genetic diversity (gene pool)

Answer 3

the number of different alleles of genes in a population

Question 4

what affect do mutations have in a population

Answer 4

they introduce new alleles which could provide selective advantage/disadvantage or neutral (does nothing)

Question 5

give the definition for natural selection

Answer 5

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 the population

Question 6

give 3 factors that affect reproductive success and differential survival

Answer 6

predation disease and competition

Question 7

what does selection pressure determine

Answer 7

it determines the spread of an allele within the gene pool, and can be both abiotic or biotic

Question 8

give some abiotic selection pressures and their impact on populations

Answer 8

pH of soil
humidity
light intensity
temperature
salinity
usually has same impact or small or large population

Question 9

give some biotic selection pressures and their impact on populations

Answer 9

number of predators
pathogens
presence of mate
food availability
number of prey available
usually has a bigger impact on bigger population

Question 10

what are 3 the adaptations of an organism called

Answer 10

anatomical
physiological
behavioural

Question 11

what are anatomical adaptations

Answer 11

body shape, colour, fur texture, structural features

Question 12

what are physiological adaptations

Answer 12

internal functions of an organism that help them thrive in a specific environment

Question 13

what are behavioural adaptations

Answer 13

something an animal does usually in response to some type of external stimulus in order to survive actions to aid survival

Question 14

what are the steps for stabilising selection

Answer 14

• there’s selection AGAINST both extremes
• only mean phenotype will have reproductive success
• alleles for mean phenotype are passed on to future generations in greater numbers
• overtime, frequency of mean alleles, coding for mean phenotype, INCREASES
• alleles coding for both extreme phenotypes decrease

Question 15

what are the steps for directional selection

Answer 15

• selection for only one extreme
• individuals with advantageous allele have increased reproductive success
• alleles for one extreme are passed on to future generations in greater numbers
• overtime, frequency of this extreme allele, coding for extreme phenotype INCREASES
• alleles coding for the other extreme phenotype decreases within population

Question 16

what is evolution by natural selection a change in

Answer 16

it is a change in the allelic frequencies within a population

Question 17

explain how selection occurs in living organisms

Answer 17

• there’s variation due to formation of new alleles by mutation
• selection pressure in habitat (abiotic/biotic)
• selection advantageous phenotype coded for by advantageous allele
• organisms better adapted for survival will reproduce so there’s differential reproductive success
• advantageous phenotype selected for organism survive and reproduce
• this occurs over many generation
• leading to an increase in advantage allele frequency

Question 18

what is differential reproductive success

Answer 18

when some individuals leave more offspring in the next generation than do others, due to their advantageous alleles.

Question 19

define gene mutation and explain how a mutation
-can have no effect on individual
- a positive effect on individual
(4)

Answer 19

• gene mutation is a change in base sequence of DNA forming a new allele
• there will be no affect on an individual because DNA sequence is degenerate so more than one codon codes for one amino acid
• however mutation can result in advantageous allele coding for a gene
  -that will give increased reproductive success

Question 20

when do you use logarithms

Answer 20

when you have a large range of values

Question 21

what is a colony (of bacteria)

Answer 21

a cluster of cells or colonies which arise from a single bacterium by asexual reproduction

Question 22

why do you perform a serial dilution

Answer 22

to count the bacteria colonies when its too concentrated

Question 23

how do you do a serial dilution

Answer 23

• take a sample of 1 part of bacteria from medium and mixing it with 9 parts water. this is a 1/10 dilution
  take 1 ml of previous dilution and add 9ml of sterile water and mix well to create a 1/100 dilution

Question 24

why is it not good to use a low dilution

Answer 24

the count is unlikely to be accurate because there are too many cells so they will be overlapping