3.7 Genetics, Evolutions and Ecosystems

Question 1

define genotype

Answer 1

the genetic constitution of an organism

Question 2

phenotype

Answer 2

the expression of this genetic constitution and its interaction with the environment

Question 3

gene

Answer 3

a length of DNA that is a sequence of nucleotide bases which code for a particular polypeptide

Question 4

allele

Answer 4

one of the different forms of a gene

Question 5

dominant

Answer 5

the allele of the heterozygote that expresses itself in the phenotype

Question 6

recessive

Answer 6

the allele of the heterozygote that is not expressed

Question 7

homozygous dominant

Answer 7

both alleles are dominant

Question 8

homozygous recessive

Answer 8

both alleles are recessive

Question 9

codominant

Answer 9

neither allele is recessive, both will be expressed in the heterozygote’s phenotype

Question 10

autosomes

Answer 10

the non-sex chromosomes, genes found here are chromosomal

Question 11

asymptomatic carriers

Answer 11

carry one of the recessive alleles so can pass onto offspring, no symptom

Question 12

monohybrid cross

Answer 12

shows the likelihood of different alleles of a gene being inherited by the offspring of certain parents

Question 13

genetic crosses show

Answer 13

the genotype of the parents, the gametes’ alleles and the offspring phenotype

Question 14

symbols for a codominant genetic cross

Answer 14

capital letters represent the genotype for the gene
superscript letters represent the alleles

Question 15

dihybrid crosses show

Answer 15

the combination of offspring for two unlinked genes
two genes with two alleles, four different gamete combinations
one allele on each side of the cross

Question 16

sex linkage, problems caused by it

Answer 16

The Y chromosome misses some matching genes on the X chromosome because X is longer.
There is a non homologous portion of the X chromosome.
This means recessive characteristics on the non homologous section of the X chromosome are more frequent in males (XX) because there is no chance of a dominant allele on Y to express itself.

Question 17

define autosomal linkage

Answer 17

two or more genes are carried on the same autosome

Question 18

explain autosomal linkage

Answer 18

Genes on the same autosome are linked because during independent segregation of meiosis 1 they stay together. Closer together, less likely to split.

Question 19

define epistasis

Answer 19

When the allele of one gene affects or masks the expression of another in the phenotype.
If the allele is recessive, 2 copies will be needed to block its’ expression.

Question 20

criteria to use chi squared

Answer 20

Sample size is relatively large, over 20
Data falls into discrete categories
Raw counts used, no percentages or rates
Comparing experimental results with theoretical ones

Question 21

what does chi squared tell you

Answer 21

if observed results were statistically different to your expected results.
Must be compared to a critical value.
A means of testing where any deviation between the observed and the expected numbers in an investigation is significant or not.

Question 22

null hypothesis

Answer 22

there is no significant difference between the two, any difference due to chance alone, so random

Question 23

alternative hypothesis

Answer 23

there is a significant difference between the two, so linked

Question 24

if chi result larger/equal to critical

Answer 24

reject null hypo, there is a significant link which is not due to chance

Question 25

if chi result lower than critical

Answer 25

accept null hypo, any link is due to chance alone

Question 26

degrees of freedom

Answer 26

number of categories minus one

Question 27

hardy weinberg principle

Answer 27

If certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next

Question 28

necessary conditions

Answer 28

Diploid organism Sexual reproduction ONLY No overlap between generations (parents do not mate with their offspring) Mating is random Large population size No migration, mutation or selection (no flow of alleles in or out and equally likely to be passed on to the next generation)

Question 29

when is HW useful

Answer 29

when building models/making predictions of how frequencies will change in future generations

Question 30

equation for allele freq

Answer 30

p + q = 1

Question 31

equation for genotype freq

Answer 31

P2 + 2pq + q2 = 1

Question 32

p and q represent..

Answer 32

p is dominant q is recessive

Question 33

Genetic variation arises from

Answer 33

Mutations Meiosis (crossing over/independent assortment) Random fertilisation of gametes

Question 34

Genetic variation

Answer 34

a species having different alleles

Question 35

Environmental variation

Answer 35

caused by differences in food, climate, and lifestyle

Question 36

Natural selection

Answer 36

individuals with a fitter phenotype are more likely to survive and pass on their alleles to their offspring. The frequency of advantageous alleles increases over time and generations.

Question 37

stabilising selection

Answer 37

Those with alleles towards the middle of the range are selected for and are more likely to survive Tends to occur where environmental conditions remain constant for a long period of time Allele frequency stays relatively stable unless environmental influence occurs Reduces the range of possible offspring

Question 38

directional selection

Answer 38

Those with a single extreme phenotype are selected for and are more likely to survive Tends to occur if there is a change in the environment and thus selection pressures Gradual change/fluctuation in allele frequency over time If the environmental conditions change, the allele on one side of the curve showing the mean ‘optimum’ characteristic is favoured and selected for (selection pressures change) so allele frequency increases.

Question 39

disruptive selection

Answer 39

Those with alleles for 2 extreme phenotypes are more likely to survive Favours extremes at the expense of the intermediate phenotypes Tends to occur when the environment favours more than one phenotype, the environment takes two or distinct forms e.g cold in winter, warm in summer Directional only favours one extreme trait, disruptive favours two.

Question 40

define hybrid

Answer 40

a sterile organisms which is the result of different species mating

Question 41

define speciation

Answer 41

the evolution of two or more new species from new existing species Species have the same genes but different alelles so can produce fertile offspring with each other and so are reproductively separate from other species

Question 42

define adaptive radiation

Answer 42

the different combinations of alleles from different phenotypes are subject to selection pressures which leads to each population becoming adapted to their own environment

Question 43

Causes of reproductive isolation

Answer 43

Geographical (physical barrier) 2. Change in: colour/pattern call/song Active time of day Reproductive times (flowering) Reproductive organs do not match

Question 44

Allopatric speciation

Answer 44

When populations of a species become geographically separated Might be different environments in different locations In order to survive, those with alleles most advantageous for survival in the environment are more likely to survive and pass on alleles to their offspring Disadvantageous alleles therefore disappear from the population when they do not breed Directional selection will occur and the allele frequency will change Overtime this will cause phenotype frequency to change which will accumulate until two groups will have become separate species

Question 45

sympatric speciation

Answer 45

When a population living in the same area become reproductively isolated Random mutations occur within a population in the same location which prevent that individual from breeding with those without the mutation Rarer type of speciation because it is difficult to become completely reproductively isolated without being geographically isolated as well

Question 46

Carrying capacity

Answer 46

the maximum number of organisms that an ecosystem can support, this changes as a result of biotic and abiotic factors

Question 47

intraspecific competition

Answer 47

When there are too many offspring for the available resources, competition occurs amongst organisms of the same species. Plentiful resources cause an increase in population size, which causes resources to become limiting and a decrease in population again (cyclic changes.) Deaths are not random; the individuals better suited to survival are more likely to survive than the less well adapted, so their more favourable allele combination is more likely to be passed on to the next generation. Next population has evolved a combination of alleles better adapted to survival.

Question 48

interspecific competition

Answer 48

Organisms of different species competing for the same resources One population has a competitive advantage over the other, so their population will increase while the other decreases. If they cannot compete equally, the less advantaged species will likely become extinct.

Question 49

define predation

Answer 49

the population of one species will affect the population size of the other

Question 50

Effect of the predator-prey relationship on population size

Answer 50

Predators eat prey, reducing prey population size Predators therefore in greater competition amongst themselves for the prey that are left Predator population is reduced as some predators are unable to obtain enough prey to survive Fewer predators are left so less prey eaten so more prey can survive and reproduce Prey population increases More prey are now available as food, so the predator population in turn increases.

Question 51

instruments for sampling

Answer 51

Quadrats/point frames Transects Mark, capture, release Nets Pitfall traps Pooters

Question 52

size as a factor for quadrats

Answer 52

If a population is not evenly distributed, a large number of small quadrats will be more representative than a small number of large ones Large or small organisms?

Question 53

number of quadrats to record within the study area

Answer 53

The large the number the more reliable the results will be Balance struck between time available and reliability (the number of quadrats) of the results

Question 54

The random position of the quadrats within the study area

Answer 54

Random sampling is necessary to produce statistically different results

Question 55

Random sampling

Answer 55

Each member of the population is equally likely to be included An unbiased sample Every part of each area must have an equal chance of being chosen Can be used for differences between contrasting habitats within a habitat

Question 56

method for random sampling

Answer 56

Lay out two long tape measures at right angles, along two sides of the study area Obtain a series of coordinates by using random numbers taken from a table or generated by a computer Place a quadrat at the intersection of each pair of coordinates and record the species within it

Question 57

systematic sampling

Answer 57

Useful where a study area has an environmental gradient Use of a transect will sample systematically along the environmental gradient. Use point, frame or grid quadrats at regular intervals along the transect line.

Question 58

running mean

Answer 58

Use point, frame or grid quadrats at regular intervals along the transect line. As your data accumulates, test for the running mean and if it fluctuates within acceptable limits it is indicated that further sampling would not improve the accuracy of your data.

Question 59

frequency

Answer 59

likelihood of a particular species occurring in a quadrat

Question 60

percentage cover

Answer 60

estimate of the area within a quadrat that a particular species covers

Question 61

abundance

Answer 61

the number of individuals of a species within a given area

Question 62

mark release capture method

Answer 62

Capture a sample without doing them harm Mark in a harmless and non obvious way Release back into habitat Wait a period of time and take another sample Count all organisms, marked and unmarked Use the equation to estimate population size

Question 63

Assumptions involved

Answer 63

-closed population -members randomly mix -marks not lost -mark doesn’t affect chances of recapture/no harm to animal

Question 64

equation for mark release recapture

Answer 64

Total population size = number caught 1st * number caught 2nd —----------------------------------------- Total marked 2nd

Question 65

decrease in productivity as the woodland matures

Answer 65

there is less light so more competition and therefore reduced photosynthesis

Question 66

use your knowledge of succession to explain the increase in biomass during the first 20 years

Answer 66

a pioneer species causes changes in abiotic conditions which increases the number of animals

Question 67

one reason for conversing woodlands

Answer 67

to protect niches

Question 68

define species

Answer 68

a group of organisms that can breed together to produce fertile offspring

Question 69

define uniform distribution

Answer 69

the same number of organisms in each region

Question 70

why use percentage cover instead of frequency

Answer 70

too many organisms to count for frequency

Question 71

describe succession in terms of types of grass populations shown on a graph

Answer 71

one grass is the pioneer species which changes the abiotic conditions so they become less hostile for another species to grow the two species that cohabit represent climax community