3.7 genetics, populations, evolution and ecosystems

Question 1

phenotype

Answer 1

The observable or biochemical characteristics of an organism.
The result of the interaction between the expression of the genotype and the environment.
The environment can alter an organism’s phenotype

Question 2

genotype

Answer 2

Is the genetic composition of an organism.
Describes all of the alleles that an organism has.
Determines the limits within which the characteristics of an individual may vary.

Question 3

allele

Answer 3

Is 1 of the different forms of a gene.
Only 1 allele of a gene can occur at the locus of any 1 chromosome.
In diploid organisms the chromosomes occur in pairs called homologous chromosomes.
Are therefore 2 loci that each carry 1 allele of a gene. If the allele for each of the chromosomes is the same, it is said to be homozygous. If its different, its said to be heterozygous.

Question 4

genes

Answer 4

A length of DNA, that is a sequence of nucleotide bases, that normally code for a particular phenotype.
A gene does this by coding for a particular polypeptide.
This polypeptide may be an enzyme that is needed in the biochemical pathway that leads to the production of the characteristics.

Question 5

monohybrid cross

Answer 5

Pure breeding green pea pod plant crossed with a pure breeding yellow plant. (homozygous). The result was that all of the offspring were green pea pods, so green must be dominant.
Gene for pea pod colour- feature ( use a particular letter to represent it, making sure it has different upper and lower case if possible), so there is 2 alleles.
Let G represent the dominant allele green.
Let g represent the recessive gene yellow.
(homozygous)
Parents- phenotype pure bred green × pure
bred yellow
Genotype GG → gg

Gamete G G g g

F1- 1st filial gen Gg Gg Gg Gg
Offspring of X
F1 phenotype green green green green
Expected Ratio All green

Question 6

autosomal linkage

Answer 6

Any 2 genes that occur on the same chromosome are linked.
2 or more genes are carried on the same autosome is autosomal linkage
Are physically joined together and cannot move.

Question 7

multiple alleles

Answer 7

A gene may have more than 2 alleles and so has multiple alleles.
E.g.. ABO. There are 3 alleles associated with the gene I ( immunoglobulin gene) :
IA- leads to the production of antigen A
IB- leads to the production of antigen B
IO- leads to the production of antigen O.
Despite there being 3 alleles, only 2 can be present in an individual at any one time.

Question 8

multiple alleles

Answer 8

A gene may have more than 2 alleles and so has multiple alleles.
E.g.. ABO. There are 3 alleles associated with the gene I ( immunoglobulin gene) :
IA- leads to the production of antigen A
IB- leads to the production of antigen B
IO- leads to the production of antigen O.
Despite there being 3 alleles, only 2 can be present in an individual at any one time.

Question 9

back cross

Answer 9

Allows you to determine the genotype of an ‘unknown’ phenotype.
Use it against a homozygous recessive

Question 10

sex linkage

Answer 10

As females have 2 X chromosomes, all gametes are the same n that they contain a single x chromosome.
Males have 1 X, 1 Y chromosome they produce 2 different gametes

Question 11

co-dominance

Answer 11

Occurs where instead of 1 allele being dominant and the other recessive, both alleles are equally dominant

Question 12

dihybrid cross

Answer 12

How two characters, determined by two different genes located on different chromosomes are inherited. Always 9:3:3:1 ratio

Question 13

chi-squared test

Answer 13

Used to test null hypothesis.
A means of testing whether any deviation between the observed and expected numbers in significant or not.
The value obtained is the read off a chi-squared distribution table to determine whether deviation from expected results is significant or not.

Question 14

what is the criteria for the chi-squared test

Answer 14

Can only be used if certain criteria is met:
1- sample size is relatively large. At least 20.
2- data must fall in discreet categories.
3- only raw counts, no %, rates etc. can be used.
4- used to compare experimental results to theoretical results.

Question 15

how do you tell if deviation is significant

Answer 15

To do so you need to know the degree of freedom.
The critical value is p=0.05.
If the deviation is equal or greater than 0.05, the deviation is not significant and null hypothesis is accepted.
If deviation is less than 0.05, the deviation is significant and null hypothesis is not accepted.

Question 16

chi-squared equation

Answer 16

X^2 = (O-E)^2 / E

Question 17

hardy-weinberg

Answer 17

Provides a mathematical equation that can be used to calculated the frequencies of the alleles of a particular gene in a population.
Makes the assumption that the proportion of dominant or recessive alleles of any gene in a population remains the same from 1 generation to the next

Question 18

hardy conditions

Answer 18

this can be the case provided that 5 conditions are met:
1- no mutations arise
2- the population is isolated. Where no alleles flow into or out of the population
3- there is no selection, where alleles are all equally likely to be passed to the next generation.
4- the population is large
5- mating within the population is random.

Question 19

hardy-weinberg equation

Answer 19

p^2 + 2pq + q^2 = 1

p + q = 1

Question 20

populations

Answer 20

A population is a group of organism of the same species that occupies a particular space at a particular time and that can potentially interbreed.
All the alleles of all the genes of all the individuals in a population at a given time are known as the gene pool (deme). The number of times an allele occurs within the gene pool is referred to as allelic frequency.

Question 21

variation due to genetic factors

Answer 21

Within a population, all members have the same genes. Genetic differences, however, occur as members of this population will have different alleles of these genes.
These differences not only occur in living individuals but also change from generation to generation.
Genetic variation arises as a result of:
Mutations- these sudden changes to genes and chromosomes may, or may not be passed on to the next generation.
Meiosis- this special form of nuclear division produces new combinations of alleles before they are passed on into the gametes
Random fertilisation- in sexual reproduction this produces new combinations of alleles and the offspring are therefore different from the parents. Which gametes fuses with which at fertilisation is a random process further adding to variety of offspring.

Question 22

variation due to environmental factors

Answer 22

Environment exerts an influence on all organisms. These influence affect the way the organisms genes are expressed.
Genes set limits, but its largely the environment that determines where, within those limits, an organism lies.

Question 23

natural selection

Answer 23

The individuals in a population that is best suited to prevailing conditions ( e.g. Better able to hide/escape predators, better able to obtain light/catch prey) will be more likely to survive than those less well adapted. Will be more likely to breed and so pass on their more favourable allele combinations to the next generation, which will therefore have a different allelic frequency from the previous one.
Populations showing little individual genetic variation are often more vulnerable to new diseases and climate changes.
A larger population, with more genetically varied individuals, the greater the chance 1 or more individuals will have the combination of alleles that lead to a phenotype which is advantageous in the struggle for survival.

Question 24

intraspecific vs interspecific competition

Answer 24

Intraspecific- Competition from individuals from the same species.
Interspecific- competition between different species

Question 25

stabilising selection

Answer 25

Tends to eliminate the extremes of the phenotype range within a population and with it the capacity for evolutionary change.
Tends to occur where the environment conditions are constant over long periods of time.

Question 26

directional selection

Answer 26

Results in 1 extreme of a range of variation being selected against in favour of the other extreme or even the average

Question 27

disruptive selection

Answer 27

Favours extreme phenotypes at the expense of the intermediate phenotypes.
Most important in bringing about evolutionary change. Occurs when an environmental factor takes 2 or more distinct form.

Question 28

allelic frequency and how variation effects it

Answer 28

The number of times an allele occurs within a gene pool is referred to as the allelic frequency.
Is affected by selection and selection is due to environmental factors. So environmental changes therefore affect the probability of an allele being passed on in a population and hence the number of times it occurs in the gene pool. Only affect the frequency of a mutant allele that is already present in the gene pool

Question 29

speciation

Answer 29

Is the evolution of new species from existing ones.
Species- group of individuals that have a common ancestry and so share the same genes but different alleles and are capable of breeding to produce fertile offspring

Question 30

forming new species

Answer 30

The most important way a new species if formed is through reproductive separation followed by a genetic change due to natural selection.
The different phenotypes each combination of alleles produce will be subject to selection pressures that will lead to each population becoming adapted to its local environment. ( known as adaptive radiation). It results in changes to allele frequencies.
Genetic drift is something that can take place in small populations. Is because the relatively few members of a small population posses a smaller variety of alleles than the members of a large population. So their genetic diversity is less.
Any mutation to 1 of these alleles that is selectively favoured will also more quickly affect the whole population because its frequency will be high. The effects of genetic drift will be higher and the population will change relatively rapidly, making it more likely to develop into a separate species.

Question 31

allopatric speciation

Answer 31

Allopatric means different countries and describes the form of separation where 2 populations become geographically separated.
Geographical separation may be the result of any physical barrier between 2 populations which prevents them from interbreeding.
Barriers include- oceans, rivers, mountain ranges and deserts.
Barriers may be a problem for 1 species but wont be for another

Question 32

sympatric speciation

Answer 32

Sympatric means same country and describes the form of speciation that results within a population in the same area leading to them becoming reproductively separated

Question 33

geographical variation

Answer 33

Populations are isolated by physical barriers such as oceans

Question 34

ecological variation

Answer 34

Populations inhabit different habitats within the same area and so individuals rarely meet

Question 35

temporal variation

Answer 35

Breeding season don’t coincide and so don’t interbreed

Question 36

behavioural variation

Answer 36

Mating is often preceded by courtship which is stimulated by different characteristics. Any mutation may cause a change in those and may prevent mating

Question 37

mechanical variation

Answer 37

Anatomical differences may prevent mating occurring

Question 38

gametic variation

Answer 38

Gametes may be prevented from meeting due to genetic or biochemical incompatibility

Question 39

hybrid sterility variation

Answer 39

Hybrids formed from the fusion of gametes from different species are often sterile because they cannot provide viable offspring.

Question 40

ecosystems

Answer 40

Are dynamic (moving) systems made up of a community and all the non-living factors of it’s environment.
Can range in size from very small to very large.
Are 2 major processes within to consider:
Flow of energy through the system
Cycling of elements within the system
Within each ecosystem, there is a number of species. Each species is made up of a group of individuals that make up a population.

Question 41

populations

Answer 41

A group of individuals of 1 species that occupy the same habitat at the same time and are potentially able to interbreed. An ecosystem supports a certain type of population of a species called the carrying capacity.
The size of a population can vary as a result of:
Effect of abiotic factors
Interactions between organisms.
Populations of different species forms a community

Question 42

communities

Answer 42

Is defined as all the populations of different species living and interacting in a particular place at the same time.

Question 43

habitats

Answer 43

Is the place where an organism normally lives and is characterised by physical conditions and other types if organisms present.
Within an ecosystem there are many habitats
Within each habitat, there is smaller units, each with their own microclimate. These are called microhabitats.

Question 44

plotting population growths

Answer 44

Where a population grows in size slowly over a period of time it is possible to plot a graph of numbers in a population against time.
Where the population grows rapidly over a short period of time, this may not be possible.
If we try to plot a graph of numbers against time using a time scale that allows differentiation of each point, the curve runs off the graph. So you use a logarithmic scale to represent the number.

Question 45

population size

Answer 45

No population continues to grow indefinitely because certain factors limit growth
E.g. availability of food, light, water, oxygen and shelter, and the accommodation of toxic waste, disease and predators.
Each population has a certain size, the carrying capacity, that can be sustained over a relatively long period and is determined by limiting factors.

Question 46

ecological niche

Answer 46

A niche describes how an organism fits into the environment. It refers to where an organism lives and what it does there. Includes all biotic and abiotic conditions to which an organism is adapted to in order to survive, reproduce and maintain a viable population.
Some species may appear to be similar but their nesting habitats or other aspects of behaviour will be different , or they may show different levels of tolerance to environmental factors such as pollutant or oxygen shortages.
No 2 species occupy the same niche. Is known as the competitive exclusion principle

Question 47

temperature and ecosystems

Answer 47

each species has an optimum temperature at which is best able to survive. The further away from it, the fewer individuals are able to survive.
In plants and cold-blooded animals, the lower the temperature. The slower their enzymes work and so the metabolic rate is reduced. Populations therefore have a low carrying capacity. At temperatures above, enzymes don’t work as efficiently as they gradually undergo denaturation.
Warm-blooded animals can maintain a relatively constant temperature regardless of external. The further away the temperature gets, the more energy is expended in trying to maintain the normal body temperature, leaving little energy for individual growth and so mature more slowly.

Question 48

light and ecosystems

Answer 48

As the ultimate energy source for most ecosystems, light is a basic necessity of life. Rate of photosynthesis increases as light intensity increases. Greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce. ( increases carrying capacity).

Question 49

pH and ecosystems

Answer 49

Affects the action of enzymes. Each enzyme has an optimum pH at which is operates at the most effectively. A population is larger where the appropriate pH exists, and smaller ( or non-existent) when the pH is not the optimum

Question 50

water and humidity and ecosystems

Answer 50

Where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions. Humidity affects transpiration rates in plants and the evaporation of water from animals. In dry conditions, the populations adapted to tolerate low humidity will be larger than those who haven’t.

Question 51

what is the criteria for the chi-squared test

Answer 51

Can only be used if certain criteria is met:
1- sample size is relatively large. At least 20.
2- data must fall in discreet categories.
3- only raw counts, no %, rates etc. can be used.
4- used to compare experimental results to theoretical results.