Aqa a level Biology topic 7

What is a dominant allele?

Allele which is always expressed in the phenotype even when theres only one copy of it

What are recessive alleles?

Alleges that only appear in the phenotype if 2 copies are present

What are codominant alleles?

Alleles that are both expressed in the phenotype because neither one is recessive

If an organism carries two copies of the same allele it said to be ........

Homozygous at the locus

If an organism carries two different alleles it is said to be......

Heterozygous at that locus

What is mono hybrid inheritance?

Inheritance of a characteristic controlled by a single gene

What do monohybrid crosses show?

The likelihood of the different alleles of that gene being inherited by the offspring of certain parents

What type of offspring would a monohybrid cross with 2 homozygous parents produce?

Will always produce all heterozygous offspring

What is a phenotypic ratio?

The ratio of different phenotypes in the offspring

What is the usual phenotypic ratio you would get if you did a monohybrid cross with two heterozygous parents?

3:1 ratio of dominant:recessive characteristics

What ratio would you expect to see if you did a monohybrid cross with 2 heterozygous parents involving codominant alleles?

1 : 2 : 1

What is dihybrid inheritance?

The inheritance of 2 characteristics which are controlled by different genes.

What can dihybrid crosses show?

The likelihood of offspring inheriting certain combinations of two characteristics from particular parents

What phenotypic ratio would you expect to see if you did a dihybrid cross with 2 heterozygous Parents?

9 : 3 : 3 : 1 dominant both : dominant first, recessive second : recessive first, dominant second : recessive both

What does sex linked mean?

The alleles that code for them are located on a sex chromosome

Which sex chromosome carries most genes?

X chromosome

Which gender is more likely to to express the characteristic of sex linked genes? Why?

Males- they have one X chromosome so they only have one copy of the allele, they expressive it even if it's recessive

What are two x linked disorders ?

Colour blindness and haemophilia

Why can't males be carriers of X-linked disorders?

Because they only have one copy of each chromosome so if they have the allele they have the disease whether is recessive or not

What is an autosome?

any chromosome that is not a sex chromosome

What are genes on the same autosome said to be? Why?

Linked - they'll stay together during the independent segregation of chromosomes in meiosis 1 and their alleles will be passed on to their offspring together

What can cause autosomal genes not to stay together during independent segregation ?

If crossing over splits them up first

What is independent segregation?

The random division of homologous chromosomes into separate daughter cells during meiosis

If two genes are autosomally linked, what ratio would you expect to see and why?

3 : 1 because the 2 autosomally linked alleles are inherited together

What is epistasis?

A phenomenon when the genotype of one gene can mask the effects of a separate gene

What happens if the epistatic allele is recessive?

Two copies of it will mask the expression of the other gene

In recessive epistasis alleles , if you cross a homozygous recessive parent with a homozygous dominant parent what phenotypic ratio would you get in the F2 generation?

9 : 3 : 4 dominant both : dominant epistasic, recessive other : recessive epistatic

What happens when the epistatic allele is dominant?

Having at least one copy will block the expression of the other

What is the chi-squared test?

Statistical test that's used to see if the results of an experiment support a theory

what are the 5 steps in the chi- squared test?

Theory

Expected results

Observed results

Null hypothesis

Chi-squared test

What is the null hypothesis

Is always " there is no significant difference between the observed and expected results"

What is the formula for the chi squared value?

The sum of = (O-E)2 / E. O = observed result E = expected result

If the chi squared value is larger or equal to the critical value then .................. the null hypothesis

Reject

If the chi squared value is less that the critical value then .................. the null hypothesis

Fail to reject the null hypothesis

What is a species?

A group of organisms that can interbreed and produce fertile offspring in nature

What is a population?

A group of individuals of the same species living in the same area at the same time.

What is a gene pool?

Is the complete range of alleles present in a population

What is the hardy- Weinberg principle?

Mathematical model that predicts the frequencies of alleles in a population won't change from one generation to the next

What is the allele frequency and what's the equation?

The total frequency of all possible alleles for a characteristic in a certain population. Is always 100% 1.0 .

P+q = 1. P = the frequency of one allele q = the frequency of the other allele

What is the genotype frequency and the equation?

The total frequency of all possible genotypes for one characteristic in a certain population is 1.0 (100%)

P2+2pq+q2 = 1 P2=frequency of homozygous dominant genotype 2pq= frequency of heterozygous genotype q2 = frequency of homozygous recessive genotype

What conditions need to be met for the hardy Weinberg principle to be true?

Large population with no immigration , emigration, mutations or natural selection

Random mating

What is intraspecific variation?

Any difference between individuals of the same species

What factors can cause variation?

Genetic or environmental factors

Which 2 things can evolution occur by?

Genetic drift, natural selection

What are selection pressures?

Pressures that affect an organisms chances of survival such as predation, disease and competition

What are the 3 types of natural selection?

Stabilising selection

Directional selection

Disruptive selection

What is stabilizing selection?

Selection against the extremes (for the averages)

What is directional selection?

Extreme phenotype more likely to survive

What is disruptive selection?

Favors individuals at both extremes of the phenotypic range

What is speciation?

The formation of a new species from an existing species

When does speciation occur?

When geographic or reproductive isolation prevents members of two populations from interbreeding.

What is geographical isolation?

Individuals in a species become separated because of a physical barrier such as earthquake or flood

What is allopatric speciation?

The formation of a new species in populations that are geographically isolated from one another and have slightly different climate

What is sympatric speciation?

formation of a new species without the presence of a geographic barrier , occur when random mutations prevent individuals from breeding

Which 3 changes cause reproductive isolation?

Seasonal changes

Mechanical changes

Behavioural changes

What is genetic drift?

A change in allele frequencies caused by random events

Why can genetic drift be a problem for small populations?

Because it may cause species to be lee able to adapt to future environmental changes

What is an ecosystem?

all of the living and nonliving things interacting in an area

What are biotic conditions?

Living features of an ecosystem

What are abiotic conditions?

Non living features of an ecosystem

What is a habitat?

The place where an organism lives

what is a niche?

Is the role of a species wi5in it's habitat what it eats, where and when it feeds.

What happens if 2 species try to occupy the same nice?

They will compete with eachother and one will be more successful

What is an adaptation?

A trait that helps an organism survive and reproduce

What is the population size?

Total number of organisms of one species in a habitat

What is the carrying capacity?

Maximum stable population size of a species that an ecosystem can support

What happens if abiotic conditions aren't ideal?

More energy will be needed to maintain eg body temp

What is interspecific competition?

When organisms of different species compete with eachother for the same recourses

What is intraspecific competition?

When organisms of the same species compete with eachother for the same recourses

Explain how intraspecific competition can cause cyclical change in population size around an eco systems carrying capacity

Because population of species grows when resources are plentiful which leads to more organisms competing so eventually the resources become limited again , and if the population grows beyond the carrying capacity there won't be enough resources so the population decreases

What is predation?

An interaction in which one organism kills another for food.

What is a broth culture?

A liquid broth containing bacteria

A broth culture with a high absorbable value has a ........... number of bacteria present

High

What is a spectrophotometer?

Measures amount of light passing through a sample

What does an exponential graph show?

Doubling In number at regular intervals

What does abundance of species mean and how is it calculated?

The number of individuals of one species in a particular area , estimated by counting the number of individuals in samples taken

What are the 2 methods of measuring abundance ?

Frequency- the number of samples a species is recorded in

Percentage cover- how much of the area you're investigating is covered by a species

What is distribution?

Where a particular species is within the area you're investigating

What are the methods for investigating populations and what are they used for?

Quadrets and transacts- non motile organisms

Nets and traps- motile organisms

What is a quadrat?

A square frame enclosing a known area divides into grids of 100

What are the advantages and disadvantages of using quadrets?

Advantage- useful for quickly investigating areas with plant species that fit within it

Disadvantage- areas with larger plants and trees would need very large quadrets

What is a belt transect?

Quadrets are placed next to eachother along the transect (line) to work out species frequency and percentage cover along it

What is an interrupted belt transect?

Quadrat placed at regular intervals

What is the mark release re capture method?

Used to measure abundance of motile species by capturing a small sample marking them releasing them and take a second sample a week later to see how many marked are caught

What equation would you use to work out the total population size in the mark release recapture method?

No. Caught in 1st sample x no. Caught in 2nd / no. Marked in 2nd sample

Which 3 assumptions does the accuracy of mark release and recapture count on?

- the marked sample has had enough time and opportunity to mix back in

- the marking hasn't affected the individuals chance of survival

- there are no changes in population size due to births, deaths, migration

What does dynamic mean?

constantly changing

What is succession?

when one community completely replaces another over time in a given area

What is primary succession?

succession that occurs on surfaces where no soil exists

What are pioneer species?

Species such as lichens that are the first to colonize the new area.

How does primary succession work?

Pioneer Species grow and die changing the environment so it is better for the next species until more complex ecosystem is built

what is climax community?

relatively stable community that results from a long period of plant and animal succession.

What is secondary succession?

after a major disturbance in an area that already has soil and once had living organisms

What does phlagioclimax mean?

When succession is stopped artificially by human activities

What is a climax community?

A stable group of plants and animals for a particular climate

What is conservation?

the protection of natural resources

What does sustainable mean?

Enough resources are taken to meet the needs of people today without reducing the ability of people in the future to meet their own needs

What are the 5 main conservation methods?

Management of succession

Seed banks

Captive breeding

Fishing quotas

Protected areas