6.2 variation Flashcards
Define genotype.
The genetic makeup of an organism.
Define phenotype
The observable characteristics of an organism
What is a dominant allele?
An allele that will always be expressed.
What is a recessive allele?
An allele that will only be expressed if two copies are present.
What does homozygous mean?
The same alleles
What does heterozygous mean?
different alleles
What is continuous variation?
Variation that has no distinct categories and no limit to the value. It is mostly quantitative.
What are examples of continuous variation?
- Height
- weight
- heart rate
- finger length
- leaf length.
How can continuous variation be represented?
By a line graph.
What is discontinuous variation controlled by?
Few genes
What is continuous variation controlled by?
Multiple genes as well as the environment.
What is discontinuous variation?
Where there is a distinct categories with no in between values, the data tends to be qualitative.
Were examples of discontinuous variation?
- Tongue rolling
- eye colour
- fingerprints
- blood group.
How can discontinuous variation be represented
On a bar graph.
What does polygenic mean?
It is controlled by many genes.
What does monogenic mean?
It is controlled by one gene.
What are the causes of genetic variation?
- alleles
- mutations
- meiosis
- sexual reproduction
- chance
What is phenotypic variation affected by
The environment.
What is chlorosis?
When there is a lack of chlorophyll in a plant, it is caused by environmental factors such as a mineral deficiency, lack of light or viral infection.
What is etiolation?
Where plants grow abnormally long and spindly due to not enough light
How is genetic variation created in crossing over during meiosis?
The non sister chromatids twist around each other and swap allels. This means that they contain the same genes, but different alleles
How does independent assortment create variation in meiosis?
The chromosomes align along the metaphase plate randomly during metaphase. 1. from each pair is passed onto each daughter cell.
How is genetic variation created during random fertilisation?
Any sperm is able to fertilise any egg, which means each individual is unlikely to have the existed before or again.
What is monogenetic inheritance
Inheritance that it controlled by a single gene.
What is dihybrid inheritance?
The inheritance of two characteristics controlled by different genes.
what is autosomal linkage?
where gene loci are located on the same autosome so stay together and don’t assort independently during meiosis, meaning they are often inherited together
what are examples of 2 sex linked diseases?
- Hemophilia A
- Colour Blindness
what is hemophilia A?
- recessive sex-linked trait found only on the X chromosome
- where blood can’t clot fast enough
what is colour blindness?
- the inability to distinguish between red and green
- a recessive sex-linked trait found only on the X chromosome
what is sex-linkage?
Where a gene is present on only one sex chromosome. This means a sex-linked disease will disproportionately affect one sex.
how can sex linkage be identified?
- Punnett squares
- pedigree diagrams
why are males more likely to have recessive sex-linked diseases?
They only have one X chromosome so if the gene is on the X chromosome they are more likely to inherit the recessive allele.
when are recombinant genes more likely to form?
when 2 gene loci are further apart on the same chromosome
what are the 4 blood groups?
- A
- B
- AB
- O
what is epistasis?
gene masking
- when the allele of one gene effects the expression of another
what are the 2 types of epistasis?
- antagonistic
- complementary
how can regulatory genes be affected by epistasis?
Transcription factors can upregulate or down regulate another gene
how can structural genes be affected by epistasis?
an enzyme that works in conjunction with an enzyme made from another gene, in a series of steps in a metabolic pathway, can mask the effect
when does epistasis occur?
when 2 genes on different chromosomes affect the same feature.
what 2 types of gene can epistasis effect?
- structural
- regulatory
what is antagonistic epistasis?
where one gene inhibits/blocks the expression of another
what are the 2 types of antagonistic epistasis?
- recessive
- dominant
what is complementary epistasis?
Where two genes work together, so if one gene isn’t expressed the whole pathway can be affected. This means at least one dominant allele of both genes is needed to get one phenotype.
what is the epistatic gene?
the gene doing the suppressing
what is the hypostatic gene?
the gene being expressed
what is recessive antagonistic epistasis?
Where the epistatic gene must have 2 recessive alleles to mask/suppress the hypostatic gene.
what is the phenotypic ratio for the F2 generation in recessive antagonistic epistasis?
9:3:4
what is the phenotypic ratio for the F2 generation in dominant antagonistic epistasis?
12:3:1
what is dominant antagonistic epistasis?
where the epistatic gene must have at least 1 dominant allele to suppress/mask the hypostatic gene
what is genetic diversity?
the genetic differences between individuals within a population, in term of alleles
what is allele frequency?
how often a particular allele occurs in a population
what is directional selection?
where individuals are favoured in 1 direction only
what is stabilising selection?
where the average individuals are favoured because there is no selection pressure.
what is a genetic bottle neck?
There is an original population, large numbers die leading to a reduced population with some alleles lost. Reproduction continues but the new population has greatly reduced genetic diversity.
what is the founder effect?
When only a small number of individuals from a large parent population start a new population, there will be reduced alleles and genetic diversity.
what is genetic drift?
the idea that characteristics are passed on by chance rather than factors that affect the individuals ability to survive and reproduce
when might the founder effect occur?
Birds migrating from the mainland to an island so that they are isolated from the original population.
what could happen in the founder effect?
- Mutations could create new alleles that become more common, creating 2 very different popualtions.
- inbreeding
- previously masked alleles being expressed
what is a gene pool?
the range of alleles within the population
what is the Hardy-Weinberg Principle?
A way of predicting the proportion of dominant and recessive alleles in a population provided that the population is isolated, mating is random and no mutations arise.
what are the equations for the Hardy-Weinberg principle?
allele frequency:
p+q=1.0
pheno/genotype:
p^2 +2pq+ q^2=1.0
What are some problems with selective breeding?
- health problems
- exaggerate certain characteristics
- reduce genetic diversity/gene pool so more susceptible to genstic diseases, potentially useful alleles lost
What are some ethical problems to selective breeding?
- domestic animals are more docile so can’t defend themselves
- livestock are more lean so are more susceptible to cold
- inbreeding means more susceptible to disease
- colour of coats loses camoflauge
What is the process of artificial selection?
You breed two organisms with the desired characteristics. then you select the offspring that also have this cut characteristic and breed them. You repeat this process.
What characteristics should you also consider when artificially selecting animals?
LINK TO EXAMPLE GIVEN
e.g.
- quality of produce
- calm temperament
- production period
What factor should you also consider when artificially selecting plants?
- resistance to abiotic factors
- uniform size
- high yield
- short stalks so are strong
Compare artificial to natural selection.
Artificial:
- faster
- few features selected
- humans choose
- non-random mating causes change
Natural:
- slower
- all features selected
- characteristics best suited to environment are chosen
- change is due to selecting for/against pheonotypes
what are introns?
non-coding regions of DNA
What are exons?
coding regions of DNA
What is speciation
The development of a new species occurs when populations of the same species become isolated. The change in allele frequency leads to a change in phenotype so they can no longer interbreed.
What are the two types of speciation?
- allopatric
- sympatric
What is allopatric speciation?
where geographic isolation causes 2 populations to have separate gene pools. Eventually allele frequencies will differ and the 2 populations will no longer be able to interbreed successfully.
What is Sympatric speciation?
where there is no geographical isolation, so speciation occurs due to reproductive isolation.
