Variation and Evolution Flashcards
What does variation mean?
differences between organisms of the same species
What are the 3 categories that are causes of variation?
different genotypes
different epigenetic modifications
different environmental effects
Which causes of variation are heritable?
different genotype
different epigenetic modifications
How can asexually reproducing organisms increase their heritable variation?
mutations of genes
What are the 4 ways that variation can be increased through sexual reproduction?
The crossing over between homologous chromosomes in prophase 1 of meiosis
The random distribution of chromosomes during metaphase 1 of meiosis
THe random ditribution of chromatids at metaphase 2 of meiosis
THe mixing of 2 different parental genotypes at fertilisation
What kind of variation is non-heritable?
different environmental effects
What are the 2 categories of variation?
discontinuous and continuous
What is discontinuous variation?
variation that can be only one state or another, and there are no intermediates. The character states are clear cut and easy to tell apart
What are some examples of discontinuous variation?
eye colour, hair colour, blood group, number of fingers, form of moth (melanic or speckled)
What does monogenic mean?
involving or controlled by a single gene
How can environment effect gene expression?
temperature for Siamese cat if cold causes melanin to be produced in extremities making areas like ears, paws, tail, face black
in early development, external experiences spark signals between neurons, which respond by producing proteins. these gene regulatory proteins head to the nucleus of the neural cell, where they either attract or repel enzymes
What is continuous variation?
can take any value in a given range, These characteristics are controlled by many genes and are therefore polygenic. The environment can influence the expression of these genes and therefore plays a role in determining phenotypic variation
What are some examples of continuous variation?
height, finger length
How is continuous variation data usually presented?
bell curve or normal distribution curve
What is over production?
when a species produce a larger number of offspring than that which can be physically supported by parents or ecosystem that they’re in
Why does population size remain roughly constant?
sunlight availability
food supply
available space
- when an organism uses more than what is available, causes the death of that part of an ecosystem, which in turn leads to death of the species.
What is intraspecific competition?
between individuals of the same species
what is interspecific competition?
between individuals of different species
What are 3 ways gene expression is regulated and results in variation?
Gene mutation
DNA methylation
Histone modification
How does gene mutation cause variation?
it changes what proteins are made
How does DNA methylation cause variation?
more methylated means the gene is less likely to be transcribed, (other genes will begin to emerge)
How does Histone modification cause variation?
adding of acetyl groups means histone is going to be less tightly packed, so protein is more accessible and results in more transcription
What is heritable variation?
a characteristic that can be passed on from parent to offspring through genes like eye colour and hair colour
What is non-heritable variation?
a characteristic that cannot be passed from parent to offspring through genes like tattoos and scars
Is variation imposed by the environment (that doesn’t consist of epigenetic change) heritable or non-heritable?
non-heritable - cannot be transmitted to offspring
What is a selection pressure?
something that puts stress on an organism and can result in decline, unless adaptation occurs - it therefore drives the selection of suitable alleles due to the environment
What does population genetics mean?
study of genetic variation within and among population and the evolutionary factors that explain this variation (allele’s frequency’s , genotypes)
What is selection?
preferential survival and reproduction of individuals with certain genotypes
suitable alleles surviving in an environment
What is a gene pool?
all the genes within a breeding population, (could potentially be inherited)
What is allelic frequency?
the number of alleles in a population, how often they occur. proportion of different alleles in a specific gene pool
What is genetic drift?
the change in frequency of an existing gene variant in the population due to random chance
What are some examples of selective agencies/pressures?
food, space, water and light
What might animals compete for?
intraspecific - competition for a mate (breeding partner)
interspecific - competition for food, territory, water
What is directional selection?
moving towards 1 phenotype, over time frequency of phenotype changes, due to reproduction
What is stabilising selection?
when extremes are removed from a population
What is disruptive selection?
When extremes are selected for in a population
What can the Hardy-Weinberg principle be used for?
calculate the genetic variation of a population
estimate the frequencies of dominant or recessive alleles
estimate the different genotypes of a characteristic
What is the equation used in the Hardy-Weinberg principle?
p^2 + 2pq + q^2
where p = dominant allele
q = recessive allele
What does the p^2 show about a organism in Hardy-Weinberg Principle?
It is homozygous for the dominant allele
what does the pq show about an organism in Hardy-Weinberg principle?
It is a heterozygous genotype
what does the q^2 show about an organism in the Hardy-Weinberg principle?
it is the homozygous for the recessive allele
What are the conditions for the Hardy-Weinberg principle to work?
only 2 alleles for a phenotypic trait
frequencies of alleles must stay the same from generation to generation
What must be in place for the frequencies of alleles to remain the same from generation to generation?
large population
diploid organisms
allele frequencies same for both species
no selection for or against a phenotype
random mating throughout the population
reproduce sexually
no mutations
population is isolated (no immigration or emigration)
What is a population bottleneck?
event that drastically reduces the size of a population only some alleles can be passed on and inherited in the next generation
What is the Founder Effect?
reduced genetic diversity which results when a population is descended from a small number of individuals in a new, isolated population
