Level 2 Bio: Genetic Variation Flashcards
Allele
Different form of a gene
What is allele frequency
A measure of the relative frequency of an allele in a population
Asexual reproduction
Reproduction only involving one parent, creates genetically identical offspring (no genetic variation)
Chiasma
The point on a chromosome where crossing over takes place
Homologous pair
A pair of matching chromosomes, containing the same genes, one from each parent
Gamete
Sex cell (sperm or egg)
Recessive allele
An allele only expressed when there is no dominant allele present
Homozygous
The genotype has 2 alleles the same (e.g BB)
Mutation
A sudden permanent change in the DNA base sequence
Mitosis
Cell division, producing 2 genetically identical daughter cells, occurs in body. Purpose is growth & repair. Full number of chromosomes
Meiosis
Cell division producing 4 genetically different daughter cells, creates gametes, occurs in sex organs, half number of daughter cells.
Sexual Reproduction
Type of reproduction, 2 parents, uses gametes, producing genetic variation in the offspring
Zygote
Cell formed when a sperm cell fuses with an egg cell.
Fertilisation
The process when the sperm cell fuses with the egg cell to form a zygote.
Dominant allele
An allele which will be expressed even if only one is present in genotype (e.g Bb)
Gene
A section of DNA that codes for a set protein and therefore a trait
Chromosome
A strand of DNA, which contains genes
Phenotype
The expression of the genotype as a visible trait
Heterozygous
The genotype with 2 different alleles (e.g Bb)
Semi-conservative
Each double DNA strand is composed of one new and one old strand
Carrier
An individual that has inherited a gene but does not display the trait
Genotype
The 2 alleles, the alleles you carry
Trait
A characteristic that is inherited (e.g eye colour)
Variation
Survival of a species through meiosis, a difference in base sequence between individuals
Haploid
A cell with half the number of chromosomes (n)
Nucleotide
A unit made up of a base, a sugar and a phosphate (base block of DNA)
DNA
A double helix shaped chemical which carries genetic information (instruction to build an organism)
Diploid
A cell with a full set of chromosomes (2n)
What is a source of variation
Meiosis
What are 4 ways of variation through Meiosis
1) Segregation
2) Independent assortment (influence on dihybrid inheritance)
3) Crossing over (recombination of alleles)
4) Linkage (Influence on dihybrid inheritance)
Homologous chromosome
Two matching chromosomes with same genes found in same loci (locus/location)
Sister chromatid
1 half of a replicated chromosome
Centromere
The area when the sister chromosomes are linked
How many rounds of cell division are there (meiosis)
2
What happens in meiosis 1 & how many chromosomes are there
Meiosis 1 separates the homologous pairs. The cell has 46 chromosomes
What happens in meiosis 2 & how many chromosomes are there
Meiosis 2 separates the chromatids. The cells now have 23 chromosomes. (4 daughter cells now have 23 chromosomes)
What does the DNA do when the cell is not dividing
The DNA is unwound & forms chromatin (unwound DNA)
What is recombinant chromosomes
Chromosomes that have exchanged sections of genes resulting in genetic variation.
What are the key points of crossing over
It can occur during Meiosis 1 when the two homologous chromosomes are lined up.
Some genetic info can be swapped from one chromosome to the other.
This breaks up the gene combinations that used to be inherited together.
Gametic variation increases due to new mixes of genes.
What does crossing over occur between and what does this mean
Crossing over occurs between “non sister” chromatids. This means that one chromatid must be on one of the homologous chromosomes and the other chromatid must be on the other chromosomes in the homologous pair.
Chiasma
Chiasma is the point on the chromosome where crossing over takes place
Recombinant Chromatid
Chromatids that have swapped some genes.
What is a summary of crossing over
It is where homologous chromosomes swap some genes.
It creates new combinations of alleles that are not seen in either parent.
Genes closer to the tips of the chromosomes are more likely to undergo crossing over.
What is Independent assortment & segregation and what does it mean
When homologous pairs line up in the middle of the cell, they line up randomly. It means that if you get your mum’s or dad’s chromosome from the homologous pair, it is completely random.
What is independent assortment a source of and what does it mean
Independent assortment is a source of variation as each gamete can have any combination of chromosomes. Meaning each gamete is unique & contains a different set of alleles to other gametes produced. This means every offspring will also be unique.
Genome
The total collection of genes possessed by an organism
What are the advantages of A-sexual reproduction?
Population can increase rapidly, only one parent needed, it is more time and energy efficient and it is faster than sexual reproduction.
What are the disadvantages of A-sexual reproduction?
No genetic variation, species only suited to one habitat and disease may effect the whole population
What are the advantages of sexual reproduction?
It produces genetic variation, the species can adapt to new environments, a disease is less likely to affect the whole population
What are the disadvantages of sexual reproduction?
It takes longer because a mate must be found, then the egg must be fertilised and then the offspring has to develop.
If the 2 alleles are dominant the GENOTYPE is:
HOMOZYGOUS DOMINANT
If the 2 alleles are RECESSIVE the GENOTYPE IS:
HOMOZYGOUS RECESSIVE
If the 2 alleles are different the GENOTYPE is:
HETEROZYGOUS
How do you answer questions in the exam?
-Define (terms)
-Explain
What is natality
The ratio of the number of births to the size of the population; birth rate.
What is mortality
The ratio between deaths and individuals in a specified population and during a particular time period
What is a gene pool
A gene pool is defined as all the ALLELES present in a population at any one time
What is allele frequency
The frequency of an allele is the proportion of that allele in a population in relation to all the alleles of the same gene.
What does a mutation create (in terms of alleles)
A mutation creates new alleles
You can get changes in allele frequencies through:
1) Mutation: New alleles.
2) Gene flow: genes can be exchanged with other gene pools.
3) Small population size & genetic drift: genes easily lost from gene pool.
4) Natural selection: Only best suited alleles survive.
5) Non-random mating: Choosing mates-selected alleles get passed on.
What is gene flow
Gene flow is the movement of genes into or out of a population (immigration (in) and emigration (out)).
What may a population do in relation to gene flow
A population may gain or lose alleles through gene flow.
What does gene flow tend to do in relation to differences between populations.
Gene flow tends to REDUCE THE DIFFERENCES BETWEEN POPULATIONS because the gene pools become more similar.
What are the 2 factors that affect gene pools
1) Population size
2) Mate selection
What are the key points on how ‘population size’ affects gene pools
1) Bigger is better
2) Bigger range of genes
3) Less likely to lose a gene or allele type from the gene pool.
4) More potential for variation
What are the key points on how ‘Mate selection’ affects gene pools
1) RANDOM= better
2) Get more variation of genes
3) SELECTED= less variation because individuals are being picked of their ‘good’ traits.
4) Some genes may be lost over time
What are the problems with low genetic variation
1) Inbreeding
2) Sperm abnormalities
3) Decreases fecundity (ability to reproduce)
4) High mortality due to proneness to sickness
5) Sensitivity to disease
What is a summary of migration
New individuals can bring new alleles into a population (IMMIGRATION), or rare alleles can be removed from the population when individuals leave (EMMIGRATION). Both of these will change the allele proportions in the gene pool. The movement of alleles between populations is called GENE FLOW. Usually gene flow between two populations causes them to remain genetically similar.
Definition of gene flow
The movement of alleles between populations.
What is evolution
Evolution is the change in characteristics of living things over long periods of time. It occurs in populations not individuals.
What are the 2 main points on evolution
1) ORGANISMS CHANGE OVER TIME. Life on earth has changed as descendants have diverged from common ancestors.
2) Evolution occurs by natural selection.
What is the process of Natural selection
Natural selection is the process by which living things with beneficial traits produce more offspring than others.
What is natural selection
Natural selection is where the best suited phenotypes (adapted organisms) survive. Also known as ‘survival of the fittest’.
What do the individuals with best suited phenotypes do (natural selection)
The individuals with phenotypes best suited will survive, reproduce and pass on their genes, while the least suited die out and their genes may get lost from the gene pool.
What does natural selection do over time
This Natural selection over time will cause a change in the allele frequency.
What are the 3 types of natural selection
1) Stabilizing
2) Directional
3) Disruptive
What does stabilizing selection do
Stabilizing selection REDUCES VARIATION by selecting against the extremes at each end of the phenotypic range.
What does stabilizing selection favour
Stabilizing selection favours the most common phenotype as the best adapted.
Before stabilizing selection=???
Before Stabilizing selection= A broad range of variation
After stabilizing selection=??
After stabilizing selection= A reduction in the amount of variation.
What does directional selection favour
Directional selection favours the phenotypes at one extreme of a phenotypic range
What is an example of directional selection
Fossil evidence shows that the average size of black bears in Europe increased with each ice age, & decreased again during the interglacials.
Before directional selection=???
Before directional selection= A broad range of variation in the population.
After directional selection=??
After directional selection= A reduction in variation at one extreme of the range.
What does disruptive selection favour
Disruptive selection favours phenotypes at both extremes of a phenotypic range.
When may disruptive selection occur
Disruptive selection may occur when environmental conditions are varied or when the environmental range of an organism is large.
Before disruptive selection=??
Before disruptive selection= A broad range of variation in the population
After disruptive selection=???
After disruptive selection= Individuals at both extremes of a phenotypic range are favoured.
What do many populations of animals do (Mate selection)
Many populations of animals do not choose their mates randomly. Mates may be chosen based on size, colouration displays & courting individuals etc.
What does mate selection cause
Mate selection causes change in gene pools as some individuals are selected for & others against.
What do mutations cause instantly?
Mutations cause instant variation in a GENE POOL (all the alleles or genes in a population). They create NEW ALLELES.
A change in ___ BASE ___________= different protein made=________ GENOTYPE=__________ DIFFERENT _________.
A change in DNA BASE SEQUENCE= different protein made= DIFFERENT GENOTYPE= POTENTIALLY DIFFERENT PHENOTYPE.
What is a beneficial mutation
Some mutations/new alleles and therefore phenotypes are beneficial to the individual. If this occurs, they will breed this new allele into the gene pool. E.g antibiotic resistance in bacteria (they have mutated to create their resistance).
What is a harmful mutation
Some mutations/new alleles and therefore phenotypes are harmful to individuals.
What are 3 reasons why a harmful mutation won’t be bred into the gene pool
1) Individuals die due to the mutation
2) Individual is hampered in its ability to catch prey/hide/run etc
3) Trait is not seen as desirable, so does not find mate to pass genes on to offspring.
What is a neutral mutation
Some mutations do not actually change the making of certain proteins, so is silent.
What do neutral mutations do
Neutral mutations do not change anything in the individual therefore do not affect them.
What are the 3 types of mutation
1) Beneficial mutation
2) Harmful mutation
3) Neutral mutation
What is genetic diversity
The differences between the genes/alleles of individuals
What is genetic drift
Genetic drift is the random changes that may occur in a population due to death or not finding a mate.
(Genetic drift) It is not that the individual can’t physically ______ (they can have offspring), but rather that they just don’t.
It is not that the individual can’t physically breed (they can have offspring), but rather that they just don’t.
What might genetic drift do to a small inbreeding population
In small, inbreeding populations, genetic drift may have pronounced effects on allele frequencies. Alleles may become:
1) Lost from the gene pool (frequency 0%)
2) Fixed as the only allele present in the gene pool (frequency 100%)
How does genetic drift affect Large gene pools?
Large gene pool: Breeding populations high (2000), fluctuations are minimal, because large numbers of individuals buffer the population against large changes in allele frequencies.
How does genetic drift affect small gene pools?
Small gene pool: Breeding population low (200). fluctuations are more severe because random changes in a few alleles cause a greater percentage change in allele frequencies.
How does genetic drift affect very small gene pools?
Very small gene pool: Breeding population very low (20), fluctuations are so extreme that the allele may become fixed (100%) or lost altogether (0%).
What is the founder affect
Occasionally, a small number of individuals may migrate away or become ISOLATED from their original population.
What will a founder population have of a parent populations gene pool and what is a consequence of the founder effect.
This COLONIZING or FOUNDER population will have a small and probably no-representative sample of alleles from the parent population’s gene pool. As a consequence of this FOUNDER EFFECT, the colonizing population may EVOLVE in a different direction than the parent population.
What are smaller founder populations subject to
Small founder populations are subject to RANDOM GENETIC DRIFT.
What is a summary of the founder effect
A SMALL NUMBER OF INDIVIDUALS colonize a new areas. The alleles they carry may NOT BE A FAIR REPRESENTATION of the original population. Rare alleles may become common, some others may be eliminated entirely in the new population.
Allele frequency
proportion of that allele in a population in relation other alleles.
What is the bottleneck effect
This is where majority (90%) of the population is lost (killed). This usually means 90% (etc) of the gene pool is also lost. The population then has a lack of genetic diversity.
Bottleneck effect leads to: (4 things)
1) Low population
2) Low genetic diversity
3) Higher inbreeding
4) Higher chance of death, disease, abnormalities due to lack of alleles.
Some populations have been subjected to events that have ALMOST _________ THEM ___ e.g disease, drought, flood, fire, climatic changes. As in the founder effect, the small number of individuals may NOT BE A REPRESENTATIVE SAMPLE of the original alleles. This can cause ‘________ _______’.
Some populations have been subjected to events that have ALMOST WIPED THEM OUT e.g disease, drought, flood, fire, climatic changes. As in the founder effect, the small number of individuals may NOT BE A REPRESENTATIVE SAMPLE of the original alleles. This can cause ‘GENETIC DRIFT’.
Occurs when a population becomes reduced to low numbers due to human action or catastrophic environmental effects.
Population bottleneck
Type of selection where selective pressures act against one extreme of a trait
Directional selection
Produces a change in the frequency of the alleles due to chance rather than by selection pressure
Genetic drift
A measure of the different genetic combinations in a gene pool.
Genetic biodiversity
The transfer of alleles (genes) from one population to another.
Gene flow
Considered to be the father of evolutionary theory
Charles Darwin
Type of selection caused by selective pressures acting against the median phenotype
disruptive selection
Name for the type of migration where individuals enter a population from another population
immigration
Occurs when a small number of individuals emigrate from a population, or become geographically isolated from their original population.
founder effect
Occurs when humans select for breeding particular individual from a population based on a certain characteristic (size, shape, colour etc)
artificial selection
The change in characterises of living organisms over long periods time.
evolution
A measure of the incidence of a particular allele in a gene pool.
allele frequency
Type of selection where selective pressures act against the two extremes of a trait
stabilising selection
Name for the process by which beneficial variations in a population tend to be preserved while unfavourable variations tend to be lost.
natural selection
A length of DNA that contains the code for one particular characteristic
gene
Name for the type of migration where individuals leave a population.
emigration
A mechanism for evolution caused by a change in the base sequence of an individuals DNA
mutation
The total number of genes of every individual in a a specific population
gene pool
What does the F1 mean
The F1 (first, filial) generation consists of all the offspring from the parents
What is a pedigree chart
A diagram that depicts the biological relationships between an organism and its ancestors
What is pure breeding
A group of identical individuals that always produce offspring of the same phenotype when interbred.
What is segregation
The process that occurs during meiosis where pairs of alleles are separated when the homologous chromosomes split
What is selective pressure
Can take many forms, including environmental conditions, availability of food and energy sources, predators, diseases, and even direct human influence. The selective pressure means that animals that don’t have these characteristics are less likely to survive and reproduce due to natural selection.
What are somatic cells
Body cells (e.g skin cells) if a mutation occurs in these cells it will not be passed on to offspring.
What is a test cross
A genetic cross between a homozygous recessive individual and a corresponding suspected heterozygote to determine the genotype of the suspected heterozygote.
