BY5.5 - Variation And Evolution Flashcards
What is Continuous Variation?
A characteristic controlled by MANY GENES (POLYGENIC EFFECT) shows GRADUAL CHANGE in the population from one extreme to another E.g Height
What is discontinuous variation?
A characteristic controlled by ONE OR TWO GENES which shows CLEAR CUT DIFFERENCES in the POPULATION Eg tongue rolling
What is Non- heritable variation caused by and what is it responsible for?
The ENVIRONMENTAL FACTORS that cause CONTINUOUS VARIATION
How does Inherited Variation cause genetic changes?
Crossing over - during prophase 1 Random Assortment - metaphase 1 Random fusion of haploid gametes Mutation
What is the gene pool?
All of the alleles within a population
What is Population Genetics?
The relative proportions of the various genotype a or allele frequency present in a population
what is the Gene Pool?
All of the alleles within a population within a population
What is evolution?
the process by which new species are formed from pre-existing ones over a period of time
How did Darwin develop his theory of natural selection?
He recognised the species changed
Organisms overproduce offspring
there is a large variation of genotypes due to gene mutation
However, numbers in the population remain constant
therefore there is a high mortality rate
changes to environmental conditions bring new selection pressures
e.g competition,predatation, disease
Individuals with beneficial alleles have a selective advantage and are more likely to survive
they then reproduce
offspring inherit beneficial alleles –> characteristics,
repeat generation after generation
beneficial allele frequency increases within the gene pool/
What is adaptive radiation?
the evolutionary diversification of many species
from a single common ancestor
why has antibiotic resistance arisen?
Random mutations produce recessive alleles coding for antibiotic resistance and are not expressed when in combination with a dominant allele
repeated exposure to antibiotics causes more bacteria to survive and pass on recessive alleles
some bacteria have developed a gene codes for penicillinase synthesis, which causes penicillin to be ineffective
in the presence of penicillin non resistant bacteria are destroyed, therefore there is a selective advantage favouring resistant bacteria.
What are populations?
Groups of interbreeding individuals of the same species
occupying the same habitat
What is a species?
A group of organisms that can interbreed to produce fertile offspring
And do not normally interbreed with any other group of organisms
Why are hybrids infertile?
different diploid no. of chromosomes
not homologous chromosomes
cannot form bivalents during meiosis prophase 1
Meiosis does not take place - no gametes produced
what name is given to breeding sub-units within populations?
Demes
When do new species arise?
when a barrier to reproduction occurs
called the isolating mechanism
Which prevents genes being exchanged between two demes
What is Allopatric isolation?
The population is physically split
preventing interbreeding between 2 demes
e.g. river
what is sympatric isolation?
when organisms inhabiting the same area are unable to reproduce
Name and describe the 4 types of sympatric isolating mechanisms:
1) reproductive isolation - different flowering times
2) Mechanical isolation - Incompatible genetalia
3) Behavioural isolation - courtship behaviour not attracting other deme
4) Hybrid inviability - development of embryo does not occur
How do new 2 new species arise from 1 old one?
1) populations become isolated
2) different mutations arise in each population –> different alleles
3) different environmental conditions in each population
4) different selection pressures
5) different gene pools develop
6) causes changes in phenotype
What are the different factors which can alter the frequency of genes in a population?
1) Mutation
2) Natural Selection
3) Genetic Drift
what is genetic drift?
variation occurring in the gene pool due to chance
How is genetic drift different to Natural Selection?
In Natural Selection, allele frequency changes due to a selective advantage,
whereas genetic drift occurs due to chance
What is the Founder Effect?
a type of genetic drift occurs when a small group from a populations colonises a new area
because the genotype of the individuals in the colony is random it can lead to reduction in genetic diversity
reduces the size of the new populations gene pool
result = genetic bottleneck
