Biology Unit 4.4 - Variation and Evolution Flashcards
Explain variation and evolution…
If a species is to survive in a constantly changing environment sources of variation are essential
How does sexual reproduction cause variation?
Produces genetic variation amongst individuals in a population:
* Crossing over during chiasmata produces new combinations and seperation of linked genes
* Chromosomes arrange themselves randomly on the spindle and seperate independently, so daughter cells contain different combinations
* Random distribution of chromatids at metaphase II
* Chromosome making up a homologous pair carries different genetic material
What is continuous variation?
Characteristics controlled by the number of genes, where differences are not clear cut e.g.,:
* Height
* Weight
* Hand span
* Length of feet
* Milk yield
What is discontinuous variation?
Characteristics that are clear cut and easy to tell apart, which are controlled by a single gene
What is non-heritable variation?
Phenotypic variation caused by environmental factors
What are the methods of creating variety?
- Prophase I - crossing over at chiasmata during synapsis where genetic material can be exchanged
- Metaphase I - random independent assortment of chromosomes along the equator
- Metaphase II - random independent assortment of chromatids along the equator
What is continuous data?
Data containing a ranger, where a T-test is used to compare means
What is discontinuous data?
Data consisting of disctint categories, where a Chi-squared test is used to compare expected and observed results
What environmental factors control population?
Biotic:
* Predation
* Parasitism
* Disease
* Competition
Abiotic:
* Natrual disaster
* Temperature
* pH
* Light intensity
What is intraspecific competition?
Compeition for resources between members of the same population or species
What is intraspecific competiton?
Competition for resources between members of different species within the same community
What is selection pressure?
Factor whis has a direct effect on the numbers of individuals in a population e.g., food supply, nesting sites and climate
What are the effect of mutations on adaptation?
New genes can appear in a species by mutation which may lead to fantastic adaptations to the environment
What is a gene pool?
Sum of all the different genes in a population, where the frequency of any given allele is known as the allele or gene frequency
What factors change allele frequency?
Environmental changes:
* Allele specific mortality or emigration
* Allele specific reproduction or immigration
* Chance
May cause some phenotypes to be selected for while others are selected against, leading to some alleles becoming more or less frequenct while others are totally lost
What is the Hardy-Weinberg principle?
The frequencies of dominant and recessive alleles and genotypes will remains contant from one generation to the next if:
* Population is large
* No selection for or against a particular phenotype
* Random mating
* No mutations
* Population is isolated
How can the Hardy-Weinberg principle be applied?
Demonstartes that a large proportion of recessive allels exist in the heterozygotes, meaning they are a reservoir for genetic variability
What is the Hardy-Weinberg equation?
p2 + 2pq + q2 = 1
p +q = 1
What is genetic drift?
Chance increases or decreases in allele frequencies over time, which has the greatest effect within small or isolated populations
Why is the frequency of the sickle-cell anemia allele still high?
Heterozygous advantage, as heterozygous individuals are less susceptible to malaria, but homozygous individuals are very susceptible to malaria
What is the origin of species?
Species are groups of closely related organisms that can interbreeding and produce fertile offspring, which often have morphological similarity
How is speciation caused by isolation?
Population is split into ateast two isolated populations with no gene exchange between the two, leading to mutation and natural selection occuring independently allowing for evolution into new species
What is allotropic isolation?
Isolation where a physical barrier prevents two population form mating and interbreeding
What is sympatric isolation?
Isolation where organisms inhabitating an area are seperated/becom reproductively isolated into two groups due to non-georgaphical reasons
What is hybdrid sterility?
Different species, which are related, can reproduce, but this leads to the production on infertile offspring
What is the cause of hybrid sterility?
The parent species have different chromosome numbers of, so they can’t produce viable gametes as chromosomes are not homologous and cannot form bivalent during prophase I of meiosis
Describe Charles Darwin’s theory of evolution?
- Reproduction leads to overproduction of offspring
- Not all offspring survive, so population number remains fairly constant
- Selection pressures are harsh but help maintain a constant population number
- Variation due to sexual reproduction, mutations and meiosis confer selective advantages and disadvantages to the offsrping, where high genetic variation is key to a species’ surivial
- Better adapted offsping have a selective advantage and are more likley to survive, while those less well adapted are more likley to die
- Offspring inherit beneficial characteristics from their parents, which is repeated every generation, causing organisms to become highly adapted to their environment
- Gradual changes overtime, may lead to the formation of a new species
