Variation and Evolution and Genetics

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  • Created by: Ruhab21
  • Created on: 08-10-20 01:14
Why is variation important to the survival of an organism?
In natural selection, variation increases the chances of survival by providing a selective advantage to changes in environment
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What are the 3 factors that cause variation?
Different environments
Organisms have a different genotype
Same genotype but different epigenetic modifications
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What type of variation can be affected by environmental factors?
Continuous variation
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In what case is variation non inheritable?
If the variation is caused by an environmental factor
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How could an environmental factor lead to an epigenetic change?
One's diet alters DNA methylation or histone acetylation so it changes the expression of the genes
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How might genetic variation be increased by sexual reproduction?
Crossing over in Prophase 1
Independent Assortment in Metaphase 1 and 2
Random fusion of gametes
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How might new alleles be produced in heritable variation?
Mutations
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What is the gene pool?
The total of all alleles for all the genes in a population
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If a recessive allele displayed a selective disadvantage, would it disappear from the gene pool? Why/why not?
No it wouldnt because heterozygotes wouldnt display the disadvantageous characteristic
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What are selection pressures?
Environmental factors which can alter the allele frequencies of the alleles present at a particular gene locus in a population
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Give some examples of selective agencies
Human impacts, climate, food supply, breeding sites
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What does the Hardy-Weinberg principle state?
The frequencies of dominant and recessive alleles and genotypes will remain constant from one generation to the next, providing certain conditions remain true.
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Why is it unlikely that the Hardy-Weinberg principle can be applied in actuality?
Mutations and emmigration/immigration occur
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Define evolution
The change in the average phenotype of a population over time
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Explain the theory of natural selection
1) Variation occurs in a population due to mutations
2) Competition increases the struggle for survival
3) The fittest have a selective advantage due to survival pressures so they survive, breed and pass on the advantageous allele
4) The process repeats o
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What occurs is the average phenotype is disadvantageous in the two types of natural selection ? (Directional and Stabilising)
It is selected against but the direction selection could go towards either extreme. Over generations, both values are selected for so the population curve has two peaks
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What are the breeding sub units in one species called and what do the individuals have in common?
Demes
Share distinct gene pools
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When does speciation occur?
When demes become isolated resulting in genetic drift
Natural selection
The founder effect of disproportionate allele frequencies in small populations
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Why does the prevention of the flow of genes between demes result in allopatric speciation?
The gene pool divides and each deme undergoes different mutations and selection pressures. The gene pools become so different that interbreeding is impossible.
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Give an example of a fertile hybrid and describe how it managed to survive
1)Common wheat
2) Endo mitosis means the chromosome number doubles without cytokinesis so the early embryo does have two of each chromosome, allowing for meiosis
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What is the founder effect?
When a new area is colonised by individuals from a population, the new gene pool may have different allele frequencies than the original gene pool BY CHANCE.
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Give an example of gametic isolation
Spermatozoa can only survive in the oviduct of the same species and wont fuse with an incompatible egg
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Describe morphological isolation and give an example
When the body parts of organisns are incompatible for mating e.g. insects with rigid exoskeletons need complementary genatalia
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What is the difference between hybrid sterility and hybrid inviability?
Inviability; fertilisation could occur but imcompatible parental genes prevent the development of the embry

Sterility; a hybrid embryo survives but its sterile. It cant produce gametes due to an odd number of chromosomes, therefore it cant form paired ho
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How might the seasons result in speciation?
Different mating seasons
Reproductive organs maturing at different times in the year
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Other cards in this set

Card 2

Front

What are the 3 factors that cause variation?

Back

Different environments
Organisms have a different genotype
Same genotype but different epigenetic modifications

Card 3

Front

What type of variation can be affected by environmental factors?

Back

Preview of the front of card 3

Card 4

Front

In what case is variation non inheritable?

Back

Preview of the front of card 4

Card 5

Front

How could an environmental factor lead to an epigenetic change?

Back

Preview of the front of card 5
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