3.7 Genetics , populations , evolution and ecosystems (A- level only) Flashcards

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1
Q

what is a genotype?

A

The genetic constitution of an organism.

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2
Q

What is a phenotype?

A

The expression of the genes and its interaction with the environment.

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3
Q

What is a homozygous allele?

A

A pair of homologous chromosomes carrying the same alleles for a single gene.

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4
Q

What is a heterozygous allele?

A

A pair of homologous chromosomes carrying two different alleles for a single gene.

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5
Q

What is a recessive allele?

A

An allele only expressed if no dominant allele is present .

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6
Q

What is a dominant allele?

A

An allele that will always be expressed in the phenotype.

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7
Q

What is multiple alleles?

A

More than two alleles for a single gene.

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8
Q

What is sex - linkage ?

A

A gene whose locus is on the X chromosome.

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9
Q

What is autosomal linkage?

A

Genes that are located on the same chromosome ( not the sex - chromosomes).

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10
Q

What is epistasis?

A

When one gene modifies or masks the expression of a different gene at a different locus.

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11
Q

What is monohybrid inheritance?

A

Genetic inheritance cross of a characteristic determined by one gene.

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12
Q

What is dihybrid inheritance?

A

Genetic inheritance cross for a characteristic determined by two genes .

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13
Q

What is co dominance ?

A

Both alleles are equally dominant and expressed in the phenotype.

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14
Q

What is gene pool?

A

All the alleles of all genes within a population at one time.

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15
Q

What is population ?

A

All the individuals of one species in one area at one time.

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16
Q

What is allele frequency ?

A

The proportion of an allele within the gene pool.

17
Q

What is the Hardy - Weinberg principle ?

A

The mathematical model which can be used to predict the allele frequencies within a population.

18
Q

What is the accuracy / conditions of the hardy - weinberg principle?

A

It assumes that there will be no change in the allele frequency between generations within a population , so it’s not perfectly accurate.

19
Q

What are the assumptions of the hardy - weinberg principle ?

A

• No migration to introduce or removal of alleles from the population.
• No mutations to create new alleles
• No selection favouring particular alleles.
• Mating is random ( no inbreeding)
• The population is large

20
Q

What is the hardy - weinberg equation?

A

p^2 + 2pq + p^2 = 1
p^2 = frequency of homozygous dominant genotype.
2pq = frequency of heterozygous genotype.
q^2 = frequency of homozygous recessive genotype.

p+q= 1
p = frequency of dominant allele
q = frequency of recessive allele

21
Q

What causes variation within a population of species ?

A
  • main source is mutation
  • meiosis (crossing over and independent segregation)
  • random fertilisation
22
Q

What are the three types of selection?

A
  • Stabilising
  • Directional
  • Disruptive
23
Q

What is disruptive selection ?

A
  • Individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles.
  • Allele frequency changes and more individuals possess the allele for the extreme trait.
  • middling trait allele becomes less frequent
  • continued disruptive selection can ultimately lead to speciation
24
Q

What is speciation ?

A

Speciation is the process that results in the creation of new species

25
Q

How does speciation happen?

A

•One original population of the same species becomes reproductively isolated.
•This means that there are now two populations of the same species but they cannot breed together.
• Results in the accumulation of differences in their gene pool

26
Q

What are the two ways that populations can become reproductively isolated ?

A

• Allopatric speciation
- Geographical barrier
• Sympatric speciation
- Changes in the reproduction mechanisms

27
Q

What is sympatric speciation?

A

Populations can become reproductively isolated due to differences in their behaviour

28
Q

How can sympatric speciation occur?

A
  • Due to random mutation which could impact reproductive behaviour such as may cause to perform different courtship behaviour
  • Due to this , individuals will not reproduce together so no gene flow between the two groups within the population
  • Overtime these reproductively isolated populations will accumulate different mutations to the extent that their DNA is so different they can’t interbreed therefore classed as two different species
29
Q

What is genetic drift?

A

This is the change in the allele frequency within a population between generations.

30
Q

What can result in evolution?

A
  • Continuous , substantial genetic drift can result in evolution
  • the smaller the population is the bigger the impact allele frequency have and this is why evolution occurs more rapidly in smaller populations