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Biology A Level > Genetics, Populations, Evolutions & Ecosystems > Flashcards

Genetics, Populations, Evolutions & Ecosystems 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 the definition of a phenotype?

A

The expression of the genotype and its interaction with the environment (Set of characteristics an organism has depends on genotype + environment)

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3
Q

What is an allele?

A

Alternative forms of the same gene

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4
Q

What is a gene?

A

A length of DNA which codes for a particular protein occupying a specific locus on a chromosome

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5
Q

What is a locus?

A

The position of a gene on a chromosome

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6
Q

What is Multiple alleles?

A

This is when one gene has more than 2 possible alleles

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7
Q

In a diploid organism, how many alleles does each genotype have?

A

2, one from the female and one from the male at fertilisation

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8
Q

What does it mean for an allele to be dominant?

A

It will be expressed in the phenotype, 1 present for expression – represented as an uppercase letter

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9
Q

What does it mean for an allele to be recessive?

A

It won’t be expressed in the phenotype, so 2 copies present for expression – lowercase letter

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10
Q

What are Co dominant alleles?

A

This is when alleles are equally dominant and equally expressed in the phenotype

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11
Q

What are genetic diagrams used for?

A

To predict the genotypes and phenotypes off the offspring produced if the parents are bred

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12
Q

When are monohybrid crosses used?

A

When considering the inheritance of one characteristic

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13
Q

What are test crosses used for?

A

To determine an unknown genotype

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14
Q

How would you conduct the test to find an unknown genotype and explain the results?

A

Cross the unknown with a homozygous recessive individual

  • If all offspring have dominant phenotype, the unknown genotype is homozygous dominant
  • If half of the offspring have the recessive phenotype, the unknown genotype is heterozygous
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15
Q

What is a dihybrid cross?

A

This is the inheritance of 2 characteristics

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16
Q

What is Autosomal Linkage?

A

This is the inheritance of genes that are located at different loci on the same chromosome. The genes are on autosomes (not sex chromosomes).

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17
Q

What process can occur during autosomal linkage?

A

As the genes are on the same chromosome, crossing over can occur when the homologous chromosomes are in a bivalent

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18
Q

The closer the 2 genes are to each other…(autosomal linkage)

A

The less likely crossing over is to occur

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19
Q

What is the chiasma?

A

The point where crossing over occurs

20
Q

What are the additional phenotypes that appear due to crossing over called?

A

Recombinants

21
Q

What is Sex Linkage

A

This refers to genes found on the sex chromosomes

22
Q

What 2 chromosomes do females have?

A

XX

23
Q

What 2 chromosomes do males have?

A

XY

24
Q

Explain the difference between X and Y?

A

Y is considered genetically empty and usually the genes are on the X chromosome in humans

25
Q

Why are males more likely to show recessive phenotypes?

A

This is because males only have 1 X chromosome, so they only require one copy of the recessive allele for expression. Females have 2 X chromosomes, so must inherit 2 recessive alleles to be affected and is less likely to happen

26
Q

What is a carrier?

A

A person carrying an allele which is not expressed in the phenotype but can be passed on to the offspring

27
Q

What is Epistasis?

A

This is when one gene affects or alters the expression of another

28
Q

What is recessive Epistasis?

A

2 copies required to mask expression of hypostatic gene

29
Q

What is Dominant Epitasis?

A

Expression of dominant allele (1 or 2) of epistatic gene masks expression of hypostatic gene

30
Q

What does the term gene pool mean?

A

The total number of genes of every individual in an interbreeding population

31
Q

What does allele frequency mean?

A

How often an allele occurs within a population

32
Q

What is the Hardy Weinberg Principle?

A

Mathematical model which predicts allele frequencies will not change from gen to gen meaning there will be no genetic change in the population over time

33
Q

What assumptions are the hardy Weinberg principle based of?

A
  • Mating is random
  • No natural selection takes place
  • No mutations
  • No gene flow / genetic drift
  • Population is large
34
Q

When is the equation used?

A

When one gene with 2 alleles, one dominant and one recessive is being considered

35
Q

What is the formula of the H.W.P

A 
p2 + 2pq + q2 = 1
p = freq of dominant allele
q = freq of recessive allele
2pq = freq of heterozygote
p2 = freq of homozygous dominant
q2 = freq of homozygous recessive

REMEMBER = p + q = 1

36
Q

What is evolution?

A

This is when the frequency of alleles changes in a population from 1 gen to the next

37
Q

What are the 2 factors that affect / cause allele frequency to change?

A
  • Natural Selection

- Genetic Drift

38
Q

What is Natural Selection?

A

‘Survival of the fittest’, individuals with alleles that give them a selective advantage reproduce more than others in the population, increasing the frequency of the favourable allele.

39
Q

What is genetic drift?

A

This is the effect of a few individuals that, by chance, fail to reproduce or have more offspring than others…thus changing the allele frequency in the next generation. This has a more pronounced effect in small populations

40
Q

What are the 3 types of selection?

A
  • Directional
  • Stabilising
  • Disruptive
41
Q

What is directional selection?

A

Occurs in a changing environment

  • One extreme in a range of the phenotype is at a selective advantage
  • Over time this feature becomes more common and the unfavourable characteristic becomes rare
  • Mode changes/standard deviation reduces
  • Antibiotic resistance in bacteria, peppered moth
42
Q

What is stabilising selection?

A
  • Occurs in an unchanging environment
  • Selection is against individuals at both extremes of the characteristic
  • Mode stays the same / standard deviation reduces
  • Birth weight in humans
43
Q

What is disruptive selection?

A
  • Occurs when the individuals with both extremes of the phenotype are selected for, those in the middle of the range are selected against
  • Banded snail, where pale and dark are more likely to survive than those with an intermediate colour
44
Q

What is speciation?

A

This is the development of new species from pre-existing ones by natural selection

45
Q

What are the 2 types of Selection?

A
  • Allopatric

- Sympatric

46
Q

Explain the process of speciation?

A
  • Reproductive isolation of part of the population from the rest of it
  • So part of the population is unable to interbreed with the rest of the population…no gene flow between the isolated groups
  • Over time the gene pools of the two groups will accumulate differences, as natural selection (and genetic drift) operates on the 2 separate parts of the population.
  • Eventually a point may be reached when the 2 parts of the population cannot interbreed to produce fertile offspring… a new species has formed from a pre-existing one.
47
Q

Explain the process of Natural Selection?

A

1) Genetic Variation in the population due to random mutations which produce new alleles of a gene
2) Selective pressure – due to competition, predation and disease
3) Differential survival + reproduction – individuals best suited = more likely to survive = reproduce and pass on favourable alleles to next generation
4) Evolutionary change – the gene pool of the population changes from one gen to the enxt; frequency will increase over time of favourable alleles

Biology A Level (7 decks)

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