Chapter 14 Flashcards

1
Q

Reasons for variation: Random assortment

A

Random assortment of chromosomes during meiosis = large number of possible combinations of chromosomes.

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2
Q

Variation: Crossing over

A

Of chromatids during meiosis = parts of chromatids attaching to different chromatids - changed sequence of alleles.

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3
Q

Variation: Non-disjunction

A

1 or more members of chromosomes pair fail to separate during meiosis.

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4
Q

Variation: Random fertilisation.

A

Infinite numbers of possible combinations of alleles in the offspring.

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5
Q

Variation: Mutations

A

Permanent changes in the DNA of a chromosome = totally new characteristic.

Changing the allele frequency.

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6
Q

Natural selection?

A

Process by which species become adapted to its environment - selection of favourable, strong genes

Having a survival advantage, passing their characteristics onto future generations

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7
Q

Random genetic drift?

A

Random, non-directional variation in allele frequencies
Due to chance events
Most powerful in small, isolated populations
Religious groups

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8
Q

Example of random genetic drift

A

“Dunkers”

  • USA, originally from Germany
  • no marriage outside their group, no interbreeding (religious beliefs)
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9
Q

Founder effect

A

When a small group moves away from homeland, establishing a new community that tends to expand

Their allele frequencies do not reflect the gene pool of the original population

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10
Q

Migration

A

Gene flow = movement from one population to another

If immigrants to certain country bring alleles that aren’t already in the population, frequency of alleles of that gene are altered

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11
Q

Two main barriers to gene flow?

A

Geographical - oceans, mountain ranges, deserts

Sociocultural - language, education and social/economic status

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12
Q

Genetic disease?

A

Allele causing inherited disease (fatal) would eventually fade from population as those with the allele die and therefore don’t pass on their gene.

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13
Q

Examples of genetic diseases: Tay-Sachs

A

Hereditary disease, occurring most frequently in those with Jewish descent
Worldwide: low, 1 : 500,000
Ashkenazi Jews: high, 1 : 2,500

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14
Q

Tuberculosis and Tay-Sachs

A

Heterozygous carriers of Tay-Sachs have an increased resistance to tuberculosis
As of discrimination, Jews were found in ghettos (isolated) which therefore began to decrease the spread or the disease as heterozygous carriers survived and reproduced

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15
Q

Examples of genetic diseases: Thalassaemia

A

Anaemia resulting from defects to haemoglobin, high frequency in people of a Mediterranean descent

Only marrying each other, isolating themselves

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16
Q

Examples of genetic diseases: Sickle cell anaemia

A

Mainly occurs in those of black African ancestry
Results in sickle shaped RBC’s
Unable to carry as much O2 so they stick and clot together

17
Q

What’s the difference when you only have the sickle cell trait?

A

Mild sickling

Has a certain advantage: providing resistance to malaria

18
Q

What is evolution?

A

Gradual change in the characteristics of a species overtime

19
Q

Darwin’s theory: based on three observations

A
  1. Variation - variation within a species, but similar characteristics within a family
  2. Birth rate - all living organisms reproduce at a greater rate than their available food supply (overcrowding)
  3. Nature’s balance - although birth rate is high, number of species remain relatively similar (survival of the fittest, struggle for existence)
20
Q

Struggle for existence and survival of the fittest

A

Darwin concluded their must be a struggle for existence and those with characteristics best suited are more likely to survive (survival of the fittest)

21
Q

Examples of natural selection in humans:

Short body, long limbs
Long body, short limbs

A

Long body, short limb: smaller surface area, smaller heat loss in cold environments (Inuits)

Short body, long limb: increased surface area, larger heat loss in hot environments (Black Africans)

22
Q

Examples of natural selection in humans:

Sickle-cell anaemia

A

People with the sickle cell trait have a resistance to malaria
They survive, reproduce, therefore their characteristics are passed on

23
Q

Speciation steps

A
  1. Variation
  2. Isolation
  3. Selection
  4. Speciation
24
Q

Speciation steps 1. Variation

A

Range of variation (mix) in an ordinary population

Sharing common gene pool

25
Q

Speciation steps 2. Isolation

A

Barrier is formed (e.g. geographical)
Divides population in half, no interbreeding
Forming a separate gene pool

26
Q

Speciation steps 3. Selection pressures

A

Change in gene frequencies

Leads to the evolution of separate subspecies

27
Q

Speciation steps 4. Speciation

A

Changes in gene frequencies may be great enough to prevent interbreeding between the two populations
Two species now exist

28
Q

Gene flow?

A

Migration

Whole bunch of genes come in, changing the make up of a population

29
Q

6 steps of evolution through natural selection:

A
  1. Variation within species.
  2. Ability to reproduce then they can raise to maturity.
  3. Excessive birth rate/limited resources ➡️ struggle for existence, survival of the fittest.
  4. Individuals with suited characteristics survive better ➡️ survival of the fittest.
  5. Favourable characteristics are passed down.
  6. Proportion of alleles that produce favourable characteristics gradually increases.
30
Q

Summary of natural selection, 6 steps (remember)

A

Variation within a species
More offspring produced than what can survive
Excessive birth rate, limited resources -> struggle for existence
Individuals with favourable characteristics pass on their traits to future generations -> survival of the fittest
Favourable characteristics increase in a gene pool

31
Q

Natural selection?

A

Those individuals who have favourable characteristics; have more chance of survival (survival of the fittest)
Pass on their traits to future generations