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Biology > Pack 10 - Genetic Diversity: Mutations, meiosis and adaptation. > Flashcards

Pack 10 - Genetic Diversity: Mutations, meiosis and adaptation. Flashcards

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1
Q

What is a mutation?

A

Any change to the quantity or the base sequence of the DNA of an organism.

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2
Q

What is any change to one or more nucleotide bases, or a change in the sequence of the bases, in DNA known as?

A

A gene mutation.

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3
Q

When can gene mutations arise spontaneously?

A

During DNA replication

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4
Q

What is the type of mutation in which a nucleotide in DNA is replaced by another that has a different base known as?

A

A substitution

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5
Q

Explain how a substitution could lead to an enzyme not functioning.

A
  • Change in nucleotide base will produce a different triplet which may translate to a different amino acid.
  • This will produce a different polypeptide - different bonds formed.
  • Different tertiary structure.
  • The active site does not fit substrate.
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6
Q

Explain how the fact the genetic code is degenerate means a substitution may have no effect on the polypeptide produced.

A
  • The substitution could lead to a triplet that codes for the same amino acid.
  • Same amino acid used - same polypeptide.
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7
Q

What is the type of mutation in which a nucleotide in DNA is lost from the normal DNA sequence?

A

Deletion

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8
Q

Explain how the deletion of a single base can lead to a completely dysfunctional polypeptide.

A
  • Deletion of one nucleotide shifts all subsequent bases.
  • The code is read in triplets, so each subsequent amino acid is different.
  • different bonds - different tertiary structure.
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9
Q

What is a frameshift mutation?

A

The insertion or deletion of a number of bases not divisible by three.

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10
Q

What is the name for the change in the structure or number of whole chromosomes?

A

Chromosome mutation.

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11
Q

What is the name for when organisms have three or more sets of chromosomes rather than two?

A

Polyploidy (mostly in plants)

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12
Q

What is the change in the individual number of chromosomes known as and how does it occur?

A

Non-disjunction - individual homologous pairs of chromosomes fail to separate during meiosis.

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13
Q

How many daughter cells does mitosis produce and how many chromosomes do they have?

A

2; same as the parent cell

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14
Q

How many daughter cells does meiosis produce and how many chromosomes do they have?

A

4; half the number of chromosomes

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15
Q

What is a gamete?

A

A sex cell.

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16
Q

What is the diploid number?

A

The number of chromosomes present in the body cells of an organism.

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17
Q

What is the haploid number?

A

The number of chromosomes present in the gametes.

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18
Q

When is the diploid number restored?

A

When two gametes fuse during fertilization.

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19
Q

Briefly - what happens during meiosis 1?

A
  • Homologous chromosomes pair up and their chromatids wrap around each other - equivalent portions may be exchanged.
  • Homologous pairs separate.
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20
Q

Briefly - what happens during meiosis 2?

A

The chromatids move apart - four cells have been formed.

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21
Q

Give two ways meiosis brings about genetic variation.

A
  • Independent segregation of homologous chromosomes.

- New combinations of maternal and paternal alleles by crossing over.

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22
Q

What is a gene?

A

A length of DNA that codes for a polypeptide.

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23
Q

What is a locus?

A

The position of a gene on a chromosome.

24
Q

What is an allele?

A

One of the different forms of a particular gene.

25
Q

What are homologous chromosomes?

A

A pair of chromosomes that have the same gene loci.

26
Q

Describe what independent segregation is during meiosis 1 and how it leads to genetic variation.

A
  • When homologous pairs arrange themselves they do so at random.
  • One of each pair will pass to each daughter cell.
  • The homologous chromosome pairs line up at the equator independent of each other.
  • Therefore the combination of paternal and maternal chromosomes in the daughter cells is a matter of chance.
  • This produces new combinations of alleles.
27
Q

Explain how random fertilisation leads to variation.

A

Each gamete produced contains different genetic make up. They fuse randomly so produce genetically different and varied offspring.

28
Q

Describe the process of genetic recombination by crossing over in 5 steps.

A
  • During meiosis 1, homologous chromatids pair up and become twisted.
  • During this twisting tensions are created so portions of the chromatid break off.
  • These broken portions might then rejoin with the chromatids of its homologous partner.
  • Usually the equivalent portions of homologous chromosomes are exchanged.
  • New genetic combinations of maternal and paternal alleles are produced within individual chromosomes.
29
Q

When does crossing over occur?

A

Prophase 1

30
Q

What is the process of crossing over? (1 point)

A

Chromatids crossing over many times during prophase 1.

31
Q

What is the process of recombination? (1 point)

A

Broken off portions of homologous chromatids recombine with opposite chromosome.

32
Q

When do homologous chromosomes pair up during meiosis?

A

Prophase 1

33
Q

What is the formula for the number of possible chromosome combinations in an organisms gametes, where n is the number of homologous pairs of chromosomes? - assuming no crossing over.

A

2^n

34
Q

What is the formula for the number of possible chromosome combinations of two organisms offspring, where n is the number of homologous pairs of chromosomes? - assuming no crossing over.

A

(2^n)^2

35
Q

Genetically how do all individuals of a species differ and how are they all the same?

A

They are the same as they posses the same genes. Genome.

They differ as they all have different combinations of alleles for each gene.

36
Q

Define genetic diversity.

A

The total number of different alleles in a population.

37
Q

Define a population.

A

A group of individuals of the same species that can interbreed and live in the same place.

38
Q

Why are species with a greater genetic diversity more likely to survive?

A

The wider the range of alleles the wider the range of characteristics. The greater the probability that some individual will possess a characteristic that enables it to survive an environment change.

39
Q

Define allele frequency.

A

number of individual allele/total number of alleles of that gene

40
Q

What is a gene pool?

A

All the alleles for all gene loci that exist for a specific population at a specific time.

41
Q

Describe natural selection in 7 steps.

A
  • Within a population there is a gene poll with a wide variety of alleles.
  • Random mutation of alleles within the gene pool are mostly harmful
  • Certain ones may give an advantage
  • These individuals will be better adapted and more likely to survive
  • More likely to live longer and reproduce successfully
  • Only individuals that reproduce successfully will pass on their alleles. this new allele is the one that is likely to be passed on
  • Over generations individuals with the advantages allele are more likely to reproduce so its allele frequency will increase. And visa versa.
42
Q

What determines whether an allele is “advantageous”?

A

The current environmental conditions.

43
Q

Define Selection.

A

The process by which organisms better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.

44
Q

What determines selection?

A

The environmental conditions an organism is exposed to at the time.

45
Q

What are the two types of selection? Describe how each effects the characterises of a population.

A

Directional - changes the characteristics of a population.

Stabilising - preserves the characteristics of a population.

46
Q

What are polygenes?

A

Characteristics determined by more than one gene.

47
Q

Which characteristics are more affected by the environment single gene or polygene?

A

polygene

48
Q

What shape do you get when you plot a the variation of a population on a graph?

A

A normal distribution curve.

49
Q

What does selection act upon? What does this have an indirect effect upon?

A

Phenotypes; the inheritance of alleles from one generation to the next

50
Q

Describe directional selection in the context of penicillin resistant bacteria. (6 steps)

A
  • Spontaneous mutation - in allele of a gene of a bacterium enabling the production of penicillinase.
  • The bacteria happened to be in a situation where penicillin was used. Therefore the bacterium had an advantage. (Rest of the population was killed).
  • This bacterium survived and so divided leading to a small penicillin resistant population.
  • This population is more likely to survive and therefore multiply than others.
  • This population increased at the expense of non-resistan bacteria. Therefore ALLELE FREQUENCY increased.
  • NDC shifts in the direction of greater resistance to penicillin.
51
Q

What is the original penicillin resistance caused by?

A

A chance mutation

52
Q

Why are mutations not always advantageous? When are they?

A

They can cause death. When the environment gives the allele an advantage.

53
Q

In stabilising selection which individuals are more likely to pass on their alleles?

A
  • Phenotypes closest to the mean.
54
Q

In stabilising selection which individuals are selected against?

A

Phenotypes that are extreme

55
Q

Explain why stabilising selection occurs in terms of birth mass.

A
  • Babies with high or low birth mass are selected against as they die and their alleles aren’t passed on so frequency decreases.
  • Babies with mass closer to the mean are selected for -characteristic is preserved.
56
Q

Natural selection results in species that are better adapted to their environment. What three types of adaptation may occur?

A

Anatomical - e.g. thick fur
Physiological - e.g. kangaroo rats oxidising fat rather than carbohydrate to produce edition water.
Behavioural - e.g. migration of swallows to avoid food shortage.

Biology (18 decks)

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