4B: Natural Selection Flashcards

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1
Q

Describe the steps involved in Meiosis

A

After interphase, a reproductive cell undergoes meiosis’s. In humans, this results in 4 haploid cells, each with half the number of chromosomes as the parent cell.
Meiosis 1: chromosomes carrying the same genes pair up and then are separated into 2 daughter cells
Meiosis 2: Sister chromosomes move apart to form a new pair of daughter cells

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2
Q

Main differences between Mitosis and Meiosis?

A

Mitosis involves 1 division whilst meiosis involves 2
Mitosis produces 2 genetically identical daughter cells whilst meiosis produces 4 genetically different cells
Mitosis produces Diploid cells, meiosis produces haploid cells

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3
Q

What is independent segregation?

A

In meiosis, homologous pairs of chromosomes line up opposite each other at the equator of the cell. It’s random which side of the equator the maternal and paternal chromosomes line up. The pairs are separated so one of each homologous chromosomes end up in the daughter cell

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4
Q

What is crossing over?

A

Chromatids can become twisted around each other. Tension on the chromatid causes some of it to snap and fall off. Where they break off, they can recombine on the opposite chromatid creating a new combination of alleles.

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5
Q

Explain how a mutation can result in new alleles of a gene

A

Many mutations are harmful but in certain environments the new allele might benefit its processor leading to reproductive success. Advantageous alleles are inherited by members of the next generation. Over many generations new alleles are increased in the population frequency

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6
Q

what are the three causes of mutations?

A

Deletion, addition and substitution of bases

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7
Q

What type of substance can increase the rate at which mutations occur

A

Mutagenic agents

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8
Q

What is the percentage difference in the amino acid sequence between mammals and insects?

A

33%

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9
Q

How are gene technologies used to study genetic diversity

A

Allow the alleles in an individual to be directly measured
Allow genetic diversity to be directly measured for example the number of different alleles for a gene and the number of individuals with each allele directly shows the genetic diversity

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10
Q

What statistical measures should be used to ensure accurate results when investigating variation?

A

Random sampling
Calculating the mean
Standard deviation

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11
Q

When does crossing over occur?

A

Prophase I

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12
Q

What is genetic diversity?

A

The degree of variation in the genes that exist in a certain population

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13
Q

What are genes?

A

Multiple versions of genes

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14
Q

2 ways in which genetic diversity is increased

A

Mutations
Gene flow ( introduction of new alleles by migration)

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15
Q

What is evolution

A

A change in the allle frequency over time

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16
Q

What is selection pressure?

A

An external factor that influences the reproductive success of an individual

17
Q

What environment does stabilising selector take place in?

A

Non-changing

18
Q

What are the 4 principles of natural selection?

A

Mutations are spontaneous
Changes in allele frequency
Some mutations are beneficial
Genes are inherited by offspring

19
Q

What phenotype in favoured in bacterial populations that are expressed to antibiotics?

A

Antibiotic resistance

20
Q

What does natural selection favour in stabilising selection?

A

average phenotype

21
Q

Explain the steps of natural selection

A

1 new alllels for a gene are created by random mutations
2 If the new allele increases the chance of that individual surviving then they are more likely to survive and reproduce
3 This reproduction passes on the advantageous allele to the next generation
4 As a result over many generations the new allele increases in frequency in the population

22
Q

Describe what happens to chromosomes in meiosis (6 marks)

A
  1. Chromosomes condense
  2. Chromosomes associate in homologous pairs
  3. Crossing over and a chiasma forms
  4. Joins to spindle fibres
  5. At the equator
  6. Homologous chromosomes move to opposite poles
  7. Chromatids separated in 2nd division
23
Q

How to we calculate the number of possible different combinations of chromosomes following meiosis?

A

2^n

24
Q

Describe and explain the processes that occur during meiosis that increase genetic variation

A
  1. Homologous chromosomes pair up
  2. Independent segregation leading to maternal and paternal chromosomes are reshuffled in any combination
  3. Crossing over leads to the exchange of alleles between homologous chromosomes
  4. Creating a new combination of alleles
  5. Random fertilisation of haploid gametes creates genetic variation between zygotes
25
Q

What does the term ‘Bivalent’ mean

A

consists of two homologous chromosomes one from each parent aligned closely together. Allows for the exchange of genetic material between the chromosomes via chiasma formation

26
Q

Random assortment?

A

The random organisation of chromosomes during the first stage of meiosis increasing genetic diversity