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A Level Biology Paper 1 > Section 4 - Chapter 9 : Diversity > Flashcards

Section 4 - Chapter 9 : Diversity 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 is known as a mutations
  • Mutations occuring during the formation of gametes can be inherited
  • Any change to one or more nucleotide bases, or a change in the sequence of the bases, in DNA is known as a gene mutation - this can happen spontaneously during DNA replication and include base substitution and base deletion.
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2
Q

What are the 3 types of mutation

A
  • Deletion
  • Substitution
  • Addition (Insertion)
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3
Q

What is a base substitution

A
  • The type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
  • Less impact than deletions and additions: will differ in an amino acid.
  • The significance of the difference will depend on the precise role - may not form the same bonds - different shape, non-functional.
  • No change if the new triplet codes for the same amino acid - degenerative
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4
Q

What are examples of mutagenic agents

A
  • UV radiation, ionizing radiation, chemicals some viruses
  • These mutagenic agents increase the probability of a mutation occuring
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5
Q

What are the 2 types of chromosome mutation

A
  • Changes in whole sets of chromosomes - organism have 3 or more sets of chromosomes rather than 2 - polyploidy (occurs mostly in plants)
  • Changes in the number of individual chromosomes - sometimes individual homologous pairs fail to separate in meiosis. The offspring have fewer or more chromosomes than normal. Down Syndrome
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6
Q

EXAM QUESTION: A mutation can lead to the production of a non-functional enzyme. Explain how

A
  1. Change/mutation in base/ nucleotide sequence (of DNA/gene)
  2. Change in amino acid sequence (primary structure)
  3. Change in hydrogen/ ionic/ disulfide bonds
  4. Change in tertiary structure
  5. Change in active site
  6. Substrate not complementary/ can’t bind no enzyme-substrate complexes form.
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7
Q

What is the importance of meiosis

A
  • During sexual reproduction gametes give rise to a new offspring. If each gamete had a “full” set (diploid) then the offspring would have 92 (this doubling would continue) To maintain chromosome numbers the number must be halved haploid - occurs in meiosis
  • Every diploid cell has 2 complete sets of chromosomes (parents). During meiosis homologous pairs separate so that only one chromosome from each pair enter the daughter cell (haploid number)
  • When 2 haploid cells fuse, diploid number is restored
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8
Q

What does diploid and haploid mean

A
  • Haploid: When a cell contains one copy of each chromosome
  • Diplod: When a cell contains 2 copies of each chromosome (1 from each parent)
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9
Q

What are the 2 types of cell division

A
  • Mitosis: Produces 2 daughter cells with the same number of chromosomes as the parent cell
  • Meiosis: Usually produces 4 daughter cells, each with half the number of chromosomes as the parent cell
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10
Q

What is the process of meiosis of the first division (also including interphase)

A
  • Interphase - DNA replicating, cell growth, organelles increase. Replicated chromosome is an x of 2 sister chromatids
  • Prophase I: Nuclear envelope disintegrates, spindles form, homologous chromosomes pair up (bivalent) and crossing over occurs creating new combinations of alleles
  • Metaphase I: Homologous chromosomes line up along the equator via spindle fibres. Independent assortment and segregation = creates unique combination of maternal and paternal chromosomes in gametes
  • Anaphase I: HC pairs pulled apart, spindle fibres contract pulled to opposite poles of the cell
  • Telophase I: Nuclear envelope reform
  • Cytokinesis: 2 daughter cells with 1/2 chromosome number. Cytoplasm divides
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11
Q

What is the process of meiosis (meiosis 2)

A
  • Prophase II: Nuclear envelope disintegrates, spindle fibres reform
  • Metaphase II: chromosomes line up in the equator by spindle fibres
  • Anaphase II: Separation of sister chromatids
  • Telophase II: Nuclear envelope reforms
  • Cytokinesis: Half chromosome - ends eith 4 genetically different gametes
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12
Q

How does meiosis bring genetic variation

A
  • Independent segregation of homologous chromosomes
  • New combinations of maternal and paternal alleles by crossing over
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13
Q

EXAM QUESTION: Meiosis results in cells that have the hapoid number of chromosomes and show gentic variation. Explain how. (6)

A
  1. Homologous chromosomes pair up/ bivalent form
  2. Crossing over/ chiasmata form
  3. Produces new combination of alleles
  4. Chromosomes separate (segregate)
  5. At random (random segregation)
  6. Produces varying combinations of chromosomes/ genes/ alleles
  7. Chromatids separated at meiosis 2 later
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14
Q

What is independent segregation of homologous chromosomes

A
  • One of each pair of chromosomes will pass to each daughter cell. Which one goes into the daughter cell and any other pair depends on how the pairs are lined up in the parent cell.
  • Since the pairs are lined up at random, the combination of chromosomes of maternal and paternal origin that go into the daughter cell is chance - independent segregation
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15
Q

The chromosomes line up alongside its homologous partner What is genetic recombination by crossing over and what are the events

A
  • The chromatids of each pair become twisted around one another
  • During the twisting process tensions are created and portions of the chromatids break off
  • These broken portion might then rejoin with the chromatids of its homologous partner
  • Usually it is equivalent portions of homologous chromosomes that are exchanged
  • In this way new genetic combinations of maternal and paternal alleles are produced
    • The chromatids cross over one another many times - crossing over
    • The broken off portions recombine wiyth another chromatid - recombination
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16
Q

How do you calculate the number of possible combinations of chromosomes for each daughter cell

(independent segregation and random assortment)

A
  • 2n where n is the number of pairs of homologous chromosomes
17
Q

Variety is further increased through the random pairing of male and female gametes. 2 different genetic complements with different alleles are combined. How do you calculate possible chromosome combinations when egg and sperm fuse

A
  • (2n)2where n = pairs of homologous chromosomes
18
Q

EXAM QUESTION: a) Why is the genetic code described as universal

b) The genetic code uses 4 bases. What is the maximum number of different DNA triplets that can be made using these 4 bases

A

a) Because the same triplet codon codes for the same amino acid in all organisms
b) 64

19
Q

EXAM QUESTION: The deletion mutation occurs. Describe how mutation alters the structure of the gene

A

Removal of 1 or more bases, causes a nucleotide frameshift

20
Q

What is Genetic Diversity and what does this mean

what is population

A
  • Is the total number of different alleles in a population
  • The greater the number of different alleles in a species the greater the genetic diversity.
  • Genetic Diversity is reduced when a species has fewer different alleles. The greater the genetic diversity, the more likely that some individuals will survive an environmental change. Wider range of characteristics. Gives a higher probability that some will possess a characteristic suited to the environment
  • A population is a group of individuals of the same species that live in the same place and can interbreed.
21
Q

What are Species and Gene Pool

A
  • Organisms that can reproduce and produce fertile offspring - they have the SAME genes but different alleles
  • Gene Pool - Total number of alleles (of all genes) in a given population. The larger the gene pool = more variety of alleles - greater diversity
22
Q

How can Genetic Diversity be increased

A
  • Mutations - forming new alleles
  • Different alleles being introduced into a population when individuals from other populations migrate into it and reproduce
23
Q

How can Genetic Diversity be reduced

A
  • Genetic Bottle Neck effect
  • Big reduction in the population (disease/ natural disaster) - reducing numbers/ variety of alleles in the gene pool
  • The founder effect - when a few individuals from the original population start a new colony (few alleles in the new gene pool)

E.g Amish Population descended from a small number of Swiss

24
Q

What is Natural Selection in the evolution of populations

A
  • Not all alleles in a population are equally likely to be passed on
  • This is because only certain individuals are reproductively successful and therefore pass on their alleles
  • Some phenotypes are more favourable than others due to variation
25
Q

What is the process of Reproductive Success and Allele Frequency

A
  • Change in the environment causes a selection pressure
  • Random mutations of alleles within the gene pool produce genetic diversity
  • Some alleles provide an advantage over others in the population.
  • Those individuals willbe more adapted to gain resources and survive and reproduce
  • Advantageous alleles are passed on
  • Over many generations the frequency of advantageous alleles in the population increases
  • The frequency of the desired characteristic increases
26
Q

EXAM QUESTION: Some antibiotics bind with specific receptors in the plasma membrane of bacteria

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in 1 bacterium

A
  1. Frequent use of antibiotic creates a selection pressure/ antibiotic kills bacteria
  2. Bacteria with random mutation/ resistance have selective advantage over others
  3. Survive to reproduce more than other types/ pass on advantageous allele/ mutated in greater numbers
  4. Frequency of advantageous allele increases in subsequent generations
  5. Frequency of resistant types increases in subsequent generations
27
Q

What is Selection

A
  • Selection is the process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.
  • Every organism is subjected to this process, based on sutiability for surviving the conditions. Different environmental conditions favour different characteristics
28
Q

What are the different types of selection and what is the type of curve called that plots variation on polygenes (more than 1 gene) with the environment

A
  • Selection may favour individuals that vary in one direction from the mean of the population. - Directional Selection and changes the characteristics of the population
  • Selection may favour average individuals. - Stabilising Selection and preserves the characteristics of a population
  • Most characteristics are influenced by more than 1 gene. These characteristics are influenced by environment . The effect of environments produces individuals to vary about the mean. Normal Distribution curve
29
Q

What is Directional Selection

A
  • Favouring individuals with alleles for characteristics of an extreme phenotype are more likely to survive and reproduce
  • whose characteristics vary from the mean.
  • Phenotypes are selected for. Genotypes are indirectly selected
  • Example antibiotics and the resistance in bacteria
30
Q

EXAM QUESTION: What is Stabilising Selection

A
  • Occurs in an unchanging environment
  • Selection against extremes/ selection for the mean, median and mode
  • The range/ Standard Deviation is reduced
  • Increasing proportion of population becomes well adapted to the environment
  • For example human birth weight.
    • Too small = large surface area to volume ratio - hard to maintain body temp
    • Too big = hard to fit in mum’s pelvis. Medium = best.
31
Q

What are the diffferences between Directional and Stabilising Selection

A
  • Directional - favours the extreme phenotype. Stabilising = favours the average individuals
  • Directional = environment changes. Stabilising = environment stays the same
  • Directional = mean changes - graph shifts. Stabilising = mean preserved, higher and narrower
  • Directional = Increase in allele frequency at either extremes (middle less likely to survive). Stabilising = Increase in allele frequency around the mean (extremes less likely to survive)
32
Q

Natural Selection results in species that are better adapted to the environment. What types of adaptations may this be

A
  • Anatomical - shorter ears/thick fur
  • Physiological - Oxidising of fat rather than carbohydrates to produce additional water
  • Behavioural - migration of swallo to avoid food shortages

A Level Biology Paper 1 (15 decks)

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