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Biology AS > Genetic Variation > Flashcards

Genetic Variation Flashcards

1
Q

Diploid

A
  • When there is two of each chromosomes

- Normal body cells have a diploid number of chromosomes and they are made during mitosis

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2
Q

Homologous Pair

A
  • Chromosomes that have the same genes at the same loci/position
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3
Q

Gametes

A
  • Haploid, there is only one of each chromosome
  • These are sperm cells in males and egg cells in females, that fuse together in fertilisation to form a diploid zygote
  • They are made during meiosis
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4
Q

Meiosis Summary

A
  • Before it starts DNA unravels and replicates so there are two copies of each chromosome called chromatids
  • DNA condenses and the sister chromatids are joined by a centromere
  • In meiosis 1 the chromosomes arrange into homologous pairs and cross over occurs then they are separated, halving the chromosome number
  • In meiosis 2 the pairs of sister chromatids, which make up each chromosome are separated when the centromere divides
  • Four haploid cells (gametes) that are genetically different from each other are produced
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5
Q

Mitosis vs Meiosis

A

Mitosis

  • One division which separates sister chromatids
  • No crossover or independent segregation of chromosomes so it produces genetically Identical daughter cells
  • Two daughter cells produced
  • Daughter cells are diploid, have the same number of chromosomes as the parent cell

Meiosis

  • Two divisions, first separate homologous pairs of chromosomes then sister chromatids
  • Cross over and independent segregation produces genetically varied daughter cells
  • Four daughter cells produced
  • Daughter cells are haploid, containing half the number of chromosomes as parent cells
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6
Q

Interphase 1 [meiosis]

A
  • DNA unwinds and DNA helicase breaks the hydrogen bonds between the bases
  • The chromatids replicate at the end of interphase
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7
Q

Prophase 1 [meiosis]

A
  • DNA condenses so chromosomes become visible, as they are fatter and shorter
  • Cross-Over: homologous pairs of chromosomes come together and pair up and the chromatids cross over each other, the point of crossing is called a chiasmata.
  • The chromatids still have the same genes but now with a different combination of alleles causing genetic variation
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8
Q

Metaphase 1 [meiosis]

A
  • Chromosomes line up in the middle

- Spindle fibers attach to the centromere (middle) of chromatids

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9
Q

Anaphase 1 [meiosis]

A
  • Chromosome pairs split when the spindle fibers contract
  • Independent Segregation: separation of chromosomes is random so the two daughter cells produced have different combinations causing genetic variation
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10
Q

Telophase 1 [meiosis]

A
  • Produces two daughter cells
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11
Q

Metaphase 2 [meiosis]

A
  • Sister chromatids line up in the middle of the cell
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12
Q

Anaphase 2 [meiosis]

A
  • Spindle fibers attached to centromeres contract
  • The sister chromatids are separated
  • Independent Segregation: the sister chromatids are randomly separated so the four daughter cells have different combinations of maternal and paternal chromosomes causing genetic variation
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13
Q

Telophase 2 [meiosis]

A
  • Four haploid cells (gametes) are produced which are non-identical
  • Random Fertilisation: sexual reproduction fertilisation is random as it happens between any egg and any sperm
  • This produces zygotes with different combinations of chromosomes increasing the genetic variation
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14
Q

Mutations

A
  • Correct meiosis in humans produces four daughters each with 23 whole chromosomes (one from each homologous pair)
  • When meiosis goes wrong this can lead to a mutation which causes inherited conditions
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15
Q

Mutagenic Agents

A
  • Increase the rate of mutations

- E.g. UV radiation, ionising radiation, some chemicals and some viruses

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16
Q

Non-disjunction

A
  • Non-disjunction is the failure of chromosomes to separate properly
  • In humans, the non-disjunction of chromosome 21 during meiosis can lead to Downs Syndrome as there is an extra chromosome 21
17
Q

Gene Mutations

A
  • The order of DNA bases in a gene determines the order of amino acids in a particular protein
  • Mutations in a gene cause the sequence of amino acids coded for and the protein formed to be altered
18
Q

Substitution

A
  • One base is substituted with another e.g. ATC ⇒ ATG
  • The degenerate nature of the genetic code means that not all substitutions will result in a change of amino acid sequence
  • Due to some substitutions still coding for the same amino acid
19
Q

Deletion

A
  • One base is deleted e.g. ATGCCT ⇒ ATCCT
  • Deletions of a base will change the number of bases present and this causes a shift in all the base triplets after it
  • Therefore causing a major change within the amino acid sequence and therefore the protein formed
20
Q

Genetic Diversity

A
  • Genetic diversity describes the number of alleles in a species or a population
  • Different versions of a single gene are called alleles
21
Q

Increasing Population Diversity

A
  • Mutations In DNA: new alleles are formed
  • Gene Flow: new alleles are introduced into a population when individuals from another population migrate into it and reproduce
  • Natural Selection: increases the proportion of advantageous alleles as those individuals with them survive
22
Q

Genetic Bottlenecks

A
  • A genetic bottleneck is an event that causes a big reduction in a population
  • E.g. when a large number of organisms die without reproducing
  • This reduces the number of different alleles in a gene pool and reduces genetic diversity
  • The survivors reproduce and larger population is created from a few individuals meaning it has fewer alleles
23
Q

The Founder Effect

A
  • A type of genetic bottleneck
  • Where a few organisms from a population start a new colony with a small number of different alleles in the initial gene pool
  • The frequency of each allele differs in the new colony than in the original population
  • E.g. a rare allele may be more be more common in the new colony leading to a higher incidence of genetic disease
  • Founder effect can be due to migration which led to geographical separation or if the new colony was separated from the original population for other reasons e.g. religion
24
Q

Natural Selection

A
  • Increases advantageous alleles in a population
  • Adaptations help organisms survive in their environment
  • Natural selection alters allele frequency in a population
25
Q

Natural Selection Theory

A
  • There is variation in a population meaning there are different alleles
  • Some variations are better suited for survival such as having an advantageous allele
  • Those with these alleles can survive and reproduce to pass the beneficial alleles to offspring who also survive and pass on their genes
  • The frequency of the beneficial allele increases from generation to generation
  • The leads to evolution as the advantageous alleles become more common in the population
26
Q

Behavioural Adaptations

A
  • Ways an organism acts that increase its chance of survival and reproduction
  • E.g. possums “play dead” to escape attack from predators
27
Q

Physiological Adaptations

A
  • Processes inside an organisms body that increase its chance of survival
  • E.g. when brown bears hibernate they lower their rate of metabolism to conserve energy so they don’t need food in months where it’s scarce
28
Q

Anatomical Adaptations

A
  • Structural features of an organisms body that increase its chance of survival
  • E.g. whales have a thick blubber which helps them keep warm in the cold sea
29
Q

Stabilising Selection

A
  • Individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
  • E.g. human birth weight
  • It occurs when the environment isn’t changing
30
Q

Directional Selection

A
  • Individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce
  • E.g. bacteria evolving to have antibiotic resistance
  • This could be in response to an environmental change
31
Q

Antibiotic Resistance

A
  • Some individuals in alleles that give them resistance to an antibiotic
  • The population is exposed to an antibiotic and this kills the bacteria that doesn’t have the resistance allele
  • The resistant bacteria survive and reproduce without competition and this allows them to pass on the allele for resistance to their offspring
  • After some time most organisms in the population will carry the antibiotic resistance allele
32
Q

Testing Effects Of Antibiotics

A
  • Anywhere the bacteria can’t grow can be seen as a clear path called an inhibition zone
  • The larger the inhibition zone, the more effective the antibiotic as it inhibits the most bacteria from growing
33
Q

Aseptic Technique

A
  • Prevent contamination of microbial cultures by unwanted microorganisms
  • Regularly disinfect work surfaces and place utensils in a beaker of disinfectant
  • Work near a Bunsen burner; hot air rises so any microbes in the air should be drawn away from the culture
  • Use sterile equipment and discard safely after use
  • Minimise time spent with the lid off the agar plate to reduce chance of airborne microorganisms contaminating the culture

Biology AS (7 decks)

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