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Biology > 3.4 Genetics and Variation > Flashcards

3.4 Genetics and Variation Flashcards

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1
Q

What is a gene?

A

Short section of DNA that codes for the amino acid sequence of a polypeptide chain or a functional RNA

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2
Q

What is a gene locus?

A

Location of a particular gene on a chromosome

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3
Q

What is a homologous pair?

A

One chromosome from each pair is maternally and paternally inherited (same genes but different alleles)

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4
Q

What is prokaryotic DNA?

A

•shorter
•circular
•not histone bound
•supercoiled to fit in cell (cytoplasm)
•no introns

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5
Q

Why is the DNA in the mitochondria and chloroplast similar to prokaryotic DNA?

A

•shorter
•circular
•not histone bound

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6
Q

What is eukaryotic DNA?

A

•linear
•longer
•wound around histone proteins and tightly coiled into chromosomes

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7
Q

Why is the direction in which new DNA strand made different for the 2 strands?

A

•DNA has anti parallel strands
•shape of nucleotides is different/aligned differently
•DNA polymerase have specific active sites
•only substrates with complimentary shape bind

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8
Q

What is a start and end codon?

A

Start: 1st codon in MRna which initiates translation

Stop: final codon that does not code for an aa and stops translation (marks end of polypeptide)

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9
Q

Why is the genetic code degenerate? (Ad)

A

Each aa (20 different) is coded for by more than one sequence of triplet bases (codon)

Ad: if mutation occurs, it may still code for the same aa

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10
Q

Why is the genetic code universal? (Ad)

A

Same codons code for the same aa in all organisms

Ad: genetic engineering possible between different species

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11
Q

Why is the genetic code non-overlapping? (Ad)

A

Each base in a gene is part of only one codon (distinct)

Ad: if mutation occurs, only affects one codon (one aa) which minimises effect of mutation

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12
Q

What are introns and exons on DNA?

A

Introns: section of DNA that do not code for sequence of aa (found between genes) polypeptide chains and functional RNA. These get spliced out of MRna

Exons: bases coding for aa sequence

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13
Q

What is the difference between a genome and proteome?

A

Genome: organism’s complete set of DNA in one cell= should never change except in mutations

Proteome: full range of proteins in one cell= changes constantly depending on which proteins currently needed

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14
Q

What is the process of transcription?

A
  1. DNA helicase will break H-bonds and unwind double helix
  2. 1 DNA strand used as template
  3. RNA nucleotides align by complementary base pairing
    (Uracil base pairs with A)
  4. RNA polymerase joins adjacent RNA nucleotides by phophodiester bond by condensation reaction
  5. Once it reaches stop signal it detaches and MRNA is released
  6. pre-mRNA spliced to remove introns

•mRNA holds code for one gene

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15
Q

What happens to pre-mRNA made by eukaryotic cells?

A

Introns are spliced out by splicesomes and exons are attached back by condensation reaction

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16
Q

What is the process of translation?

A

1.ribosome attaches to start codon
2.tRNA complementary anticodon aligns opposite mRNA and provide specific AA for each codon (anticodon binds to codon)
3. 2 AA join by peptide bonds in ribosome (ATP used)
4. Ribosome moves along the next codons (2 codons at a time)
5. Ribosome reaches stop codon and detaches as no AA is coded

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17
Q

How do 2 different amino acids differ from each other?

A

They have different R groups

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18
Q

How are the sructures of tRNA and mRNA different?

A

•tRNA is clover, mRNA is linear OR tRNA has hydrogen bonds
•tRNA has amino acid binding site
•tRNA has anticodon, mRNA has codons

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19
Q

What is a gene mutation and how is it caused and increased?

A

•change is base sequence (sub/add/delete) and change in aa sequence (Trna codes different aa) so different final protein

•mutation randomly occur due to errors in DNA replication
•mutations in no. of chromosomes can arise spontaneously by non-disjunction in meiosis (homologous chromosomes or sister chromatids do not separate)

•increased by mutagens e.g ionising radiation, carcinogens

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20
Q

What are the different types of mutations and which have the most impact on protein?

A

•substitution/addition/deletion

Deletion+addition as they cause a change in all the codons after the mutation (frame shift)

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21
Q

What features of the genetic code reduce the impact of mutations?

A

•degenerate: may code for the same aa
•introns may be changed and they are non-coding
•in substitution, only one codon changed as there is no frame shift

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22
Q

What is meiosis and its process?

A

•Meiosis produces daughter haploid cells that are genetically different from each other
•2 nuclear divisions:
*meiosis 1: homologous chromosomes separate
*meiosis 2: sister chromatids separate

23
Q

How are genetically different daughter cells formed in meiosis?

A

•crossing over:
1.homologous pairs of chromosomes form a bivalent
2.a chiasmata forms (twist)
2.equal lengths of (non-sister) chromatids exchanged
3.producing new combos of alleles
(Prophase 1)

•independent segregation:will cause genetic variation as it allows different combinations of maternal and paternal chromosomes (different allele combination)

24
Q

What is the difference between mitosis and meiosis

A

Meiosis | Mitosis
•2 nuclear •nuclear division
divisons • 2 diploid cells
•4 genetically genetically
different identical
haploids •no pairs
•pairs of • no crossing
homologous over
chromosomes
•crossing over

25
Q

What increases genetic variation?

A

•random fertilisation, where increased combination of alleles

26
Q

What is genetic diversity?

A

The number of different alleles of genes in a population, (group of individuals of the same species), which allows natural selection

27
Q

What is the process of natural selection that allows evolution?

A

•random mutation can give an advantageous allele to be better adapted to an environment
•more likely to survive and reproduce
•advantageous allele is inherited by offsprings in the next generation
•over many generations, the new allele increases in frequency in the population

28
Q

What is stabilising selection?

A

•In a stable environment, natural selection will favour “average” organisms best adapted to that environment (increases this population)
•extreme alleles are selected against
•selection pressure for too high and too low
•standard deviation/range is lowered
E.g human birth rates = better to have a medium size

29
Q

What is directional selection?

A

•takes place when environmental change produces a new selection pressure that favours extreme phenotype, as it gives them an advantage

30
Q

Give an example of directional selection

A

Antibiotic resistance:
•resistant bacteria selected against
•BUT, new environmental factor= penicillin will kill normal bacteria
•resistant will survive, reproduce and pass on resistant gene
•new population made by directional selection

31
Q

What is a species?

A

Similar organisms that can reproduce to produce a fertile offspring

32
Q

What are 2 features of a hierarchy?

A

1.smaller groups are placed within larger groups
2.no overlap between groups
DKPCOFGS

Groups: taxa

33
Q

How are animals universally named?

A

Binomial system: Genus species

34
Q

What are homologous features?

A

Similar physical features found in different organisms that share a common ancestor

35
Q

Why do different species look similar?

A

1.live in similar environments
2.have similar selection pressures
3.similar alleles will have the selective advantage
4.produce similar proteins so have similar characteristics

36
Q

What are genetic diversity comparison used to generate classification?

A

•DNA and mRNA sequence
•amino acid sequence
•immunological-comparing similarity in self-antibody shape

37
Q

What is phylogenetic classification?

A

•Arranges species into groups according to evolutionary origins/relations
•how closely related organism are
•all organisms will have evolved from common ancestors

38
Q

What causes mutation in gametes?

A

mutations in no. of chromosomes can arise spontaneously by non-disjunction in meiosis (homologous chromosomes or sister chromatids do not separate)

39
Q

Why does courtship behaviour cause successful mating?

A

1.recognise own species to make fertile offsprings
2.recognise mate of opposite sex to reproduce
3.identify fertile and sexually mature mate to breed
4.form pair bond to increase chance of survival of offsprings
5.synchronise mating for successful fertilisation (e.g fertile window)

40
Q

What are pheromones?

A

Chemical substances that act as a signal to attract a mate of the same species

41
Q

What is a phylogenetic group?

A

Organisms will share common ancestry

42
Q

Why are offsprings from different specie we infertile?

A

Uneven no. of chromosomes from each parent and chromosomes cannot pair so meiosis cannot occur. Haploid gametes do not form

43
Q

What are the different kingdoms?

A

Animal, Fungi and Plants

44
Q

How is info on DNA/aa sequences used to construct a phylogenetic tree?

A

1.similar sequence= same group/closely related
2.greater difference means the longer ago the groups diverged

45
Q

What is species richness?

A

It is a measure of the no. of different species in a community

46
Q

What is species diversity?

A

The no. of different species and the no. of individuals of each species within any one community

47
Q

What is ecosystem diversity?

A

The range of different habitats within a particular area

48
Q

What is index of diversity?

A

Describes the relationship between the total no. of individuals of all species in a community and the no. of individuals in each species

49
Q

How do you calculate index of diversity and what does it tell you?

A

N(N-1)
———-
Sum of n(n-1)

N=total no. of organisms of all species
n=total no. of organisms of each species

The greater the value, the greater the species diversity

50
Q

What are human activities that reduce biodiversity?

A

•selective breeding (fewer alleles)
•pesticides/herbicides/fertilisers
•deforestation =loss of habitat

51
Q

How can you obtain data to give more precise values of index of diversity?

A

•more samples to get a mean
•randomised samples e.g quadrats

52
Q

Why is meiosis important?

A

•halves no. of chromosomes (haploids)
•full no. of chromosomes is restored during fertilisation (diploid)

53
Q

Why do populations show very low levels of genetic diversity?

A

1.hunting
2.inbreeding
3.genetic bottleneck
4.population may have started with small no. of individuals

54
Q

Why does hunting reduce genetic diversity?

A

1.hunting reduced population size so only few alleles left
2.organisms today from one/few surviving populations
3.inbreeding occurred

Biology (8 decks)

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