Genetics, Biodiversity and Classification Flashcards
(69 cards)
1
Q
what is a gene?
A
a section of DNA that contains a code for making a polypeptide and functional RNA - the code is a specific sequence of bases
2
Q
what is a locus?
A
location of a particular gene on a chromosome
3
Q
what is an allele?
A
one of a number of alternative forms of a gene
4
Q
what are homologous pairs?
A
chromosomes that have exactly the same genes, but might have different alleles and are exactly the same size
5
Q
how is DNA stored in a eukaryote?
A
- stored as chromosomes in nucleus
- chromosomes in eukaryotic cells are linear in shape
- to tightly coil DNA to fit in nucleus as chromosomes, DNA tightly wound around histones (a protein) to form nucleosomes
6
Q
what is a nucleosome?
A
complex of DNA wrapped around a histone
7
Q
how is DNA stored in prokaryotic cells?
A
- prokaryotes also carry DNA in chromosomes but the DNA molecules are shorter + circular
- DNA is NOT wound around histones and instead supercoils to fit in the cell
8
Q
describe the DNA found in chloroplasts and mitochondria
A
- short and circular
- not protein bound
9
Q
what are the three key features of the genetic code?
A
- degenerate
- universal
- non-overlapping
10
Q
what is a start codon? what does it do?
A
- first codon on the DNA and mRNA
- initiates translation
11
Q
what is a stop codon? what does it do?
A
- final codon
- does not code for an amino acid + therefore there is no complementray anticodon with a particular amino acid
- so in translation causes the ribosome to detach, therefore stopping translation
12
Q
why is the genetic code described as being degenerate? why is this an advantage?
A
- most amino acids can be coded for by more than one codon
- if a point mutation occurs, even though the codon will be different, it may still code for the same amino acid and therefore have no effect
13
Q
why is the genetic code described as being universal? why is this an advantage?
A
- the same triplet of bases codes for the same amino acid in all organisms
- means genetic engineering is possible
14
Q
why is the genetic code described as being non-overlapping? why is this an advantage?
A
- each base in a gene is only part of one codon that codes for one amino acid
- therefore each codon is read as a discrete unit
- if point mutation occurs, will only affect 1 codon and therefore only 1 amino acid
15
Q
what are introns? where are they found?
A
- sections of DNA that do NOT code for amino acids and therefore polypeptide chains
- found in eukaryotic DNA but not in prokaryotic DNA
- get spliced out of mRNA molecules
16
Q
what are exons?
A
sections of DNA that code for a sequence of amino acids
17
Q
what is a genome?
A
complete set of DNA in one cell
18
Q
what is a proteome?
A
full range of proteins in one cell
19
Q
compare a genome to a proteome
A
- the genome is the complete set of DNA in one cell whereas the proteome is the full rangeof proteins one cell
- genome should never change whereas the proteome of the cell is constantly changing depending on which proteins are currently needed
20
Q
where does transcription take place?
A
nucleus
21
Q
outline the process of transcription
A
- DNA helicase breaks hydrogen bonds between bases, helix unwinds + bases exposed and act as a template
- only one chain of the DNA acts as a template
- free mRNA nucleotides in nucleus align opposite exposed complementary DNA bases
- RNA polymerase bonds together the RNA nucleotides to form pre-mRNA
22
Q
what happens to pre-mRNA after transcription?
A
- has to be modified to become mRNA ready to leave the nucleus and take part in translation
- introns are spliced out by splicesome proteins leaving only exons behind
23
Q
outline the process of translation
A
- once modified mRNA left nucleus, attaches to ribosome in cytoplasm
- ribosome attaches to start codon
- tRNA molecule with complementary anticodon to start codon aligns opposite mRNA + is held in place by ribosome
- ribosome move along mRNA molecule to enable another complementary tRNA to attach next to codon on mRNA
- the 2 amino acids that were delivered by tRNA molecule are joined by a peptide bond - catalysed by an enzyme + requires ATP
- continues until ribosome reaches stop codon at end of mRNA molecule. stop codon doesnt code for amino acid + so ribosome detaches + translation ends
- polypeptide is now created and will enter the golgi body for folding + modification
24
Q
which 2 mechanisms introduce variation in organisms?
A
- independent segregation (of homologous chromosomes)
- crossing over (between homologous chromosomes)
25
what is independent segregation? how can the number of combinations this produces be calculated?
- in meiosis 1, homologous pairs of chromosomes line up opposite each other at the equator of the cell
- it is random which side of the equator the parernal and maternal chromosomes from each pair lie
- these pairs are separated so one of each homologous pair ends up in the daughter cell, which creates a large number of possible combinations of chromosomes in the daughter cells produced
- calculate using 2n, where n = number of homologous pairs (e.g. in humans 223)
26
what is crossing over?
- when homologous pairs line up opposite each other at the equator in meiosis 1, parts of the chromatids become twisted around each other
- this puts tension on the chromatids causing parts of the chromatids to break
- broken parts of the chromatid recombine with another chromatid, resulting in new combos of alleles
27
compare meiosis and mitosis
**meiosis:** 2 nuclear divisions, haploid cell (one set of chromosomes), introduces genetic variation
**mitosis:** 1 nuclear division, diploid cells (two sets of chromosomes), creates genetically identical cells
28
how can meiosis be identified in a life cycle diagram?
- meiosis invoves a diploid **(2n)** parent cell dividing to become a haploid cell **(n)**, so look for where 2n becomes n
29
other than independent segregation and crossing over, which other factor indroduces genetic variation? how can the new amount of combinations be calculated?
- random fertilisation
- creates new combos of alleles
- there are (2n)2 combinations of chromosomes (before crossing over is considered)
30
what is non-disjunction?
when the chromosomes or chromatids do not split equally during anaphase
31
what is polyploidy? when does it occur?
- changes in the whole sets of chromosomes
- occurs when organisms have 3 or more sets of chromosomes rather than the usual 2
- mainly occurs in plants
32
how does polyploidy occur?
1. each homologous pair is doubled due to DNA replication in interphase
2. non-disjunction in meiosis 1, ALL chromosomes fail to separate equally
3. normal division in meiosis 2, chromatids separate equally
4. when the 2n gamete is joined with an n gamete in fertilisation, a 3n (triploid) is formed
* non-disjunction may occur in meiosis 2 instead of meiosis 1
33
what is aneuploidy? when does it occur?
- changes in the number of individual chromosomes
- sometimes individual homologous pairs of chromosomes fail to separate during meiosis, resulting in a gamete having one more or one fewer chromosome
- on fertilisation with a gamete with the normal number of chromosomes, the resultant zygote will have more or fewer chromosomes than normal in all their body cells
34
how does aneuploidy occur?
1. each homologous pair is doubled due to DNA replication in interphase
2. non-disjunction in meiosis 1, ONE chromosome pair fails to separate equally
3. normal division in meiosis 2, chromatids separate equally
4. when the n+1 gamete is joined with an n gamete in fertilisation, a 2n+1 zygote is formed
5. when the n-1 gamete is joined with an n gamete in fertilisation, a 2n-1 zygote is formed
* non-disjunction may occur in meiosis 2 instead of meiosis 1
35
what is genetic diversity? why is it important?
- number of different alleles of genes in a population
- natural selection can only occur if there is genetic diversity within a population
36
what is evolution?
change in allele frequency over many generations in a population
37
what is natural selection? why is it necessary?
- process that leads to evolution in populations
- results in species becoming better adapted to their environment
- adaptations may be anatomical, physiological or behavioural
38
describe the process of natural selection
1. new alleles for a gene are created by random mutations
2. if the new alleles increase the change of survival for the individual organism then they are more likely to survive + reproduce
3. this reproduction passes on the advantageous allel to the next generation
4. as a result, over many generations the new allele increases in frequency in the population
39
what is directional selection?
- one of the extremes has the selective advantage
- occurs when there is a change in environment
- the modal trait changes
40
what is stabilising selection?
- the modal trait has the selection advantage
- occurs when there is no change in environment
- modal trait remains the same
- standard deviation decreases as individuals with the extreme trait decreases
41
what is a species?
a group of similar organisms that can breed to make fertile offspring
42
what are courtship rituals?
a sequence of actions which is unique to each species and are how animals identify member of their own species to reproduce with
43
explain why courtship is important
**- enable successful reproduction:**
- enables them to recognise own species and opposite sex
- synchronises mating behaviour - indicates sexually mature and in season (releasing egg)
**- to ensure survival of offspring:**
- form a pair bond
- choose a strong and healthy mate
44
what determines a courtship ritual? explain how studying courtship rituals can be useful
- courtship ritual genetically determined so the more similar a sequence is, the more similar their DNA base sequence is
- the more similar a courtship ritual sequence between different species is, the more closely related the species are (allows us to see the relationships between different species)
45
in the binomial system, what does the first name represent?
genus
46
in the binomial system, what does the second name represent?
species
47
why do different species look similar?
- live in similar environment
- have similar selection pressures
- similar alleles will have the selection advantage
- produces similar/same proteins + therefore have similar characteristics
48
what is a hierarchy?
smaller groups arranged within larger groups, with no overlap between groups
49
give an example of a hierarchy and the taxa it comprises
- domain
- kingdom
- phylum
- class
- order
- family
- genus
- species
50
why is it necessary to organise organisms into hierarchies and taxas?
to understand relationships between organisms and track changes
51
how were organisms originally classified? what are some more modern + accurate ways of classifiying organisms?
- orginally based on visibible similarities (e.g. appearance, behaviour, fossils)
- DNA sequence
- mRNA sequence
- amino acids sequence
- immunological (comparing similarity in self-antibody shape)
52
what is phylogenetic classification?
- arranges species into groups according to their evolutionary origins and relationships
- shows which species share common ancestors + how closely related they are
- all organisms have evolved from shared common ancestors, which is shown on a phylogenetic tree
53
what is species diversity?
the number of different species + individuals within each species in a community
54
what is genetic diversity?
the variety of genes amongst all the individuals in a population of one species
55
what is ecosystem diversity?
the range of different habitats
56
what is species richness?
the number of different species in a particular area at the particular time
57
how does farming reduce biodiversity?
- destruction of hedgerows
- selective breeding (narrows gene pool)
- monocultures
- overgrazing
- filling in ponds and draining wetlands
58
how can biodiversity be measured?
- index of biodiversity is a measure of species diversity
- calculation to measure the relationship between the number of species in a community + the number of individuals in each species
59
what is the difference between species richness and index diversity?
index of diversity takes into account the numer of individuals in each species
60
the formula for simpson's diversity index is D = [ N(N-1) ] / Σn(n-1)
what variables to each of these letters represent?
D= Simpson's diversity index (larger value = greater species diversity)
N = total number of organisms of all species
n = total number of organisms of a particular species
61
what is an addition mutation?
- one or more bases are added
- usually causes a frame shift
62
what is a deletion mutation?
- one or more bases are removed
- usually causes a frame shift
63
what is a substitution mutation?
- one or more bases replaced
- could produce: stop codon, different amino acid or same amino acid (due to degenerative nature of the genetic code)
64
what is a duplication mutation?
- one or more bases repeated
- usually causes a frame shift
65
what is an inversion mutation?
group of bases separate from DNA sequence and rejoin in reverse order
66
what is a translocation mutation?
group of bases separate from one chromosome and rejoin another chromosome
67
what is a mutagenic agent?
increases the probability of a mutation occurring
68
give 4 examples of mutagenic agents
- UV radiation
- ionising radiation
- chemicals
- viruses
69
what is a silent mutation?
change in the nucleotide sequence that results in the same amino acid sequence
