3.4 Genetic information, variation and relationships between organisms Flashcards
(70 cards)
1
Q
Describe Eukaryotic DNA
A
Long
Linear
Associated w/ Histones (proteins)
Coiled
2
Q
Describe Prokaryotic DNA
A
Short
Circular
Not Associated w/ Histones (proteins)
3
Q
Describe DNA in mitochondria and chloroplasts
A
Similar to prokaryotic DNA
Short
Circular
Not associated with proteins
4
Q
What is a gene?
A
Section of DNA that codes for the amino acid sequence of a polypeptide and functional RNA (tRNA and rRNA)
5
Q
What is a locus/loci?
A
Specific linear position of a gene on a certain chromosome
6
Q
What is a histone?
A
Proteins which together with DNA
7
Q
What is the nature of the genetic code?
A
Triplet (sequence of three DNA bases) for specific amino acid
Universal
Non-overlapping
Degenerate
8
Q
What is an exon?
A
Portion(s) of DNA within a gene that codes for proteins
9
Q
What is an Intron?
A
Portion(s) of DNA within a gene that does not code for proteins
10
Q
What is an Allele?
A
Alternative form of a gene with different base sequences (and therefore codes)
11
Q
Define genome
A
The complete set of genes in a cell
12
Q
Define proteome
A
The full range of proteins that a cell/genome is able to produce
13
Q
Define Homologous Pair of chromosomes
A
Pair of chromosomes with the same gene but different alleles
14
Q
Describe the structure of messenger RNA (mRNA)
A
Single stranded Straight chain helix Made during transcription Codon Pentose sugar = ribose A,C,G,U = bases
15
Q
Describe the structure of Transfer RNA (tRNA)
A
Single polynucleotide chain Ribose Three leafed Clover-shaped molecule Amino acid binding site Anticodon Held by hydrogen bonds short
16
Q
What are similarities between trna and mrna?
A
Both single polynucleotide strands
17
Q
What are the differences between tRNA and mRNA?
A
- mRNA single helix / straight, whereas tRNA folded into clover shape
- mRNA is a longer, variable length, whereas tRNA is shorter
- mRNA contains no paired bases or hydrogen bonds, whereas tRNA has some paired bases and hydrogen bonds
18
Q
Describe the process of Transcription
A
Occurs in the nucleus
DNA helix unwound by DNA Helicase = Hydrogen bonds broken
Formation of template strand
RNA nucleotides align next to exposed nucleotide bases on template strand
RNA polymerase joins adjacent nucleotides through condensation reaction
Forms phosphodiester bonds
When reached to stop codon pre-mRNA detached from DNA
Splice the pre-mRNA (removal on introns)
Creation of mMRNA
19
Q
What is meant by post transcriptional modification?
A
Splicing of Pre-mRNA
20
Q
Describe the process of Translation
A
mRNA attaches to ribosomes
tRNAs codon binds to mRNA codon
Begins with start codon
tRNA will attract specific amino acids with two trna molecules at a time
Two amino acids joined by condensation reaction using ATP
Formation of peptide bond
tRNA attaches and ribosome moves along mRNA to next codon
Continues until stop codon
21
Q
What is the role of ATP in translation?
A
Releases energy through its hydrolysis
The bond between amino acid and tRNA molecules → Peptide bond
22
Q
What is the role of tRNA?
A
Attaches and transports specific amino acid (relation to anticodon)
Two trnas bring amino acid together for peptide bond
Degenerate genetic code
23
Q
What is the role of the ribosomes in translation?
A
Attaches to mRNA and houses tRNA allowing codon-anticodon complementary base pairing
Factory for protein synthesis
24
Q
What is a gene mutation?
A
A change in the base sequence of DNA (chromosomes)
25
What are the types of mutation?
Substitution
| Deletion
26
How can a mutation lead to the formation of a nonfunctional protein
- Change in base / triplet sequence of DNA / gene
- Changes sequence of codons on mRNA
- Changes sequence of amino acids in the primary structure of the polypeptide
- Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein
- Changes tertiary structure / shape of the protein (and active site if enzyme)
- (if enzyme) substrate can’t bind to active site and form an enzyme-substrate complex
27
Explain Base deletion
One base is removed from DNA sequence
Alters the codon sequence from point of mutation known as frameshift
Changes sequence of codons on MRNA
Change in amino acid primary structure of polypeptide
Changes bonds in Tertiary structure of protein
Shape of protein changes due to different amino acids being codes for
28
Explain ‘base substitution’
The nucleotide in DNA is replaced with another nucleotide = Causes change in one triplet
Changes one mRNA codon and one amino acid codon
Sequence of amino acids in primary structure changes
OR
2. Due to the degenerate nature of the genetic code, the new triplet may still code for the same amino acid (primary structure remains the same.
29
What is the role of mutagenic agents?
Increase the rate of gene mutation
30
What are mutagenic agents?
Environmental factors that increase the mutation rate of cells
31
Give an example of a mutagenic agent?
UV, X-rays(ionising radiation) or toxic chemicals
32
Describe Process of Meiosis 1
Condensed Dna replicates so there are two copies of each chromosome → sister chromatids held by centromere
M1
Prophase I = Bivalents and spindle fibre formation. Crossing over occurs increasing genetic variation. Nuclear envelope breaks down
Metaphase I = Chromosomes line up in the equator of the cell with spindle fibres attached to centromeres. Independent assortment
Anaphase I - Spindle fibres pull chromosomes apart to opposite poles of the cell → independent segregation
Telophase I - Chromosomes uncoil, spindle fibres break down, nuclear envelope forms around → two new Haploid daughter cells
33
Describe the process of Meiosis II
Prophase II
Nuclear envelope breaks down
Chromosomes condense
Spindle fibres form
Metaphase II
Chromosomes line up along the equator of the spindle
Anaphase II
Centromeres divide and chromatids are pulled to opposite ends
(Four groups of chromosomes that have ½ number than original parent cell)
Telophase II
Nuclear membranes form around each group of chromosomes
Cytokinesis
Cytoplasm divides as new cell surface membranes are formed → four haploid cells that are genetically varied
34
How does meiosis create genetic variation
Crossing over between homologous chromosomes → alleles exchanged between chromosomes
New combinations of maternal and paternal alleles
Independent segregation → random alignment of homologous pair at equator = random selection of chromosome to each daughter cell
- Creates different combinations of maternal and paternal chromosomes and alleles in daughter cells
Random fertillisation when two gametes fuse to form a zygote
35
What is the importance of meiosis?
- Two divisions – creates haploid gametes (half number of chromosomes)
- Diploid number restored at fertilisation
- Maintains chromosome number from one generation to the next
- Independent segregation and crossing over creates genetic variation
36
Describe the non-disjunction mutation that occurs in meiosis
Homologous chromosomes fail to separate during M1 (OR sister chromatids fail to separate in M2) during anaphase
One gamete has extra copy of a chromosome and the other has none
Zygote will have one fewer (dies) or one extra (survives) chromosome
Arises spontaneously
Causes genetic diseases exp. Down syndrome in humans - extra copy of chromosome 21
37
Explain the different outcomes of mitosis and meiosis
Mitosis produces diploid cells whereas meiosis produces haploid cells
There are two divisions in Meiosis whereas there is only one division in mitosis
Daughter cells are genetically identical in Mitosis but in Meiosis, the daughter cells are genetically varied
Crossing over and Independent segregation only in Meiosis
Mitosis produces two daughter cell but Meiosis produces 4 daughter cells
38
What is genetic diversity?
Number of different alleles of a gene in a population
39
Explain the principles of natural selection in the evolution of population
1. Random DNA mutations cause the variation of alleles in a population
2. Selection pressure / change in environment
3. Those with advantageous allele have increased chance of survival and reproduction – differential survival/reproductive success
4. Those surviving pass advantageous allele to offspring
5. Frequency of advantageous allele and (named) characteristic increases in the population
6. Over many generations / long period of time
40
In terms of alleles, what is evolution?
Change in allele frequency over time
41
Describe directional selection
Occurs when there is a change in the environment due to new selection pressure/allele in population
Frequency of allele in population increases
Mean variation within population will shift towards one characteristic (phenotype)
one extreme phenotype is more likely to survive and produce
42
Describe stabilising selection
Restricts the variation within a characteristic around the mean
Selection pressure acts either side of the mean
Both extremes of phenotypes less likely to survive and reproduce
Mean phenotype remains the same
43
Describe disruptive selection
Maintains frequencies of two different sets of alleles - both extremes
Causes continues existence of two or more distinct phenotypes in species
Occurs in environment that show variation
Individuals with intermediate phenotypes or alleles are selected against
44
Name the three categories of adaptation Natural selection can provide
Anatomical
Physiological
Behavioural
45
Define ‘species’
A group of organisms (that have a common ancestry + share the same gene) that are capable of breeding together to produce fertile offspring
46
Why may offspring from 2 different species mating be infertile?
They will have an odd number of chromosomes so cant perform meiosis to produce (haploid) sex cells (gametes)
47
Explain the necessity of courtship behaviour to successful mating
Allows recognition of members of the same species to produce fertile offspring through successful mating
48
Give at least 2 roles of courtship in species recognition?
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Indication of sexual maturity
Attraction of opposite sex
Stimulate release of gametes
Establishes a pair bond to raise children
Synchronise mating
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49
What is the phylogenetic classification system?
Process of classifying organisms based upon evolutionary origins and relationships
50
What is a hierarchy?
Where Smaller groups are placed within larger groups with no overlap between each group
51
What is each group in the phylogenetic classification system called?
Group = taxon
52
Give the names of the taxonomic ranks
- Domain (Delicous )
- Kingdom (King)
- Phylum (Prawns)
- Class (Curry)
- Order (or)
- Family (Fat)
- Genus (Greasy)
- Species (Sausages)
53
What is the advantage of binomial naming of specious (using genus and species)
Universal = no confusion as many organisms have more than one common name
54
What advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms?
Genome sequencing
Compare the order of base sequence of the whole genome of different species
Higher match =more closely related
Immunology
DNA→mRNA→ sequence of amino acids in polypeptide
Tertiary structure of protein tells about sequence
If same antibody binds to a specific antigen then closely related
55
Define Biodiversity
The variety of living organisms in an area
56
What are the three components of Biodiversity
Species diversity = the number of different species and the number of individuals of each species within a community
Genetic diversity = variety of genes/alleles in the population of species
Ecosystem diversity = range of habitats from a small local community to the whole earth
57
What is species richness?
The measure of the number of different species in a community
58
What is the index of diversity?
The formula used to quantify the biodiversity of a habitat
59
What is species evenness?
Comparison of size of population of different species within a particular area
60
What is the lowest possible of Index of Diversity?
1
61
What is the impact of Agriculture on Biodiversity
Removal of woodland and hedgerows
Monoculture (causes one desirable species )
Use of pesticides, herbicides and inorganic fertilisers
Increasing competition → Crops better competitors e.g light/nutrients
62
What is conservation?
Sustainable management of earth's natural resources that maximise preservation
63
What is variation?
Differences between individuals, within a species (intraspecific) or between different species (interspecific)
64
State the features of continuous variation
No distinct categories
Quantitative
Strongly influenced by the environment
65
How can we compare genetic diversity?
Frequency of measurable observable characteristics
Bases sequence of DNA
Base sequence of mRNA
The amino acid sequence of the proteins encoded by DNA and mRNA
66
State the features of discontinuous variation
Distinct, discrete categories
Qualitative
Unaffected by environment
67
How and why has gene technology caused a change in the methods of investigating
genetic diversity?
Before genetic diversity was measured by looking at frequency of observable characteristics:
Limitations:
many observable features coded for by more than one gene → different to distinguish
Could be modified by environment so differences may be result of environment conditions rather than different alleles
Gene technology ☑ - Directly obtain DNA sequences = more accurate:
Different alleles of same gene have different base sequences → can compare base sequences of same gene in different organisms→ find out number of that gene in a population
Can produce slightly different amino acids sequences which can be compared
68
How would you take a representative sample and why?
Random sample
Eliminates bias
Exp. number generator for coordinates for quadrats
69
Why is using a large sample size beneficial when investigating variation within a species?
Minimise effects of chance
| Anomalies have less influence and can be identified
70
What does it mean if the standard deviation of two values overlap?
Any difference between the two may be due to chance, there is no significant difference (consider they are technically similar values)
