Ch 3: Genetic Variation Flashcards
1
Q
What is intraspecific variation>
A
variation between members of the same species
2
Q
What are the types of variation?
A
- morphological - variation in the shape and structure of the organism (including internal anatomy)
- biochemical - variation in the chemical structure and composition of organisms
- physiological - variation in the way individuals carry out metabolism and maintain their bodily processes
- behavioural - differences in the way individuals perceive, react and think (individual’s cognition and the way they translate this into behaviour
3
Q
What are the sources of allele variation?
A
- each copy of a particular gene is not necessarily identical (allele), each species posses two alleles for any gene, a single gene determines the trait but it is the combination of alleles that determine what exactly is expressed
- alleles are transmitted from generation to generation via meiosis and fertilisation, variation in meiosis and fertilisation and environmental change contribute to genetic variation (and phenotypic)
4
Q
What is a mutation?
A
a change to a gene or chromosome or the porcess that generates these changes
5
Q
How do mutations affect body/somatic cells?
A
- only occur in the affected body cell and the daughter cells produced from mitosis, all other cells in the organis lack the mutation
- an example is cancer, mutations accumalate in particular regions of the DNA that accelerate the rate of cell division and abolish the cell’s ability to undergo apoptosis or increase the rate of mutations in a cell
6
Q
How do mutations affect reproductive/germ-line cells?
A
- these affect gametes and potentially can be inherited or passed on to the next generation so that they are incorporated into every cell of the offspring
- often results in developmental abnormalities that cause the affected embroyo/foetus to be spontaneously aborted, if carried throu to birth the mutation may result in congenital disorders with varying serverity
- occasionally the encoded protein may chang or enhance its function which can enhance the survival of the organism
- if the mutation is continuously passed on, a new allele has entered the pop.
7
Q
Describe the type of mutation that occur due to errors in cell division? (spontaneous mutation)
A
- spontaneous mutation: occur during the S phase (synthesis) of the cell cycle when DNA is exposed for replication and vulnerable to damage
- arise because the exposed nitrogen bases convert backwards/forwards between different chemical forms
- may also occur by highly corrosive chemicals containing oxygen that readily react with DNA to cause damage to the DNA structure. These reactive oxygen species may be generated by the cell’s own metabolism or by the action of mutagens. Enzymes usually remove many of them but if there is an excess of chemicals damage occurs
8
Q
Describe the type of mutation that occur due to errors in cell division? (G2 phase)
A
- during G2, DNA is proofread and any errors that are detected are repaired, repair often depends on the DNA strand being intact, so that it can be a template for proofreading and restoring the damaged complementary strand.
- if a mutation is not repaired/repaired incorrectly the mutation becomes a part of the DNA sequence and persists through subsequent cell divisions
9
Q
How often do mutations occur due to errors in cell division and what are mutation rates?
A
DNA repair mechanisms are usually highly effective, so mutations are relatively rare
- mutation rates (no. of changes/gene copy in a population over time) vary for different species
- a low mutation rate demonstrate a tremondous accuracy with which DNA is replicated and make it hard for geneticists to investigate mutations
10
Q
What are mutagens?
A
agent capable of inducing a mutation
11
Q
What are physical mutagens?
A
various types of radiation that cause DNA damage, they often affect the nitrogen bases causing distortions in the double helic or double stranded breaks which are complete breaks in the chromosome
main types
- UV light - cause a structural distortion by cross linking nucleotides
- X-rays - cause gene and chromosome aberrations
- nuclear radiation - base breaks in DNA strands
12
Q
What are chemical mutagens?
A
compunds that icnrease the frequency of some types of mutations
- some act directly as a substituting base i.e. 5-bromo uracil resembles thymine but can bond with A or G, the ambiguous pairing affects DNA replication leading to a CG pair replacing a TA pair
- some damage the structure of the existing nitrogen bases in the DNA i.e. replacing AT with GC or losing/gaining a nucleotide
13
Q
What are biological agents?
A
mutations cause by invasive pathogens i.e. bacteria and viruses
main types
- bacteria and viruses getting horizontal
- jumping genes
14
Q
How do bacteria and viruses getting horizontal affect DNA?
A
- horizontal gene transfer is a process by which genetic material from one organism becomes incorporated into the genome of another organism
- bacteria: a plasmid is inserted, the integrated bacterial DNA ‘hijack’ the host cell to produce nitrogen and carbon rich compounds that the bacteria uses as a nutritional source, hormones are produced that stimulate the plant cells to rapidly divide and grow which can form a cancerous tumour
- viruses: viral genome is transferred to the host nucleus when it is copied dozens of times and inserted into the host cell DNA, DNA repair is shut worn, increased replication of cells leads to increased replication of the virus often leading to cancer
15
Q
How do ‘jumping genes’ affect DNA?
A
- method of achieving horizontal gene transfer in germ-line cells, transposable elements (jumping genes) are an example, they are capable of replication and spontaneous relocation in the genome, consequently the transposable elements generate changes in the seqeunce of DNA they insert themselves into and continue to be a source of genetic change
- i.e. haemophilia
16
Q
What are types of gene mutations?
A
- point mutation: as single nucleotide within the DNA sequence is affected
- single nucleotide polymorphosis: differences between sequences in the nucleotides at one position
- subsitution - when one nucleotide is replace ny another, source of novel SNPs
- synonymous/silent: occurs when the substituion of base results in a codon that codes for the same amino acid as the original codon
- missense: when a single nucleotide substitution changes the amino acid
- nonsens: when a single point mutation creastes a new stop codon within the original gene sequence, results in an incomplete polypeptide
- insertions and deletions - one or more nucleotides are added/lost from a site within the original gene (indels)
- the effect of an indel is often called a frameshift mutation in which the reading from for the corresponding amino acids has been nudged away from the orginal and all codons downstream of the mutation are affected
17
Q
What are the effects of gene mutations?
A
- neutral mutations: the product is unchanged and so neither is the indvidual’s survival, can either be be missense or synonymous mutations
- deleterious mutations: decreases an organism’s chance of survival and reproduction, make up majority of mutations. Typically nonsense mutations because they result in the production of an incomplete protein that is non-functional
- beneficial mutations: increases an organism’s chances of survival and reproduction, can be a missense or nonsense mutation
18
Q
What are types of mutation in chromosome number?
A
- monoploidy: a cell/organism that has a functional genome consisting of one copy of each chromsome (1 n) i.e. mainly insects
- polyploidy: results in 3 or more copies of each chromosome, beneficial in some plant, lethal in chromosomes
- aneuploidy: an addition/loss of one chromosome, occurs during non-disjunction where identical chromosomes instead separate, go into the same cell i.e. DOwn syndrome
19
Q
What are types of mutations that occur due to variation in chromosome structure?
A
- deletions: when a double strand breaks at 2 positions, the section in between drops out and the 2 ends rejoin, leads to an absence of genes and has profound effects, all but the shortest deletions are fatal
- inversions: if a chromsome breaks in 2 places and the segment in the middle rotated before rejoining, may disrupt a gene, fuse two together or reduce fertility
- translocations: section of one chromomsome breaks pff and re-attaches to another chromosome, often results in cancer
- duplications: an extra copy of a section of chromosome and inserted into another/the same chromosome, frequently harmful
20
Q
What is a mutant?
A
cell or organism that bears a mutation
21
Q
What are the role of homeobox genes?
A
a gene that codes for proteins that regulate body formation and patterning in the developing embryo
- a specific combination of poistional protein activates each homeobox gene, once expressed the product of each homeobox gene is a protein which binds to DNA to activate gene expression, the genes expressed are those required for the formation of the intended body part/organ at that position within the developing embryo
- homeobox proteins are thus regulatory proteins
22
Q
What are the determinants of sex?
A
- the Y chromosome has genes that set the organism on the path to developing as male
- the most influential gen is the sex determing region Y (SRY ) gen, located on the P, small arm of the Y chromosome, the gene encodes a protein that binds to DNA to activate the expression of many genes, in particular testes development
- if the individual lacks a Y chromosome and is unaffected by the SRY gene, they begin devleoping into a female, if both X chromosomes are active twice the required concentrations of proteins are being produced inside each cell, cells then shut down on of the X chromosomes, achieved by changes to the chromatin structure of the X chromosome, occurs randomly
