Topic 4-mutations Flashcards
How do gene mutations occur?
-A change in the DNA base sequence of chromosomes
What are the 5 types of errors that can occur?
-Substitution
-Deletion
-Inversion
-Addition
-Duplication
How does a mutation affect the order of amino acids and proteins?
-The order of DNA bases in a gene determines the order of amino acids in a particular protein
-If a mutation occurs the sequence of amino and protein can be altered
What effect does substitution have?
-The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet
-Not all substitution mutations will result in a change to the amino acid sequence of the protein
What effect do deletions have?
-Changes the number of bases present which will cause a shift in all the base triplets after
Are mutations random?
Yes
Give an example of when a mutation can occur
When DNA is misread during replication
Give some examples of mutagenic agents
-UV radiation
-Ionising radiation (gamma, x-rays)
-Chemicals such as mustard gas, caffeine and colchicine
-Some viruses
What do mutagenic agents increase?
The probability of mutations occurring
What are chromosome mutations?
-When cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes
What are chromosome mutations caused by?
-Errors during meiosis
What do chromosome mutations lead to?
-Inherited conditions because the errors are present in the gametes (the heredity cells)
What is chromosome disjunction?
Failure of the chromosomes to separate properly
What is Down syndrome caused by?
-A person having an extra copy of chromosome 21 or an extra copy of it
How does Down syndrome occur?
-Chromosome 21 fails to separate properly during meiosis so one cell gets an extra copy and another does not get a copy
-When the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have three copies of chromosome 21
What are the three sources of variation?
-Crossing over (prophase 1)
-Independent segregation (metaphase 1)
-Random combination (fertilisation)
How does crossing over lead to variation?
-In prophase 1 the formation of homologous pairs (bivalents) during synapsis allows for the tangling of chromatids
-The pair of homologous chromosomes have 4 chromatids (2 for each chromosome)
-When the homologous chromosomes lie next to each other the chromatids can intertwine and exchange sections (recombination)
-Chromosomes still contain the same genes but a different combination of allele
-The point at which the chromatids cross over is called chiasma
How does independent segregation lead to variation?
-During metaphase 1 it is purely by chance which way round homologous pairs lie when they pair and line up on the equator (synapsis)
-The paternal chromosomes may pass into the same cell or different ones during anaphase 1
How many possible combinations of chromosomes are there?
-8,388,608
-As there is 23 pairs of chromosomes in humans
How do you calculate the possible combinations?
(n)
2 = n is the number of chromosomes
How do you calculate the amount of zygotes?
(2n ) squared
How do hereditary mutations occur?
-You can inherit them from your parents
-The mutation is present in gametes, therefore it exists in all cells of the body
How do acquired mutations occur?
-Occur in individual cells after fertilisation
-An acquired mutations can be caused my mutagens however for most they have no specific cause
What is the main difference between inherited an acquired mutations ?
-An acquired mutation starts in one cell of the body and is found only in the offspring of that cell
What is a frameshift?
-The addition/deletion mutation that is likely to result in change to the amino acid sequence but a substitution may not
What are changes in the number of chromosomes during anaphase known as?
-Aneuploidy- loss or gain of a chromosome
Give 3 examples of conditions developed due to mutations
-Down syndrome
-Kinfelsers syndrome- Males have an extra X chromosome
-Polyploidy-one or both gametes are diploid which fuse to form a polyploidy on fertilisation
-Extremely rare in humans, more common in plants
What is non disjunction?
-Failure of a pair of homologous chromosomes to separate in meiosis 1 (anaphase )
-Failure of sister chromatids to separate during meiosis 2 (anaphase 2)
-Failure of sister chromatids to separate during mitosis (anaphase)
Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation
-Frequent use of antibiotics creates a selection pressure
-A mutation is formed in a single bacteria to make them resistant to the antibiotic
-The surviving bacteria reproduces asexually through binary fission
-They then pass on advantageous allele/mutated alleles in greater numbers
-This means that the allele frequency increases and eventually it becomes more popular in the population
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