Chapter 9 - Genetic diversity and mutation Flashcards
what is a gene mutation
any change to the quantity or the base of the DNA of an organism
what is a substitution mutation
when one base is substituted for another
why are mutations bad
order of DNA in a gene determines the amino acid sequence which codes for a certain protein. If this is altered it may lead to the protein lacking characteristics that are important for its role
what is a deletion mutation
one base is deleted from the DNA sequence
why do deletion mutations cause a large change to the organisms
every base after the one that has been deleted experiences a frameshift and moves one to to the left because bases are read in triplets the codons aren’t read correctly
what will adding a base result in
a frameshift to the right
what is a silent mutation
because the DNA code is degenerate a substitutions mutation may result in the same amino acid being coded for and so have no effect on the organisms
what is a mutagenic agent
something that increases the likelihood of a mutation eg UV radiation and ionising radiation
what are chromosome mutations
spontaneous changes in the number of or structure of whole chromosomes
what are the two forms of chromosome mutations
changes in whole set of chromosomes changes in the number of individual chromosomes
when will changes to whole sets of chromosomes occur
when organisms have three or more sets of chromosomes rather than the normal two
what is a chance to a whole set of chromosomes called
polyploidy and it occurs mainly in plants
what is non-disjunction
when homologous pairs of chromosomes fail to separate during meiosis leading to changes in the number of individual chromosomes and sometimes syndromes like Downs
what causes downs syndrome
extra copy of chromosome 21
how many daughter cells are produced meiosis
4
how many divisions take place during meiosis
2
what is a haploid number
number of chromosomes gametes have half the normal amount
what is the diploid number
the full set of 46 chromosomes
what happens during the first division of meiosis
homologous chromosomes pair up and their chromatids wrap around each other. one chromosomes from each pair goes into one of the daughter cells
what happens during the second division of meiosis
centromere is divided and the sister chromatids move to each end of the cell
what is a gene
a length of dna that codes for a polypeptide
wha is the locus
position of a gene on a chromosome or dna molecule
what is an allele
different forms of a gene
what are homologous chromosomes
one maternal and one paternal chromosome which have the same gene loci
are daughter cells genetically different in meiosis or mitosis
meiosis
process of meiosis
dna unravels and replicates so there are 2 copies of each chromosome.
dna forms two chromosomes made from 2 chromatids joined at the centromere
first division - chromosomes form homologs pairs which separate halving the chromosome number
second division - the centromere divides to separate the sister chromatids making up each chromosome
four genetically different haploid cells are produced
what is independent segregation
each homologous pair of chromosomes comprises of one paternal and one maternal chromosome when the pair separates it is completely random which chromosomes end up in which daughter cell
the four daughter cells will have completely different combinations of maternal and paternal chromomses
when does independent segregation occur
when the homologous pairs are separated during meiosis
during which process will homologous chromosomes pair and separate
meiosis
what is another war in which genetic variation is induced
each haploid has a very different genetic makeup and when two of these use randomly at fertilisation variety is seen in the offspring
what is crossing over chromatids
homologous pairs of chromosomes pair up, chromatids twist around each other and parts of the chromatids break off due to the tension
these broken parts of chromatids usually rejoin with the chromatids of its homologous partner
this creates genetic variation in the maternal and paternal chromosomes.
chromosomes have the same genes but have different combination of alleles
what is chiasmata
point at which chromosomes snap and swap alleles
what is recombination
when the broken off sections of chromatids join with another chromatid
what is the formula for the possible number of chromosomes in each daughter cell
2^n where n is the number pairs of homologous chromosomes
what is the formula for the number of chromosomes in each daughter cell taking into account the random pairing gametes
(2^n) ^2
what is an allele
different form of a gene
what is genetic diversity
total number of different alleles in a population
when is genetic diversity reduced
when a population has fewer alleles
process of natural selection 6
- gene pool contains wide variety in any population .
- random mutations may result in a new allele,
- certain environment could give the possessor an advantage, better adapted to survive competition.
- they will live longer and grow more healthily increasing -their chance of producing offspring.
- their offspring are likely to have the new allele and more likely to survive and reproduce
- over time the proportion of the population with this allele will increase
what is a genetic bottleneck
an event that causes a big reduction in a population
what is the founder effect
just a few organisms from a population start a new colony with a very small gene pool
why might the founder effect lead to an increase in genetic diseases
frequency of each allele in the new colony may be different from that of the original colony - eg rare alleles could become more common
why could the founder effect occur
migration leads to geographical separation
what is directional selection
population mean will move towards one extreme
what is stabilising selection
population men will move more towards the average
what is disruptive selection
population will have two extreme that have large and less in the average
what will disruptive selection lead to
speciation
what does direction selection do
changes the characteristics of.a population
what does stabilising selection do
maintains the characteristics of a population
how does directional selection work for example in bacteria
- individuals will fall either left or right of the mean and posses a phenotype which is well suited to the conditions
- these will be more likely to survive and breed
- the bacteria that survive divide by binary fission to build a small population that was resistant
- this population was more likely to survive and breed in the presence of penicillin
- the number of the resistant population increased and the frequency of the advantageous allele did too.
- this leads to a distribution curve shifting
how does stabilising selection work
eg with babies weight
- humans have a range of birth weights
- small babies are less likely to survive because they can’t maintain their body temperature
- large babies are less likely to survive because of north difficulties
- conditions are more favourable to middle sized babies so the weight of human babies tends to shift towards the middle
with what type of selection is the environment not changing
stabilising
what are the three types of adaptations
behavioural
physiological
anatomical
what are behavioural adaptations
ways that an organisms acts that increase its chance of survival and reproduction
what are physiological adaptations
processes inside an organisms body that increases its chance of survival and reproduction
what are anatomical adaptations
structural feutres of an organisms body which increases its chance of survival and reproduction
why are some breeds of animals sterile
have an odd number of chromosomes so they can’t pair during meiosis to produce gametes
