genetic diversity Flashcards
gene mutations
what is a gene/point mutation?
a change in the base sequence of DNA (which can cause a frameshift)
when does a gene mutation occur?
- can occur during the formation of gametes
- or during DNA replication
what are the 3 types of point mutation?
- Addition
- Deletion
- Substitution
are all mutations harmful?
no, there are some neutral mutations, which do not change the amino acid that it codes for. mutations can be harmful, helpful (unlikely) and neutral
which part of DNA/ nucleic acid experiences the mutation?
- the bases in the nucleotide
what are the 3 types of point mutation?
- Addition
- Deletion
- Substitution
what point mutation is sickle cell anaemia caused by?
substitution
what is a substitution mutation?
- a random base in the base sequence of DNA is substituted to a different base so changes the way the base sequence is read/ codes for a different amino acid
- Affects only one codon the way the triplet is read
what is an insertion mutation?
- where a new base is inserted ino the base sequence of DNA. this causes a frame-shift to occur.
what is a deletion mutation?
- where a random base is deleted from the base sequence of DNA
- a nucleotide is lost from the normal base DNA sequence
what is a frameshift?
since bases are read in codons/triplets. this changes the way the base sequence is read and changes the amino acid it codes for.
how can the rate of mutation be increased?
by mutagenic agents
examples of mutagenic agents?
- High energy radiation e.g. UV light
- Ionising radiation e.g. X rays and
gamma rays. - Alpha particles, beta particles
- Chemicals e.g. Mustard gas,
benzene, pesticides
what are aquired mutations?
occur in cells after conception, so cannot be transmitted to children e.g. some cancers
what are hereditary mutations?
A gene change in a gamete that becomes incorporated into the DNA of every cell in the body of the offspring. Passed from parents to offspring e.g. Cystic fibrosis
what two genes is the rate of cell division controlled by?
- proto-oncogene - stimulates cell division
- Tumour suppressor gene - slows or inhibits cell division.
what happens if a point mutation occurs in a proto-oncogene?
If a point mutation occurs in a proto-oncogene it can form an oncogene. This can stimulate excessive cell division, leading to the formation of a tumour.
what happens if a point mutation occurs in a tumour suppressor gene?
If a point mutation occurs in a tumour suppressor gene it can become inactivated. This allows the rate of cell division to increase unregulated.
what is a chromosome mutation?
a change in the number or structure of the
chromosomes. It is caused by errors that occur during cell division.
what are the 4 types of chromosome mutations?
- deletion
- inversion
- duplication
- translocation
chromosome mutations an arise spontaneously and take which three forms?
- polyploidy
- non-disjunction
- changes in chromosome structure
explain what is non-disjunction mutation?
changes in the number of individual chromosomes. homologous pairs of chromosomes fail to separate during meiosis or chromatids fil to separate in anaphase II
what is the result of a non-disjunction chromosome?
Results in gametes with extra chromosomes
draw a diagram showing non-disjunction mutation
what is important about non-disjunction mutations?
they are lethal
give a condition which is caused by non-disjunction mutations?
down syndrome - extra chromosome 47
what is polyploidy mutation?
changes in whole sets of chromosomes occur when organisms have 3 or more sets of chromosomes rather than the usual two
mostly in what organisms does polyploidy mutations occur in?
plants and Many of these polyploid organisms
are fit and well-adapted to their environments.
draw a diagram showing polyploidy mutations?
why can triploids not divide?
so they reproduce?
To make gametes homologous pairs need to
divide
Triploids do NOT have homologous pairs=
STERILITY
Triploids can only reproduce ASEXUALLY
how are triploids used as an advantage?
Used in fish farming to make extra big fish- no energy waste in reproduction
what is the third mutation?
- Changes in chromosome structure
During meiosis it is normal for homologous pairs of chromosomes to form chiasmata. The chromatids break at these points and re-join with the corresponding portion of chromatid on its homologous partner. It is not surprising that from time to time mistakes arise during this process.
what is meiosis?
a type of cell division that results in the formation of four genetically diverse daughter cells, each with half the number of chromosomes as the parent cell
why is meiosis called a reduction division?
because starting cell has 46 chromosomes and ending cells have 23 chromosomes
what happens before meiosis?
describe what this process is?
interphase - this is where the cell griws, dna replication occurs and carries out cell processes
what happens in interphase of meiosis?
DNA duplicates
what happens in prophase I
chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents and crossing over occurs
what is crossing over?
two homologous chromosomes cross over to from bivalents. the chromatids form chiasmata’s
what happens in metaphase I?
spindle fibres from opposing centrosomes connect to bivalents at the centromere and align then along the middle of the cell
what happens in Anaphase I?
Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles
what happens in telophase I?
chromosomes decondense, nuclear membrane may reform, cell divides by cytokinesis to form two haploid daughter cells
what happen in meiosis II?
sister chromatids are separated (they may not be the same due to crossing over)
what happens in prophase I?
chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
what happens in metaphase II?
spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
what happens in anaphase II?
spindle fibres contract and separate the sister chromatids, chromatids (now chromosomes) move to opposite poles
what happens in telophase II?
chromosomes condense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
what are the causes of variation in gametes?
Crossing over
Independent segregation
Random fertilisation
Environmental factors
Gene mutation
Chromosome mutation
explain how crossing over leads to variation?
draw a diagram to show this.
Chromatids of duplicated homologous chromosomes become twisted
Breaks can occur
Parts of the chromatids are exchanged between homologous pairs
Exchange is random: Different mix of alleles in every gamete
show how independent segregation in Anaphase I leads to variation
draw a diagram to show this.
Homologous pairs attach to spindle fibres opposite each other in a random order.
The maternal and paternal chromosomes are not always on one side.
explain how random assortment leads to variation?
draw a diagram to show this.
The arrangement of each pair of homologous chromosomes during the first division is completely random; each pair lines up independently of any other pair. In a cell with3 pairs of chromosomes (2n = 6) the arrangements shown here are all equally possible.
The daughter cells contain different assortments of the chromosomes (some have all the paternal ones, some have all the maternal ones and some different combinations of both). The significance of this is that, while all these different gametes carry the same genes, they will be carrying different combinations of the alleles of those genes. Gametes are not genetically identical.
what is an allele?
a different variation of a gene located on a particular (lochi) on a homologous pair
what is genetic diversity?
the total number of different alleles in a population
what is the gene pool?
total information from all the genes and alleles of the breeding individuals ina population at a particular time.
if a population has more genetic diversity it has more..? and more..?
more different alleles and genes and more likely to survive environmental change
why is a poulation with more genetic diversity more likely to survive environmental change?
- wider range of alleles so a wider range of characteristics. which gives a grater likely they will possess a charctaristics that suits it’s new environmental conditions
what process enables genetic diversity to occur?
natural selection
why are not all alleles passed on?
only certain individuals are reproductively successful and so pass on their alleles
within every poulation there is a …? containing a wide variety of …?
gene pool containing a wide variety of alleles
random mutations of alleles within this gene pool in a …?
but in certain environments…?
- new mutation which is harmful
- the new allele of the gene may give its possessor an advantage over other individuals in the poulation.
what is this process called?
Natural selection
explain how the process of natural selection results in only the most successful individuals surviving?
- mutations result in genetic variation within a population
- individuals with certain advantageous alleles are more likely to survive in competition with others
- more likely to obtain the available resources better so able to grow more and live longer, which means they’re able to pass on their advantageous alleles to the next generation of offspring’s
- now new individuals also advantageous and reproduce more
- overtime individuals with the new advantageous alleles increases in the population and non-advantageous decreases
Types of selection
different environmental conditions favour…?
different characteristics in the population
what is directional selection?
selection favours individuals in one direction from the mean of the population and changes the characteristics of the population
what is stabilising selection?
selection may favour average individuals and preserves the characteristics of a population
most characteristics are influenced by…?
polygenes - more than one gene
the effect of the environment on polygenes produces individuals in a population that vary about the mean. when you plot this variation you get a ..?
normal distribution curve
how will the mean change overtime/ why does this happen?
if the environmental conditions change, the phenotypes best suited to the new conditions are most likely to survive. some individuals who fall to the left or the right of the mean will possess a phenotype more suited to the new conditions. these individuals will be more likely to survive and breed more offspring. overtime the mean will move in the direction of those individuals
draw what a direction selection graph looks like?
draw a graph which shows stabilising selection?
explain why individuals closest to the mean are favoured?
if environmental conditions are stable, it is individuals with the closest to the mean hat ae favoured. these individuals are more likely to pass on their alleles. stabilising selection tends to eliminate the phenotypes at the extremes
give an example ?
infants with the highest and lowest birth masses are more likely to die while those around the mean are more likely to survive and less likely to die. the population characteristics are being preserved rather than changed
what are anatomical adaptions?
such as short ears and thick fur in arctic foxes compared to foxes in warmer climates
what are physiological adaptions?
for example oxidising fat rather than carbohydrate in kangaroos rats to produce additional water in a dry dessert environment
what are behavioural adaptions?
such as the autumn migration of swallows from UK to Africa to avoid food shortages in the UK winter
