Topic 8 Flashcards
In crossing over Bits of maternal and paternal chromatids join together at the
Chiasmata
What does crossing over give rise to
Genetic variation, making new combinations of alleles on chromosomes.
What are the 3 types of mutation
- Point mutation - substitution, insertion , deletion
- Chromosomal mutation translocation - part of chromosome breaks off and attaches on a different chromosome
- Chromosome mutation polysomy
Changing one base for another may not affect the primary structure of a protein why’s this
Substitution may code for the same amino acid
Due degenerate nature of the genetic code
What’s polygenic
Many genes
What’s autosomal gene linkage
Both genes found on the same homologous chromosome pair
When linked genes are located close to each other
on the chromosome …
recombination events eg crossing over) during mieosis will rarelt occur
Recombination takes place in mieosis 1
If genes are located further apart from each other
on a chromosome (loosely linked)
The number of
recombination events will be higher.
In unlinked genes the same 2 genes
on separate
chromosomes in different homologous pairs
the genes
from each
chromosome are
not linked at all so the
characteristics are
inherited independently
whats a dihybrid cross
the inheritance of 2 genes is considered at the same time
when will u get the ratio 9:3:3:1
in a dyhibrid cross if 2 heterozygous parents for both genes are crossed you get that ratio
however you may not get the 9:3:3:1 ratio if..
theres autosomal linkage or crossing over in mieosis u will get 3:1 instead (most the time)
crossing over DURING MIESOSIS RESULTS IN
new combinations of alleles in the gametes, so the predicted gametes in ur punnet square may differ
What is the chi squared test used for?
Is the difference between observed and expected data significant or due to chance?
When will mendellian genetics not occir
If the patterns. R sex linked
What’s a sex linked disorder
A genetic condition caused by a mutation in a gene located on a sex chromosome, These disorders are often associated with the X chromosome because it carries more genes than the Y
Haemophilia is
A sex linked disorder caused by Mutations in the gene responsible for producing clotting factors found on the X chromosome , it affects the bloods ability to clot properly , excessive bleeding
What’s the inheritance of haemophilia
Males have XY so if the X chromosome carries the faulty gene the male will have haemophilia
Females have XX the female must inherit two faulty genes one from each parent to have haemophilia, females with one faulty gene are carriers
What’s the hardy weinberg equation?
What does each letter represent ?
p2 + 2pq + q2 = 1
p+q=1
p2 = frequency of homozygous dominant genotype (AA)
2pq = frequency of heterozygous genotype (Aa)
q2 = frequency of homozygous recessive genotype (aa)
What’s hardy weinberg equation used for
to calculate and predict the allele frequencies in a population’s gene pool under certain conditions
What are these conditions needed for the hardy Weinberg to be applied ? Theoretically stable
-no mutations ,
- The population is large
-no selection pressure
how does mieosis give rise to genetic variation in gametes
crossing over, swapping of sections of choromsomes
What is population bottleneck
The effect of a catastrophic event that dramatically reduces the size of a population by more than 50% and causes a severe decrease in the gene pool of a population , results in large changes in allele frequency
When there’s very low allele freq the animals ..
Have little genetic diversity and Are very vulnerable to environmental change
What’s the founder effect
the loss of genetic variation
that occurs when a small number of individuals leave
the main population and set up a new population,
-
LESS RESISTANCE TO ENVIRONMENTAL CHANGE
If some of the founders are carrying lots of mutations then the main population
Will have reduced allele frequency
What’s the difference between a bottleneck and founder effect
Founder effect is voluntary whereas bottle neck is forced
What is stabilising
It reduces variation in the population , conserves phenotypes already present , selects against extreme phenotypes
What’s directional natural selection
Shows a change from one phenotype to another , which is more advantageous to the environment, a selection pressure is applied
What is disruptive selection
Disruptive selection favours extreme traits over the average, increasing genetic diversity and potentially leading to speciation
What’s Genetic drift
Genetic drift is the random change in allele frequencies in a population due to chance, especially in small populations. It can lead to the loss of genetic variation over time.
Example: The founder effect
Compare and contrast stabilising and disruptive selection
Both change frequency of alleles
Both select against some phenotypes
Disruptive select againsts the middle phenotype
Stabilising selects against extremes
The allele for one defect in cone cells is recessive and carried on the X chromosome , why are more men than women colour blind
Females inherit 2 X chromosomes
So if they inherit one recessive and one dominant allele the recessive allele won’t be expressed
