week 6 Flashcards
whats the difference between discrete and continuous distributions
discrete - random variables takes on only specific values
continuous - random variable can take any value from an interval
what does theoretical and empirical mean
empirical = calculated after trials
theoretical = calculated before trials
what is the equation for calculating the probability of events before the trials
P(event) = no of ways event can happen / no of total outcomes
what is the equation for calculating the probability of events after the trials
P(event) = no of times event happened / no of total trials
what is a 1 factor cross
involved one factor that is controlled by a single gene
state Mendel’s first law and how it relates to meiosis
law of equal segregation
states every individual contains 2 alleles for each trait and these alleles separate during meiosis such that each gamete only contains one of these alleles, so the offspring receives homologous chromosomes from the parent organisms, one allele for each trait from each parent
each gamete has an equal probability of obtaining either member of the gene
explains the first division of meiosis
what experiments did mendel conduct
using pea plants he observed how the variation of the phenotype could be understood as the combination of alleles from the genotype acquired by an individual as the product of the random combination of a single copy of each gene from the two parents
what is mendels second law
law of independent assortment
unlinked or distantly linked segregating gene pairs behave indepedently
The alleles of different genes assort independently of one another during gamete formation - mendel
how is sex determined in the fruit fly, drosophila melanogaster
by the ratio of autosomes to X chromosomes, acts in a cell autonomous manner
how does sex linkage work
X linked genes- males always express, females can be carriers
Y linked - passed exclusively from father to son eg SRY gene
what are segregation patterns like of alleles from two physically linked genes
If two genes are completely linked (very close together), they are inherited as a unit, showing no recombination.
If genes are partially linked (some distance apart), recombination can occur, producing new allele combinations in offspring.
If genes are on different chromosomes or very far apart on the same chromosome, they assort independently following Mendel’s second law.
what are the meiotic and chromosomal basis of segregation patterns of alleles from 2 physically linked genetic loci
meiotic combination occurs during prophase I and allows for increased genetic diversity bc of the new allele combos, reduces linkage between genes that are further apart leading to recombinant phenotypes
this disrupts the physical linkage of genes, and the frequency of meiotic combination is proportional to the physical distance between genetic loci
what diseases are associated with an XXY and X0 karyotype
XXY = Klinefelter’s syndrome in males
X0 = Turner syndrome in females
shows that presence of Y chromosome (and therefore SRY gene) drives male sexual development from the default female pathway
define aneoploidy
individuals inheriting an abnormal number of sex chromosomes - occurs from errors in meiosis
what’s the impact of non-paternity on Y chromosome inheritance
can disrupt Y chromosome lineage tracing as a child may inherit a Y chromosome from an unexpected source
what is X linked haemophilia
haemophilia A and B are caused by mutations in blood clotting factors - F8 and F9 genes respectively
because these are on the X chromosome, males often show symptoms while females are asymptomatic carriers
define karyotype
a complete set of chromosomes in a cell arranged by size shape and banding pattern
used to detect chromosomal abnormalities through microscopic analysis
how can genetic disease be due to abnormalities in karyotype
cause developmental disorders due to an imbalance in gene dosage
how is down syndrome caused
occurs due to an extra copy of chromosome 21 cause by a non-disjunction during meiosis I or II
risk increases with maternal age as eggs are arrested in prophase I for decades
why are only certain aneuploidies observed
most are lethal due to severe gene dosage imbalances
some are viable like downs syndrome, turner/Klinefelter’s syndrome
how is sickle cell anaemia caused
a single based missense mutation on the beta-haemoglobin gene on chromosome 11, A->T mutation
it is an autosomal recessive disease
what is the pathway from mutant DNA to physical symptoms in sickle cell aneamia
- DNA mutation in HBB gene (A → T mutation).
- Altered mRNA transcribed from mutant gene.
- Abnormal haemoglobin (HbS) synthesized.
- HbS polymerization under low oxygen → RBCs become rigid and sickle-shaped.
- Blocked capillaries → oxygen deprivation, pain, organ damage.
- Shortened RBC lifespan → anaemia due to rapid destruction.
single amino acid change leads to a wide variety of symptoms
how does the sickle cell allele provide protection against malaria
the malaria parasite (plasmodium) cannot thrive in sickled cells
how does balancing selection maintain the deleterious allele in the population suffering from sickle cell anaemia and malaria
HbSS individuals suffer from sickle cell disease.
HbAA individuals are vulnerable to malaria.
HbAS individuals have a survival advantage, preserving the allele in the population.
heterozygotes have a distinct advantage
