practical 4 study Flashcards
what is the law of segregation?
describes how alleles for a gene wll segregate so each gamete only contains 1 allele
what is random fertilization
it adds to genetic variation because sperm can only fuse with one ovum
what is the law of independent assortment
due to random orientation of homologs during metaphase of meiosis 1, different chromosomes will assort independently of one another into gametes
the assortment of one pair will not affect the other
what are the cases in which different genes will be assorted into gametes independently?
when they are on different chromosomes or when they are on the same chromosome but are far enough apart that they recombination frequency is 50%
at what phase is the combination of maternal and paternal chromosome for a gamete determined
at metaphase 1
what is crossing over? what does it produce
corssing over is when non sister chromosomes synapse and exchange alleles through recombination at prophase 1
this produces recombinant chromosomes
when will linked genes not recombine?
when they are very close together they are less likely to be recombined
what are pure breeding strains
they are individuals that are homozygous for a trait of interest, they are created by inbreeding for many generations
what are tester strains? what are they used for?
testers are homozygous recessive and are used to determine whether genes assort independently or are linked
in the case of independent assortment, what are the proportions of the f2 generation when a dihybridheterozygote is crossed with a test strain?
the proportions will be equal for all 4 phenotypes, each will be 1/4
how genes are linked, how will the F2 ratios change?
the phenotypes will be the same but will exist in different ratios
when genes are linked, what phenotypes will make up the majority/minority of the offspring?
the parental phenotypes will be the majority while the minority will be made up of the recombinant phenotypes
if a diheterozygote has 100% linked genes, what will the ratios be for a cross with a tester?
50% wild type and 50% mutant
what does it mean when genes are partially linked?
it means they are on the same chromosome but they are far enough apart that some crossing over/recombination occurs
what can the proportion of recombinant progeny tell us?
it can be used to determine how far apart the two loci are
how do you calculate recombination frequency
of recombinant offspring/ total offspring
what is probability?
probability is the fraction of time that a particular event will occur
what is the sampling rule? how is it calculated?
it is the probability of any chance event occurring
it is the # of event A/ total # of events
what is the product rule? how is it calculated?
it is the probability that two independent chance events will both occur in a defined order
it is calculated by multiplying the probability of A x the probability of B
when tossing a coin twice, what is the probability of getting tails the first and second toss?
what rule should be used to calculate this?
the product rule should be used.
=( 1/2 chance of tails) x (1/2 chance of heads) = 1/4 chance of TT
what is the sum rule?
it is the probability of either event occurring
it is calculated by the sum of two probabilities
(probability of A) + (probability of B)
when tossing a coin, what is the probability of getting heads or tails?
what rule should be used to calculate this
the sum rule should be used
(1/2) + (1/2) = 1
in the binomial expansion equation, what is n?
n is the total number of events
in the binomial equation, what is x
x is the number of events in one category (ex. 1 tail in a group of 4 tosses)
in the binomial expansion equation, what is p
p is the probability of x event occuring (ex. 1/2 chance of tails)
in the binomial expansion equation, what is q
q is the probability of the other event occurring
how do we determine if there is a significant relationship between observed and expected values?
chi-square test
what are the three main reasons for a lack of perfect match between observed and expected values
experimental errors
incorrect hypothesis
sampling errors
what is a sampling error
they are errors where the fraction used is not representative of the entire population
what is the null hypothesis?
there is no statistical difference between observed and expected results
what is an alternative hypothesis?
there is a statistical difference between observed and expected results
how do you calculate the expected values for Chi-sqaure
the fraction of a event expected x the total number of events
how do you calculate the degrees of freedom
df=n-1
n is the number of categories
what does a p value of 0.05% mean
it means that there is a 5% chance that results are due to chance alone
if the calculated X^2 value is less than or equal to the critical X^2 value, what does that say about the null hypothesis
there is no statistically significant difference between the observed and expected values, we fail to reject the null hypothesis
if the calculated X^2 value is greater than the critical X^2 value, what does that say about the null hypothesis
we can reject the null hypothesis, there is a statistical difference between the observed and expected results
what is X-linked inheritance?
genes that are located on sex chromosomes (X)
what is the genome of drosophila
diploids with 4 pairs of chromosomes
what is a 100% linked gene?
genes on a chromosome that are so close that they will not cross over/recombine/assort independently
what are the phenotypic differences between male and female drosophila
sex combs in males, male external genitalia, and abdominal structure and pigmentation
when are genes more likely to recombine/cross over
when there is greater distance between loci
if there is no crossing over/recombination, what will the phenotypes be for a diheterozygote test cross
we will only see wild type and double mutants
if there is some crossing over,what will the phenotypes be for a diheterozygote test cross
we will see some recombinant flies
if genes are completely unlinked, what will the phenotypes be for a diheterozygote test cross
you will see 4 phenotypes in equal proportions
