practical 4

Question 1

what is the law of segregation?

Answer 1

alleles on homologous chromosomes will segregate so each gamete carries one allele for each trait

Question 2

what is the law of independent assortment

Answer 2

homologs will orient randomly during metaphase of meiosis I, these homologs will assort independently of one another in gametes

Question 3

what are the requirements for genes to assort independently

Answer 3

if genes are located on different chromosomes

if the genes are located on the same chromosome but are far enough apart that the recombination frequency is 50%

Question 4

what is the result of independent assortment?

Answer 4

it leads to different recombinations of maternal and paternal chromosomes depending on the orientation of homologous pairs in metaphase I

Question 5

what is crossing over

Answer 5

nonsister chromatids in homologous pairs synapse in prophase I and exchange genes, the DNA from two parents is combined into a single chromosome

Question 6

when can crossing over not occur

Answer 6

when genes are very close together they are less likely to recombine

Question 7

what happens to assortment if the recombination frequency for genes is 50%?

Answer 7

they will assort independently as if they were located on different chromosomes

Question 8

what is pure breeding

Answer 8

organisms bred are all homozygous at the traits of interest

Question 9

what are the “tester” strains? what are they used for?

Answer 9

tester strains are homozygous recessive and are used to determine whether genes can assort independently or if they are linked

Question 10

what are 100% linked genes? what are partially linked genes?

Answer 10

100% linked genes will not cross over
partially linked genes will have some crossing over

Question 11

what is the recombinant frequency

Answer 11

the proportion of recombinant progeny can be used to estimate how far apart the two loci are from one another on the chromosome

Question 12

if two loci are 100% linked (no crossing over) what will the results of a diheterozygote x tester cross be?

Answer 12

you will have equal proportions of the wildtype dominant and mutant

Question 13

what is the sampling rule? when does it apply for events A and B

Answer 13

it is the probability of any chance of event A, it is equal to the amount of times A occured divided by the total number of events

Question 14

what is the product rule, when does it apply for events A and B

Answer 14

the product rule describes the probability of events A and B occuring in that defined order. it is found by the product of the probability of Ax prob. B

Question 15

for the probability of A and B occuring, are the events dependent on eachother?

Answer 15

no they are independent

Question 16

what is the sum rule, how does it apply for events A or B

Answer 16

probability of either event occurring “A or B” it is found by adding prob. A + prob B.

Question 17

how is the unordered sequence of events calculated?

Answer 17

this is for multiple events occurring in an undefined order. it is calcualted by the binomial expansion equation

Question 18

using the binomial expansion equation. If you toss a coin 4 times, what is the probability you will get HTTT

What is n?
what is x
what is p
what is q?

Answer 18

n is the total number of events: 4
x: is the number of one particular event (getting heads) = 1
p is the probability of x=1/2
q is the probability of the other event: 1/2 (getting tails)n

Question 19

what are the three main causes of a lack of a perfect match in an experiment between the expected and observed results?

Answer 19

1) experimental errors 2) incorrect hypothesis 3) sampling errors

Question 20

how do sampling errors occur

Answer 20

they are errors made by a non representative sampling

Question 21

what is the purpose of a chi-square test?

Answer 21

it is used to determine if there is a significant difference in the sampling differences or if the results are due to chance

Question 22

when analyzing the differences between the expected and observed data, what is the null hypothesis?

Answer 22

there is no statistical difference between the observed data and the expected data

Question 23

if the calculated X^2 value is less than or equal to the critical X^2 value, what can we do with the null?

Answer 23

we fail to reject the null hypothesis, this means there is no statistically significant difference between the observed and expected results

Question 24

if the calculated X^2 value is greater than or equal to the critical X^2 value, what can we do with the null hypothesis

Answer 24

we can reject the null hypothesis, this means there is a significant difference between the observed and expected values that cannot simply be attributed to chance/sampling error

Question 25

what is the critical X^2 value?

Answer 25

the critical X^2 value is calculated based on the degrees of freedom and the p value

Question 26

what does it mean if the p-value is 0.05?

Answer 26

5% of the tie, we may falsely accept/reject the null hypothesis

Question 27

how do we calculate the degrees of freedom?

Answer 27

df=n-1 where n is the number of categories in the data set

Question 28

what does it mean when the p value associated with the data set is between 0.1 and 0.2?

Answer 28

it means that variation between 10-20% will be the result of a sampling error

Question 29

what is X-linked inheritance?

Answer 29

genes that are located on the X-chromosome

Question 30

what is the genome of drosophila

Answer 30

diploid with 4 pairs of chromosomes

Question 31

what are the phenotypic differences between male and female drosophila

Answer 31

1) presence of "sex combs" in males 2) male external genitalia 3) abdominal structure and pigmentation

Question 32

what is a 100% linked gene?

Answer 32

genes that are on the same chromosome that are so close together that they do not recombine

Question 33

when are genes on the same chromosome more likely to recombine

Answer 33

when they are further apart

Question 34

what is recombination frequency used for?

Answer 34

it is used to estimate the relative difference between different genes

Question 35

when are genes completely unlinked?

Answer 35

when recombination frequency reaches 50%, they will assort independently and give equal proportions of the phenotypic classes

Question 36

what is true breeding

Answer 36

when two homozygously bred flies are crossed

Question 37

when crossing doubly homozygous flies (w+, sn+) and (w,,sn) what is the result when genes are linked/no crossing over occurs?

Answer 37

there will be equal proportions of wild type and double mutant flies

Question 38

when crossing doubly homozygous flies (w+, sn+) and (w,,sn) what is the result when genes have crossing over

Answer 38

we will see some recombinant flies, the amounts of these will increase with gene distance

Question 39

if the genes are completely unlinked in a true breeding cross, what is the result and why?

Answer 39

we will see equal proportions of the phenotypic classes since the genes will assort independently