linkage 1,2- lecture 12,13

Question 1

linkage

Answer 1

The tendency for genes or segments of DNA closely positioned along a chromosome to segregate together at meiosis, and therefore be inherited together

(opposite of independent assortment)

Question 2

Manhattan plot

Answer 2

A Manhattan plot, which plots the association statistical significance as –log10(p-value) in the y-axis against chromosomes in the x-axis, is a good way of displaying millions of genetic variants in one figure. One can easily spot regions of the genome that cross a particular significance threshold

Question 3

x linked genes

Answer 3

men inherit baldness from their maternal lineage

Question 4

sex influenced autosomal trait

Answer 4

(dominant in males and recessive in females) or vice versa, differently expressed due to hormonal environments

Question 5

centimorgan

Answer 5

A centimorgan (abbreviated cM) is a unit of measure for the frequency of genetic recombination. One centimorgan is equal to a 1% chance that two markers on a chromosome will become separated from one another due to a recombination event durin g meiosis (which occurs during the formation of egg and sperm cells).

Question 6

recombinant frequency

Answer 6

number of recombinant progeny/total number of progeny *100

Question 7

recombination

Answer 7

Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent

genetic maps reflect distance based on how
often, on average, recombination occurs between two loci. The further
apart two loci are the higher the chance that a crossing over will take
place and thus the greater the genetic distance between them.
Conversely, if two loci are located very close together, there is very little
chance for crossing over to take place. Thus, there is a correlation
between physical and genetic distance, but that correlation is not perfect
(more on this point later). Thus, when using genetic maps to identify the
location of a gene we are taking advantage of the normal cellular
process of recombination

Question 8

There are two types of maps used in locating genes: name them and explain how they are similar and different

Answer 8

genetic and physical maps.

Both maps contain useful, but different, information and thus complement one another.

A physical map measures distance between two loci in the genome in base pairs (e.g., determined by DNA sequencing), while a genetic map measures distances in the frequency of recombination events

Question 8

complete linkage

Answer 8

no recombination occurs between the two genes

Question 9

complete independence

Answer 9

independent assortment

Question 10

testcross

Answer 10

is a cross between a heterozygous and a homozygous recessive individual, the latter is also referred to as the tester. Testcrosses are useful as you can determine offspring genotype simply by observing phenotype (as the offspring inherit only recessive alleles from the tester parent).

Question 11

partial linkage

Answer 11

the proportion of recombinant progeny will fall somewhere in between 0 and 0.5 (or 0 to 50%). The proportion of recombinant progeny
can then be used to determine the genetic distance between the loci of
interest

Question 12

phase

Answer 12

refers to the particular arrangement of alleles on a chromosome

Question 13

recombinant frequency

Answer 13

The frequency with which a single chromosomal crossing occurs between two genes during meiosis

number of recombinant progeny/total progeny * 100

Question 14

results of a test cross with complete linkage, independent assortment, linkage with crossing over

Answer 14

Question 15

what influences the probability of recombination

Answer 15

distance between genes

Question 16

what breaks up linkage between genes

Answer 16

recombination

Question 17

in a test cross what is the maximum frequency of recombinant gametes

Answer 17

50%

Question 18

recombination

Answer 18

the rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.

Question 19

complete (or absolute) linkage

Answer 19

In genetics, complete (or absolute) linkage is defined as the state in which two loci are so close together that alleles of these loci are virtually never separated by crossing over. The closer the physical location of two genes on the DNA, the less likely they are to be separated by a crossing-over event.

Question 20

independent assortment

Answer 20

The idea behind independent assortment is that genes are inherited independently of one another. In other words, the genetic factors that control crest and sex are physically separate. Because the genetic factors are physically separate, they segregate independently during gamete (egg and sperm) formation.

Question 21

chi square test usage

Answer 21

Question 22

testing for independent assortment

Answer 22

Question 23

contingency table

Answer 23

2 by 2 table of the number of progeny with each genotype

Question 24

worked problem contingency table

Answer 24

Question 25

what is the physical distance between genes related to

Answer 25

the rate of recombination between them

Question 26

3 point cross question

Answer 26

Question 26

determining the order of genes

Answer 26

Question 27

deletion mapping

Answer 27

Deletion mapping is a process by which a DNA feature (mutation, DNA polymorphism, or MIC-limited DNA segment) can be genetically mapped to a segment of a MIC chromosome, defined by deletion ends, using a panel of deletion homozygotes.

Question 28

hemizygous

Answer 28

Simply stated, homozygous describes two identical alleles or DNA sequences at one locus, heterozygous describes two different alleles at one locus, and hemizygous describes the presence of only a single copy of the gene in an otherwise diploid organism.

Question 29

phase

Answer 29

Phase refers to the particular arrangement of alleles on a chromosome

Question 30

three major points to remember about crossing over

Answer 30

(1) crossing over breaks up the physical linkage between alleles/genes (2) the distance between any two loci influences the probability of crossing over (i.e., the further apart two loci are, the higher the chance there is of a recombination event occur between them) (3) the maximum frequency of recombination between any two loci is 50%. This final point stems from the fact that only two of the four sister chromatids are involved in crossing over

Question 31

recombination frequency (RF)

Answer 31

(Number of recombinant progeny / total number of progeny) * 100 the percentage of recombinant progeny produced in a cross. The RF ranges from 0%, in the case of complete linkage, to 50% in the case of independent assortment. The fewer recombinant progeny produced, the lower the RF, and the tighter the association between two genes. Note, when performing these calculations, there will be two types of recombinant progeny and two types of parental progeny