Biochemistry 8

Question 1

A central focus of medical genetics is the

Answer 1

identification of
mutations that cause disease.

Question 2

Several types of maps are used in the field of genetics:

Answer 2

1. Cytogenetic Map
2. Physical Map
3. Genetic or linkage map

Question 3

Cytogenetic Map

Answer 3

representing
the visual appearance of a
chromosome when stained and
visualized under the microscope.

Question 4

Physical Map

Answer 4

representing
actual physical distances, usually
measured in base pairs.

Question 5

Genetic or Linkage map

Answer 5

which represents the linear order of genes in a chromosome, with their distance proportional to the frequency of recombination, based on the frequency of meiotic crossovers.

Question 6

Principle of independent assortment (second
law of Mendel)

Answer 6

states that genes will be transmitted to the next generation independently of one another

Question 7

Mendel’s second law contrasted with the

Answer 7

chromosome theory: presenting chromosomes as linear structures with genes located at specific sites

Question 8

Morgan’s (and Sturtevant’s) work unified both ideas with his work on

Answer 8

crossing over

Question 9

The second law of Mendel holds as long as

Answer 9

genes are in different chromosomes, or far apart on the same chromosome

Question 10

If two loci occupy the same region of a chromosome they are said to be

Answer 10

lined

Question 11

Morgan and Sturtevant proposed that crossovers are more likely to occur between

Answer 11

loci that are situated close together

Question 12

The distance between two loci can then be estimated by the

Answer 12

recombination frequency in families

(If alleles A and B undergo recombination 5% of the times (in a large number of meiosis studied in families), their
recombination frequency is 5%.)

Question 13

If two genes are unlinked: recombination frequency

Answer 13

50%

Question 14

If two genes are linked: recombination frequency is

Answer 14

less than 50% (more likely to be inherited together)

Question 15

Linkage disequilibrium

Answer 15

refers to the tendency for some alleles at two linked locations to occur together more often than
expected by chance.

Question 16

genetic distance

Answer 16

between two loci is measured in centimorgans, where one centimorgan = 1 cM = 1% = 1 Mbp

Question 17

If two genes are far apart in the same chromosome or in different chromosomes, they
are

Answer 17

unlinked, recombination frequency is 50%

During meiosis, there is 50% times when genes remain in the same chromosome (non-recombinant, AB and ab) and 50% times when genes are separated due to crossing over (recombinant, Ab and aB), i.e. 50% recombination frequency.

Question 18

If two genes are close in the same chromosome, they are

Answer 18

linked: recombination
frequency is <50%. Crossing over sometimes, but not always, will separate them. The closer they are, the lower the recombination frequency. If A and B were the same gene, the recombination frequency would be 0%.

Question 19

Crossing-over takes place in

Answer 19

prophase I of meiosis I

Question 20

the average chromosome experiences

Answer 20

1-3 crossover events during meiosis

Question 21

_______ chromosomes have a higher (1.5X) frequency of recombination

Answer 21

females

Question 22

The combination of allels in each chromosome is

Answer 22

haplotype (from haploid genotype) ex: A1B1 and A2B2 haplotype

Question 23

As a result of crossover, new combinations of alleles can be?

Answer 23

Formed, in a process called recombinaiton

Question 24

What is needed for gene mapping

Answer 24

1. DNA from members of families in which a certain trait is prevalent, and 2. DNA markers

Question 25

DNA markers or genetic markers

Answer 25

typically, non-coding DNA polymorphisms used to follow a disease-causing allele through a family, i.e. they “mark” the chromosome on which a disease causing allele is located. The marker does not a cause a disease but is close to the gene that IS causing the disease.

Question 26

DNA markers do not (by themselves) identify the gene responsible for the trait, but can roughly

Answer 26

indicate where the responsible gene is in the genome

Question 27

If a gene is close to a DNA marker, they will likely

Answer 27

stay together during recombination and be passed on together from parent to child

Question 28

If each family member with a disease also inherits a particular DNA marker, it is very likely that

Answer 28

the gene responsible for the disease lies near that marker

Question 29

The more DNA markers, the more likely is to have at least

Answer 29

one marker near the diseased gene

Question 30

The Human Genome Project provided information to develop

Answer 30

dense maps of markers evenly spaced across the entire genome.

Question 31

Three steps determine linkage and recombination frequencies

Answer 31

1. Establish the arrangement of genes in each chromosome (aka linkage phase) 2. Determine a hypothesis if linkage is present 3. Calculate recombination frequency

Question 32

Each marker can have

Answer 32

several alleles

Question 33

Track transmission of?

Answer 33

The marker provided and the transmission of the disease (form affected individuals in pedigree)

Question 34

The marker is not the

Answer 34

cause of the disease, but helps to determine which chromosome is being transmitted by a parent

Question 35

The actual cause of the genetic disease will be a?

Answer 35

nearby mutation which can be identified in subsquent DNA sequencing analysis

Question 36

The closer two linked loci are (e.g. gene and marker), the lower the

Answer 36

recombination frequency between them. Useful markers are <1 cM from the gene. The recombination frequency can be used to estimate the proximity between a gene and a linked marker.

Question 37

Genetic diagnosis will determine whether the individual at-risk has

Answer 37

inherited the disease causing gene

Question 38

Direct diagnosis

Answer 38

looks for a known mutation, using molecular biology techniques (DNA sequencing, etc). No markers.

Question 39

Indirect diagnosis

Answer 39

based on linked markers to infer whether the individual has inherited the DNA segment containing the disease-causing mutation

Question 40

Genetic testing reveals mutations, not the presence of a

Answer 40

disease (reduced penetrance, mosaicism, additional mutations).

Question 41

No genetic test is

Answer 41

100% accurate

Question 42

Pros for Direct Disease

Question 43

Q3 Sibling 2 is

Answer 43

affected

Question 44

Q4, individual III-1 is

Answer 44

affected, but has a more severe manifestation because the band has a larger size (more expansion of trinucleotide repeat)

Question 45

Q5, individual 6 is

Answer 45

is not affected

Question 46

Q6 X linked

Answer 46

-X chromosome from the mother -Not diseased -Will be a female because there are two bands