Top6-Ch7-P168-202End

Question 1

Crossing over between linked genes produces nonrecombinant and recombinant offspring. See example in answers of a diagram.

Answer 1

Question 2

Explain coupling and repulsion configuration and how they differ. Also what is another name for both configurations.

Answer 2

Coupling (or cis) configuration is an arrangement where wild type alleles are found on one chromosome and mutant alleles are found on the other chromosome.

Repulsion (or trans) configuration is when each chromosome contains one wild type and one mutant allele.

Question 3

Recombination is?

Answer 3

the sorting of alleles into new combinations

Question 4

Interchromosomal recombination is?

Answer 4

sorting of alleles on different chromosomes (independent assortment) or random segregation of chromosomes in anaphas I of meiosis and is the kind of recombination that Mendel discovered while studying dihybrid crosses.

Produces 50% nonrecombinant gametes and 50% recombinant gametes.

Question 5

Intrachromosomal recombination is?

Answer 5

the sorting of alleles on the same chromosome (crossing over), the exchange of genetic material in prophase I of meiosis.

Often produces less than 50% recombinant gametes, however, if genes are far apart on same chromosome then intrachromosomal recombination also produces 50% recombinant gametes.

Question 6

Physical evidence of recombination as presented by Creighton and McClintock in 1931.

Answer 6

Question 7

The recombination frequency is?

Answer 7

determining the proportions of the types of offspring.

Question 8

What is a three point testcross?

Answer 8

a testcross for three genes

Question 9

Three types of crossover can take place among three linked loci

Answer 9

Question 10

1. Recombination provides the order of genes and _____ distances
2. double cross overs will ____ be counted and underestimate distances

Answer 10

1. relative
2. not

Question 11

Recombination between _____ genes can be used for gene ______

Answer 11

different, mapping

Question 12

To determine the gene order you do what first then what second?

Answer 12

First, determine order of loci

Then, determine cross overs

Question 13

To map genes what is needed? What is an efficient way to obtain this information?

Answer 13

information abou the location and number of crossovers in the gametes that produced the progeny of a cross is needed.

An efficient way to obtain this information is to use a three point cross test in which an individual heterozygous at three linked loci is crossed with an individual that is homozygous recessive at the three loci.

Question 14

Recombination between different genes can be used for gene mapping but it ________ frequencies

Answer 14

underestimates

Question 15

Gene mapping in humans uses? Give an example.

Answer 15

pedigree analysis
Example: linkage of nail-patella syndrome and ABO blood group system.

nail-patella syndrome is a rare autosomal dominant disorder characterised by abnormal fingernails and absent or rudimentary kneecaps.

Question 16

Molecular markers can be used for?

Answer 16

gene mapping

Question 17

What was one of the earliest molecular markers? Explain a bit about it.

Answer 17

RFLPs - restriction fragment length polymorphisms which are variations in DNA sequence detected by cutting the DNA with restriction enzymes.

Question 18

What are microsatellites?

Answer 18

Molecular markers which is detecting variable numbers of short DNA sequences repeated in tandem.

Question 19

What is the ultimate mapping tool?

Answer 19

Sequencing

Question 20

Recombination established linkage groups but gives no information on ______ ________.

Answer 20

chromosomal location

Question 21

1. Physical chromosome methods were developed to determine?
2. Is this dependant on crossing over?

Answer 21

1. chromosomal location of genes
2. No

Question 22

Linkage analysis is?

Answer 22

is based on the observation that genes that reside physically close on a chromosome remain linked during meiosis. Genetic linkage analysis is a powerful tool to detect the chromosomal location of disease genes. It is a more traditional approach

Question 23

What is genome wide association

Answer 23

looks at traits in combination with suites of alleles, or looking for nonrandom associations between the presence of a trait and alleles at many different loci scattered across the genome.

It looks for associations between traits and particular suites of alleles in a population.

For instance (see below) a gene involved with bipolar diseases is linked to a certain haplotype.
Crossing over reduces this link
Fast reduction means not close together

Question 24

What is haplotype?

Answer 24

wikipedia: is a combination of alleles (DNA sequences) at adjacent locations (loci) on a chromosome that are transmitted together.

free dictionary: a combination of alleles (for different genes) that are located closely together on the same chromosome and that tend to be inherited together

Question 25

What is linkage disequilibrium?

Answer 25

**text**: the nonrandom association between alleles in a haplotype. **slides**: Non random association of the trait with a certain haplotype **wikipedia**: is the non-random association of alleles at two or more loci, that may or may not be on the same chromosome.

Question 26

What is deletion mapping?

Answer 26

absence of one or more of the bands that are normally on a chromosome reveals a chromosome deletion, a mutation in which part of the chromosome is missing. Genes can be assigned to regions of chromosomes by studying the association between a gene's phenotype or product and particular chromosomal deletions.

Question 27

Explain somatic cell hybridization

Answer 27

is the fusion of different types of cells. to do this cells that will divide indefinitely are used (from tumours or altered by viruses) and are cultured in laboratory to create a **cell line**. Human and mouse cell lines can fuse to create cells with two nuclei which is called a **heterokaryon**. The two nuclei gradually fuse then as cell divides then all but a few human chromosomes are lost. The presence of extra human chromosomes in the mouse genome makes it possible to assign human genes to specific chromosomes.

Question 28

Genes can be localised to a specific part of a chromosome by using somatic-cell hydrisation. See diagram on next page.

Answer 28

In cell line 1 the gene product is present when chromosome 4 is intact. The gene product is absent in cell line 2 when the entire chromosome 4 is absent. The gene product is absent in cell line 3 when the short arm is missing.

Question 29

What is **in situ hybridization**?

Answer 29

where researchers actually see genes through a radioactive probe that fluoresces under ultraviolet light so that it can be visualised.

Question 30

Recombination rates vary ________ between species and between chromosomes in one species

Answer 30

extensively

Question 31

There are __ times more recombination in humans than in mice and rats

Answer 31

2

Question 32

Human chromosomes \_\_\_\_ and _____ have highest recombination level, ___ and ___ the lowest

Answer 32

21 and 22 2 and 4

Question 33

Might recombination hotspots be species specific?

Answer 33

Yes