Genetics 3050 Chapter 5
How often do double crossover phenotypes occur?
0.06%
In genes 50 map units apart, crossing over can be expected in ___% of the tetrads
100
When was somatic cell hybridization made possible?
1960s
How frequently do NONcrossover F2 phenotypes occur?
94%
At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur? A) at the 4-strand stage of meiosis, after synapsis of homologous chromosomes, and before the end of prophase I B) in S phase of meiosis C) during bivalent formation, after synapsis of homologous chromosomes, and before the end of prophase I D) during synapsis at the four-strand stage of meiosis E) during synapsis in prometaphase
A) at the 4-strand stage of meiosis, after synapsis of homologous chromosomes, and before the end of prophase I
Who was the student in Morgan's laboratory who first realized that the sequence of genes could be determined by Morgan's proposal that two genes located relatively close to each other are less likely to form chiasma between them than if the two genes were relatively far apart?
A. H. Sturtevant
Recombination frequencies between linked genes are
Additive
In order to determine gene sequence during mapping, one must have
Analysis of multiple corssovers
After chromosomes are lost from numerous generations, gene products are synthesized and ________ to the chromosomes present
Assigned
What did somatic cell hybridization make possible?
Assigning of human genes to their respective chromosomes
This gene encodes for the DNA Helicase enzyme playing a critical role in DNA replication by separating the double strands of DNA
BLM gene
This is a rare autosomal recessive disorder characterized by short stature, predisposition to the development of cancer, COPD, cognitive developmental problems and genomic instability. Caused by mutations in DNA helicase protein
Bloom Syndrome
Synapsed chromosomes in meiosis wrap around each other
Chiasmata
X-shaped intersection with points of overlap and are the actual point of genetic exchange
Chiasmata
What indicate the relative location of genes on chromosome
Chromosome maps
What are the units of genetic transmission in meiosis?
Chromosomes
In _______ genetics, synteny describes the physical co-localization of genetic _____ on the same ___________ within an individual or a species
Classical Loci Chromosome
What is linkage without crossing over?
Complete Linkage
What type of linkage always produces paternal gametes?
Complete Linkage
What serves as the bases for determining the distance between genes/chromosome mapping
Crossing over
Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome? A) a mating between consanguineous individuals B) too large a sample size C) the genes are very close together on the chromosome, such that there is never a crossover between them D) the genes are very far apart on the same chromosome, such that there is always a crossover between them E) the genes are very far apart on the same chromosome, such that there is never a crossover between them
D) the genes are very far apart on the same chromosome, such that there is always a crossover between them
If complete linkage occurs, we expect ________. A) a 9:3:3:1 ratio in the F2 B) a 1:1:1:1 ratio in the test cross C) to see only recombinant phenotypes in the F2 of the appropriate test cross D) to see only parental phenotypes in the F2 of the appropriate test cross E) to see all four types of offspring
D) to see only parental phenotypes in the F2 of the appropriate test cross
Methods for determining the linkage group and genetic map in humans involve which of the following? Tetrad analysis and bromodeoxyuridine Chiasmatype and classical analyses Twin spots and tetrad analysis Zygotene and pachytene DNA synthesis DNA markers
DNA Markers
Chromosome mapping is now done using
DNA Markers, DNA Sequencing, and Annotated Computer Databases
What are the short segments of DNA with known sequence and location
DNA markers
What are DNA markers?
DNA markers are unique DNA sequences whose sequence and chromosomal location are known
What is a double crossover used to determine?
Distance between three linked genes
What is a single crossover used to determine?
Distance between two linked genes
When a double exchange of genetic material occurs, what has taken place?
Double crossover
Which of the following best describes why mapping is most accurate when genes are close together on a chromosome? This is not true; relative distance of two loci on a chromosome has no effect on accuracy of mapping. Double crossover events yield a result that looks the same as no crossover in a two gene mapping experiment and this throws off the calculations. The centromere gets in the way. Double crossover events yield a result that looks the same as one crossover in a two gene mapping experiment and this throws off the calculations. This is not true; mapping genes is most accurate when genes are far away from each other. Submit
Double crossover events yield a result that looks the same as no crossover in a two gene mapping experiment and this throws off the calculations.
Which of the following statements is true? A) A centromere and its surrounding genes constitute a linkage group. B) The chromosomal theory of inheritance denotes that linked alleles will never be separated. C) Linkage without crossing over leads to all recombinant chromosomes. D) The linkage ratio is best seen in genes on nonhomologous chromosomes. E) If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently.
E) If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently.
The frequency of exchange provides an _______ of the relative ______ between 2 genes
Estimate Distance
The progeny from the cross of the P parents are called the first _____ generation, designated F1.
Filial
Determining the ____ ______ was classically done by analysis of multiple crossovers
Gene Order
What is must be true of the two alleles in-order to do a double crossover?
Genes MUST be heterozygous
What are patch-like appearance when stained and viewed under a microscope
Harlequin Chromosomes
____________ means the trait can be passed from parent to progeny.
Heritable.
What is the product/purpose of fusing nuclei of two cells into a single hybrid cell?
Heterokaryon Somatic Cell Hybridization
Which of the following statements is true? The chromosomal theory of inheritance denotes that linked alleles will never be separated. Linkage without crossing over leads to all recombinant chromosomes. The linkage ratio is best seen in genes on nonhomologous chromosomes. If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently. A centromere and its surrounding genes constitute a linkage group.
If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently.
Genes farther apart ______ the probability of undetected crossovers
Increase
What is the relationship between the degree of crossing over and the distance between two genes?
It is direct: as the distance increases, the frequency of recombination increases. Submit
2 genes located close to each other along a chromosome are _____ likely to have a chiasma
Less
As the distance between two genes increases, the mapping experiments become _____ accurate
Less
What term is applied when two genes fail to assort independently, that is, they tend to segregate together during gamete formation?
Linkage
What term is applied when two genes fail to assort independently, that is, they tend to segregate together during gamete formation? A) discontinuous inheritance B) Mendelian inheritance C) linkage D) tetrad analysis E) dominance and/or recessiveness
Linkage
A ________ is all the genes on a single chromosome. A) linkage group B) recombination group C) chromosomal conglomeration D) genetic allele formation E) gene loci line
Linkage Group
A ________ is all the genes on a single chromosome.
Linkage group
Complete linkage between 2 genes due to close proximity resulting in a unique F2 phenotypic ratio
Linkage ratio
Mendel did NOT encounter what kinds of relationships
Linkage relationships
What generates recombinant gametes?
Linkage with crossing over
What genes are located on the same chromosome and are inherited together?
Linked Genes
What type of genes do not follow the law of independent assortment?
Linked Genes
As cells are cultured after numerous generations, the chromosomes from one parent cell are _____
Lost
1% recombination frequency between genes
Map unit (centimorgans)
What types of genes are linked on the same chromosomes that segregate together?
Meiotic Consequences
These are short and repetitive sequences found throughout the genome
Microsatellites
Is linkage present in independent assortment?
NO
Are map units exact distances?
No, they are relative
Crossing over occurs between ____________ on homologous chromosomes
Non-Sister
What are the three criteria for three-point mapping?
Parent must be heterozygous for al three genes under consideration Phenotypic class must reflect genotype of gametes of parents Sufficient number of offspring must be produced for representative sample
True-breeding plants, when used for crossing (mating) with other plants that have an alternative form of the same trait, are called the ________ generation, designated P
Parental
When crossing over occurs, what types of gametes are produced?
Paternal and Recombinant
These are generated when specific DNA sequences are recognized and cut by restriction enyme
RFLPs
What are the earliest examples of DNA markers?
RFLPs and microsatellites
Linked genes are Inherited together, unless
Recombination occurs
What does crossing over result in
Recombination of genes
Due to special nearby relationship, sister chromatids are used as substrates for __________ _____, have the capacity to repair DNA damage
Recombinational Repair
What does RLFPs mean?
Restriction fragment length polymorphisms
These are used by geneticists to identify and locate related genes
SNPs
When F1 individuals are crossed to each other or ____-_____, their progeny are designated F2.
Self-Fertilized
This type of crossover occurs between two non-sister chromatids and recombination is observed in 50% of the gametes
Single crossover
What are used to screen for disease?
Single-Nucleotide Polymorphisms
Evaluated in Bloom Syndrome and can be related to tumor formation when occurring with increased frequency
Sister Chromatid Exchange
What occur during mitosis and do not produce new allelic combinations
Sister Chromatid Exchange
What are reciprocal exchanges similar to crossing over but occur during in sister chromatids Mitotic Recombination Function in DNA repair and initiated by DS breaks
Sister Chromatid Exchanges
Who complied all data from crosses and noted the recombination frequencies between linked genes?
Sturtevant
Who was Morgans student?
Sturtevant
What are heterokaryons that are cultured in vitro when the nuclei of two cells (maybe from different species) are fused together
Synkaryon
What can be used to determine gene function
Synteny
What is the term for where 2 genetic loci have been assigned to the same chromosome but still may be separated by a large enough distance in map unit that genetic linkage has not been demonstrated?
Synteny
What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?
The Genome Sequence of a species
When is synteny testing used?
The compare the presence/absence of a gene product with a particular chromosome
Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome? Too large a sample size The genes are very far apart on the same chromosome, such that there is always a crossover between them A mating between consanguineous individuals The genes are very far apart on the same chromosome, such that there is never a crossover between them The genes are very close together on the chromosome, such that there is never a crossover between them Submit
The genes are very far apart on the same chromosome, such that there is always a crossover between them
What advantage do DNA Markers confer?
They are used as landmarks
Who proposed the term "crossing over"
Thomas Hunt Morgan
A _____ or _________ is a morphological or physiological feature of an organism, such as flower color, also used to signify a particular form of a trait or character, such as white flowers.
Trait or Character
A trait is ______ _______ when it occurs in one particular form through many generations of breeding individuals that share that trait.
True Breeding
Single crossover event produce what?
Two noncrossover gametes (parental) Two crossover gametes (recombinant)
What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete? A) whole genome sequencing B) the inclusion of the X and Y chromosomes in SNP experiments C) the use of synteny D) positive interference E) negative interference
Whole Genome Sequencing
The genes A B C occur in that order in fruit flies. A is 10 map units from B, and B is 20 map units from C. If you test crossed triply heterozygous A B C/abc how much recombination would you expect between genes A and B? a.10% b.20% c.30% d.50% e.0.2%
a) 10%
Synteny testing allows researchers to _____ a.assign genes to specific chromosomes b.map the physical positions of genes on chromosomes c.map the relative positions of genes on chromosomes d.determine physical distances (in nucleotides) between genes e.determine map distances (in recombination frequency) between genes
a) assign genes to specific chromosomes
Two genes that are 60 map units apart are expected to show _____ a.independent assortment b.25% recombination c.30% recombination d.50% recombination e.60% recombination
a) independent assortment
Three genes on the Drosophila X chromosome are examined pairwise. It is determined that they have the following recombination rates:(1) yellow, white 0.5%(2) white, miniature 34.5%(3) yellow, miniature 35.4%Which two genes are physically closest together? a.Yellow and white b.White and miniature c.Yellow and miniature d.All three are about equally spaced e.One cannot tell from this information
a) yellow and white
The genes A B C occur in that order in fruit flies. A is 10 map units from B, and B is 20 map units from C. What is the expected frequency of double crossovers? a.0.02% b.2% c.10% d.20% e.30%
b) 2%
The genes A B C occur in that order in fruit flies. A is 10 map units from B, and B is 20 map units from C.How far is A from C? a.0.2 map units b.10 map units c.20 map units d.30 map units e.40 map units
d) 30 map units
Linkage affects expected ratios because it violates which of Mendel's postulates? a.That there are two alleles for a gene in diploid organisms b.Segregation of alleles at meiosis c.Alleles have dominant-recessive relationship d.That homologs independently assort in meiosis e.Linkage does not affect ratios
d) that homologs independently assort in meiosis
Harlequin chromosomes are a demonstration of _____ a.double crossovers b.three-strand double exchange c.gene conversion d.mitotic recombination e.sister chromatid exchange
e) sister chromatid exchange FIGURE 5.16 Demonstration of sister chromatid exchanges (SCEs) in mitotic chromosomes from a Bloom syndrome patient, which display elevated numbers of SCEs. Chromosomes with SCEs are sometimes called harlequin chromosomes because of the alternating patterns they exhibit using various differential stain techniques that involve growing cells for two rounds of DNA replication in the presence of a base analog. In this example, regions of sister chromatids stained blue have one strand of the DNA labeled with a base analog while regions of sister chromatids stained green/yellow have both strands of the DNA labeled with a base analog.
What does the number of linkage groups correspond to
haploid number of chromosomes
Genes are the same chromosome are parts of a
linkage group
SNPs
single nucleotide polymorphisms
