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HMB265H1 Lecture Notes - Lecture 6: Mendelian Inheritance, Epistasis, Cross Gene

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emeraldcrow840
20 May 2018
School
UTSG
Department
Human Biology
Course
HMB265H1
Professor
Maria Papaconstantinou

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Lecture 6: Extensions fo Mendelian Genetics Part 2
Complementation
• Two mutant strains are crossed together to produce a wild-type phenotype
o This is done because the mutation for each of the strains was in separate genes which means that when
they were the crossed the other chromosome complements the lack of the WT phenotype
o The WT allele provides what the other allele lacks
• Two mutant alleles CANNOT complement each other so the phenotype is mutant – indicator of allelism
o When mutant alleles at same locus cannot complement each other they are allelic
• Complementary gene action
o Gives a modified Mendelian ratio (9:7)
o 2 genes are interacting in the same pathway controlling tomato fruit colour
• Complementation testing is once of the most powerful tests in genetic analysis
• Simultaneously a test for allelism- must be one or the other
o works when the phenotype is recessive
• Allows one to uncover how many different genes control a trait
• If no complementation, must be allelic
o Mutation is in the same gene
Epistasis
• Epistasis occurs when one locus masks the effects of another locus acting on the same trait
• The locus that is doing the masking is said to be epistatic to the other
• Epistatic ratios allow a geneticist to hypothesize about the order of genes in a particular pathway
• Importantly, this is only a hypothesis that depends on assumptions about the nature of the pathway
o In the biochemical pathway, the epistatic
gene encodes an upstream step
o R1 is epistatic to R2
• Tomato fruit was an example of recessive
epistasis
o The homozygous recessive allele at one
locus hides the effect of the other locus
o In the biochemical pathway the epistatic
gene encodes an upstream step
Recessive Epistasis
• Homozygous recessive allele at one locus hides effect of the other locus
• In a developmental pathway, the epistatic gene encodes a downstream step
• In a biosynthetic pathway, the epistatic gene encodes an upstream step
o Will get a 9:3:4 ratio
o E is epistatic to B
▪ Dog fur colour
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Expression vectors inprokaryotes do not make functional eukaryotic gene products inbacteria very well because

Answer Not sure which one ?!

· the codon sequence for prokaryotes is differentthan the codon sequence in eukaryotes

· there are no disulfide bridges formed in proteinsnormally made in prokaryotes

· prokaryotic expression vectors cannot translateeukarytic sequences

· eukaryotic genes have introns, and prokaryotesdon't

· eukaryotic genes have exons and prokaryotesdon't


I create a knockout mouseusing the agouti/black fur system \. When I cross the agoutioffspring of the originally engineered mouse, I find a ratio of 2agouti mice to 1 black furred mouse. What is the bestexplanation?

Answer not sure which one?!

· The gene knocked out was recessive.

· The gene knocked out was dominant.

· The gene knocked out was a lethalgene.

· The knockput was integrated into a random spot,and did not knockput the original gene.

A restriction enzyme cuts DNAand leaves the following end

xxCTGCA
xxG

Which of the following could be the sequence of the correspondingend of the other end of the cut DNA?

Answer

· xxG
xxCTGCA

· xxC
xxGTGCA

· xxCCGAT
xxG

· xxGGCTA
xxC


An SNP always occurs dueto

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· a one base-pair change.

· a three base-pair change.

· a single restriction site change.

· a single amino acid change.

· None of these.


I PCR out a mutated gene in apatient with Lisenbee chorea (the inability to dance in acoordinated fashion) and I compare it to another patient with thatsame disease phenotype. One subject had a mutation on chromosome 4,and the other subject couldn't rock it because of a mutation onchromosome 5. This is an exampe of

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· pleitropy

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· allelic heterogeneity

· dominant negative mutation

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In his experiments, Mendelnoted that when two traits are involved in a genetic cross, theyare inherited independently of each other. Though Mendel didn'tknow about chromosomes, this still holds true (mostly)because

Answer

· genes on the same chromosome are often mixedthrough meiotic crossover during the formation ofgametes.

· variant alleles of the same gene do not interferewith the phenotypic expression of the gentoype in different geneticloci.

· most higher organisms are diploid, making only twoalleles available for every genetic locus, and there is a 50/50chance of geting either allele from a single parent.

· expression of phenotypes can vary from thegenotypes because of encironmantal influences.

· chromosomes often recombine

Anticipation is caused by amutation that increases in expressivity over subsequentgenerations.

Answer

· True

· False

Question 44

I have a genotype that shouldproduce a specific phenotype, but some of the individuals with thegenotype do not demonstrate any evidence of the phenotype. I wouldconsider this an example of

Answer

· allelic heterogeneity.

· locus heterogeneity.

· penetrance.

· expressitivity.

· sheer luck.

Question

Which of the following doesnot occur during the PCR reactions?

Answer

· Changes in the reaction temperature by athermocycler

· Denaturation at high temperatures

· Synthesis of oligonucleotide primers

· Extension of primers by DNA polymerase

· Annealing of oligonucleotide primers

Question

DNA markers, or variantnon-coding regions of DNA, are DNA polymorphisms that are usefulfor genetic mapping.

Answer

· True

· False

A mosaic is an organismwith

Answer

· multiple genotypes within one organism

· multiple alleles within one genotype

· more than one color of fur

· transgenes added to the zygote beforedevelopement

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Question

Genotype causesphenotype.

Answer

· No, gentoype just influences phenotype.

· Yes, genotype is the DNA sequence that createsphenotype.

Question

A true genetic chimera can becreated by

Answer

· mutating a gene early on in the development of anorganism resulting in different alleles being present in theadult

· multiple fertilized eggs or zygotes fusing to formone embryo

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Question

The ABO blood group can bestbe explained by the concept of _______.

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· dominant traits

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· locus heterogeneity

· vampirism

If a loss of functionmutation creates a dominant phenotype, it may be becauseof

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· haploinsufficiency

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· allelic heterogeneity

· locus heterogeneity

Please select the best matchfor each.

Answer

· PCR: Technique used to generatecopies of a DNA fragment

· Southern blot : Screeningprocedure used to assay DNA fragments

· RFLPs : DNA fragments generatedby restriction enzymes that vary in length betweenindividuals

· Northern blot : Screeningprocedure used to assay mRNA fragments

· Electrophoresis Movement ofmacromolecules in an electrical field

Answer

A.

Screening procedure used toassay DNA fragments

B.

Movement ofmacromolecules in an electrical field

C.

Screening procedure used toassay mRNA fragments

D.

DNA fragments generated byrestriction enzymes that vary in length betweenindividuals

E.

Technique used to generatecopies of a DNA fragment

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· pleitropy

· locus heterogeneity

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Question 62

Mutations in the somaticchromosomes may be inherited by the next generation.

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· True

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A degenerate PCR primer withmany variant sequences must be used to make multiple copies of agene

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· if only the protein sequence of the gene productis known to construct the primers

· if the DNA you are using is cDNA to constructthe primers

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· if the DNA you are trying to copy iscDNA

· if the vector is prokaryotic and the transformedcell is eukarytotic

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Please select the best matchfor each term.

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· Restriction enzyme


· PCR C

· Plasmid

· YAC A

· Dideoxynucleotide

Answer

A.

Endonuclease isolated frombacteria

B.

Eukaryotic cloningvector

C.

Method for amplification ofDNA sequences

D.

Small circular fragment ofDNA

E.

Molecule used in DNAsequencing

Question

A couple goes on MauryPovitch, and the results are in: you are not the father. But noother man impregnated the female (granted, unlikely for a MauryPovitch guest, but work with me here) and he must be the father.DNA analysis claims otherwise, though the child definitely wasmom's (poor thing). What may be going on here?

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· the child is parthenogenic because the motheractually impregnated herself like a shark, and the child's DNA isall mom's

· the child had a mutation that changed the genethat is used to trace paternity

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· the dad may have germ-line mosaicism, meaning thatthe genotype of his sperm is different from his somaticgenotype

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