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MBG 1000 Chapter Notes - Chapter 5: Pleiotropy, Zygosity, Epistasis

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limecicada923
17 Apr 2016
School
University of Guelph
Department
Molecular Biology and Genetics
Course
MBG 1000
Professor
Christine Schisler

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Document Summary

Single genes do not act as independently as mendel"s experiments suggested. Changes in gene expression, inheritance of mitochondrial genes, and linkage may seem to oppose mendel"s laws but do not. When gene expression appears to alter mendelian ratios. A lethal genotype does not appear as a progeny class. Homozygosity for lethal recessive alleles stops development before birth, eliminating an offspring class. A gene can have multiple alleles because its sequence can deviate in many ways. Different allele combinations may produce different variations of the phenotype. In incomplete dominance, the heterozygote phenotype is intermediate between those of the homozygotes; in codominance, two different alleles are expressed. In epistasis, one gene influences expressions of another. Genotypes vary in penetrance and expressivity of the phenotype. A gene with more than one expression is pleiotropic. In genetic heterogeneity, different genes cause the same phenotype.

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Related Questions

These all relate to exceptions to the inheritance patterns encountered by Mendel.​

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.
-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.
-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.
-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.
-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.
-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.
-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.
-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

QUESTION 1

Jim is blood type A, his brother John is type O and his sister Jane is type AB. What are the genotypes of their parents?
A.
IAi and IBi
B.
IAIA and IBIB
C.
IAi and IBIB
D.
IAIB and ii
E.
IAIA and IBi

QUESTION 2

Which of the following is true for alleles that show incomplete dominance?
A.
Heterozygotes have a genotype like the dominant allele.
B.
Homozygotes have a genotype like the recessive allele.
C.
Heterozygotes have a phenotype intermediate between the dominant and recessive alleles.
D.
Homozygotes have the same phenotype as the heterozygotes.
QUESTION 3

Which principle of inheritance concluded that when games are formed in meiosis, the two alleles of each gene separate from one another, and each gamete receives only one allele?
A.
independent assortment
B.
heterozygosity
C.
segregation
D.
dominance
QUESTION 4

Which term best describes a condition in which alleles at one locus can alter the expression of alleles at another locus?
A.
polygenic inheritance
B.
codominance
C.
multiple alleles
D.
pleiotropy
E.
epistasis
QUESTION 5

A single unit of genetic information located on a chromosome defines:
A.
a trait
B.
an allele
C.
a chromosome
D.
a locus
E.
a gene
QUESTION 6

The physical expression (appearance or function) of an organism's genes defines:
A.
genotype
B.
a single characteristic
C.
physiology
D.
mutation
E.
phenotype
QUESTION 7

Palomino horses (golden color with a blond mane) are an incompletely dominant trait produced by the combination of the chestnut color allele and the cream color allele. If you wanted to produce as many palominos as possible, which mating strategy below would be the best choice?
A.
Chestnut x Cream
B.
Palomino x Cream
C.
Palomino x Chestnut
D.
Palomino x Palomino
QUESTION 8

Which term best describes the effect of a single gene on multiple aspects of the phenotype?
A.
epistasis
B.
pleiotropy
C.
multiple alleles
D.
codominance
E.
polygenic inheritance
QUESTION 9

Which term best describes the separate expression of both alleles for a single trait in the same cell?
A.
multiple alleles
B.
codominance
C.
pleiotropy
D.
epistasis
E.
polygenic inheritance
QUESTION 10

One form of a gene found on a single chromosome defines:
A.
an allele
B.
a locus
C.
a chromosome
D.
a trait
E.
a gene
QUESTION 11

A chocolate lab (whose mother was a yellow lab) is mated with a black lab whose genotype is BbEe. What fraction of the offspring would be expected to be yellow labs?
A.
1/4
B.
none
C.
1/2
D.
3/16
E.
1/8
QUESTION 12

What type of allele is always expressed regardless of whether the individual is homozygous or heterozygous for it?
A.
Both the dominant and recessive alleles
B.
Recessive allele
C.
Allosteric allele
D.
Lethal allele
E.
Dominant allele
QUESTION 13

Given the parents AABBGgHhrr × AabbGgHhRr, assume simple dominance and independent assortment. What proportion of the progeny will be expected to have the genotype AaBbggHHrr?
A.
1/256
B.
1/64
C.
1/16
D.
1/32
E.
1/128
QUESTION 14

___________________ is defined as having two of the same type of allele for a particular trait.
A.
Homozygous
B.
Dominance
C.
Incomplete dominance
D.
Heterozygous
E.
Genotype

QUESTION 15

The physical position of an allele on a single chromosome defines:
A.
an allele
B.
a chromosome
C.
a gene
D.
a locus
E.
a trait
QUESTION 16

Which term best describes two or more genes affecting the phenotype in an additive fashion?
A.
codominance
B.
polygenic inheritance
C.
multiple alleles
D.
pleiotropy
E.
epistasis

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

Answer

· 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

Answer

· pleitropy

· locus heterogeneity

· allelic heterogeneity

· dominant negative mutation

· penetrance

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

· a wt phenotype but a mutated genotype

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

· adding a transgene to the genome of an organismduring fetal development only

· adding cells of a different species to an adultorganism

· adding a transgene to the genome of an animal atany stage in development

Question

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

Answer

· dominant traits

· recessive traits

· allelic heterogeneity

· locus heterogeneity

· vampirism

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

Answer

· haploinsufficiency

· penetrance

· expressivity

· 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

A gene mutates, and theprotein produced has a novel way of interacting with the cell, andcreates a new phenotype because of this new functionality. This iscalled

Answer

· pleitropy

· locus heterogeneity

· allelic heterogeneity

· dominant negative mutation

· gain of function dominant mutation

Question 62

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

Answer

· True

· False


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

Answer

· 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

· if the DNA you are using is genomic DNA to becopied

· if the DNA you are trying to copy iscDNA

· if the vector is prokaryotic and the transformedcell is eukarytotic

Question

Please select the best matchfor each term.

Answer

· 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?

Answer

· 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

· the child is a mosaic because he is actually a setof twins fused early during fetal development, and therefore camefrom 2 eggs and 2 sperm

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

· mitochondrial DNA only comes from mom, so there isno way to tell whobthe baby's father is