Chapter 2 - Mendal's Laws (part II)
What is the F2 generation of a dihybrid cross for Dominant Epistasis I?
12:3:1
What is the F2 generation of a dihybrid cross for Dominant Epistasis II?
13:3
What is the F2 generation of a dihybrid cross for Redundancy?
15:1
If a trait is controlled by two codominant alleles of one gene, what phenotypic ratio is expected in the offspring of a mating of two heterozygotes?
1:2:1
For a dihybrid cross involving recessive epistasis, what phenotypic ratio is expected in the F2 generation?
9:3:4
What phenotypic ratio resulting from a dihybrid cross (e.g., Aa Bb x Aa Bb) is indicative of reciprocal recessive epistasis? Multiple choice question.
9:7
Define Gene redundancy.
A specific phenotype is produced when only one of two genes is functional.
What is a heterogeneous trait?
A trait that can result from a mutation in one of a number of different genes
Some humans appear to have blood type O, when in fact they are homozygous recessive for a second gene (genotype hh) which masks the effects of any ABO allele that might be present. Such humans are said to exhibit a ____________ phenotype.
Bombay
How do geneticists limit the number of variables under investigation at one time?
By studying inbred populations of experimental organisms
Which genotypes will result in blood type A?
I^A,i I^A,I^A
Which of the following phenomena expand (i.e., increase) the number of phenotypic classes among the F2 offspring of a cross?
Incomplete dominance and Codominance
Define redundancy
Only one dominant allele of either of 2 genes is necessary to produce phenotype.
What term describes how many members of a population who have a particular genotype exhibit the expected phenotype?
Penetrance
If a genetic cross between two dihybrids results in a 9:3:4 phenotypic ratio, what type of genetic interaction is most likely to exist between the two genes?
Recessive epistasis
Which of the following statements about the sickle-cell mutation is an example of its pleiotropic effects?
The mutation causes changes in blood cell shape and confers resistance to malaria.
Define pleiotropy and give an example.
The phenomenon in which one gene affects many traits. Ex. Sickle cell anemia
A pure-breeding tall plant is crossed with a pure-breeding short plant. The hybrid offspring from this cross are all short. Which allele of the gene for height is dominant?
The short allele is dominant.
The ABO blood group is determined by a single gene that has three different alleles. How many alleles of this gene does each person have?
Two
Suppose there is a biochemical pathway for producing blue flower color that goes from white--->magenta--->blue. A dominant allele for gene 1 provides an enzyme that converts white--->magenta. A dominant allele for gene 2 provides an enzyme that converts magenta--->blue. Recessive alleles of gene 1 and gene 2 are nonfunctional. A plant that has the homozygous recessive genotype for gene 1 would have ______ petals
White
What is epistasis?
a gene interaction in which the effects of alleles at one gene hide the effects of alleles at another gene.
Define recessive epistasis.
a gene interaction in which the effects of recessive alleles at one gene hide the effects of alleles at another gene.
The proportion (or percentage) of an allele of a gene out of all of the number of copies of that gene in a population is called the
allele frequency
A modifier gene is a gene that ____.
alters the phenotype produced by alleles of other genes
Define reciprocal recessive epistasis.
an interaction between alleles of two different genes where the homozygous recessive genotype of each gene prevents the phenotypic expression of (is epistatic to) the dominant allele of the other gene.
In humans, the Bombay phenotype is characteristic of people that
are homozygous recessive for a second gene that masks the effects of any ABO alleles.
Suppose there is a biochemical pathway for producing blue flower color that goes from white--->magenta--->blue. A dominant allele for gene 1 provides an enzyme that converts white--->magenta. A dominant allele for gene 2 provides an enzyme that converts magenta--->blue. Recessive alleles of gene 1 and gene 2 are nonfunctional. A plant with magenta petals must have ______.
at least one dominant allele for gene 1 but two recessive alleles for gene 2
A mutation is defined as a _____.
change in the genetic material
An allele that is lethal only under certain circumstances, such as high temperature, is called a(n) temperatureBlank 1Blank 1 temperature , Incorrect Unavailable lethal allele.
conditional
An allele that is lethal only under certain circumstances, such as high temperature, is called a(n). _____ lethal allele.
conditionally
Expressivity is best defined as the ____.
degree to which a genotype is expressed in a phenotype
A trait for which the phenotypes fall into clear-cut categories, such as green peas or yellow peas, is an example of a(n) ______ trait.
discrete
The type of genetic interaction in which the effect of an allele of one gene masks the effects of alleles of a second gene is called
epistatic
A phenocopy is a phenotype that results from _____.
exposure to environmental agents
A discontinuous trait is a trait whose phenotypes _____.
fall into discrete categories
Because deafness can result from a mutation in one of many different genes, it is considered a(n) _____ trait.
heterogeneous trait
The Bombay phenotype results from an allele, h, that is recessively epistatic to the IA, IB, and i alleles. Which genotype(s) for the H gene always result(s) in a blood type that appears to be O?
hh
Only 75% of people who inherit a dominant mutation in the retinoblastoma gene will develop the disease is an example of?
incomplete penetrance
Retinoblastoma is caused by a dominant mutation in a single gene. However, only 75% of people who carry the mutant allele develop retinoblastoma. This is an example of...
incomplete penetrance
When the alleles of a gene exhibit incomplete dominance or codominance as opposed to complete dominance, the number of resulting phenotypic classes among the F2 offspring of a dihybrid cross will _____.
increase
Geneticists often study inbred populations of experimental organisms to study specific traits. The purpose of using inbred populations is to
limit the number of variables being studied.
Redundant genes are genes that _____.
may specify nearly identical proteins with the same function
A gene that alters the phenotype produced by the alleles of another gene is called a ______ gene.
modifier
A change in phenotype that arises due to exposure to an environmental agent, such as a chemical, and resembles a phenotype caused by mutant alleles of specific genes is called a(n) ______.
phenocopy
The term penetrance describes the ____.
proportion of individuals with a particular genotype who exhibit the expected phenotype
A trait is controlled by two genes that work in succession, and a dominant allele of each gene is required to produce a certain phenotype. The interaction between the alleles of the two genes is referred to as ____________________ epistasis.
reciprocal recessive epistasis
At least one dominant allele of each gene must be present to produce the pigment is an example of what kind of epistasis?
reciprocal recessive epistasis
Two genes that specify nearly identical proteins that perform the same function are called ________ genes.
redundant
In fruit flies, individuals carrying a mutant allele of the shibire gene develop normally at 22oC but become immediately paralyzed when exposed to temperatures above 29oC. The paralysis is reversed as long as the temperature returns to 22oC within a few hours. This allele is most likely a(n) ______.
temperature-sensitive allele
Define Expressivity.
the degree or intensity with which a particular genotype is expressed as a phenotype.
When geneticists use the term genetic background, they are referring to ____.
the set of unknown modifier genes that influence the action of a known gene
A conditional lethal allele is an allele that is lethal only ____.
under certain environmental conditions
In some people with retinoblastoma, only one eye is affected. In other people, both eyes are affected is an example of?
variable expressivity
Retinoblastoma is caused by a dominant mutation that results in the formation of tumors in the retina. Some people with this mutation develop tumors in both eyes. Others who have the same mutation develop tumors in only one eye. This is an example of ____.
variable expressivity
Define variable expressivity.
when the severity of a genetic disorder shows significant difference in different affected individuals