Connect ch 2 genetics
Which of the following phenomena expand (i.e., increase) the number of phenotypic classes among the F2 offspring of a cross?
- Codominance - Incomplete dominance
Which of the following situations is an example of a phenocopy?
Ingestion of thalidomide by a pregnant woman can result in a condition in the fetus that is similar to an inherited trait called phocomelia.
Match each type of gene interaction with the phenotypic ratio observed in the F2 generation of a dihybrid cross.
Recessive epistasis ---> 9:3:4 Dominant epistasis ---> 12:3:1 Reciprocal recessive epistasis ---> 9:7 Redundant gene action ---> 15:1
When dominant epistasis occurs between alleles of two genes, it often indicates that their functions are ____.
antagonistic
In mice, tail length may be reduced due to the presence of a dominant mutation, T. Which line of experimental evidence would support the hypothesis that one or more modifier genes influence the length of the tail when the T mutation is present?
The tail length is variable in different inbred strains of mice that carry the T allele regardless of the environment in which they are raised.
White leghorns have a doubly dominant genotype for feather color (AA BB) while white wyandottes have a doubly recessive genotype (aa bb). A cross between these chickens produces white birds with the hybrid genotype. The alleles of these two genes exhibit dominant epistasis: B is epistatic to A, such that chickens containing the A allele have red feathers only in the absence of the B allele. Based on that information, would you expect to see red-colored chickens in the F2 generation (produced by crossing the above-mentioned F1 hybrids) and in what ratio?
Yes; 13 white:3 red
In the 1960s, pregnant women were sometimes prescribed thalidomide. Use of this drug disrupted limb development in fetuses. The resulting phenotype was very similar to a rare inherited trait called phocomelia. This is an example of _____.
a phenocopy
To determine whether the same recessive mutant phenotype observed in two different strains results from mutations in the same gene or in different genes, a geneticist would perform a(n) _____ test.
complementation
Expressivity is best defined as the ____.
degree to which a genotype is expressed in a phenotype
A phenocopy is a phenotype that results from _____.
exposure to environmental agents
Because deafness can result from a mutation in one of many different genes, it is considered a(n) _____ trait.
heterogeneous
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
When an allele is conditional lethal, the environmental condition that results in lethality is called the ______ condition, and the condition that is not lethal is called the ______ condition.
restrictive permissive
The phenotypic values of a continuous trait _____.
vary over a range of values
Which of the following genotypes could be represented with the notation A- bb?
- Aa bb - AA bb
Which of the following phenotypes are associated with mutations in the β-globin gene?
- Destruction of blood cells (hemolysis) - Sickling of red blood cells - Inefficient transport of oxygen
If a genotype is represented as H- J-, which of the following genotypes could it represent?
- HH JJ - Hh JJ - Hh Jj - HH Jj
The ABO blood type is determined by a gene with three alleles, IA, IB, and i. A recessive allele, h, of another gene, is epistatic to all three alleles of the ABO gene because hh homozygotes do not produce substance H to which sugar A and or B can be added. Which of the following genotypes would result in a blood type that appears to be O?
- Hh ii - hh IAi - hh IAIB
Which of the following traits show continuous variation?
- Human height - Human skin color
Which of the following genotypes will result in blood type A?
- IAIA - IAi
Regarding the ABO blood groups in humans, which two of the following pairs of alleles exhibit complete dominance?
- IB is completely dominant to i. - IA is completely dominant to i.
In sweet peas, production of purple pigment is controlled by two genes. Allele A specifies a functional version of Enzyme A, and allele B specifies a functional version of Enzyme B. Alleles a and b result in nonfunctional forms of these two enzymes. Which of the following genotypes will result in a white flower instead of a purple flower?
- aa bb - aa BB - Aa bb
Assuming normal gene transmission, what is the likelihood that a man with type O blood and a woman with type AB blood could have a child with type O blood? (Assume no involvement of the Bombay phenotype.)
0%
In humans, the frequency of gametes that carry a mutation in a particular gene is approximately between _____.
1 in 10,000 and 1 in 1,000,000
The mutation rate for human genes varies from one gene to another. Which of the following mutation rates falls within the known range of mutation rates for human genes?
1 in 100,000
Manx cats have shortened tails due to the autosomal dominant allele M that affects spine formation. This allele is lethal in homozygotes. The autosomal recessive allele m leads to normal tail development. If two Manx cats are mated to each other, what is the fraction of viable offspring expected to have normal tail lengths?
1/3
In chickens, feather color can be black or splash (white with black spots). If a black rooster is crossed to a splash hen, the offspring show an intermediate blue color. If a blue rooster is crossed to a blue hen, what fraction of the offspring will be expected to have black feathers?
1/4
Which of the following F2 phenotypic ratios in a dihybrid cross is consistent with dominant epistasis between the alleles of two genes?
12:3:1
What phenotypic ratio is most likely to be observed in the F2 generation of a dihybrid cross involving two genes that have redundant functions?
15:1
If a trait is determined by genes that all have two alleles exhibiting incomplete dominance and the trait is distributed over five distinct phenotypic classes, the trait is most likely controlled by _____.
2 genes
A trait is determined by three different genes, each with two alleles exhibiting incomplete dominance. The alleles of each gene contribute either nothing (0) or the same amount (1) to the phenotype. How many distinct phenotypic classes are possible?
7
What is a heterogeneous trait?
A trait that can result from a mutation in one of a number of different genes
Which of the following statements about reciprocal recessive epistasis, involving two genes that affect pigment production, is correct?
At least one dominant allele of each gene must be present to produce the pigment.
White leghorns have a doubly dominant genotype for feather color (AA BB) while white wyandottes have a doubly recessive genotype (aa bb). A cross between these chickens produces white birds with the hybrid genotype. When F1 hybrids are allowed to cross, the F2 generation exhibits a ratio of 13 white-feathered chickens to 3 red-feathered chickens. What could explain that?
B is epistatic to A such that the presence of A results in red feathers only in the absence of B.
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
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
In fruit flies, the absence of wings can result from homozygosity for recessive mutations in different genes. Two different wingless strains are crossed with one another. In the F1 generation, all of the flies are wingless. Which of the following statements is correct?
Complementation did not occur, so the mutations in the two strains must be in the same gene.
In sweet peas, the wild-type color is purple. Two different strains with white flowers are crossed with one another. In the F1 generation, all of the flowers are purple. Which of the following statements about this cross is correct?
Complementation occurred, so the mutations in the two strains must be in different genes.
Which cross in this diagram represents the expected outcome if alleles A1and A2 are codominant to one another?
Cross #4
Which of the following situations is an example of the effect of environmental factors on an inherited disease?
Diet and exercise influence the penetrance and expressivity of heart disease in people with a genetic predisposition to this type of disease.
Which of the following situations is an example of variable expressivity?
In some people with retinoblastoma, only one eye is affected. In other people, both eyes are affected.
In pea plants, the production of starch in the seed is catalyzed by an enzyme that can be specified by two alleles: the allele R1, which specifies a functional enzyme, and the allele R2, which specifies a non-functional enzyme. If we consider the activity of this enzyme in plants with the genotype R1R1 to be 100%, plants with the genotype R1R2 exhibit 50% activity, while plants with genotype R2R2 exhibit 0% activity. Plants with the genotype R1R2 have an intermediate amount of starch in their seeds (when compared to plants with R1R1 or R2R2 genotypes). What is this an example of?
Incomplete dominance
Can geneticists predict the penetrance and expressivity of a trait?
No, penetrance and expressivity are determined empirically by observation.
Which of the following situations is an example of incomplete penetrance?
Only 75% of people who inherit a dominant mutation in the retinoblastoma gene will develop the disease.
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
What genetic interaction is characterized by a 9:7 phenotypic ratio in the F2 generation of a dihybrid cross (such as Aa Bb x Aa Bb)?
Reciprocal recessive epistasis
What type of genetic interaction would be suggested by a dihybrid cross resulting in a 15:1 phenotypic ratio in the F2 generation?
Redundant gene action
For harebell plants, dominant alleles for two separate genes are needed to produce blue petal color. For snapdragon plants, the presence of a dominant allele for either of two genes leads to red petal color. Which one is an example of redundant gene action?
Snapdragon plants
The table shown here compares the genotypes and phenotypes resulting from various combinations of the wild-type (HbβA) and sickle-cell (HbβS) alleles. Which of the following statements about the dominance relationships of these alleles is correct?
The sickle-cell allele is recessive to the wild-type allele for red blood cell shape at sea level but dominant for malaria resistance.
In lentils, a cross between pure-breeding spotted lentils and pure-breeding dotted lentils results in heterozygotes that are both spotted and dotted. Which of the following statements best describes the dominance relationship of the spotted and dotted alleles?
The spotted and dotted alleles are codominant.
A scientist is investigating a human disease caused by a recessive allele. When studying a particular family, the scientist reconstructs the following pedigree. What conclusion can be drawn from this pedigree?
This disease exhibits locus heterogeneity.
What is the purpose of a complementation test?
To determine whether the same recessive phenotype results from mutations in one gene or two different genes
Deafness in humans is a heterogeneous trait. Which of the following supports that?
Two deaf parents can have hearing offspring.
An allele that can lead to the death of a homozygous individual is called _____.
a recessive lethal allele
In mice, the AY allele specifies the production of a yellow coat in heterozygous individuals that carry the AY allele and the wild-type A allele. However, homozygous AYAY mice die early in their development. The AY allele is therefore ____.
a recessive lethal allele
In mice, the agouti gene determines coat color. A scientist studies a natural population of mice and discovers that the allele that specifies dark gray (or agouti) coat color has a frequency of 99% in that population. Because of its high frequency, this allele would be considered _____.
a wild-type allele
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
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.
Because individuals heterozygous for the sickle-cell trait produce both normal hemoglobin and sickled hemoglobin, in terms of their effects on the production of β-globin proteins, the HbβA and HbβS alleles are considered ______.
codominant
The gene that controls the ABO blood group has three different alleles with different dominance relationships. The IA allele is ______.
codominant with the IB allele and completely dominant to the i allele
When a gene has multiple alleles that are present at high frequency within a population and considered to be wild type, geneticists refer to the alleles as _____ variants.
common
An allele that is lethal only under certain circumstances, such as high temperature, is called a(n) ____ lethal allele.
conditional
A trait that varies over a range of values that produce a bell curve when charted on a graph is called a(n) ______ trait.
continuous
As shown in this graph, human skin color exhibits a broad distribution over a range of phenotypic values. This is an example of
continuous variation
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.
discontinuous
Parents can unknowingly pass on a dominant lethal allele for Huntington disease to their offspring because the ______.
disease symptoms often do not appear until after the parent has had children
A list of alleles that are arranged in order from the one that is dominant to all the other alleles, to the one that is recessive to all the other alleles, is called a(n) _________ _________.
dominance series
In a dominance series, all of the alleles of a gene are listed in order from the one that is _________ to all the other alleles, to the one that is __________ to all the other alleles.
dominant recessive
Alleles of two different genes have antagonistic functions. The alleles are most likely to exhibit _____.
dominant epistasis
If a dihybrid cross results in a phenotypic ratio of 12:3:1, the most likely type of genetic interaction between the genes involved is ______.
dominant epistasis
A heterozygous animal has a wild-type allele of a gene that specifies a crucial molecule for viability, and a nonfunctional allele of that gene. As the animal has a normal phenotype, production of sufficient quantities of the functional protein by the ______ allele compensates for the production of a non-functional protein by the ______ allele.
dominant; recessive
The ability to prevent the symptoms of phenylketonuria by restricting the diets of patients who inherit the disease is an example of ________ effects on a phenotype.
environmental
Some people inherit a genetic predisposition to develop lung cancer. However, whether or not they actually develop lung cancer is strongly influenced by whether or not they smoke. This is an example of ____.
environmental effect on a phenotype
The phenotype associated with phenylketonuria, an autosomal recessive disorder in which individuals are unable to metabolize phenylalanine, can be altered by a restricted diet with limited amounts of phenylalanine. This is an example of _____.
environmental effects on a phenotype
In an epistatic interaction between two genes, the allele that is masking the effects of another gene is called the _____ allele, and the gene that is being masked is called the _____ gene.
epistatic hypostatic
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 _______.
epistatis
The degree or intensity with which a particular genotype is expressed in a phenotype is referred to as ________.
expressivity
A discontinuous trait is a trait whose phenotypes _____.
fall into discrete categories
In some cases, geneticists suspect the existence of but have not yet identified any modifier genes for a particular trait. In this case, the set of unknown modifier genes that might influence the action of known genes is called the _____.
genetic background
A mutant allele is defined as an allele that _____.
has an allele frequency that is less than 1%
In areas where malaria is endemic, the sickle-cell allele is often widespread because ____.
heterozygotes (HbβA HbβS) survive and pass on their genes more successfully than either homozygote
The sickle-cell allele is common in parts of the world where malaria is endemic because ____.
heterozygotes are better able to survive and pass on their genes than either homozygote
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
The term "common variant" is used to refer to a _____.
high-frequency allele of a polymorphic gene
If the F2 generation of a cross between two pure-breeding lines exhibits a 1:2:1 phenotypic ratio, the type of dominance being observed is most likely _____.
incomplete dominance or codominance
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
Huntington disease is a lethal condition for which symptoms begin to appear in middle age. This is an example of ____.
late-onset lethality
In mice, the mutant T allele of the tail-length gene results in a shorter tail. However, in different inbred lines, the reduction in tail length is variable. This suggests the presence of one or more _____.
modifier genes
An allele that is rare within a population is called a(n) ________ allele.
mutant
A change in the genetic material is called a(n) ___________.
mutation
The penetrance and expressivity of a trait are quantified by ____.
observing and counting the genotypes and phenotypes of many individuals in a population
Pleiotropy is a situation in which ______.
one gene affects several different characteristics
In a certain plant, flower color is controlled by a gene with multiple alleles. When an apricot strain is crossed with a white strain, the F1 plants all have apricot flowers, and the F2 consist of 3/4 apricot and 1/4 white. When a white strain is crossed with an orange strain, the F1 plants all have orange flowers, and the F2consist of 3/4 orange and 1/4 white. When an apricot strain is crossed with an orange strain, the F1 plants all have orange flowers, and the F2 consist of 3/4 orange and 1/4 apricot. What is the correct dominance series for these alleles?
orange > apricot > white
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
Among the Maori people of New Zealand, a recessive mutation that affects the function of cilia and flagella results in respiratory problems and male sterility. The effect of this mutation on the respiratory and reproductive systems is an example of ____.
pleiotropy
The allele for sickle-cell disease leads to multiple changes in the individual's phenotype, including the type of hemoglobin produced, the shape of red blood cells, the onset of anemia and reduced susceptibility to malaria. The name for these multiple effects on phenotype is ______.
pleiotropy
The mutation that causes cystic fibrosis affects a protein that transports chloride ions across the cell membrane. As a result of this mutation, patients accumulate mucus in their lungs and are susceptible to respiratory infections. Mucus can also block the pancreatic duct, which leads to digestive problems. Finally, the defect in the chloride transporter changes the composition of sweat. The effects of this mutation on the lungs, the pancreas, and the sweat glands are an example of _____.
pleiotropy
In genetic notation, a wild-type allele is often designated with a superscript
plus sign.
Allele frequency is defined as the ____.
proportion of a certain allele out of all of the copies of a gene in a population
The term penetrance describes the ____.
proportion of individuals with a particular genotype who exhibit the expected phenotype
For Labrador Retrievers the dominant allele B for gene 1 leads to black coat while the recessive allele b leads to brown coat. Alleles of gene 2 can change this color, with the dominant allele E having no effect but genotype ee changing either black or brown to yellow color. This is an example of ____.
recessive epistasis
Suppose that the covering on corn kernels can have a purple color due to the dominant allele P of gene 1. Alleles of gene 2 can mask this color, with the dominant allele C having no effect but genotype cc changing the purple color to colorless. This is an example of ______.
recessive epistasis
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
Two genes that specify nearly identical proteins that perform the same function are called ______ genes.
redundant
For snapdragon flowers, the presence of a dominant allele for gene A or a dominant allele for gene B leads to red petals. Only the aa bb genotype leads to white petals. This is an example of _____.
redundant gene action
If an allele is conditional lethal, the environmental condition that results in lethality is called the _____.
restrictive condition
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
Himalayan coloring in rabbits is due to a dominant allele that specifies a tyrosinase enzyme which participates in the production of the dark pigment melanin. In cold temperatures, dark coloring is only found in the ears, nose and feet of the animal. White coloration develops on body areas where blood flow keeps the animal warm. The tyrosinase enzyme is most likely a _____.
temperature-sensitive enzyme
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
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
Inefficient transport of oxygen, sickling of red blood cells, and destruction of blood cells are all phenotypes associated with mutations in the _____.
β-globin gene
An allele is considered wild type if it is present in a population at a frequency of ____.
1% or more
In snapdragons, flower color exhibits incomplete dominance: hybrids of a cross between pure-breeding red and white-flowered parents yields offspring with pink flowers. If the pink-flowered plants are allowed to self-fertilize, what fraction of the offspring will be pink?
1/2
In lentils, two genes control seed color. The genotypes and phenotypes are summarized in the table. If tan lentils with genotype Aa bb are crossed with gray lentils with genotype aa Bb, what phenotypic ratio will be observed among the offspring?
1/4 brown, 1/4 tan, 1/4 gray, 1/4 green
For summer squash, the dominant allele Y for gene 1 leads to yellow color while the recessive allele y leads to green color. Alleles of gene 2 can prevent color formation, with the dominant allele W leading to white squash while the recessive allele w does not interfere with color development. For the cross Yy Ww x Yy Ww, what is the fraction of offspring that will be white?
12/16
In a cross between pure-breeding tan lentils and pure-breeding gray lentils, four different phenotypes occur among the F2 progeny. In the F2 generation, 9/16 of the lentils are brown, 3/16 are tan, 3/16 are gray, and 1/16 are green. Based on these data, how many genes control lentil seed color?
2
Suppose a man with type A blood and a woman with type B blood have a child with type O blood. What is the likelihood that they could have a child with type AB blood at a later time? (Assume no involvement of the Bombay phenotype.)
25%
What phenotypic ratio is expected to result from a cross between two individuals that are heterozygous for a recessive lethal allele?
2:1
Which of the surface antigens related to blood type would be found on the red blood cells of an individual with the IAIB genotype?
Each red blood cell would carry both surface antigen A and surface antigen B.
This table represents the phenotypes associated with various genotypes of the two genes that control seed color in lentils. If a brown lentil with genotype AA Bb is crossed with a gray lentil with genotype aa Bb, what phenotypes will be observed among the offspring?
3/4 brown, 1/4 tan
For harebell plants, dominant alleles for two separate genes are needed to produce blue petal color. Suppose Gene 1 has alleles P and p and Gene 2 has alleles B and b. Only plants with at least one P allele and at least one B allele will have blue petals; all other genotypes lead to white petals. For the cross Pp Bb x Pp Bb, what fraction of the offspring are expected to have white petals?
7/16
Suppose that the covering on corn kernels can have a purple color due to the dominant allele P of gene 1. The genotype pp leads to a colorless covering. Alleles of gene 2 can mask the purple color, with the dominant allele C having no effect but genotype cc changing the purple color to colorless. Alleles of gene 2 have no effect on plants with genotype pp for gene 1. For the cross Pp Cc x Pp Cc, what fraction of the plants are expected to have colorless covering on their corn kernels?
7/16
In fruit flies, dominant alleles for two different genes are required for red eye color. Suppose Gene 1 has alleles R and r and Gene 2 has alleles E and e. Only flies with at least one R allele and at least one E allele will have red eyes; all other genotypes lead to white eyes. For the cross Rr Ee x Rr Ee, what fraction of the offspring are expected to have red eyes?
9/16
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?
9:7
What is epistasis?
A gene interaction in which the effects of an allele of one gene mask the effects of the alleles of a second gene
Which of the following would be considered a universal blood donor?
A person with a blood type O
What fraction of the normal levels of functional protein product of a gene should be found in a cell that is heterozygous for normal and nonfunctional mutant alleles of that gene?
Approximately 50%
Which ABO blood types will produce anti-A antibodies?
B and O
Why are people with blood type AB considered universal recipients?
Because they don't make either anti-A or anti-B antibodies
What antibodies will be produced by an individual with blood type O?
Both anti-A and anti-B antibodies
Two pure-breeding lines are crossed with one another. The F1 progeny look like one of the true-breeding parents, and the F2 generation has a 3:1 ratio of phenotypes. What type of dominance relationship is this?
Complete dominance
Which cross in this diagram represents the expected outcome if alleles A1and A2 exhibit incomplete dominance?
Cross #3
Which description matches the appropriate pattern involving two genes?
Epistasis ---> Expression of the alleles of one gene is masked by alleles of a different gene. Reciprocal recessive epistasis ---> Two parents with the same recessive phenotype produce only offspring with a different phenotype. Gene redundancy ---> A specific phenotype is produced when only one of two genes is functional.
Match each blood type genotype to the correct phenotype.
IAIB --> Blood type AB IAi --> Blood type A IBIB --> Blood type B ii --> Blood type O
A heterozygous individual has a phenotype that is intermediate between the phenotypes of its two homozygous parents. What is this an example of?
Incomplete dominance
In cats, the autosomal dominant allele M affects spine formation in a way that causes the development of shortened tails. Cats with such shortened tails are called Manx cats. The M allele is lethal in homozygotes. The autosomal recessive allele m leads to normal tail development. What is the genotype for a Manx cat?
Mm
Two pure-breeding plants are crossed with one another. The first plant is homozygous for allele A1 and has white flowers. The second plant is homozygous for allele A2 and has blue flowers. The A1A2 hybrids all have blue flowers. Which allele is dominant?
The A2 allele is dominant to A1.
In a classic experiment, a cross between two heterozygous yellow mice produced both yellow and agouti offspring. The yellow coat color was thought to be due to an allele dominant with respect to the allele that specifies agouti coat color. Surprisingly, instead of the typical 3:1 ratio, the ratio of phenotypes was 2 yellow: 1 agouti. How can this be explained?
The allele for yellow coat is lethal in homozygotes.
In humans, what is the molecular basis of the ABO blood groups?
The alleles IA and IB encode two functional, but slightly different forms of the same enzyme.
Epistasis is a genetic interaction in which the genotype for one gene masks the effects of the genotype for a second gene. Which of the following statements is correct?
The epistatic allele masks the effects of the hypostatic allele.
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.
How would the pattern of allele segregation and the phenotypic ratio in the F2 generation of Mendel's monohybrid cross have been affected if the alleles showed incomplete dominance rather than complete dominance?
The pattern of allele segregation will be the same, but the phenotypic ratio in the F2 will be different.
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.
Which statement accurately describes Mendel's law of segregation for genes with alleles that exhibit incomplete dominance or codominance?
When incomplete dominance or codominance is observed, the alleles involved still follow a typical Mendelian segregation pattern.
In sweet peas, production of purple pigment is controlled by two genes. Allele A specifies a functional version of Enzyme A, and allele B specifies a functional version of Enzyme B. Alleles a and b result in nonfunctional forms of these two enzymes. What color flower will be produced by the genotype A- bb?
White
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
Genotypes that share the presence of dominant alleles, such as AA BB, AA Bb, Aa BB, and Aa Bb, make up a(n) ______ _______.
genotypic classes
In lentils, when a marbled strain is crossed with a clear strain, the F1 are all marbled, and the F2 have a phenotypic ratio of 3/4 marbled and 1/4 clear. When a marbled strain is crossed with a spotted strain, the F1 are all marbled, and the F2 have a phenotypic ratio of 3/4 marbled and 1/4 spotted. When a clear strain is crossed with a spotted strain, the F1 are all spotted, and the F2 have a phenotypic ratio of 3/4 spotted and 1/4 clear. What is the correct dominance series for these three alleles?
marbled > spotted > clear
The phenomenon in which one gene affects many traits is called _______.
pleiotropy
In lentils, seed color is determined by two genes (A and B). When a classic dihybrid cross is performed, the nine different genotypes in the F2 generation can be categorized into 4 genotypic classes. This is possible because
the dominance and recessiveness of the alleles at both genes is complete.
Suppose two genes, each with a dominant and recessive allele characterized by complete dominance, affect one trait in an additive manner. If a cross is made between two individuals who are heterozygous for both genes ______.
the offspring will show four variants of the trait in a 9:3:3:1 ratio.
Genotypic classes, such as A- B-, are defined in terms of ______.
the presence or absence of dominant alleles of each gene
When gene symbols are written in genetic notation, a superscript plus sign (+) is often used to designate
the wild-type allele.
When tan lentils are crossed with gray lentils, the F1 generation consists entirely of brown lentils. When these brown lentils are crossed with one another, the F2 generation consists of 9/16 brown lentils, 3/16 tan lentils, 3/16 gray lentils, and 1/16 green lentils. These data support the hypothesis that ________ gene(s) control(s) lentil seed color.
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