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GBIO 151 chapter 11 practice test
Terms in this set (41)
Which is a basic difference between Mendel's particulate hypothesis and the hypothesis of blending inheritance
1. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that mutation is the major source of new gene combinations.
2. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that the two alleles at any given locus are always different.
3. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity.
4. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that the traits governed by genes in the egg are different from the traits governed by genes in the sperm.
5. All of the choices are correct.
he blending inheritance hypothesis, but not the particulate hypothesis, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity.
- The blending hypothesis maintained that the genetic material contributed by the two parents mixes in a manner analogous to the way blue and yellow paints blend to make green.
if a plant variety is true-breeding for a dominant trait, then ____
if the plant were allowed to self-pollinate over many generations, all of the progeny would have the dominant trait
- true-breeding means that self-pollination would produce progeny that all have the same phenotype as the parent. In this case, the parent shows the dominant trait, so the progeny would as well.
A = big apples; R = red apples; a = small apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents?
AArr and aaRr
- Trees that produce big yellow apples could be AArr or Aarr. Trees that produce small red apples could be aaRR or aaRr. Because all the offspring are big, the big parent must be homozygous for A. Because half the apples are red and half are yellow, the red parent must be heterozygous for red. The conclusion is that the cross must be AArr x aaRr.
Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will __________.
all be tall with a genotypes of Tt
- Like Mendel's original purple with white cross, all the F1 offspring will show the dominant phenotype.
The F1 generation differed from the F2 in Mendel's experiments in that __________.
all of the F1 showed the dominant phenotype, but only three-fourths of the F2 did
- All of the F1 were heterozygous and therefore showed the dominant phenotype. In the F2, one-half were heterozygous, and another quarter were homozygous for the dominant allele.
physically, what are different alleles?
Different alleles are different DNA sequences found at the same locus on homologous chromosomes.
- from a physical standpoint, an allele is a variant of DNA sequence that codes for a particular gene
In a certain plant, the alleles A, B, and C are completely dominant to the alleles a, b, and c. A plant with the genotype AABbcc will have the same phenotype as a plant with the genotype __________.
- Individuals with one or two dominant alleles at a locus are indistinguishable, so AA and Aa have the same phenotype (as do BB and Bb). Remember the phenotype is the organisms appearance or observable traits.
Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome would indicate that the tall parent plant was heterozygous?
The ratio of tall offspring to short offspring is 1:1.
- half of the offspring would be heterozygous and the other half homozygous recessive
what is indicated when a single-character test cross yields offspring that all have the dominant phenotype
The parent with the dominant phenotype was homozygous.
- if all the progeny show the dominant phenotype, the parent must have been homozygous, transmitting the dominant allele to all of the offspring
if an organism that is homozygous dominant is crossed with a heterozygote for that trait, the offspring will be ____
all of the dominant phenotype
-The offspring of an AA x Aa cross are either AA or Aa. All will express the dominant phenotype
In Mendel's monohybrid cross of purple-flowered and white-flowered peas, all members of the F1 generation had the __________ phenotype because their genotype was __________ at the flower-color locus
- All F1 individuals of the purple x white cross were phenotypically purple and heterozygous (Pp).
If the two traits that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located near each other on the same chromosome, then the F2 generation __________
would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment
- if the two characters are located on the same chromosome, they will not segregate independently
in carryout out his breeding studies, mendel examined characters that had which property
1.The characters each were controlled by a single gene.
2. It was possible to isolate true-breeding varieties for each trait.
3. They were controlled by loci that were (or behaved as if they were) on different chromosomes.
4. The traits varied in an either-or fashion.
5. All of the choices are correct.
all of the choices are correct
the law of independent assortment ____
1. states that the alleles at different loci segregate independently from one another during a dihybrid cross
2. applies only to genes that are present on different chromosomes (or behave as if they were)
3. can account for a 9:3:3:1 ratio seen in the F2 generation
4. The first and second choices are correct.
5. The first, second, and third choices are correct.
The first, second, and third choices are correct.
homologous pairs of chromosomes often ____
contain different alleles
- homologous chromosomes may carry different alleles at one or more loci
if each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce
- 100x100=10,000. the rule of multiplication applies to these events
Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr x PpRr will have white flowers and wrinkled seeds?
- Pp x Pp would produce 3/4 purple and 1/4 white. Rr x Rr would produce 3/4 round and 1/4 wrinkled; (1/4)(1/4) = 1/16 would have white flowers and wrinkled seeds.
if a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous
- One-quarter of the offspring will be homozygous for the dominant allele, one-quarter will be homozygous for the recessive allele, and the remaining half will be heterozygous
An individual with the genotype AABbCcDD can make how many different kinds of gametes?
- The individual varies only at loci B and C (not at A and D, which are homozygous), and there are two possible alleles at each loci (2^2 = 4)
A red bull is crossed with a white cow and all of the offspring are roan, an intermediate color that is caused by the presence of both red and white hairs. This is an example of genes that are __________.
- roan is caused by the presence of both red and white hairs
Flower color in snapdragons is an example of incomplete dominance. When a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with another pink-flowered plant, the progeny plants will be __________.
25% red, 50% pink, and 25% white
- Breeding the F1 hybrids of the snapdragon cross produces F2 offspring, with a phenotypic ratio of 1 red: 2 pink: 1 white
which choice describes the expression of Tay-Sachs disorder in humans at the biochemical level
- This is the phenotype observed at the biochemical level. The activity level of the lipid-metabolizing enzyme in heterozygotes is intermediate.
Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?
A,B, AB, or O
- The genotype of the man with type B blood could be IBIB or IBi, so his gametes could be IB or i. The genotype of the woman with type A blood could be IAIA or IAi, so her gametes could be IA or i.
Which mating cannot produce a child with blood type O? The letters refer to blood types (phenotypes).
O x AB
- every child of an AB individual will carry either the A or the B allele with the O allele as the recessive trait
A woman with type O blood is expecting a child. Her husband is type A. Both the woman's father and her husband's father had type B blood. What is the probability that the child will have type O blood?
- The woman must be ii. The husband is A but must be a carrier of the i allele, as his father was B. (The father did not give him a B allele, so he must have given him a recessive i allele, and the mother gave him his A allele.) The cross ii x IAi yields a 50% probability that the child will be ii, or type O by phenotype
a single genetic locus that controls more than one trait is said to be ____
- the ability of a gene to affect an organism in multiple ways is called pleiotropy
Color in squash is controlled by epistatic interactions in which color is recessive to no color. At the first locus white squash (W) is dominant to colored squash (w). At the second locus yellow (Y) is dominant to green (y). What is the phenotype of a squash with the genotype wwYy?
- The genotype at the first locus is homozygous recessive for colored squash, and the genotype at the second locus is heterozygous. Yellow is dominant. Therefore, the squash is yellow.
Tail length in a certain species of armadillo falls along a continuum, following a normal distribution. Assuming that environmental factors do not play an important role in determining tail length, this type of variation probably reflects __________.
- Characters that vary along a continuum, following a normal distribution, are often controlled by multiple genes, each contributing to the phenotype in an additive fashion.
Mendel's theory of particulate inheritance ____
can explain inheritance patterns for virtually every sexually reproducing organism but does not explain multifactorial characters
- Although many patterns of inheritance have been discovered, they can still be explained using the concept of alleles (Mendel's hereditary "particles"). Multifactorial characters are influenced by environmental influences, so they are not strictly governed by Mendel's theory.
Tay-Sachs disease runs in Rebecca's family. On a family pedigree, she saw a shaded circle. This represented a __________.
female with Tay-Sachs
- the circle indicated a female and the shading indicates the disease
Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is __________.
- The probability of their next child having alkaptonuria is one-fourth because they are both heterozygous (carriers) for the trait, and the trait is recessive.
Tom's brother suffers from phenylketonuria (PKU), a recessive disorder. The brothers' parents do not have PKU. What are the chances that Tom, who is normal for this trait, is a carrier of PKU?
- The parents must both be carriers of PKU. Tom, who is not affected, has a 1/3 chance of not being a carrier and a 2/3 chance of being a carrier.
A couple, both descended from eastern European (Ashkenazic) Jews, visit a genetic counselor before trying to have children. In view of their ethnic background, the counselor recommends that they be tested to see if they are carriers for __________
- There is a disproportionately high incidence of Tay-Sachs disease among Ashkenazic Jews.
Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Why do cases continue to arise, even though people with the disease rarely live to reproduce?
The harmful allele "hides" within heterozygous individuals, and one-fourth of the offspring of two heterozygotes would be afflicted.
-Cystic fibrosis is inherited as a Mendelian recessive trait. Affected individuals usually have unaffected parents, both of whom are carriers of the recessive allele.
the genetic disease cystic fibrosis is caused by a defective allele that ____
encodes a defective chloride-channel membrane transport protein
- The absence of the transport protein leads to a high concentration of extracellular chloride, causing a thick, sticky mucus to accumulate outside of cells. This mucus interferes with the normal function of numerous organs.
In people with sickle-cell disease, red blood cells break down, clump, and clog the blood vessels. The blood vessels and the broken cells accumulate in the spleen. Among other things this leads to physical weakness, heart failure, joint pain, and brain damage. Such a suite of symptoms can be explained by __________.
the pleiotropic effects of the sickle-cell allele
- Pleiotropy refers to the ability of certain genes to affect multiple characters
When two average-height parents give birth to a child exhibiting achondroplasia, it is most likely due to a new mutation. This is because __________.
achondroplasia is caused by an allele that is always expressed, therefore the parents must not have the allele
- Achondroplasia, a form of dwarfism, is due to a dominant allele
It is far more common to find human genetic disease caused by __________ alleles than by __________ alleles because __________
recessive ... dominant ... harmful recessive alleles can survive in the heterozygote without any selection pressure against them
- Lethal dominant alleles are much less common than lethal recessive ones because the effects of lethal dominants are not masked in heterozygotes.
Huntington's disease is an example of a genetic disorder caused by __________.
a lethal dominant allele that afflicts an individual later in life
- By the time symptoms are evident, the individual may have already transmitted the allele to his or her children.
Heart disease, diabetes, cancer, alcoholism, and many mental illnesses can best be described as __________.
multifactorial disorders with a possible polygenic component
- these disorders involve several genes and environmental factors
How does codominance at the molecular level help to explain why evolutionary processes haven't resulted in the elimination of the sickle-cell allele among people of African descent?
Individuals with normal and sickle-cell hemoglobin in their red blood cells are usually healthy and, when infected by the malaria parasite, have lower parasite densities and, thus, reduced malaria symptoms.
- The presence of both normal and sickle-cell hemoglobin reflects a codominance of normal and sickle-cell traits in heterozygous individuals. By carrying only one sickle-cell allele, an individual is usually healthy and is protected from the lethal effects of malarial. Thus, the allele is retained in the population by this selective advantage. The prevalence of the allele among African-Americans is a remnant of their ancestry in Africa, where malaria is common.
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