biology test 3
A thoroughbred racehorse could have at most ________ alleles of the same gene.
2
Humans have ________ pairs of homologous chromosomes.
23
Consider a gene with two alleles that show complete dominance. When two heterozygotes for this gene breed, they have a 25 percent chance of producing a homozygous recessive offspring. The next time these two individuals breed, what are the chances that they will once again have a homozygous recessive progeny?
25%
Among children with parents who are both carriers of Tay-Sachs, an autosomal recessive disorder, chances are that
50 percent will be carriers.
A pea plant that is heterozygous for the flower color gene makes gametes. What is the probability that a specific gamete contains the recessive allele for flower color?
50%
Sickle-cell disease is an inherited chronic blood disease caused by an autosomal recessive allele. Suppose a man who is homozygous recessive for the sickle-cell gene fathers a child by a woman who is a carrier for sickle-cell. What are the chances their children will exhibit the disease?
50%
Suppose D were dominant and d were recessive, and you could label the D allele in the P generation with a radioactive substance that could be inherited over several generations. You create hybrids by mating your radioactive DD individuals to dd individuals. Finally, you cross two F1 individuals (with the Dd genotype). In 1,000 offspring, how many would you predict would be radioactive?
750
Which of the following would explain two chromosomes in an individual cell that contain some, but not all, of the same genes at the same loci?
A chromosomal alteration has occurred.
Which of the following statements is NOT true?
A genotype is always expressed in the phenotype.
A person is genetically XX and develops as a male. How can this be explained?
A piece of a Y chromosome has become attached to one of the X chromosomes.
If a genetic disorder is caused by a dominant allele, individuals with which of the following genotypes would be affected by the disorder?
AA and aa
Which of the following must be true for a woman who is heterozygous for a given gene?
All of her eggs will contain one allele or the other, but not both alleles.
The coat color in a Siamese cat is determined by a temperature-sensitive allele that allows the brownish pigment melanin to be produced in extremities of the body. What might explain this phenomenon?
Alleles are used to produce proteins that function best in specific temperature ranges.
Which of the following choices represents the genotype of an individual diploid organism?
BbCCdd
The leaf color of a certain plant is controlled by one gene. For that gene, the allele G= orange and g= green. You have a plant with orange leaves, but do not know whether that plant's genotype is GGor Gg. Which of the following would help you determine the plant's genotype?
Cross the plant to a plant with green leaves.
Which of the following statements explains how genetically identical plant clones can exhibit dramatic phenotypic variation?
Environmental conditions under which plants are grown can cause variations in phenotypes
Which of the following represents all of the possible gametes that can be formed by an individual with the generic makeup of FfGgHH?
FGH, FgH, fGH, fgH
Why are X-linked recessive genetic disorders more commonly seen in males?
Females must receive two copies of the recessive allele to exhibit the disorder, but males need only one copy.
Both members of a couple are carriers for a recessive disease allele. If the couple has four children, which of the following statements must be true?
Fifty percent of the children could be carriers of the disease.
During cell division a piece of a chromosome breaks off and reattaches to the same chromosome, but the piece is now in reverse order. How would this abnormality affect the chromosome?
Genes in the section that was inverted could lose normal function.
A karyotype of an individual with mild mental retardation shows three copies of the X chromosome. If this individual decides to have children, how is her chromosomal abnormality likely to affect her offspring?
Half of her eggs will contain an extra copy of the X chromosome.
If a father is affected by an X-linked condition and the mother is a carrier, what is the probability of their children being affected?
Half of the sons will be affected.
Which of the following statements regarding genes is NOT true?
In sexually reproducing species, each cell contains a single copy of every gene.
Which of the following statements would indicate a pedigree that shows the inheritance pattern of a recessive X-linked disease?
Most affected individuals are males.
which of the following is true for mutations
Mutations will affect the genotype, which may affect the phenotype.
Because an individual with an XX genotype is a female, is an individual with an XO (no second sex chromosome) a male?
No, because the Y chromosome contains the gene that makes an embryo male.
Would it be necessary to have both the genotype and phenotype for an organism if you are attempting to predict the inheritance pattern for a trait, such as hair color, in offpsring?
No; knowing the genotype will indicate the phenotype.
What information in a pedigree would indicate a condition is likely dominant?
None of the affected individuals have unaffected parents.
In a particular plant, two genes control leaf shape and color. Round leaves (R) are dominant to jagged leaves (r). Yellow fruits (Y) are dominant to white fruits (y). A true-breeding round-leaved, yellow-fruited plant is mated with a jagged-leaved, white-fruited plant. What are the genotypes of the plants involved in this cross?
RRYY x rryy
In humans, the "master sex switch" that determines whether an embryo will become a male is the
SRY gene.
Which of the following did Gregor Mendel notice in garden peas?
Some plants always produced offspring with flowers that were the same color as the parent plant's flowers
In which of the following situations would it become nearly impossible to predict the phenotype of an individual with a known genotype?
The environment affects the phenotype.
Why did Mendel analyze thousands of plants while conducting his research?
The likelihood of seeing a clear pattern is higher with a larger data set.
Two organisms that are true-breeding for a certain genetic characteristic are mated and their offspring analyzed. Which of the following statements about this situation is true?
The offspring are either 100 percent homozygotes or 100 percent heterozygotes.
If a recessive allele causes a fatal disease that kills the affected individual before he or she can reproduce, why doesn't that allele quickly become extinct in the population?
The recessive allele is carried in the genome of heterozygotes, who do not suffer from the disease
Which of the following statements is a basic summary of one of Mendel's laws?
The separation of alleles for one gene does not affect the separation of alleles for other genes
If you compare a sperm cell in a human to a skin cell from the same individual, which of the following differences would you expect to find?
The sperm cell would contain only one allele for a given gene; the skin cell would contain two alleles
The gene for a certain sex-linked trait is found only on the Y chromosome. If the male parent carries this gene, which of the following statements about the inheritance of that trait is true?
The trait will be expressed in 100 percent of the male offspring.
Which of the following is true
Their sons have a 50 percent chance of having the disorder.
Which of the following might explain how two separate genes control a single trait?
There are two genes to control two separate steps in a pathway.
Autosomal dominant diseases are exhibited by anyone who carries at least one dominant allele for that gene. How is it that dominant lethal genes, such as the one that causes Huntington disease, can persist in a population
These diseases usually take effect later in life after people have had children.
Which of the following statements about homologous chromosomes is true?
They contain the same genes in the same locations.
The figure shown indicates two Labrador retrievers that are both homozygous recessive for fur color. Why is one dog brown and the other is yellow?
This is an example of epistasis.
In which of the following situations would looking at a pedigree be most useful?
Three young boys who are first cousins show symptoms of a neurological disorder.
Which of the following expresses Mendel's law of segregation?
Two alleles of a gene separate during meiosis and end up in different gametes.
Which of the following statements is NOT true
Two organisms with the same genotype are homozygous.
A female who is a carrier of the sex-linked gene
XAXa
Which of the following genotypes represents a human male?
XY
Which of the following genetic changes would NOT be passed from parent to child?
a mutation in a skin cell
A karyotype from an adult male indicates a chromosomal abnormality, which does not affect his health. Which of the following abnormalities is most likely seen?
a translocation between chromosome 14 and chromosome 15
An allele is
a version of a gene
We need a hammer to pound nails into a board. Even if we have the nails, we cannot pound them without first getting hold of a hammer. This is similar to the genetic relationship known as
asa.heterozygosity.c.epistasis
The parents in the figure shown are carriers of a genetic disorder. Based on the Punnett square, the allele that causes the disorder must be
autosomal
If the male in generation II was affected, what would the pattern of inheritance most likely be?
autosomal dominant
Chromosomes that are not involved in sex determination are called
autosomes
The 9:3:3:1 ratio of phenotypes that occurs in the F2 generation of the cross shown can be explained using
both of Mendel's laws of genetic inheritance.
If two different alleles for the same trait have an equal effect on the phenotype, the alleles are
codominant
Most human genetic characters are
controlled by more than one gene
Which of the following did Mendel use to help him form the law of independent assortment?
dihybrid crosses between pea plants
Two copies of the same gene on a single chromosome would indicate a(n) ________ had occurred.
duplication
Two genes control fur color in Labrador retrievers. The first gene determines whether the pigment to be deposited in the hairs will be black or brown. The second gene determines whether the pigments are put into the dog's hairs at all. A dog homozygous for the recessive allele of this second gene will be yellow because no pigment is deposited in its hairs. This is an example of
epistasis
The X chromosome in humans is
found as a pair in females.
In the Punnett square shown below, the lettered circles on the top and left of the square (indicated by the arrows) represent the
gametes that may be produced by each parent involved in the cross.
Mendel used ________ as his research organism to study patterns of genetic inheritance.
garden peas
Feather color in a certain species of bird is controlled by a pair of alleles that exhibit incomplete dominance. If birds that are homozygous for one allele are black and birds that are homozygous for the other allele are white, then heterozygous birds would be
gray
In the pedigree shown, the individual indicated represents a(n)
healthy female.
A carrier is an individual with a ________ genotype who does not express the recessive trait but can pass it along to offspring.
heterozygous
The pedigree shown diagrams an X-linked gene. The individual indicated is ________ for the gene.
heterozygous
The two strands of a DNA molecule are held together by ________ bonds between their base pairs.
hydrogen
A chestnut-colored horse is mated with a cremello (cream-colored) horse. Over a 10-year period, all of their offspring are palominos. This pattern of inheritance is best explained by
incomplete dominance.
A karyotype shows a chromosomal abnormality that does not change the length of any of the chromosomes. Which abnormality is indicated?
inversion
When Mendel proposed the law of segregation, which of the following pieces of information did he NOT have?
knowledge of the location of the alleles for flower color
The figure shown illustrates
law of segregation
The karyotype shown is from a(n)
male
Mendel's laws of segregation and independent assortment both have their biological basisin events that take place during
meiosis
In a genetic cross of Gg with Gg guinea pigs, none of the four offspring were gg. This
neither supports nor disproves Mendel's law of independent assortment
A ________ is a chart that shows genetic relationships within a family over several generations.
pedigree
Which of the following information is available in a Punnett square showing the inheritance pattern for an autosomal recessive disorder?
percentage of all children likely to be affected by the disorder
One of the first medical tests a newborn receives determines if the child has phenylketonuria (PKU). PKUis the result of a mutation in a single gene that causes mental retardation and a host of other phenotypes (light hair and skin color, eczema, and a "mousy" smell). By detecting PKU early, doctors are able to reduce the effect of this condition with a modified diet. PKU is an example og
pleiotropy
The observation that individuals afflicted with albinism also always have vision problems is an example of
pleiotropy
A Punnett square is used to
predict the outcome of a genetic cross
Most inherited human genetic disorders are inherited as ________ alleles.
recessive
The genetic disorder followed through the pedigree shown is
recessive and autosomal.
Most inherited human disorders are the result of
recessive mutations of genes located on autosomes.
An allele that appears more frequently in males is most likely
sex-linked
The gender of a human child is determined by the
sperm
In humans, X-linked genetic diseases
tend to be expressed more in males than in females.
In Mendel's controlled mating experiments the individuals produced by crossing two true-breeding parents are referred to as
the F1 generation
One chromosomal abnormality that is usually fatal is
the addition of an extra autosomal chromosome.
which of the following does not represent a phenotype
the alleles in a mouse that control hair color
Which of the following is the mechanism described by Mendel that results in a new combination of alleles in a pea plant seed?
the separation of alleles for two different genes during meiosis
The pleiotropy that occurs when a single gene controls multiple skeletal traits in dogs, such as leg bone length and skull size, may be explained because
the skeletal traits are related in the overall function of the dog.
The figure shown indicates two diseases with genetic links that are common in industrialized nations. The fact that both are about 80-90% avoidable indicates that
these diseases are most likely affected by environmental factors in addition to genes.
If two parents are heterozygous for an autosomal recessive disease,
they are both considered genetic carriers for the disease.
Which of the following statements is true of Mendel's laws?
they correctly explain how genes are inherited
In a karyotype of a male, which of the following would indicate an abnormality?
three copies of chromosome 22
Mendel's manuscript discussing his pea-breeding results is considered one of the two most important scientific papers of the nineteenth century because he was the first to explain how
traits are passed from one generation to the next.
What is the smallest number of traits that are needed to test Mendel's law of independent assortment?
two
On chromosomes within an individual, there are ________ alleles for a given gene found on ________ chromosomes
two; homologous
What information is NOT visible in a karyotype?
whether the individual carries genetic mutations
