Biology 1408 CH 9 Mastering Biology

Which statement regarding genotypes and phenotypes is false? A: An organism with two different alleles for a single trait is said to be homozygous for that trait. B: The expressed physical traits of an organism are called its phenotype. C: Alleles are alternate forms of a gene. D: The genetic makeup of an organism constitutes its genotype.

A: An organism with two different alleles for a single trait is said to be homozygous for that trait.

Blood samples are taken from the heel of newborn babies to test for a mutation in the PKU gene. Why is this so important? A: PKU can be completely treated with dietary management of the amino acid phenylalanine, preventing any negative outcomes in the child, but the diet needs to be started immediately. B: PKU inevitably leads to mental retardation, reduced skin pigmentation, and other behavior problems and the family needs to plan for care for the child. C: PKU is lethal in newborns if not treated immediately. D: The government must track all cases of PKU to be sure the disease does not spread through the population.

A: PKU can be completely treated with dietary management of the amino acid phenylalanine, preventing any negative outcomes in the child, but the diet needs to be started immediately.

Which statement regarding sickle-cell disease is false? A: Sickle-cell disease causes white blood cells to be sickle-shaped. B: Persons who are heterozygous for sickle-cell disease are also resistant to malaria. C: The multiple symptoms of sickle-cell disease result from the actions of just one allele. D: About 1 in 10 African Americans is a carrier of sickle-cell disease.

A: Sickle-cell disease causes white blood cells to be sickle-shaped.

Which statement regarding cross-breeding and hybridization is false? A: The hybrid offspring of a cross are the P1 generation. B: The offspring of two different varieties are called hybrids. C: The parental plants of a cross are the P generation. D: The hybrid offspring of an F1 cross are the F2 generation.

A: The hybrid offspring of a cross are the P1 generation.

A testcross is A: a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest. B: a mating between two individuals of unknown genotype. C: a mating between an individual of unknown genotype and an individual heterozygous for the trait of interest. D: a mating between two individuals heterozygous for the trait of interest.

A: a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest.

A carrier of a genetic disorder who does not show symptoms is most likely to be ________ to transmit it to offspring. A: heterozygous for the trait and able B: homozygous for the trait and unable C: homozygous for the trait and able D: heterozygous for the trait and unable

A: heterozygous for the trait and able

Genes located close together on the same chromosomes are referred to as ________ genes and generally ________. A: linked; do not sort independently during meiosis B: codependent; do not sort independently during meiosis C: linked; sort independently during meiosis B: homologous; are inherited together

A: linked; do not sort independently during meiosis

How many sex chromosomes are normally in a human gamete? A: one B: two C: three D: four

A: one

Mendel conducted his most memorable experiments on A: peas. B: roses. C:fruit flies. D: guinea pigs.

A: peas.

The chromosome theory of inheritance states that A: the behavior of chromosomes during meiosis and fertilization accounts for patterns of inheritance. B: chromosomes that exhibit mutations are the source of genetic variation. C: the behavior of chromosomes during mitosis accounts for inheritance patterns. D: humans have 46 chromosomes.

A: the behavior of chromosomes during meiosis and fertilization accounts for patterns of inheritance.

The phenotypic ratio resulting from a dihybrid cross of two heterozygote individuals showing independent assortment is expected to be A: 3:1. B: 9:3:3:1. C: 1:2:1. D: 9:1:1:3.

B: 9:3:3:1.

The individual features of all organisms are the result of A: only the environment in which the organism develops. B: both the interaction between genetics and the environment. C: only the genes present. D: both the environment and the needs of the individual.

B: both the interaction between genetics and the environment.

For most sexually reproducing organisms, Mendel's laws A: help us understand the global geographic patterns of genetic disease. B: cannot strictly account for the patterns of inheritance of many traits. C: can predict whether offspring will be male or female with 100% accuracy. D: explain the biological mechanisms behind why certain genes are dominant or recessive.

B: cannot strictly account for the patterns of inheritance of many traits.

The expression of both alleles for a trait in a heterozygous individual illustrates A: polygenic inheritance. B: codominance. C: pleiotropy.

B: codominance.

The mechanism that "breaks" the linkage between linked genes is A: pleiotropy. B: crossing over. C: codominance. D: independent assortment.

B: crossing over.

Which trait is an example of incomplete dominance in humans? A: skin color B: hypercholesterolemia C: albinism D: ABO blood groups

B: hypercholesterolemia

Most people afflicted with recessive disorders are born to parents who were A: both affected by the disease. B: not affected at all by the disease. C: slightly affected by the disease, showing some but not all of the symptoms.

B: not affected at all by the disease.

Which statement is true about the determination of sex in humans? A: An individual with an X and a Y will always be male. B: The SRY gene alone can determine maleness. C: An individual may have some genes producing proteins for maleness and other genes producing proteins for femaleness. D: Any individual without a Y chromosome will always become a female.

C: An individual may have some genes producing proteins for maleness and other genes producing proteins for femaleness.

Any gene located on a sex chromosome A: is called a recessive gene. B: will exhibit pleiotropy. C: is called a sex-linked gene. D: will exhibit codominance.

C: is called a sex-linked gene.

Amniocentesis and chorionic villus sampling allow for ________ and ________ of the fetus so that it can be tested for abnormalities. A: imaging; karyotyping B: direct observation; biochemical testing C: karyotyping; biochemical testing D: sexing; imaging

C: karyotyping; biochemical testing

Sex-linked conditions are more common in men than in women because A: men acquire two copies of the defective gene during fertilization. B: most genes associated with the sex-linked conditions are linked to the Y chromosome, which determines maleness. C: men need to inherit only one copy of the recessive allele for the condition to be fully expressed. D: the sex chromosomes are more active in men than in women.

C: men need to inherit only one copy of the recessive allele for the condition to be fully expressed.

What is the usual complement of sex chromosomes in a human male? A: two Y chromosomes and zero X chromosomes B: one Y chromosome and zero X chromosomes C: one X chromosome and one Y chromosome D: two X chromosomes and one Y chromosome

C: one X chromosome and one Y chromosome

The alleles of a gene are found at ________ chromosomes. A: different loci on nonhomologous B: different loci on homologous C: the same locus on homologous D: the same locus on nonhomologous

C: the same locus on homologous

Which term refers to a situation where a single phenotypic character is determined by the additive effects of two or more genes? A: incomplete dominance B: pleiotropy C: codominance D: polygenic inheritance

D: polygenic inheritance