Chapter 6 Mastering Genetics

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 36 chromosomes would be triploid. TRUE or FALSE

TRUE

Duplications and deletions can be detected during meiosis by the presence of extrachromosomal loops that do not pair properly with their homolog. TRUE or FALSE

TRUE During meiosis, the presence of a chromosomal loop signals that a duplication or deletion has occurred.

Gene duplications provide an explanation for the origin of gene families. TRUE or FALSE

TRUE they tend to have similar functions

Which of the following statements about allopolyploid individuals is true? They are generated from exposure to colchicine. They can be formed when two sperm simultaneously fertilize an ovum within the same species. They result from a mating between individuals of the same species. They may be sterile and unable to produce offspring.

They may be sterile and unable to produce offspring. Polyploid individuals are sterile if they produce genetically unbalanced gametes; both autopolyploid and allopolyploid individuals may be sterile.

What is a gain of one chromosome in addition to an otherwise diploid genome.

Trisomy

Which of the following statements about the products produced when nondisjunction occurs during meiosis I is true?

Two products of the second meiotic division have both the maternal and paternal chromosomes of a set and the other two products have none for that set. Nondisjunction during meiosis I yields two gametes that are missing a particular chromosome after meiosis II.

The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as ________.

46, 5p-

How do we know that specific mutant phenotypes are due to changes in chromosome number or structure?

A variety of studies, many tracing to early work with specialized (polytene) chromosomes in Drosophila and aneuploidy in other organisms, demonstrated that as chromosome structures or numbers are altered, phenotypic consequences are likely.

What is the case of polyploidy when the chromosomes originate from the hybridization of two different species, usually closely related.

Allopolypoidy

What is an autotetraploid derived from two known original species.

Amphidiploid

Which of the following arrangements would yield the greatest reduction in gamete viability?

An inversion heterozygote for a large inversion Correct. A large heterozygous inversion will result in greater numbers of genes that are duplicated or deleted when crossing over occurs.

What is a general condition when an organism gains or loses one or more chromosomes but not a complete set.

Aneuploidy

What is the addition of one or more extra sets of chromosomes, identical to the normal haploid complement of the same species.

Autopolypoidy

What is a polyploid that has two extra sets of chromosomes, identical to the normal haploid complement of the same species.

Autotetraploid

How do we know that the extra chromosome causing Down syndrome is usually maternal in origin?

Before the advent of polymorphic markers, maternal involvement in trisomy 21 was strongly suspected because of the striking influence of maternal age on incidence.

How many chromosomes would be found in an allopolyploid plant if its parents had diploid numbers of 4 and 6 respectively?

Diploid number of 5

What is a trisomy of chromosome 18 in humans.

Edwards Syndrome

What is a general condition where complete haploid sets of chromosomes are present.

Euploidy

An individual with Patau syndrome would be called a triploid. TRUE or FALSE

FALSE

Inversion loops do NOT form during meiosis in paracentric inversion heterozygotes. TRUE or FALSE

FALSE Loop formation allows pairing within inverted regions of homologous chromosomes regardless of whether the centromere is included in the inversion.

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 25 chromosomes would be triploid. TRUE or FALSE

False

Females with only one X chromosome do not develop; this condition is lethal. TRUE or FASLE

False Females with only one X chromosome are viable but have Turner syndrome, which is characterized by underdeveloped ovaries. Males that lack an X chromosome do not develop; this condition is lethal.

A cross between a tetraploid and a diploid member of the same species will produce offspring that can undergo sexual reproduction. TRUE or FALSE

False Offspring from this cross would be triploid and produce gametes with an uneven number of homologous chromosomes, making sexual reproduction unlikely.

Which of the following syndromes is not paired with its causative chromosomal aberration? Cri du chat syndrome - deletion Down syndrome - Robertsonian translocation Huntington disease - duplication Fragile X syndrome - deletion

Fragile X syndrome is an example of a trinucleotide repeat disorder, which shows increasing severity with increased copy number of a specific three‑base sequence.

A variety with 27 chromosomes has been discovered, but it is sterile. Why?

Individual organisms with 27 chromosomes are TRIPLOIDS (3n) and are more likely to be sterile because there are TRIVALENTS at meiosis I that cause a relatively high number of unbalanced gametes to be formed.

How do we know that the mutant Bar-eye phenotype in Drosophila is due to a duplicated gene region rather than to a change in the nucleotide sequence of a gene?

Investigation of the polytene chromosomes of Drosophila showed that the Bar-eye phenotype was caused by a chromosomal duplication of the 16A region on the X chromosome. Unequal crossing over that resulted in reduced or increased numbers of 16A regions reverted or enhanced the Bar-eye phenotype, respectively.

How do we know that human aneuploidy for each of the 22 autosomes occurs at conception, even though most often human aneuploids do not survive embryonic or fetal development and thus are never observed at birth?

Karyotype analysis of spontaneously aborted fetuses has shown that a significant percentage of abortuses are trisomic, and every chromosome can be involved.

What is a loss of one chromosome from an otherwise diploid genome.

Monosomy

The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. Which of the following errors most likely produces this condition?

Nondisjunction during either meiosis I or II in the female gamete Nondisjunction during either meiosis I or II can produce a gamete that will result in a trisomic zygote. Since the incidence of Down syndrome increases with maternal age, it is likely that this error occurs in the female gamete.

What phenotype would be expected in balanced translocation heterozygotes in the absence of position effects?

Normal, because they have a normal amount of genetic material Balanced translocation heterozygotes have a normal amount of genetic material, but it is in a translocated configuration. As long as there are no position effects, these individuals can be phenotypically normal.

What is an inversion that has breakpoints that do not include the centromere

Paracentric Inversion

What is a trisomy of chromosome 13 in humans.

Patau Syndrome

What is an inversion that has breakpoints that include the centromere

Pericentric Inversion

What is the general term for a condition in which the chromosome number is NOT a multiple of a complete set?

aneuploidy The term aneuploid is derived from roots that mean not true ploidy

How did cultivated American cotton originate?

as an amphidiploid between an Old World and a New World species of cotton plant

Certain varieties of chrysanthemums contain 18, 36, 54, 72, and 90 chromosomes; all are multiples of a basic set of nine chromosomes. How would you describe these varieties genetically?

autopolyploids

All of the following could result from meiosis in a pericentric inversion heterozygote in which a single crossover occurred within the inversion loop except a _______. chromosome with some duplicated regions chromosome with two centromeres chromosome with some deleted regions completely normal chromosome

chromosome with two centromeres Correct. When the centromere is contained within the inversion, it is neither duplicated nor deleted.

Certain varieties of chrysanthemums contain 18, 36, 54, 72, and 90 chromosomes; all are multiples of a basic set of nine chromosomes. What feature do the karyotypes of each variety share?

even number of basic haploid chromosome sets