A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:

A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:

A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
Phenotypes Leaves Stems Roots Number
1 a + + 14
2 a + c 0
3 a b + 32
4 a b c 440
5 + b + 0
6 + b c 16
7 + + c 28
8 + + + 470
Total 1,000

1) Which of the following are the phenotypes of the parents in this cross?

A) 2 and 5
B) 1 and 6
C) 4 and 8
D) 3 and 7
E) 1 and 2

Answer:  C

2) In which progeny phenotypes has there been recombination between genes A and B?

A) 1, 2, 5, and 6
B) 1, 3, 6, and 7
C) 2, 4, 5, and 8
D) 2, 3, 5, and 7
E) in all 8 of them

Answer:  A

3) If recombination is equal to distance in centimorgans (cM), what is the approximate distance between genes A and B?

A) 1.5 cM
B) 3 cM
C) 6 cM
D) 15 cM
E) 30 cM

Answer:  B

4) What is the greatest benefit of having used a testcross for this experiment?

A) The homozygous recessive parents are obvious to the naked eye.
B) The homozygous parents are the only ones whose crossovers make a difference.
C) Progeny can be scored by their phenotypes alone.
D) All of the progeny will be heterozygous.
E) The homozygous recessive parents will be unable to cross over.

Answer:  C

5) The greatest distance among the three genes is between a and c. What does this mean?

A) Gene a is closest to b.
B) Genes are in the order: abc.
C) Gene a is not recombining with c.
D) Gene a is between b and c.
E) Distance ab is equal to distance ac.

Answer:  D

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.

1) How many of their daughters might be expected to be color-blind dwarfs?

A) all
B) none
C) half
D) one out of four
E) three out of four

Answer:  B

2) What proportion of their sons would be color-blind and of normal height?

A) none
B) half
C) one out of four
D) three out of four
E) all

Answer:  B

3) They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes?

A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Answer:  E

The pedigree in Figure 15.3 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely

The pedigree in Figure 15.3 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely

A) mitochondrial.
B) autosomal recessive.
C) sex-linked dominant.
D) sex-linked recessive.
E) autosomal dominant.

Answer:  A

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in Figure 15.2. What is the order of these genes on a chromosome map?

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in Figure 15.2. What is the order of these genes on a chromosome map?

A) rb-cn-vg-b
B) vg-b-rb-cn
C) cn-rb-b-vg
D) b-rb-cn-vg
E) vg-cn-b-rb

Answer:  D

Between which two genes would you expect the highest frequency of recombination?

Between which two genes would you expect the highest frequency of recombination?

A) A and W
B) W and E
C) E and G
D) A and E
E) A and G

Answer:  E

Suppose that a gene on human chromosome 18 can be imprinted in a given pattern in a female parent but not in a male parent. A couple in whom each maternal meiosis is followed by imprinting of this gene have children. What can we expect as a likely outcome?

Suppose that a gene on human chromosome 18 can be imprinted in a given pattern in a female parent but not in a male parent. A couple in whom each maternal meiosis is followed by imprinting of this gene have children. What can we expect as a likely outcome?

A) All sons but no daughters will bear their mother's imprinting pattern.
B) All daughters but no sons will bear their mother's imprinting pattern.
C) All sons and daughters will have a 50% chance of receiving the mother's imprinting pattern.
D) All the children will bear their mother's imprinting pattern but only daughters will then pass it down.
E) Each of the children will imprint a different chromosome.

Answer:  D

Which of the following produces a Mendelian pattern of inheritance?

Which of the following produces a Mendelian pattern of inheritance?

A) genomic imprinting
B) a mitochondrial gene mutation
C) a chloroplast gene mutation
D) viral genomes that inhabit egg cytoplasm
E) a trait acted upon by many genes

Answer:  E

A certain kind of snail can have a right-handed direction of shell coiling (D) or left-handed coiling (d). If direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?

A certain kind of snail can have a right-handed direction of shell coiling (D) or left-handed coiling (d). If direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?

A) 1/2 Dd:1/2 dd; all right coiling
B) all Dd; all right coiling
C) 1/2 Dd:1/2 dd; half right and half left coiling
D) all Dd; all left coiling
E) all Dd; half right and half left coiling

Answer:  A

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore, in which body systems would you expect most mitochondrial gene mutations to be exhibited?

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore, in which body systems would you expect most mitochondrial gene mutations to be exhibited?

A) the immune system and the blood
B) the excretory and respiratory systems
C) the skin and senses
D) the nervous and muscular systems
E) the circulation system

Answer:  D

Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?

Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?

A) mitochondrial inheritance
B) chloroplast inheritance
C) genomic imprinting
D) infectious inheritance
E) sex-linkage

Answer:  B

Genomic imprinting is generally due to the addition of methyl (CH3) groups to C nucleotides in order to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?

Genomic imprinting is generally due to the addition of methyl (CH3) groups to C nucleotides in order to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?

A) Methylation of C is permanent in a gene.
B) Genes required for early development stages must not be imprinted.
C) Methylation of this kind must occur more in males than in females.
D) Methylation must be reversible in ovarian and testicular cells.
E) The imprints are transmitted only to gamete-producing cells.

Answer:  D

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would be considered Mendelian?

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would be considered Mendelian?

A) a gene whose expression varies depending on the gender of the transmitting parent
B) a gene derived solely from maternal inheritance
C) a gene transmitted via the cytoplasm or cytoplasmic structures
D) a gene transmitted to males from the maternal line and from fathers to daughters
E) a gene transmitted by a virus to egg-producing cells

Answer:  D

Which of the following is true of aneuploidies in general?

Which of the following is true of aneuploidies in general?

A) A monosomy is more frequent than a trisomy.
B) 45 X is the only known human live-born monosomy.
C) Some human aneuploidies have selective advantage in some environments.
D) Of all human aneuploidies, only Down syndrome is associated with mental retardation.
E) An aneuploidy resulting in the deletion of a chromosome segment is less serious than a duplication.

Answer:  B

At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is an embryo with 45, X?

At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is an embryo with 45, X?

I. an error in anaphase I
II. an error in anaphase II
III. an error of the first postfertilization mitosis
IV. an error in pairing

A) I or II only
B) II or IV only
C) III or IV only
D) I, II, or III only
E) I, II, III, or IV

Answer:  E

Which of the following is known as a Philadelphia chromosome?

Which of the following is known as a Philadelphia chromosome?

A) a human chromosome 22 that has had a specific translocation
B) a human chromosome 9 that is found only in one type of cancer
C) an animal chromosome found primarily in the mid-Atlantic area of the United States
D) an imprinted chromosome that always comes from the mother
E) a chromosome found not in the nucleus but in mitochondria

Answer:  A

What is a syndrome?

What is a syndrome?

A) a characteristic facial appearance
B) a group of traits, all of which must be present if an aneuploidy is to be diagnosed
C) a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
D) a characteristic trait usually given the discoverer's name
E) a characteristic that only appears in conjunction with one specific aneuploidy

Answer:  C

At which phase(s) is it preferable to obtain chromosomes to prepare a karyotype?

At which phase(s) is it preferable to obtain chromosomes to prepare a karyotype?

A) early prophase
B) late telophase
C) anaphase
D) late anaphase or early telophase
E) late prophase or metaphase

Answer:  E

In 1956 Tijo and Levan first successfully counted human chromosomes. What is the reason it took so many years to do so?

In 1956 Tijo and Levan first successfully counted human chromosomes. What is the reason it took so many years to do so?

A) Watson and Crick's structure of DNA was not done until 1953.
B) Chromosomes were piled up on top of one another in the nucleus.
C) Chromosomes were not distinguishable during interphase.
D) A method had not yet been devised to halt mitosis at metaphase.
E) Chromosomes were piled up on top of one another in the nucleus, chromosomes were not distinguishable during interphase, and a method had not yet been devised to halt mitosis at metaphase.

Answer:  E

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?

A) The woman inherited this tendency from her parents.
B) One member of the couple carried a translocation.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One member of the couple underwent nondisjunction in gamete production.
E) The mother had a chromosomal duplication.

Answer:  D

Down syndrome has a frequency in the U.S. population of ~1/700 live births. In which of the following groups would you expect this frequency to be significantly higher?

Down syndrome has a frequency in the U.S. population of ~1/700 live births. In which of the following groups would you expect this frequency to be significantly higher?

A) people in Latin or South America
B) the Inuit and other peoples in very cold habitats
C) people living in equatorial areas of the world
D) very small population groups
E) No groups have such higher frequency.

Answer:  E