Chapter 8

Question 1

chromosome mutation

Answer 1

Difference from the wild type in the number or structure of one or more chromosomes; often affects many genes and has large phenotypic effects.

Question 2

chromosome rearrangement

Answer 2

Change from the wild type in the structure of one or more chromosomes.

Question 3

chromosome duplication

Answer 3

Mutation that doubles a segment of a chromosome.

Question 4

tandem duplication

Answer 4

Chromosome rearrangement in which a duplicated chromosome segment is adjacent to the original segment.

Question 5

displaced duplication

Answer 5

Chromosome rearrangement in which the duplicated segment is some distance from the original segment, either on the same chromosome or on a different one.

Question 6

reverse duplication

Answer 6

Duplication of a chromosome segment in which the sequence of the duplicated segment is inverted relative to the sequence of the original segment.

Question 7

segmental duplication

Answer 7

Regions larger than 1000 bp that are almost identical in sequence in eukaryotic genomes.

Question 8

chromosome deletion

Answer 8

Loss of a chromosome segment.

Question 9

pseudo dominance

Answer 9

Expression of a normally recessive allele owing to a deletion on the homologous chromosome.

Question 10

haploinsufficient gene

Answer 10

Must be present in two copies for normal function. If one copy of the gene is missing, a mutant phenotype is produced.

Question 11

chromosome inversion

Answer 11

Rearrangement in which a segment of a chromosome has been inverted 180 degrees.

Question 12

paracentric inversion

Answer 12

Chromosome inversion that does not include the centromere in the inverted region.

Question 13

pericentric inversion

Answer 13

Chromosome inversion that includes the centromere in the inverted region.

Question 14

position effect

Answer 14

Dependence of the expression of a gene on the gene’s location in the genome.

Question 15

dicentric chromatid

Answer 15

Chromatid that has two centromeres; produced when crossing over takes place within a paracentric inversion. The two centromeres of the dicentric chromatid are frequently pulled toward opposite poles in mitosis or meiosis, breaking the chromosome.

Question 16

acentric chromatid

Answer 16

Lacks a centromere; produced when crossing over takes place within a paracentric inversion. The acentric chromatid does not attach to a spindle fiber and does not segregate in meiosis or mitosis; so it is usually lost after one or more rounds of cell division.

Question 17

dicentric bridge

Answer 17

Structure produced when the two centromeres of a dicentric chromatid are pulled toward opposite poles, stretching the dicentric chromosome across the center of the nucleus. Eventually, the dicentric bridge breaks as the two centromeres are pulled apart.

Question 18

translocation

Answer 18

Movement of a chromosome segment to a non-homologous chromosome or to a region within the same chromosome. Also, movement of a ribosome along mRNA in the course of translation.

Question 19

nonreciprocal translocation

Answer 19

Movement of a chromosome segment to a non-homologous chromosome or region without any (or with unequal) reciprocal exchange of segments.

Question 20

reciprocal translocation

Answer 20

Reciprocal exchange of segments between two non-homologous chromosomes.

Question 21

Robertsonian Translocation

Answer 21

Translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, resulting in a chromosome with two long arms and usually another chromosome with two short arms.

Question 22

alternate segregation

Answer 22

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N1 and N2 and the chromosomes containing the translocated segments are T1 and T2, then alternate segregation takes place when N1 and N2 move toward one pole and T1 and T2 move toward the opposite pole.

Question 23

adjacent 1 segregation

Answer 23

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N1 and N2 and the chromosomes containing the translocated segments are T1 and T2, then adjacent-1 segregation takes place when N1 and T2 move toward one pole and T1 and N2 move toward the opposite pole.

Question 24

adjacent 2 segregation

Answer 24

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N1 and N2 and the chromosomes containing the translocated segments are T1 and T2, then adjacent-2 segregation takes place when N1 and T1 move toward one pole and T2 and N2 move toward the opposite pole.

Question 25

fragile site

Answer 25

Constriction or gap that appears at a particular location on a chromosome when cells are cultured under special conditions. One fragile site on the human X chromosome is associated with intellectual disability (fragile-X syndrome) and results from an expanding trinucleotide repeat.

Question 26

fragile x syndrome

Answer 26

A form of X-linked intellectual disability that appears primarily in males; results from an increase in the number of repeats of a CGG trinucleotide.

Question 27

copy-number variation

Answer 27

Difference among individual organisms in the number of copies of any large DNA sequence (larger than 1000 bp).

Question 28

aneuploidy

Answer 28

Change from the wild type in the number of chromosomes; most often an increase or decrease of one or two chromosomes.

Question 29

polyploidy

Answer 29

Possession of more than two haploid sets of chromosomes.

Question 30

nullisomy

Answer 30

Absence of both chromosomes of a homologous pair (2n − 2).

Question 31

monosomy

Answer 31

Absence of one of the chromosomes of a homologous pair.

Question 32

trisomy

Answer 32

Presence of an additional copy of a chromosome (2n + 1).

Question 33

tetrasomy

Answer 33

Presence of two extra copies of a chromosome (2n + 2).

Question 34

Down Syndrome (trisomy 21)

Answer 34

Characterized by variable degrees of intellectual disability, characteristic facial features, some retardation of growth and development, and an increased incidence of heart defects, leukemia, and other abnormalities; caused by the duplication of all or part of chromosome 21.

Question 35

primary down syndrome

Answer 35

Caused by the presence of three copies of chromosome 21.

Question 36

familial down syndrome

Answer 36

Caused by a Robertsonian translocation in which the long arm of chromosome 21 is translocated to another chromosome; tends to run in families.

Question 37

translocation carrier

Answer 37

Individual organism heterozygous for a chromosome translocation.

Question 38

Edward Syndrome (trisomy 18)

Answer 38

Characterized by severe intellectual disability, low-set ears, a short neck, deformed feet, clenched fingers, heart problems, and other disabilities; results from the presence of three copies of chromosome 18.

Question 39

Patau Syndrome (trisomy 13)

Answer 39

Characterized by severe intellectual disability, a small head, sloping forehead, small eyes, cleft lip and palate, extra fingers and toes, and other disabilities; results from the presence of three copies of chromosome 13.

Question 40

trisomy 8

Answer 40

Presence of three copies of chromosome 8; in humans, results in intellectual disability, contracted fingers and toes, low-set malformed ears, and a prominent forehead.

Question 41

uniparental disomy

Answer 41

Inheritance of both chromosomes of a homologous pair from a single parent.

Question 42

mosaicism

Answer 42

Condition in which regions of tissue within a single individual have different chromosome constitutions.

Question 43

gynandromorph

Answer 43

Individual organism that is a mosaic for the sex chromosomes, possessing tissues with different sex-chromosome constitutions.

Question 44

autopolyploidy

Answer 44

Condition in which all the sets of chromsomes of a polyploid individual possessing more than two haploid sets are derived from a single species.

Question 45

allopolyploidy

Answer 45

Condition in which the sets of chromosomes of a polyploid individual possessing more than two haploid sets are derived from two or more species.

Question 46

unbalanced gametes

Answer 46

Gamete that has a variable number of chromosomes; some chromosomes may be missing and others may be present in more than one copy.

Question 47

amphidiploidy

Answer 47

Type of allopolyploidy in which two different diploid genomes are combined such that every chromosome has one and only one homologous partner and the genome is functionally diploid.