8. Variation in Chromosome Structure and Number

Question 1

genetic differences among members of the same species or among different species.

Answer 1

Genetic Variation

Question 2

genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene.

Answer 2

Allelic Variation

Question 3

a scientist who studies chromosomes under the microscope.

Answer 3

Cytogeneticist

Question 4

describes a chromosome with the centromere near the middle.

Answer 4

Metacentric

Question 5

describes a chromosome in which the centromere is slightly off center.

Answer 5

Submetacentric

Question 6

describes a chromosome with the centromere significantly off center, but not at the end.

Answer 6

Acrocentric

Question 7

describes a chromosome with its centromere at one end.

Answer 7

Telocentric

Question 8

a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell.

Answer 8

Karyotype

Question 9

the chromosomal banding pattern that is observed when the chromosomes have been treated with the chemical called Giemsa stain.

Answer 9

G Bands

Question 10

condition in which a segment of DNA is missing.

Answer 10

Deletion

Question 11

condition in which a segment of chromosomal material is missing.

Answer 11

Deficiency

Question 12

the repetition of a segment of DNA more than once within a chromosome and/or within a genome.

Answer 12

Duplication

Question 13

a change in the orientation of genetic material along a chromosome such that a segment is flipped or reversed from the normal order.

Answer 13

Inversion

Question 14

(1) rearrangement in which one segment of a chromosome breaks off and becomes attached to a different chromosome or a different part of the same chromosome; (2) event that occurs when a ribosome moves from one codon in an mRNA to the next codon.

Answer 14

Translocation

Question 15

rearrangement in which one piece of a chromosome becomes attached to a different chromosome.

Answer 15

Simple Translocation

Question 16

rearrangment in which two different chromosomes exchange pieces.

Answer 16

Reciprocal Translocation

Question 17

deletion in which a segment is lost from the end of a linear chromosome.

Answer 17

Terminal Deletion

Question 18

deletion in which an internal segment is lost from a linear chromosome.

Answer 18

Interstitial Deletion

Question 19

short DNA sequences that occur many times within a species’ genome.

Answer 19

Repetitive Sequences

Question 20

recombination that occurs at homologous sites within chromosomes, where the sites are not alleles of the same gene. Such misaligned crossovers are often due to the occurrence of repetitive sequences.

Answer 20

Nonallelic Homologous Recombination

Question 21

an increase in the copy number of a gene. Can lead to the evolution of gene families.

Answer 21

Gene Duplication

Question 22

two or more genes within a single species that are similar to each other because they were derived from the same ancestral gene.

Answer 22

Gene Family

Question 23

describes attributes that are the result of homology. In the case of genes, this term describes two genes that are derived from the same ancestral gene.

Answer 23

Homologous

Question 24

homologous genes within a single species that constitute a gene family.

Answer 24

Paralogs

Question 25

a type of structural variation in which a segment of DNA that is 1000 bp or more in length commonly exhibits copy number differences among members of the same species.

Answer 25

Copy Number Variation (CNV)

Question 26

a duplication in which a small segment of a chromosome has more than one copy of the same gene.

Answer 26

Segmental Duplication

Question 27

a hybridization technique to determine if cells (e.g., cancer cells) have changes in chromosome structure, such as deletions or duplications.

Answer 27

Comparative Genomic Hybridization (CGH)

Question 28

the phenomenon in which two single-stranded DNA molecules from different sources bind to form a hybrid molecule.

Answer 28

Hybridization

Question 29

an inversion in which the centromere is located within the inverted region of the chromosome.

Answer 29

Pericentric Inversion

Question 30

an inversion in which the centromere is found outside the inverted region.

Answer 30

Paracentric Inversion

Question 31

a change in phenotype that occurs when the location of a gene changes from one chromosomal site to a different one.

Answer 31

Position Effect

Question 32

a diploid individual that carries one normal chromosome and a homologous chromosome with an inversion.

Answer 32

Inversion Heterozygote

Question 33

the loop structure that is formed when the homologous chromosomes of an inversion heterozygote attempt to align themselves (i.e., synapse) during meiosis.

Answer 33

Inversion Loop

Question 34

a fragment of a chromosome that lacks a centromere.

Answer 34

Acentric Fragment

Question 35

describes a chromosome with two centromeres.

Answer 35

Dicentric

Question 36

the region between the two centromeres in a dicentric chromosome.

Answer 36

Dicentric Bridge

Question 37

specialized repeated sequences found at the ends of eukaryotic chromosomes.

Answer 37

Telomeres

Question 38

a translocation, such as a reciprocal translocation, in which the total amount of genetic material remains normal or nearly normal.

Answer 38

Balanced Translocation

Question 39

a translocation in which a cell has too much or too little genetic material compared with a normal cell.

Answer 39

Unbalanced Translocation

Question 40

the structure produced when two telocentric chromosomes fuse at their short arms.

Answer 40

Robertsonian Translocation

Question 41

the structure that is formed when chromosomes that have undergone a reciprocal translocation attempt to synapse during meiosis. This structure contains two normal (nontranslocated) chromosomes and two translocated chromosomes. A total of eight chromatids are found within the cross.

Answer 41

Translocation Cross

Question 42

condition in which an individual has a lowered fertility.

Answer 42

Semisterility

Question 43

describes an organism in which the chromosome number is an exact multiple of a chromosome set.

Answer 43

Euploid

Question 44

describes an organism or cell with three sets of chromosomes.

Answer 44

Triploid

Question 45

describes an organism or cell with four sets of chromosomes (i.e., 4n).

Answer 45

Tetraploid

Question 46

describes an organism or cell with three or more sets of chromosomes.

Answer 46

Polyploid

Question 47

not euploid. Refers to a variation in chromosome number such that the total number of chromosomes is not an exact multiple of a set (or of the number n).

Answer 47

Aneuploid

Question 48

describes a diploid cell or organism with one extra chromosome (i.e., 2n + 1).

Answer 48

Trisomic

Question 49

describes a diploid cell or organism that is missing a chromosome (i.e., 2n − 1).

Answer 49

Monosomic

Question 50

event in which chromosomes do not segregate properly during mitosis or meiosis.

Answer 50

Nondisjunction

Question 51

describes a species, such as certain bees, in which one sex is haploid (e.g., male) and the other sex is diploid (e.g., female).

Answer 51

Haploidiploid

Question 52

in a diploid individual, the phenomenon in which certain cells of the body are polyploid.

Answer 52

Endoplolyploidy

Question 53

aggregation of chromosomes found in certain cells, such as Drosophila salivary cells, in which homologous chromosomes have synapsed and replicated many times and the copies lie side by side.

Answer 53

Polytene Chromosome

Question 54

the central point where the chromosomes of a polytene chromosome aggregate.

Answer 54

Chromocenter

Question 55

the event in which chromosomes do not segregate properly during meiosis.

Answer 55

Meiotic Nondisjunction

Question 56

an event in which chromosomes do not segregate properly during mitosis.

Answer 56

Mitotic Nondisjunction

Question 57

describes an organism that contains sets of chromosomes from two or more different species.

Answer 57

Alloploid

Question 58

event in which all of the chromosomes fail to segregate properly during meiosis or mitosis and remain in one of the two daughter cells.

Answer 58

Complete Nondisjunction

Question 59

condition in which the cells of part of an organism differ genetically from those of the rest of the organism.

Answer 59

Mosaicism

Question 60

a polyploid produced within a single species due to nondisjunction.

Answer 60

Autopolyploid

Question 61

describes an organism that contains one set of chromosomes from two different species.

Answer 61

Allodiploid

Question 62

describes an organism that contains two (or more) sets of chromosomes from two (or more) species.

Answer 62

Allopolypoid

Question 63

describes an organism that contains two sets of chromosomes from two different species.

Answer 63

Allotetraploid