Chapter 17

Question 1

Define acentric chromosome

Answer 1

• a chromosome having no centromere

Question 2

Define acentric fragment

Answer 2

• a chromosome fragment having no centromere

Question 3

Define adjacent-1 segregation

Answer 3

• in a reciprocal translocation, the passagr of a translocated and a normal chromosome to each of the pole

Question 4

Define allopolyploid

Answer 4

• a polyploid formed from the union of 2 separate chromosome sets and their subsequent doubling

Question 5

Define alternate segregation

Answer 5

• in a reciprocal translocation the passage of both normal chromosomes to one pole and both translocated chromosomes to the other pole

Question 6

Define amphidiploid

Answer 6

• a polyploid formed from the union of 2 separate chromosome sets and their subsequent doubling
• an allopolyploid

Question 7

Define anaphase bridge

Answer 7

• in a dicentric chromosome, the segment between the centromeres being drawn to opposite poles at nuclear division

Question 8

Define aneuploid

Answer 8

• a genome having a chromosome number that differs from the normal chromosome number for the species by a small number of chromosomes

Question 9

Define autopolyploid

Answer 9

• polyploid formed from the doubling of a single genome

Question 10

Define balanced rearrangement

Answer 10

• a change in the chromosomal gene order that does not remove or duplicate any DNA
• the 2 classes of balanced rearrangement are inversions and reciprocal translocations

Question 11

Define balancer

Answer 11

• a chromosome with multiple inversions, used to retain favourable allele combinations in the uninverted homolog

Question 12

Define bivalent

Answer 12

• 2 homologous chromosomes paired at meiosis

Question 13

Define chromosome mutation

Answer 13

• any type of change in chromosome structure or number

Question 14

Define deletion

Answer 14

• the removal of a chromosomal segment from a chromosome set

Question 15

Define deletion loop

Answer 15

• the loop formed at meiosis by the pairing of a normal chromosome and a deletion-containing chromosome

Question 16

Define deletion mapping

Answer 16

• the use of a set of known deletions to map new recessive mutations by pseudodominance

Question 17

Define dicentric bridge

Answer 17

• in a dicentric chromosome, the segment between the centromeres being drawn to opposite poles at nuclear division

Question 18

Define dicentric chromosome

Answer 18

• a chromosome with 2 centromeres

Question 19

Define disomic

Answer 19

• an abnormal haploid carrying 2 copies of one chromosome

Question 20

Define dosage compensation

Answer 20

• the process in organisms using a chromosomal sex-determination mechanism (such as XX vs XY) that allows standard structural genes on the sex chromosome to be expressed at the same levels in females and males, regardless of the number of chromosomes
• in mammals, dosage compensation operates by maintaining only a single active X chromosome in each cell
• in Drosophoila, it operates by hyperactivating the male X chromosome

Question 21

Define Down syndrome

Answer 21

• an abnormal human phenotype, including mental retardation, due to a trisomy on chromosome 21
• more common in babies born to older mothers

Question 22

Define duplication

Answer 22

• more than one copy of a particular chromosomal segment in a chromosome set

Question 23

Define embryoid

Answer 23

• a small dividing mass of monoploid cells, produced from a cell destined to become a pollen cell by exposing it to cold

Question 24

Define euploid

Answer 24

• a cell having any number of complete chromosome sets or an individual organism composed of such cells

Question 25

Define gene balance

Answer 25

- the idea that a normal phenotype requires a 1:1 relative proportion of genes in a genome

Question 26

Define gene-dosage effect

Answer 26

1) proportionality of the expression of some biological function to the number of copies of an allele present in the cell 2) a change in phenotype caused by an abnormal number of wild-type alleles (observed in chromosomal mutations)

Question 27

Define genetic load

Answer 27

- the total set of deleterious alleles in an individual genotype

Question 28

Define hexaploid

Answer 28

- a cell having six chromosome sets or an organism composed of such cells

Question 29

Define homeologous chromosome

Answer 29

- partly homologous chromosomes, usually indicating some original ancestral homology

Question 30

Define insertional duplication

Answer 30

- a duplication in which the extra copy is not adjacent to the normal one

Question 31

Define intragenic deletion

Answer 31

- a deletion within the gene

Question 32

Define inversion

Answer 32

- a chromosomal mutation consisting of the removal of a chromosome segment, its rotation through 180*, and its reinsertion in the same location

Question 33

Define inversion heterozygote

Answer 33

- s diploid with a normal and inverted homolog

Question 34

Define inversion loop

Answer 34

- a loop formed by meiotic pairing of homologs in an inversion heterozygote

Question 35

Define Klinefelter syndrome

Answer 35

- an abnormal human male phenotype due to an extra X chromosome (XXY)

Question 36

Define monoploid

Answer 36

- a cell having only one chromosome set (usually as an aberration) or an organism composed of such cells

Question 37

Define monosomic

Answer 37

- a cell or individual that is basically diploid but has only one copy of one particular chromosome type and thus has chromosome number 2n+1

Question 38

Define multigenic deletion

Answer 38

- a deletion of several adjacent cells

Question 39

Define nonallelic homologous recombination (NAHR)

Answer 39

- crossing over between short homologous units found at different chromosomal loci

Question 40

Define nondisjunction

Answer 40

- the failure of homolog (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles

Question 41

Define nullisomic

Answer 41

- refers to a cell or an individual organism with one chromosomal type missing - has a chromosome number like n-1 or 2n-1

Question 42

Define paracentric inversion

Answer 42

- an inversion not including the centromere

Question 43

Define parthenogenesis

Answer 43

- the production of offspring by a female with no genetic contribution from the male

Question 44

Define pentaploid

Answer 44

- an individual organism with with 5 sets of chromosomes

Question 45

Define pericentric inversion

Answer 45

- an inversion that includes the centromere

Question 46

Define polyploid

Answer 46

- a cell having 3 or more chromosome sets pr an organism composed of such cells

Question 47

Define polytene chromosome

Answer 47

- a giant chromosome in specific tissues of some insects, produced by an endomitotic process in which the multiple DNA sets remain bound in a haploid number of chromosomes

Question 48

Define position-effect variegation

Answer 48

- PEV | - variegation caused bt the inactivation of a gene in some cells through its abnormal juxtaposition with heterochromatin

Question 49

Define pseudodominance

Answer 49

- the sudden appearance of a recessive phenotype in a pedigree, sue to a deletion of a masking dominant gene

Question 50

Define pseudolinkage

Answer 50

- the appearance of linkage from 2 genes on translocated chromosomes

Question 51

Define rearrangement

Answer 51

- the production of abnormal chromosomes by the breakage and incorrect rejoining of chromosomal segments - ex inversions, deletions and translocations

Question 52

Define segmental duplication

Answer 52

-

Question 53

Define semisterility

Answer 53

-

Question 54

Define tandem duplication

Answer 54

-

Question 55

Define tetraploid

Answer 55

-

Question 56

Define translocation

Answer 56

-

Question 57

Define triploid

Answer 57

-

Question 58

Define trisomic

Answer 58

-

Question 59

Define trivalent

Answer 59

-

Question 60

Define Turner syndrome

Answer 60

-

Question 61

Define unbalanced rearrangement

Answer 61

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