Chp. 9 Chromosome Variation

Front 1

Chromosome Mutations

Back 1

Variations in the number and/or structure of chromosomes.

Front 2

Chromosome rearrangements

Back 2

Mutations that change the structure of individual chromosomes.
-duplications
-deletions
-inversions
-translocations

Front 3

Chromosome duplication

Back 3

Part of a chromosome is doubled.
-tandem
-displaced
-reverse

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tandem duplication

Back 4

duplicated region is exactly adjacent to the original region.

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displaced duplication

Back 5

The region of duplication is some distance away from the original, even on another chromosome.

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Reverse duplication

Back 6

The region of duplication is in the reverse order of the original.

Front 7

Chromosomal deletions

Back 7

Loss of a chromosome segment. Phenotypic consequences depend on the size, location, and which genes make up the segment.

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Pseudodominance

Back 8

The expression of a recessive mutation due to a deletion of the same locus on a homolog.

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Haploinsufficiency

Back 9

Only a single copy of a gene is present which is not sufficient to produce a wild-type phenotype(two copies required for normal function.

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Inversion

Back 10

Chromosome segment is reversed in gene order.

Front 11

Paracentric inversions

Back 11

inversions that do not include the centromere.

Front 12

Pericentric inversion

Back 12

includes the centromere

Front 13

Position effect

Back 13

alteration in the expression of a gene due to a change in its position on a chromosome.

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Dicentric chromatid

Back 14

Contains 2 centromeres due to a crossover with a gene whose centromeres position was altered due to a chromosomal rearrangement.

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Acentric chromatid.

Back 15

Contains no centromeres due to a crossover with a gene whose centromeres position was altered due to a chromosomal rearrangement. Usually lost during cell division.

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Dicentric Bridge

Back 16

Created when spindle fibers from opposite poles attach to the centromeres of a dicentric chromatid.

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Translocation

Back 17

Movement of genetic material between NONhomologous chromosomes

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Nonreciprocal translocation

Back 18

Chromosome segment moves from one chromosome to another without any reciprocal exchange. Least common form of translocation.

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Reciprocal translocation

Back 19

2-way exchange of material between chromosomes.

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Robertsonian translocation

Back 20

The q arms of an acrocentric chromosome share a common centromere due to a translocation and the p-arms also share a centromere creating 1 very long chromosome, and 1 very short chromosome. The short chromosome is usually lost during division due to it's size.

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alternate segregation

Back 21

The 2 normal copies of a gene are pulled to one gamete, and the 2 translocated copies are pulled to the opposite due to homologous centromeres migrating to opposite poles.

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Adjacent1 segregation

Back 22

one normal and one translocated copy of the nonsister chromatids are pulled to each gamete due to the normal and translocated chrmosomes sharing a homologous centromere.

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Adjacent2 segregation

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Very rare, one normal, and one translocated copy of chromosomes sharing nonhomologous centromeres are pulled to each 1' or 2' meiocyte.

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Aneuploidy

Back 24

A change in the number of individual chromosomes. Caused by loss of a chromosome during cell division possibly due to a deletion. Small chromosome lost due to Robertsonian trans. Nondisjunction during cell division in mitosis or meiosis 2.
-Nullisomy
-monosomy
-trisomy
-tetrasomy

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Polyploidy

Back 25

Change in the number of sets of chromosomes.

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Nullisomy

Back 26

The loss of both members of a homologous pair = 2n-2

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monosomy

Back 27

loss of a single chromosome = 2n-1

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Trisomy

Back 28

gain of single chromosome = 2n+2

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Tetrasomy

Back 29

gain of a homologous pair = 2n+2

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Trisomy 21

Back 30

Primary Down's Syndrome. Caused by a nondisjunction event of chromosome 21 during meiosis II.

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Familial Down's syndrome

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2n=46. Caused by a robertsonian translocation between chromosomes 21 and 14. q-arm of 21 and the p-arm of 14 translocate.

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Translocation carriers

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2n=45. Have 2 copies of the q-arms of 14 and 21, but only one copy of the p-arms. normal phenotype, but have an increased chance of passing on down's with gametes that contain one normal and one translocated copy of 21.

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Aneuploidy and maternal age.

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incidence increases w/maternal age, and most often occur due to maternal non-disjunction.

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Uniparental Disomy

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

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Mosaicism

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Nondisjunction event in mitosis that leads to patches of abnormal tissue surrounded by patches of normal tissue.

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Gynandromorphs

Back 36

XX/XO mosaics of female organisms with patches of X-linked recessive tissues.

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Polyploidy

Back 37

the presence of more than 2 sets of chromosomes. Common in plants and sometimes seen in eukaryotes
-triploids
-tetraploids
-pentaploids
...

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Autopolyploidy

Back 38

Chromosome sets are from a single species. Caused by non-disjunction events in meiosis or mitosis that can lead to polyploidic organisms or patches of polyploidic tissues. Whole sets of chromosomes fail to disjoin.

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Unbalanced gametes

Back 39

produced by autotriploids and have varying numbers of chromosomes in their karyotype.

Front 40

Allopolyploidy

Back 40

Sets of chromosomes from different species that are sufficiently related that hybridization can occur.