Chapter 9 Chromosome Variation

Human Trisomies

- Down's Syndrome (Trisomy 21) - Most trisomies are lethal! - Trisomy 13 and 18 are rare and lethal by age 3. - Triplo-X (XXX) is viable because the extra X's are inactivated! - Kleinfelter's syndrome (XXY) also has X's inactivated.

What CAUSES chromosome rearrangements?

- chromosome breakage/repair - errors in crossing over b/w homologs - errors crossing over between nonhomologs

What is the difference between a paracentric and a pericentric inversion?

A paracentric inversion does not include the centromere; a pericentric inversion includes the centromere

displaced duplication

AB*CDEFG --> AB*CDEFGEF Misplaced

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AABBCCDDMMNNOOPP

Allotetraploidy

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AABBCCDDMNOP

Allotriploidy

Chromosome 8 & 14 Reciprocal Translocation

Burkitt Lymphoma

Chromosome 9 & 22 Reciprocal Translocation

Chronic Myelogenous Leukemia

In mammals, sex-chromosome aneuploids are more common than autosomal aneuploids, but, in fish, sex-chromosome aneuploids and autosomal aneuploids are found with equal frequency. Offer a possible explanation for these differences in mammals and fish. (Hint: Think about why sex chromosome aneuploids are more common than autosomal aneuploids in mammals.)

In mammals, the higher frequency of sex chromosome aneuploids compared to autosomal aneuploids is due to X-chromosome inactivation and the lack of essential genes on the Y chromosome. If fishes do not have chromosome inactivation and both their sex chromosomes have numerous essential genes, then the frequency of aneuploids should be similar for both sex chromosomes and autosomes.

paracentric inversion

Next to centromere but does not include it

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AABBDD

Nullisomy C

There are THREE possible ways such chromosomes can separate in anaphase I.

Only alternate segregation produces viable gametes.

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • E D C F G

Paracentric inversion of CDE

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • C F E D G

Paracentric inversion of DEF

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) C • B A D E F G

Pericentric inversion of ABC

Fertile Polyploids

Polyploids in plants are derived from hybridization events between closely related species. Ex) grapes and their branches

increase the amount of genetic material in all chromosomes?

Polyploidy

Compound Chromosomes

Result from TRANSLOCATIONS accompanied by DELETIONS. Involves HOMOLOGS or SISTER CHROMATIDS. If there is only ONE CENTROMERE then it is stable.

Some people with Turner syndrome are 45,X/46,XY mosaics. Explain how this mosaicism could arise.

Such mosaicism could arise from mitotic nondisjunction early in embryogenesis, in which the Y chromosome fails to segregate and is lost. All the mitotic descendents of the resulting 45,X embryonic cell will also be 45,X. The fetus will then consist of a mosaic of patches of 45,X cells and patches of normal 46,XY cells. If the gonads are derived from 45,X cells, the individual will develop as a female with Turner syndrome.

A chromosome has the following segments, where • represents the centromere:A B • C D E F G What types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B A B • C D E F G

Tandem duplication of AB

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? MMNNOOOOPP

Tetrasomy O

Human Monosomy

The ONLY viable monosomy in humans is XO - Turner syndrome

Nullisomy

loss of both members of a homologous pair of chromosomes (2n-2) - type of aneuploidy

Monosomy

loss of one member of a homologous pair (2n-1) - type of aneuploidy

Duplication

mutation that doubles a region of a chromosome.

Inversion

reversal of a region

Translocation

the TRANSFER of a region to another chromosome

reciprocal translocation

two-way exchange of segments between the chromosomes

Meiosis

Crossing over can occur within the inversion loops

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A • C D E F G

Deletion of B

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • C D E

Deletion of FG

decrease the amount of genetic material in a particular chromosome?

Deletions

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • C D E A B F G

Displaced duplication of AB

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AAABBCCDDD

Ditrisomy A and D

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • C F E D F E D G

Duplication and inversion of DEF

A chromosome has the following segments, where • represents the centromere:A B • C D E F GWhat types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.) A B • C D E F C D F E G

Duplication of CDEF, inversion of EF

Tetrasomy

Gain of a pair of homologous chromosomes (2n+2) - type of aneuploidy

Deletion of Chromosome

LOSS of a region - this is worse b/c it is losing genes

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AABBCDD

Monosomy C

Polyploidy

a FULL SET of extra chromosomes Ex) triploid

Aneuploidy

a change in the number of INDIVIDUAL chromosome. Ex) trisomy-21

Autopolyploidy

due to chromosome duplication within a species

Allopolyploidy

due to hybridization of two species

increase the amount of genetic material in a particular chromosome?

duplication

reverse duplication

duplication is inverted- backwards

tandem duplication

duplication of a chromosome segment that is adjacent to the original segment- immediately follows itself

Robertsonian translocation

fusion b/w non-homologous chromosomes at their CENTROMERES.

Trisomy

gain of a SINGLE chromosome (2n+1) - type of aneuploidy

nonreciprocal translocation

genetic material moves from one chromosome to another without any reciprocal exchange

pericentric inversion

includes centromere

move DNA from one chromosome to a nonhomologous chromosome?

Translocations

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AAABBBCCCDDD

Triploidy

Nondisjunction

Trisomies result from the failure of chromosomes to separate.

Species I is diploid (2n = 8) with chromosomes AABBCCDD; related species II is diploid (2n = 8) with chromosomes MMNNOOPP. What types of chromosome mutations do individual organisms with the following sets of chromosomes have? AAABBCCDD

Trisomy A