Samenvatting week 5
Ch 17
17.1 changes in chromosome number
Polyploids are often larger and have larger component parts than their diploid
relatives
Euploid: a cell having any number of complete chromosome sets or an individual
organism composed of such cells
Autopolyploids: which have multiple chromosomes sets originating form within one
species (3n)
o They arise spontaneously
o Can be made from a 4n and 2n
o Sterile one unpaired chromosome at meiosis
Aneuploid: a genome having a chromosome number that differs form the normal
chromosome number for the species by a small number of chromosomes
Polyploids with odd numbers of chromosomes sets, such as triploids, are sterile or
highly infertile because their gametes and offspring are aneuploid
If the chromosomes pair as bivalents or quadrivalents, the chromosomes segregate
normally, producing diploid gametes.
Allopolyploids: which have sets from two or more different species, form only between
closely related species: however the different chromosome sets are only
homeologous, not fully homologous as they are in autopolyploids
o They need to be close enough in every aspect (number of chromosomes) but also
what kind of chromosome and how they look and what kind of genes they contain
o Amphidiploid: a polyploid formed from the union of two separate chromosome
sets and their subsequent doubling
In nature, allopolyploidy seems to have been a major force in the evolution of new
plant species
Allopolyploid plants can arise in nature or be synthesized by crossing related species
and doubling the chromosome of the hybrid or by fusing diploid cells
Aneuploid organisms result mainly form nondisjunction in a parental meiosis
Crossovers are needed to keep bivalents paired until anaphase I. if crossing over fails
for some reason, first-division nondisjunction occurs
Aneuploidy is nearly always deleterious because of gene imbalance; the ratio of gene
products is different form that in euploids, and this difference interferes with the
normal function of the genome
Nondisjunction: the failure of homologs (at meiosis) or sister chromatids (at mitosis) to
separate properly to opposite poles
Aneuploid organisms result mainly from nondisjunction in a parental meiosis
Crossovers are needed to keep bivalents paired until anaphase I. if crossing over fails
for some reason, first-division nondisjunction occurs
Ch 17
17.1 changes in chromosome number
Polyploids are often larger and have larger component parts than their diploid
relatives
Euploid: a cell having any number of complete chromosome sets or an individual
organism composed of such cells
Autopolyploids: which have multiple chromosomes sets originating form within one
species (3n)
o They arise spontaneously
o Can be made from a 4n and 2n
o Sterile one unpaired chromosome at meiosis
Aneuploid: a genome having a chromosome number that differs form the normal
chromosome number for the species by a small number of chromosomes
Polyploids with odd numbers of chromosomes sets, such as triploids, are sterile or
highly infertile because their gametes and offspring are aneuploid
If the chromosomes pair as bivalents or quadrivalents, the chromosomes segregate
normally, producing diploid gametes.
Allopolyploids: which have sets from two or more different species, form only between
closely related species: however the different chromosome sets are only
homeologous, not fully homologous as they are in autopolyploids
o They need to be close enough in every aspect (number of chromosomes) but also
what kind of chromosome and how they look and what kind of genes they contain
o Amphidiploid: a polyploid formed from the union of two separate chromosome
sets and their subsequent doubling
In nature, allopolyploidy seems to have been a major force in the evolution of new
plant species
Allopolyploid plants can arise in nature or be synthesized by crossing related species
and doubling the chromosome of the hybrid or by fusing diploid cells
Aneuploid organisms result mainly form nondisjunction in a parental meiosis
Crossovers are needed to keep bivalents paired until anaphase I. if crossing over fails
for some reason, first-division nondisjunction occurs
Aneuploidy is nearly always deleterious because of gene imbalance; the ratio of gene
products is different form that in euploids, and this difference interferes with the
normal function of the genome
Nondisjunction: the failure of homologs (at meiosis) or sister chromatids (at mitosis) to
separate properly to opposite poles
Aneuploid organisms result mainly from nondisjunction in a parental meiosis
Crossovers are needed to keep bivalents paired until anaphase I. if crossing over fails
for some reason, first-division nondisjunction occurs
