Ch 6 Chromosome Variation Flashcards
chromosome mutations
individual chromosomes may lose or gain parts, and the order of genes within a chromosome may become altered
4 basic types of chromosomes
metacentric, submetacentric, acrocentric, telocentric
karotype
complete set of chromosomes possessed by an organism
chromosome rearrangements
mutations that change the structure of individual chromosomes
can also arise through errors in crossing over or when crossing over occurs between repeated DNA sequences
4 basic types of rearrangements
duplications, deletions, inversions, translocations
chromosome duplication
a mutation in which part of the chromosome has been doubled
tandem duplication
the duplicated segment is immediately adjacent to the original segment
Ex: AB-CDEFEFG
displaced duplication
the duplicated segment is located some distance from the original segment
Ex: AB-CDEFGEF
reverse duplication
the duplication is inverted
Ex: AB-CDEFFEG
segmental duplications
the human genome contains numerous duplicated sequences; defined as duplications greater than 1000 base pairs (1000 bp) in length
chromosome deletion
the loss of a chromosome segment
Ex: AB-CDEFG will go to AB-CDG
pseudodominance
expression of a normally recessive mutation and it is an indication that one of the homologous chromosomes has a deletion
haploinsufficient gene
when a single copy of a gene is not sufficient to produce a wild-type phenotype
chromosome inversion
a chromosome segment is inverted-turned 180 degrees
paracentric inversions
inversions that do not include the centromere
pericentric inversions
inversions that include the centromere
position effect
if a genes position is altered by an inversion, their expression may be altered
dicentric chromatid
one of the four chromatids has two centromeres
acentric chromatid
a chromatid that lacks a centromere
dicentric bridge
the action of two homologous chromosomes stretching the dicentric chromatid across the center of the nucleus forming this structure
translocation
the movement of genetic material between nonhomologous chromosomes or within the same chromosomes
nonreciprocal translocation
genetic material moves from one chromosome to another without any reciprocal exchange
Ex: AB•CDEGF and MN•OPQRS
Segment EF moves to second without any transfer, now AB•CDG and MN•OPEFQRS
reciprocal translocation
two-way exchange of segments between the chromosomes
Ex: AB•CDEFG and MN•OPQRS will become AB•CDQRS and MN•OPEFG
Robertsonian translocation
the long arms of two acrocentric chromosomes become joined to a common centromere through a translocation, generating a metacentric chromosome with two long arms and another chromosome with two very short arms
aneuploidy
change in the number of individual chromosomes
Three types: 1) acentric chromosome, 2) small chromosomes can get lost (Robertsonian), 3) nondisjunction
polyploidy
an increase in the number of chromosome sets
nondisjunction
the failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis
leads to some gametes or cells that contain an extra chromosome and other gametes or cells that are missing a chromosome
4 types of aneuploidy conditions
nullisomy, monosomy, trisomy, tetrasomy
nullisomy
loss of both members of a homologous pair of chromosomes; represented as 2n-2
monosomy
loss of a single chromosome, represented as 2n-1
trisomy
the gain of a single chromosome, represented as 2n+1
tetrasomy
gain of two homologous chromosomes, represented as 2n+2
down syndrome, or trisomy 21
is the most common autosomal aneuploidy in humans
primary down syndrome
three full copies of chromosome 21 (and therefore a total of 47 chromosomes)
usually arises from spontaneous nondisjunction in egg formation
familial down syndrome
has a tendency to run in families
about 4% of people have 46 chromosomes, but an extra copy of part of chromosome 21 is attached to another chromosome through a translocation
translocation carriers
people with this translocation do not have down syndrome
possess only 45 chromosomes, their phenotypes are normal because they have two copies of the long arms of chromosomes 14 and 21 and apparently the short arms of these chromosomes carry no essential genetic information
two types of polyploidy
autopolyploidy and allopolyploidy
autopolyploidy
all chromosome sets are from a single species
allopolyploidy
chromosome sets are from two or more species
gene dosage effect
Imbalances in the amounts of gene products
The amount of a particular protein synthesized by a cell is often directly related to the number of copies of its corresponding gene
More sensitive in animals; plants more tolerant
