Chapter 16: Variations in Chromosome Structure and Number Flashcards
(46 cards)
Chromosomal Mutation??? (Chromosomal aberrations)
- variations from the normal wild type condition in chromosome structure or chromosome number.
Chromosomal mutations can arise via what two ways?
- spontaneously
- induced experimentally (chemicals / radiation)
What are the four common types of chromosomal mutations involving changes in structure?
- Deletions
- Duplications
- Inversions
- Translocations
All four common types of chromosomal mutations involve what common origin?
- the structure mutations arise when one or more breaks in the chromosome have occurred.
L> wherever the break occurs, broken ends remain without the specialized sequences found at the end of chromosomes (telomeres) that prevent their degradation.
Chromosomal Deletions?
- mutation in which part of the chromosome is missing
- it starts where breaks occur in the chromosome.
Deletions are mutations in which part of the chromosome is missing and usually occur where there are break-in the chromosome due to possibly what five things?
- heat
- radiation
- viruses
- chemicals
- recombination errors
Can deletion mutations be reverted to the wild type state?
NO
If a deletion involves the loss of a centromere, the result is what?
- an acentric chromosome which is usually lost during meiosis.
Pseudodominance? (think deletions)
- the deletion of a dominant allele of a heterozygote results in the appearance of the phenotype of the recessive allele. This unexpected expression of the recessive allele is caused by the absence of the dominant allele.
Consequences of deletions??
L> think homozygote vs heterozygote
- In heterozygote condition, they may function normally but remaining allele may be recessive for deleterious condition and cause severe consequences. If loss of a centromere you get an a centric chromosome which may be lost in meiosis. This could cause fatal consequences. When homologous chromosomes line up after a deletion event there are resulting loops of unpaired DNA.
- not usually noted in homozygotes because they usually die if the deletion is large enough.
Explain Ectrodactyly?
- causes? (3)
- frequency of occurrence?
- chromosome involved ? number of mutations?
- phenotypic expression?
- translocations, inversions and deletions
- 1/90000 babies
- absence of the central digit ray
- five different genetic mutations known all on chromosome 7 concerning homeobox genes( aka ones that have to do with body plan)
Hypertrichosis???
- chromosome involved?
- frequency ?
- known cases
- cause?
- rearrangement of chromosome 8
- 1/billion people
- 50 ever recorded since the middle ages
- due to the disruption in the cross talk cell communication between the epidermis and the dermis as hair follicles form in a three month old fetus. and essentially at the hair line to the toes…
- normally: signals from the dermis form follicles at the three month mark as individual follicles form…. a signal is sent to prevent the area around it from developing follicles as well.
What is a duplication mutation??
a chromosomal mutation that results in the doubling of a segment of chromosome
What are the three types of duplication mutations?
- Tandem Duplication
- Reverse Tandem Duplication
- Terminal Tandem Duplication
Tandem duplications??
- when the mutation generates duplicated segments that are adjacent to each other with the order of the genes in both segments the same as the order of the original
ex: original -> ABCDEFGH
Mutated: ABCBCDEFGH
Reverse Tandem Duplication??
- when the order of the genes in the duplicated segment is the opposite of the order of the original.
Ex: original : ABCDEFGH
Mutated: ABCCBDEFGH
Terminal Tandem Duplication??
- when the duplicated segments are arranged in tandem at the end of a chromosome
ex: original: ABCDEFGH
mutated: ABABCDEFGH
Heterozygote duplications result in what?
loops of unpaired genes
What are multi gene families?
a set of genes inherited by duplication and variation in some ancestral gene. The duplications can be clustered on the same chromosome or dispersed on to other chromosomes.
Example of multi gene families from lecture?
-hemoglobin and myoglobin families
L>immunoglobulants (antibodies), histocompatibility antigens (gene products on cells that prevent you from being a tissue donor)
Reiterated genes??
completely identical for robustness and since you need a whole lot of them ..hundreds of them on tandem on chromosomes
L>histones, rRNA, tRNA
Phenotypic effects in Drosophila for Duplications - Bar mutation on X chromosome (explain) ie gene involved inheritance expression L> Homozygous L>heterozygous L> hemizygous
- 16Agene: bar gene…. 1 copy=regular eye in drosophila … but if you have a duplication of this on one of your alleles… more copies of the gene= smaller eye
- inheritance is similar to x linked mutation
- as soon as you have this duplication it is immediately expressed
L> eye is vertical and slit shaped
L> smaller eye than wild type but larger than if homozygous for bar mutation
L> similar to homozygous for bar mutation.
Explain the evolution of the Bar Mutation!
- unequal crossing over due to homologous chromosomes pair improperly or crossing over events in the misfired region results in gametes with a duplication or deletion.
When discussing Bar mutation what does B^D indicate?
double bar mutation
( 3 copies of 16A)
L> two evolutionary pathways?
L> single duplication on one and deletion of other via unequal crossing
L> unequal crossing of chromosomes with double 16A respectively resulting in one chromosome with three and one with one
