Flashcards in Chromosome Mutations Deck (50):
Change from normal chromosome structure and or number.
-Change in gene expression pattern if the organism is viable
-detectable through karyotyping
Common occurrences of chromosome mutations:
-6/1000 live births
-if survive embryonic stage:
*mental and developmental disorders and infertility
Variations in chromosome number
True ploidy level; # of chromosomes in the individual's cells is a multiple of the normal haploid set.
ex. humans- haploid: 23; diploid: 46
Not a multiple of the normal haploid set; one or more extra or missing chromosomes.
ex. humans- haploid: 23; Turner Syndrome: 45,X
Homologous chromosomes during anaphase I or sister chromatids during anaphase II don't segregate properly.
-fertilzation of aneuploid gametes leads to aneuploid progeny.
Both homologous chromosomes are absent
One chromosome is missing
-Turner Syndrome: 2n-1
One extra chromosome
Two extra chromosomes
Example of aneuploidy: Trisomy 21
Down Syndrome in humans
-consequences: problem with gene dosage
Trisomy 21 and Advance Maternal Age
Oocytes are arrested in prophase I
-each month, after puberty, meiosis continues in the one egg.
Ploidy levels of somatic cells
At least two sets
Somatic cell; result from meitotic division.
Result from meiosis; germ-line cells which will fuse with other haploid cells
Different Types of Polyploidy
Extra set of chromosomes is identical to the normal haploid set
Chromosomes come from two different species to produce a hybrid
When only certain cells within an organism are polyploidy.
Changes in chromosome structure (4 major types)
How do changes in chromosomes occur?
-Breaks in the chromosome
-General errors in recombination
When part of a chromosome or a sequence of DNA is missing.
If deleted piece contains recessive allele
If deletion of a dominant allele and unmasking of a recessive allele.
Deletion reduces gene dosage
Deletion removes a centromere (nondisjunction-->aneuploidy)
gene encoding telomerase is missing
when part of a chromosome is copied abnormally, resulting in extra genetic material from the duplicated segment.
-Slippage during S phase can also cause this to happen
-Gene amplification; more gene product
-Unequal crossing over can induce a deletion
Consequences of duplication
Reduced number of eye facets due to extra negatively influencing 16A allele.
Bar allele in Fruit Flies; example of duplication
Duplications might result in _______.
ex. hemoglobin subunits and rRNA genes
Multiple genes with related functions near each other on the same chromosome
Type of homolog, 2 or more genes in an organism that have similar or identical functions.
when a segment of a chromosome is reversed from end to end. (breakage and rearrangement within itself)
Two types of inversions
Inversion that doesn't include the centromere
Inversion that does include the centromere
What causes breakage for an inversion to happen
location of gene in chromosome can effect how much of that gene is transcribed
-over-expression of genes that are not meant to be silenced
Consequences of Inversions: Position effect
Rearrangement of parts between nonhomologous chromosomes.
Occurs when the transfer of chromosome material is one way
Occurs when chromosomes swap parts
Consequences of Translocations
-Non- wild type gene order
Philadelphia chromosome in chronic myelogenous leukemia (CML)
Example of a translocation
Happen because of trinucleotide repeat expansion
-Narrow sites of some chromosomes that are prone to breakage
*breakage would cause a deletion