Chromosome Variation Flashcards
What is involved in karyotyping?
Chromosomes are prepared from actively dividing cells.
They are halted in metaphase.
Chromosomes are arranged according to size.
What is involved in chromosome painting?
The use of fluorescent-tagged chromosome specific DNA sequences to visualize specific chromosomes or chromosome segments by in situ DNA hybridization and fluorescence microscopy.
What are two types of chromosome mutations?
Aneuploidy
Polyploidy
You are examining the chromosomes taken from a developing embryo. You notice that a chromosome is missing. What kind of chromosome mutation is this?
Aneuploidy
What is polyploidy?
Organisms that contain more than two complete paired (homologous) sets of chromosomes.
You are studying the chromosomes of an organism and note that there is a duplication. What type of chromosome mutation is this?
Chromosome rearrangement
You are studying the chromosomes of an organism and note that there is a trisomy. What type of chromosome mutation is this?
Aneuploidy
You are studying the chromosomes of an organism and note that there is an autotriploid. What type of mutation is this?
Polyploidy
What occurs during chromosome duplication?
A segment of the chromosome is duplicated.
What occurs during chromosome inversion?
A segment of the chromosome is turned 180 degrees.
What occurs during chromosome deletion?
A segment of the chromosome is deleted.
What occurs during translocation?
A segment of a chromosome moves from one chromosome to a nonhomologous chromosome, or to another place on the same chromosome.
What occurs to a chromosome that is heterozygous for a duplication?
The duplicated chromosome loops out during pairing in prophase I.
What are three effects of deletions?
Imbalances in gene product
Expression of a normally recessive gene (pseudodominance)
Haploinsufficiency
When does a deletion loop form?
During prophase I.
In prophase I, the normal chromosome must loop out in order for the homologous sequences of the chromosomes to align.
What is a paracentric inversion?
An inversion in which the breakpoints are confined to one arm of a chromosome; the inverted segment does not span the centromere.
What is pericentric inversion?
An inversion in which the breakpoints occur on both arms of a chromosome. The inverted segment spans the centromere.
True or false: problems arise in meiosis for homozygous individuals who have inversions.
False
When do homologous sequences align in inversions?
Only if the two chromosomes form an inversion loop.
What occurs in heterozygous individuals when they have an inversion in meiosis?
Individuals with para- or peri- centric inversion often have nonfunctional gametes due to loss of large amounts of genetic material during meiosis.
Homologous sequences align only if the two chromosomes form an inversion loop.
In an individual heterozygous for a paracentric inversion, the chromosomes ….
Form an inversion loop during pairing in prophase I.
What would occur to a heterozygote with one normal chromosome and one chromosome with an inverted segment during meiosis?
In prophase I of meiosis, the chromosomes form an inversion loop, which allows the homologous sequences to align.
What occurs in a heterozygous individual in which there is a single crossover within a paracentric inversion?
Abnormal gametes
What occurs in a heterozygous individual that has a single crossover within a pericentric inversion?
Abnormal gametes are formed
A dicentric chromosome is produced when crossing over takes place in an individual heterozygous for which type of chromosome rearrangement?
Paracentric inversion
What are the two types of translocations?
Nonreciprocal translocation
Reciprocal translocation
Robertsonian translocation
What occurs during robertsonian translocation?
The short arm of one acrocentric chromosome is exchanged with the long arm of another, creating a large metacentric chromosome and a fragment that often fails to segregate and is lost.
What can be concluded from translocations in meiosis?
Gametes resulting from adjacent-1 and adjacent-2 segregation are nonviable because some genes are present in two copies whereas others are missing.
What occurs during a translocation in meiosis?
An individual heterozygous for one translocation possesses one normal copy of each chromosome and one translocated copy of each.
Because each chromosome has sections that are homologous in two other chrmosomes, a crosslike configuration forms in prophase I of meiosis.
In anaphase I, the chromosoems separate in one of three different ways.
What is the outcome of a Robertsonian translocation?
One metacentric chromosome and one chromosome with two very short arms.
What are 3 causes of aneuploidy?
Deletion of a centromere during mitosis and meiosis
Robertsonian translocation
Nondisjunction during meiosis and mitosis
What are the 4 types of aneuploidy?
Nullisomy
Monosomy
Trisomy
Tetrasomy
What is a nullisomy?
A loss of both members of a homologous pair of chromosmoes 2n - 2
What is a monosomy?
A loss of a single chromosome 2n - 1
What is a trisomy?
A gain of a single chromosome 2n + 1
What is a tetrasomy?
The gain of two homologous chromosomes; 2n + 2
A diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species?
2n + 1 = 36 + 1 = 37
What are two examples of sex-chromosome aneuploids?
Turner syndrome, XO
Klinefelter syndrome, XXY
What results from trisomy 18?
Edward syndrome
What results from trisomy 13?
Patau syndrome?
Why are sex-chromosome anueploids more common than autosomal aneuploids in humans and mammals?
There is no mechanism of dosage compensation for autosomal chromatids.
Autosomes carry more genes.
Most autosomal aneuploids are spontaneously aborted.
Autopolyploidy occurs from ___
Single species
Allopolyploidy occurs from ___
Two species
What do most allopolyploids arise from?
Hybridization between two species followed by chromosome doubling.
What is the significance of polyploidy?
It causes an increase in cell size.
It gives larger plant attributes
And it may give rise to new species.
Species A has 2n = 16 chromosomes and species B has 2n = 14. How many chromosomes would be found in a allotriploid of the two species?
2a + b = 16 + 7 = 23
A + 2b = 8 + 14 = 22
What are the four different chromosome morphologies?
Metacentric
Submetacentric
Acrocentric
Telocentric
