Lec 9. Chromosome variation II Flashcards
What is metacentric?
centromere in the middle
What is submetacentric?
chromosome with somewhat smaller arm
What is acrocentric?
chromosome with small arm
What is telocentric?
chromosome with no arm
Which chromosomes have a satellite that can be recognized by a secondary constriction?
13,14,15,21,22
What does P stand for pertaining to chromosomes?
P is the short arm
What does q stand for pertaining to chromosomes?
q is the long arm
What does the satellite contain?
NOR (nucleolar organizer region)
What does NOR do?
Can be detected by silver staining and is a useful landmark for chromosome indentification
What do chromosome mutations include?
Rearrangements, aneuploids and polyploids
What are the three steps to karyotyping?
Chromosomes prepared from actively dividing cells. Halted in metaphase with colchicine. Chromosomes arranged according to size.
What are the 4 types of banding?
G,Q,C,R
What stain is used for G bands?
Giemsa stain
What stain is used for Q bands?
Quinacrine stain
What do C bands show?
Reveals centromeric heterochromatin
What do R bands show?
Region rich in C-G base pairs
What does G banding show?
Heterochromatin stains intensely(A-T rich) and euchromatin (G-C) stains lightly.
What does Q banding show?
Florescent stain for A-T rich regions
What does T banding show?
Telomeric banding after heat denaturation
What is the G-banded chromosome band resolution?
400-600
What phase do chromosomes need to be for G-banding?
Metaphase
How is chromosome painting done?
Fluorescent-tagged chromosome specific DNA sequences.
What is aneuploidy?
the loss or gain of chromosomes
What is polyploidy?
Those containing more than 2 complete paired homologous sets of chromosomes
What is an ex of aneuploidy?
trisomy
What is an ex of polyploidy?
Autotriploid
Chromosome rearrangements alter
chromosome structure
What are the 4 types of rearrangements?
Duplication,deletion,inversion,translocation
What does inversion mean?
a segment of chromosome is turned 180
What does translocation mean?
a segment of chromosome moves to another place of the same chromosome
Chromosomal rearrangements usually happen because of what?
mispairing of repeated regions of the genome
In an individual heterozygous for a duplication, the duplicated chromosome loops out during pairing in what phase?
Prophase I
What region is prone to damage?
The duplicated region which LOOPs
What does the Bar phenotype in Drosophila results from?
X-linked duplication
What is a deletion?
Loss of chromosomal segment
What are 3 effects of deletions?
imbalances in gene product, expression of a normally recessive gene, haploinsufficiency
What is the notch phenotype produced by?
chromosome deletion
What does the notch gene do?
Huge for development especially the heart
Symptoms: Austism, ADHD, learning disability, large head, wide-set eyes, schizophrenia, loose joints, underdeveloped parts of brain. What disease is this?
1q21.1 duplication syndrome
Symptoms: TAR, Autism, epilepsy, dysmorphism, missing kidneys, cancer. What disease is this
1q21.1 deletion syndrome
Symptoms: Heart defect, developmental problems. Most common micro deletion sydrome. What is the disease?
DiGeorge Syndrome: 22q11.2 deletion
Symptoms: Severe neurodevelopmental disorder. Occurs 1 in 40k. What is the disease?
15q13.3 microdeletion
What is paracentric inversion?
An inversion in which the breakpoints are confined to one arm of a chromosome without the centromere
What is pericentric inversion?
An inversion in which the breakpoints occurs on both arms of a chromosome, involves the centromere.
Do problems arise in homozygous individuals when inversions occur in meiosis?
No
Do problems arise in heterozygous individuals when inversions occur in meiosis?
Yes
Why do problems arise in heterozygous individuals with inversions in meiosis?
Homologos sequences align only if the 2 chromosomes form an inversion loop, this loops causes stress on the DNA. Individuals with para and peri inversions often have nonfunctional gametes due to loss of large amounts of genetic material during meiosis.
True or False? Translocations can only be unbalanced
False. Can be either balanced or unbalanced
What is reciprocal translocation?
an exchange of material between nonhomologous chromosomes
What is nonreciprocal translocation?
Transfer of genes from one chromosome to another nonhomologous chromosome
What is Robertsonian translocation?
Translocation in chromsomes that results in two of the long arms coming together and the short arms coming together as well. resulting in losing the short arms and keeping one big chromosome (two long arms).
What human chromosome is said to have resulted from Robertsonian translocation?
chromosome 2
What chromosome differs in humans and chimpanzees due to a pericentric inversion?
Chromosome 4
What chromosome differs in humans and gorrillas due to a paracentric inversion?
chromosome 7
What are the terms for variation in chromosome number?
Aneuploidy and ployploidy
What is aneuploidy?
An increase or decrease in the number of individual chromosomes
What are 3 causes of aneuploidy?
Deletion of centromere during mitosis and meiosis. Robertsonian translocation. Nondisjunction during mitosis and meiosis
What are the types of aneuploidy?
Nullisomy, monosomy, trisomy, tetrasomy
What is nullisomy?
loss of both members of a homologous pair of chromosomes. 2n-2
What is monosomy?
loss of a single chromosome. 2n-1
What is trisomy?
Gain of a single chromosome. 2n+1
What is tetrasomy?
gain of two homologous chromosomes. 2n+2
What are some examples of aneuploidy in sex-chromsomes of humans?
Turner syndrome XO. Klinefelter Syndrome XXY
What is a good example of aneuploidy in plants?
Jimson weed
What are some examples of aneuploidy in autosomal aneuploids?
Trisomy 21. Familial down syndrome.
How does Trisomy 21 happen?
Primary down syndrome caused by the presence of three copies of chromosome 21. 75% random nondisjunction in egg formation
How does Familial down syndrome happen?
Robertsonian translocation between chromosome 21 onto any other chromosome
What carriers are at increased risk for producing children with down syndrome?
Translocation carriers
The incidence of primary down syndrome and other aneuplouds increases with what?
Increases with older age from both men and women
What are some examples of aneuploidy in autosomal aneauploids in humans ordering them from most common to least common?
trisomy 21, trisomy 18: edwards syndrome, 13: Patau syndrome, and Trisomy 8.
Why is there a drastic decrease in frequency of trisomic syndrome from chromosome 18 to chromosome 8?
The size of chromosome and the size og genes involved
What is the cause of Cri-du-chat syndrome?
Deletion on chromosome 5
What is the cause of Fragile X syndrome?
Duplication on X chromosome
What is the cause of Acute myelogenous leukemia?
Translocation in which part of chromosome 22 moved to 9
What is the cause of Klinefelter syndrome?
extra X chromosome in males
What is the cause of Turner syndrome?
One X chromosome missing in females
What are two categories of polyploidy?
Autopolploidy and allopolyploidy
What is polyploidy?
Presence of more than two sets of chromosomes
What is autopolyploidy?
From single species. whole genome has been duplicated
What is allopolyploidy?
From two or more species
In what two ways can autopolyploidy arise from?
Nondisjunction in mitosis or meiosis
In what way do most allopolyploids arise from?
From hybridization between two species followed by chromosome doubling.
What is the significance of polyploidy?
Increase in cell size, larger plant attributes and evolution may give rise to new species.
What is an allohexaploid?
the fusion of genomes from 3 separate species
What is an example of an allohexaploid?
Chromosomes of wheat
What leads to cancer?
Genomic instability
what is the link between cancer and polyploidy?
One of the initiator events of cancer is polyploidy
