FUN Quiz 3 Flashcards
What are the 3 Large scale types of genetic variation with a brief description of each.
Aneuploidy: One or more individual chromosomes in extra copy, or missing
Translocations/Inversions/ring chromosomes: Mixed Chromosomes
CNVs Copy Number Variants: Relatively large sections of DNA duplicated or deleted
How are ring chromosomes formed?
2 ends of the same chromosome fuse together
Distinguish briefly between heterochromatin and euchromatin. Also explain how it is shown in a karyoptype
Heterochromatin represent the dark band in karyotypes. They are AT rich yet gene poor
Euchromatin represent the light bands, are GC rich, and hence gene rich.
What are the Classifications of chromosomes based on centromereposition
Metacentric: Centromere in the middle
Submetacentric: Not in the middle nor at the terminal with one arm significantly longer than the other
Acrocentric: Centromere at terminus. Leftover DNA contains no genetic content.
What are the two arms of a chromosome and what differentiates them
Short arm is the P arm and long arm is the q arm
With the banding nomenclature of 1p13.3, where is the approximate location of the gene in question?
1: Chromosome number
p: Short arm of the chromosome
1: Region
3: Band
.3: Sub-band
Define Aneuploid
There is an abnormal chromosome number
What are the two types of chromosome abnormalities?
Numerical aberrations: incorrect number of chromosomes
Structural aberrations:
Involving 1 chromosome: Duplication, deletion, inversion, ring chromosome
Involving 2 chromosomes: Translocations;
Reciprocal translocations
Robertsonian translocations
Define Euploid
Correct number of chromosomes
Distinguish between Reciprocal translocations and Robertsonian translocations
Reciprocal translocations is the change of DNA between two non-homologous chromosomes. (Not normal cross-over)
Robertsonian Translocations: This occurs when two Acrocentric chromosomes fuse together to form one hybrid chromosome
How does Aneuploidy occur?
Chromosomal disjunction
What is Chromosomal disjunction?
It is the failure of chromosomes to separate and segregate normally either in mitosis or meiosis
Compare chromosomal disjunction in mitosis and meiosis.
When chromosomal disjunction occurs in meiosis, non-disjunction results in imbalanced gametes. If any of these gametes fertilise, all cells derived from the resulting embryo will have a chromosome imbalance.
When it occurs in mitosis, non-disjunction produces two cell-lineages derived from a single zygote causing Mosaicism
Individuals who are mosaic for a particular chromosomal aberration usually have less severe symptoms => Mitosis disjunction is less severe than meiosis disjunction. The earlier the disjunction happens during development, the more severe the outcome.
Distinguish between disjunction occurring in the first meiotic division and the second
If disjunction happens in the first division, gametes contain either both parental chromosomes or neither. If it happens in the second division, then gametes will contain two identical copies of the same chromosome.
Give three clinical signs of Down Syndrome
Developmental delay Variable intellectual disability Characteristic facial features Congenital heart defects Premature aging Risk of leukemia
What are the two ways Down syndrome can occur and which is predominant?
Trisomy (predominant), and Robertsonian translocation
What factor affects risk of trisomy 21?
Maternal age, risk increases with age
Give 3 Human Aneuploid Syndromes
Down Syndrome: Trisomy 21
Turner Syndrome: Monosomy X
Kleinefelter syndrome: XXY
Triple X Syndrome: idk
IF you included Edwards syndrome or Patau syndrome then good for you
What are the gametes produced in the following case as well as their viability when paired with a normal gamete:
Chromosome 14 and 21 fuse together by Robertsonian translocation.
Answer should only reflect chromosomes 14 and 21 in terms of gametes.
Full answer in PowerPoint
Trisomy 14 Dead Monosomy 14 Dead Trisomy 21: Down syndrome Monosomy 21: Dead T(14;21): carrier Normal
What are the two different types of structural chromosomal abnormalities and give one difference
Unbalanced abnormalities involves the loss or gain of genetic material. They often have developmental delays
Balanced abnormalities do not involve the gain or loss of genetic material. Heterozygous individuals can be at risk of passing on the abnormality to offspring.
What are the indications for prenatal cytogenetics?
- Abnormal ultrasound
- Advanced maternal age/biochemical test
- Previous birth of child with trisomy
- Infertility, recurrent spontaneous abortion
- Carrier of heritable chromosome abnormality
What are the clinical indications for post-natal Cytogenetics
Dysmorphic features
Developmental delay
Clinical features of chromosomal syndrome
What is a micro deletion syndrome
Syndrome that involves deletions that are often to small to detect by G banding
What are the viable methods for diagnosis?
Molecular cytogenetic methods including Array CHG and FISH