Genome architecture Flashcards
Cytogenetics
It is the study of chromosomes and their role in heredity
It involves testing tissue, blood or bone marrow samples in a labratory to look for chromosome chanes, including broken, missing, rearranged, or extra chromosomes
Why is Cytogenetics NB
Changes in certain chromosomes may be a sign of a genetic disease or condition or some types of cancer
Therefore cytogenetics can be used to assist in diagnosing a disease or condition, plan treatment, or find out how well treatment is responding
Chromosomes
Chromosomes are the condensed form of chromatins (one-half of a duplicated chromosome), which in turn are made up of deoxyribonucleic acid (DNA) and proteins called histones
Centromere
Centromere is found at the centre of chromosomes and consists of a complex combination of proteins and DNA
Types of chromosomes
Metacentric
Submetacentric
Acrocentric
Telocentric
Centromere function
They play a vital role during the division of cells and ensure the accurate segregation of chromosomes
Studies indicate that the segregation of chromosomes without centromeres may be impaired, resulting in the loss of cells
Metacentric chromosomes
Have the centromere in the centre so both sections are equal
-Normaly have X shape
-Human metacentric chromosomes: 1, 3, 16, 19 and 20
Submetacentric chromosomes
Have the centromere slighlty offset from the centre.
-This slight offset leads to some asymmetry in the length of the two sections
-Chromosomes: 2, 4-12, 17-18 and X Chromosome
Acrocentric chromosomes
Have a centromere that is severely offset from centre
Have one very long arm and one very short arm
You arent able to see p-arm in karyotype
-Typically most genetic diseases are found in these chromosomes
-Chromosomes: 13-14, 21-22 and Y
Telocentric
Human cells that are healthy do not have telocentric centres
-However, the improper dividing of centromeres (misdivision of centromeres) of the chromosomes may lead to the development of telesomes
-Other species, such as those in the taxon, have telocentric chromosomes
Karyotyping
-Karyotyping refers to the investigative genomic process of pairing and ordering an organism’s chromosomes
-These pairings and ordering provide a genome-wide snapshot of an individual’s chromosomes
-Standardised staining procedures show structural features for each chromosome.
Molecular Cytogenetics
-The molecular address of a gene pinpoints the location of that specific gene in terms of nucleotides
-It describes the precise position of a gene on a chromosome and indicates the size of the gene
-Knowing the molecular location also allows researchers to determine exactly how far a gene is from other genes on the same chromosome
Numerical abnormalities
-Trisomy (an extra chromosome)
-Monosomy (a missing chromosome)
Structural abnormalities
-Translocations: A whole chromosome or segments of chromosomes inappropriately join with other chromosomes
-Deletions and duplications of various parts of chromosomes
Aneuploidy
The most common chromosomal abnormality caused by an extra or missing chromosome
Karyotype
The full set of chromosomes in a person’s cells
Genotype
The genetic constitution determined by the karyotype
Phenotype
The person’s clinical spectrum of findings consisting of outwards appearance which includes:
-Biochemical
-Physiologic
-and physical makeup determined by the genotype and environmental factors
Mosaicism
A single fertilised egg develops 2 or more cell lines differing in genotype
Non-disjunction
-Failure of homologues (same-diploid chromosomes) to seperate in Anaphase I and consequently four affected daughter cells are produced
-Failure of sister chromatids to seperate in Anaphase II-Non-disjunction-
(subsequently, only tow daughter cells are affected)
Conditions resulting from non-disjunction
-Patau’s syndrome
-Edwards Syndrome
-Down syndrome
-Klinefelter Syndrome
Down syndrome
-95% of cases, the extra chromosome is typically maternally derived
-Neonates with trisomy 21 are often placid, rarely cry and have hypotonia (abnormally low level of muscle tone)
-Children have a flat facial profile (particularly flattening of the bridge of the nose)
- A proportion of neonates do not have obviously unusual physical characterisitcs at birth and gradually develop more noticeable characterisitic facial features during infancy
Down syndrome developed symptoms
-The eyes are slanted upward, and epicanthal folds at the inner corners usually present
-The mouth is often held open with a protruding, furrowed tongue that may lack the central fissure, and ears are often small and rounded
-The hands are often short and broad and often have a single transverse palmar crease
-The fingers are often short, with clinodactyly (incurving) of the 5th digit, which often has only two phalanges (finger bones)
Patau’s syndrome
-It is caused by trisomy 13
-It is characterised by severe intellectual diability and physical abnormalities in many body parts
-Children with trisomy 13 have heart defects, brain or spinal cord abnormalities, and very small or poorly developed eyes (microphthalamia)
-They are also characterised by extra fingers or toes, an opening in the lip (cleft lip) with or without an opening in the roof of the mouth ( a cleft palate), and weak muscle tone (hypotonia)
-Infants are deaf and blind and rarely survive more than a few weeks or months. the syndrome is associated with advanced maternal age (35+ years old)
Klinefelter Syndrome
-Klinefelter syndrome is a chromosomal condition in which a boy child is born with an extra X chromosome (XXY)
-It causes weak bones, type 2 diabetes, heart disease and blood clots, dental problems, autoimmune diseases and breast cancer
Turner Syndrome
Only affects females as it is monosomy X
-Symptoms iclude: short height, failure of the ovaries to develop and heart defects
Edwards Syndrome
-Trisomy 18
-Symptoms include: slow growth before birth and low birth weight
-They could also have heart defects and abnormalities of other organs that develop beofre birth
-Other feautres include: small, abnormally shaped head, a small jaw and mouth and clenched fists with overlapping fingers
-Many individuals die before or within their first month
Polyploidy
There is a presence of an extra set of chromosmes in the cells
This means that there is a completely new set of chromosomes present
Aneuploidy
-It is the presence of an abnormal number of chromosomes in a cell
-there is an extra or missing chromosome present in this case
