Chromosome Structure and Abnormalities - 21.01.26

These flashcards cover key vocabulary and concepts related to chromosome structure, abnormalities, and genetic conditions discussed in the lecture.

Centromere

The part of a chromosome that links sister chromatids and is involved in chromosome separation during cell division.

Karyotype

The number and appearance of chromosomes in the nucleus of a eukaryotic cell.

Polyploidy

A condition where a cell has more than two paired (homologous) sets of chromosomes.

Isochromosome

A chromosome that has lost one arm and replaced it with a mirror image of the other arm.

Robertsonian Translocation

A translocation between two acrocentric chromosomes wherein the short arms fuse.

Acrocentric Chromosome

Chromosomes that have the centromere close to one end, leading to a long arm and a very short arm.

Nondisjunction

The failure of homologous chromosomes to separate properly during cell division, leading to gametes with an abnormal number of chromosomes.

Dysmorphology

The study of congenital structural anomalies, predominantly physical features, in individuals.

Chromosome Arms

What letter is used to designate the short arm of a chromosome?

The short arm is designated by the letter $p$.

Chromosome Arms

What letter represents the long arm of a chromosome?

The long arm is designated by the letter $q$.

Chromosome Structure

What is the function of the centromere during cell division?

The centromere links sister chromatids together and is the site involved in chromosome separation during cell division.

Chromosome Mapping

How would you define an 'Ideogram'?

An ideogram is a diagrammatic representation of a chromosome that highlights its specific banded structure.

Professionals in Genetics

What does a cytogeneticist study?

A cytogeneticist is a scientist who specializes in the study of chromosomes, including their structure, function, and any resulting abnormalities.

Visualization

What is a 'Karyotype'?

A karyotype is the organized visual profile of the number and appearance of all chromosomes within the nucleus of a eukaryotic cell.

Chromosomal Abnormalities

What is the difference between Trisomy and Monosomy?

1. Trisomy

   • A condition where there are three copies of a specific chromosome instead of the usual two.

2. Monosomy

   • A condition involving the absence of one chromosome from the normal pair.

Chromosomal Abnormalities

How is Polyploidy defined in genetics?

Polyploidy is a condition where a cell contains more than two paired (homologous) sets of chromosomes.

Structural Variations

What characterizes an 'Isochromosome'?

An isochromosome is a chromosome that has lost one of its arms and replaced it with a mirror-image copy of the remaining arm.

Structural Variations

What occurs during a Robertsonian Translocation?

This is a specific type of translocation occurring between two acrocentric chromosomes where the short arms are lost and the long arms fuse together.

Genetic Syndromes

Which chromosomal extra copy causes Down Syndrome?

Down Syndrome is caused by the presence of an extra copy of chromosome $21$ ($Trisomy\ 21$).

Genetic Syndromes

What is the chromosomal basis for Turner Syndrome?

Turner Syndrome results from a complete or partial absence of one $X$ chromosome in females, often leading to physical traits like short stature.

Genetic Syndromes

How does Klinefelter Syndrome manifest chromosomally?

It occurs in males who possess an extra $X$ chromosome (typically $XXY$), often affecting fertility and physical development.

Centromere Position

What defines an 'Acrocentric Chromosome'?

Chromosomes that have the centromere located very close to one end, resulting in one significantly long arm and one very short arm.

Genetic Mutations

Contrast Deletion and Translocation.

1. Deletion

   • A segment of DNA is missing from the chromosome.

2. Translocation

   • Parts are rearranged or swapped between non-homologous chromosomes.

Diagnostic Techniques

How does FISH (Fluorescence In Situ Hybridization) work?

It is a laboratory technique that uses fluorescent probes to detect and localize the presence or absence of specific DNA sequences on chromosomes.

Cell Division Errors

What is Nondisjunction?

The failure of homologous chromosomes or sister chromatids to separate properly during cell division, leading to an abnormal number of chromosomes in daughter cells.

Clinical Manifestations

Which physical traits are often studied in relation to chromosomal abnormalities?

1. Congenital Heart Disease

   • Heart abnormalities present at birth (common in Down Syndrome).

2. Polydactyly

   • The presence of extra fingers or toes.

3. Dysmorphology

   • The study of structural anomalies and unusual physical features.

What is the purpose of using colchicine in the process of obtaining cell cultures?

to inhibit spindle fibre formation (i.e. arresting the cell during the metaphase) which allows for better visualisation of the condensed chromatin structure

What are the 5 most notable acrocentric chromosomes?

13, 14, 15, 21, & 22

What does 9q34 notation mean in relation to gene identification?

9 = chromosome number

q = long arm

3 = band location on arm of chromosome

4 = sub-band location

What is trisomy 18 more commonly known as?

Edwards syndrome

What is trisomy 13 more commonly known as?

Patau syndrome

What type of structural chromosomal abnormality is responsible for Cri du Chat Syndrome?

Deletion of part of chromosome 5

What goes wrong when an inversion occurs in a chromosome?

segment of a chromosome is reversed

What is the difference between pericentric and paracentric inversions?

pericentric inversions involve the centromere and change the length of the arms

paracentric inversions do not and occur only in one arm of the chromosome.

What are the physical manifestations of Edwards syndrome?

small features:

• micrognathia = small jaw

• low-set malformed ears (elfin features)

• clenched fists with overlapping fingers

What are the clinical presentations of a baby with trisomy 13?

Patau syndrome symptoms:

• cleft lip

• polydactyly

• holoprosencephaly = brain fails to divide

• congenital heart defects

What does mosaicism refer to in relation to Turner’s syndrome?

occurs where some patients may possess a mixture of 46 XX cells and 45 X cells

What is the advantage of using FISH as a chromosome analysis technique?

can identify smaller deletions that are not detectable by standard karyotyping

What is 22q11 deletion more commonly known as?

DiGeorge syndrome

What is the recommended method for detecting DiGeorge syndrome?

FISH = Fluorescence In Situ Hybridization

What does CATCH - 22 refer to?

the clinical features of DiGeorge Syndrome:

Cardiac defects

Abnormal facial features

Thymic hypoplasia

Cleft palate

Hypocalcemia

What are the clinical manifestations of Cri du Chat Syndrome?

• distinctive high-pitched crying

• delayed development

• intellectual disability

• physical abnormalities e.g. small head & facial features.