Simplified chromosomal disorders

What is aneuploidy

Having too many or too few chromosomes.

Which three autosomal trisomies are covered

Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

What causes Down syndrome most often

An extra chromosome 21.

Is Down syndrome usually inherited

No. Most cases happen randomly; some translocation cases can be inherited.

What are common features of Down syndrome

Developmental and learning difficulties, low muscle tone, characteristic facial features, and increased risk of heart, hearing, vision, thyroid, and digestive problems.

What is a Robertsonian translocation

Fusion of the long arms of two acrocentric chromosomes, with loss of their short arms.

Which chromosomes can take part in Robertsonian translocations

Chromosomes 13, 14, 15, 21, and 22.

What causes Edwards syndrome

An extra chromosome 18 (trisomy 18).

What are key features of Edwards syndrome

Clenched fists with overlapping fingers, rocker-bottom feet, heart defects, low-set ears, and a small lower jaw.

What causes Patau syndrome

An extra chromosome 13 (trisomy 13).

What are key features of Patau syndrome

Extra fingers or toes, cleft lip/palate, small eyes, small head, heart problems, and intellectual disability.

What is Turner syndrome's usual karyotype

45,X

What are key features of Turner syndrome

Short stature, webbed neck, absent or delayed menstruation, and underdeveloped ovaries.

Why are there no Barr bodies in typical Turner syndrome

There is only one X chromosome, so there is no extra X to inactivate.

What is Klinefelter syndrome's usual karyotype

47,XXY

What are key features of Klinefelter syndrome

Male external genitalia, tall stature, small testes, reduced fertility or infertility, and sometimes breast development.

What is X-inactivation

The process where one X chromosome is switched off in each typical XX body cell.

What is a Barr body

An inactive, condensed X chromosome visible in the cell nucleus.

What is the Lyon hypothesis

The idea that only one X chromosome is active in each typical female somatic cell.

How many Barr bodies are usually present in XX cells

One.

How many Barr bodies are usually present in XY cells

Zero.

How many Barr bodies are usually present in XXY cells

One.

What is a chromosome deletion

Loss of a chromosome segment and the genes in it.

What is a chromosome duplication

An extra copy of a chromosome segment.

What is a chromosome inversion

A chromosome segment breaks off and reattaches in the reverse direction.

What is a chromosome translocation

A chromosome segment attaches to a different, non-homologous chromosome.

What is a ring chromosome

A chromosome whose ends fuse into a ring after terminal material is lost.

What is the difference between balanced and unbalanced rearrangements

Balanced: no overall genetic material lost or gained. Unbalanced: genetic material is lost or gained.

Why can chromosome deletions be harmful

They remove genes and can disrupt normal development or function.

What is Cri du chat syndrome caused by

A deletion on the short arm of chromosome 5 (5p).

What is the key feature of Cri du chat syndrome

A distinctive kitten-like cry; speech and learning difficulties and a small head can also occur.

What chromosome region is associated with DiGeorge syndrome in the lecture

A microdeletion at 22q11.2.

What are key features of DiGeorge syndrome

Heart abnormalities, cleft palate or speech difficulties, facial differences, and immune problems linked to an underdeveloped thymus.

What is the Philadelphia chromosome

A translocation between chromosomes 9 and 22, written t(9;22).

What cancer is associated with the Philadelphia chromosome

Chronic myelogenous leukaemia (CML).

What is BCR-ABL

A fusion gene formed by the chromosome 9;22 translocation that can drive uncontrolled cell division in CML.

Which translocation is associated with Burkitt lymphoma in the lecture

t(8;14).

What is a microdeletion

Loss of a small chromosome segment that may remove several genes.

What is a microduplication

An extra copy of a small chromosome segment.

Which syndrome is associated with deletion at 7q11.23

Williams Beuren syndrome.

Which syndromes are linked to changes at 15q11q13 in the lecture

Prader Willi syndrome and Angelman syndrome.

Which disorders are linked to 17p11.2 deletion or duplication

Deletion: Smith Magenis syndrome. Duplication: Potocki Lupski syndrome.

What is FISH

Fluorescence in situ hybridization; it uses labelled probes to look for specific chromosome regions.

What is karyotyping

Examining chromosomes to assess their number and structure.

What is QF-PCR used to detect in the lecture

Common trisomies, sex chromosome aneuploidy, triploidy, and some mosaicism.

Which test is usually fastest in the lecture's comparison

QF-PCR, with results in about 24 hours.

What is one limitation of FISH

It only detects abnormalities in the regions targeted by its probes.

What is one limitation of QF-PCR

It does not detect balanced chromosome rearrangements.

What can karyotyping detect that QF-PCR does not

Balanced chromosome rearrangements and a wider range of chromosome abnormalities.

What is a copy number variant (CNV)

A deletion or duplication that changes the number of copies of a DNA region.

How can chromosome rearrangements contribute to cancer

They can disrupt genes or create fusion genes that change cell growth.

What is the main difference between trisomy and monosomy

Trisomy means one extra chromosome; monosomy means one chromosome is missing.

What does +21 mean in a karyotype

An extra chromosome 21.

What does 45,X mean

A total of 45 chromosomes with only one X chromosome.

What does 47,XXY mean

A total of 47 chromosomes, with two X chromosomes and one Y chromosome.

What does del(5p) mean

A deletion on the short arm of chromosome 5.

What does t(9;22) mean

A translocation involving chromosomes 9 and 22.