Chromosome Variations and Structural changes Genetics

What is aneuploidy?

An abnormal number of chromosomes caused by gain or loss of individual chromosomes.

What causes aneuploidy?

Non-disjunction during cell division.

What is monosomy?

A condition where one chromosome is missing (2n-1).

What is an example of monosomy?

Turner Syndrome (XO).

What is nullisomy?

A condition where both homologous chromosomes are missing (2n-2), which is lethal in humans.

What is trisomy?

A condition with an extra copy of a chromosome (2n+1).

What is an example of trisomy?

Down Syndrome.

What is tetrasomy?

A condition with two extra copies of a chromosome (2n+2).

What is euploidy?

Variation in entire sets of chromosomes, such as monoploid (n), diploid (2n), triploid (3n), and tetraploid (4n).

What is polyploidy?

Having more than two sets of chromosomes (3n, 4n, etc.), common in plants but rare in animals.

What is uniparental disomy (UPD)?

A condition where both copies of a chromosome come from one parent.

How can uniparental disomy occur?

Through trisomy rescue, where a zygote loses one chromosome, leaving two from the same parent.

What is non-disjunction?

The failure of chromosomes to separate properly during cell division.

What are the consequences of non-disjunction in meiosis I?

Homologous chromosomes do not separate, resulting in all gametes being abnormal.

What are the consequences of non-disjunction in meiosis II?

Sister chromatids do not separate, leading to half normal and half abnormal gametes.

What is the significance of polyploidy in plants?

It is important for evolution and agriculture, leading to larger fruits and increased vigor.

What is autopolyploidy?

Polyploidy resulting from chromosome duplication within the same species.

What is allopolyploidy?

Polyploidy resulting from the combination of chromosomes from different species.

What is a deletion in chromosome structure?

The loss of DNA from a chromosome, which can be terminal (end) or intercalary (middle segment).

What is a duplication in chromosome structure?

The presence of extra gene copies, which can be tandem, reverse tandem, or dispersed.

What is an inversion in chromosome structure?

A segment of DNA is reversed; can be paracentric (not including centromere) or pericentric (including centromere).

What is a translocation in chromosome structure?

The movement of chromosome segments, which can be reciprocal (two chromosomes swap) or non-reciprocal (one-way transfer).

Robertson Translocation + Down Syndrome

Fusion of two acrocentric chromosomes (14+21)

-short arms lost

-long arms join

Familial Down syndrome is caused by:

Robertsonian translocation of chromosomes 21 and 14

Maternal age effect

older women are more likely to produce an oocyte with an extra or missing chromosome due to mistakes in chromosome distribution during meiosis I

Edwards syndrome (trisomy 18)

have small jaws, small eyes, and malfored low set ears. They also have rocker bottom feet (also seen in Patau). But the key buzzword is clenched hands with overlapping fingers.

Patau syndrome (trisomy 13)

Characterized by severe intellectual disability, a small head, sloping forehead, small eyes, cleft lip and palate, extra fingers and toes, and other disabilities; results from the presence of three copies of chromosome 13.

Cri du chat (cry of the cat)

syndrome that results from a specific deletion in chromosome 5; the child's cries sound like the mewing of a cat and the child will die in infancy/early childhood

Prader-Willi Syndrome (PWS)

• missing paternal material

• caused by deletion or UPD

Angelman Syndrome (AS)

caused by a deletion of chr. 15 from mother

neurogenetic disorder causing neurological impairment

Chronic Myelogenous Leukemia (CML)

caused by a translocation between chromosomes 9 and 22 (Philadelphia chromosome)

Burkitt's lymphoma

Translocation involving chromosome 8 and activates MY

C oncogene