Karyotypes and Aneuploidy (LEC)

What is a karyotype?

A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell.

How is a karyotype obtained?

A karyotype is obtained by collecting cells (often from blood), culturing them to enhance mitosis, arresting the cells during metaphase, and then using microscopy to analyze the chromosomes.

What abnormalities can a karyotype detect?

A karyotype can detect deletions, duplications, inversions, translocations, and other chromosomal abnormalities.

What are microdeletions?

Microdeletions are deletions that are smaller than 5 Mb and are usually not visible by standard karyotype analysis.

What is the minimum size of deletions that can generally be observed by karyotype analysis?

Deletions larger than 5 Mb are usually visible by standard karyotype.

What alterations in chromosomes are observable through karyotype analysis?

Karyotype analysis can reveal large alterations in chromosomal structure and number, including evident banding patterns.

What is euploidy?

Euploidy refers to a chromosome number that is an exact multiple of the haploid number, such as diploidy, triploidy, and tetraploidy.

What is diploidy?

Diploidy is the normal human complement of chromosomes, where there are two of each chromosome, totaling 46 chromosomes.

What is triploidy?

Triploidy is a condition where an organism contains three copies of each chromosome, totaling 69 chromosomes. It is not compatible with life.

What is tetraploidy?

Tetraploidy is a chromosomal condition where there are four copies of each chromosome, totaling 92 chromosomes. It is lethal.

What is aneuploidy?

Aneuploidy is the addition or loss of one or more chromosomes, leading to an abnormal chromosome number.

What is monosomy?

Monosomy is the loss of a single chromosome, resulting in an abnormal number of chromosomes, which is often not compatible with life.

What is Turner Syndrome?

Turner Syndrome is a form of monosomy, specifically 45, XO, where one sex chromosome is absent, affecting female development.

What is Klinefelter Syndrome?

Klinefelter Syndrome is an aneuploidy condition characterized by 47, XXY, resulting in male individuals having an extra X chromosome.

What is 'super male'?

'Super male' refers to individuals with 47, XYY, which is an aneuploidy condition caused by the presence of an extra Y chromosome.

What is 'super female'?

'Super female' refers to individuals with 47, XXX, which is an aneuploidy condition caused by the presence of an extra X chromosome.

What is Down Syndrome?

Down Syndrome is a trisomy condition where there is an extra copy of chromosome 21, leading to various developmental challenges.

What is Edward Syndrome?

Edward Syndrome is a trisomy condition characterized by the presence of an extra chromosome 18, resulting in severe developmental issues.

What is Patau Syndrome?

Patau Syndrome is a trisomy condition caused by an extra chromosome 13, leading to significant physical and intellectual disabilities.

What is mosaicism in chromosomal aneuploid conditions?

Mosaicism is the presence of two or more populations of cells in one individual with different genotypes due to nondisjunction events during cell division.

How can mosaic Turner Syndrome (45, XO) occur?

Mosaic Turner Syndrome can happen when a fertilized egg (46, XX) experiences mitotic nondisjunction during embryogenesis, leading to some cells being 45, XO while others remain 46, XX or become 47, XXX.

What is a mixed somatic/germline mosaic?

A mixed somatic/germline mosaic is a condition where some cells in a person's body have one genotype, while other cells have a different genotype, affecting both somatic and germline tissues.

What is a confined germline mosaic?

A confined germline mosaic is where all cells in the body are of one genotype, but the cells of the gametes have a different genotype, leading to a higher risk of having children with a genetic disorder.

How can a person be mosaic for Down Syndrome (Trisomy 21)?

A person may be mosaic for Down Syndrome if nondisjunction occurs as a post-zygotic event during embryonic development, resulting in one cell type with a normal karyotype and another with Trisomy 21.

What is trisomy rescue in the context of Down Syndrome?

Trisomy rescue occurs when nondisjunction happens during oogenesis, leading to Trisomy 21 at conception. During post-fertilization mitosis, one of the extra chromosome 21s is evicted, resulting in a mosaic with both normal karyotype and Trisomy 21 cells.

What are the incidence rates for some chromosomal aneuploid conditions?

• Trisomy 21 (Down Syndrome): 1 in 830 live births

• Klinefelter Syndrome (47, XXY): 1 in 1,000 live births

• Turner Syndrome (45, XO): 1 in 4,000 live births

• Trisomy 18: 1 in 7,500 live births

• Trisomy 13: 1 in 22,700 live births