Unit 3: Cytogenetics - Chromosome Abnormalities & Chromosomal Disorders

These flashcards cover key vocabulary terms and concepts related to cytogenetics, chromosome abnormalities, and their implications.

Cytogenetics

The study of chromosomes and their role in heredity and genetic disorders.

Autosomal chromosomes

Chromosomes that are not sex chromosomes; humans have 22 pairs of autosomes.

X-chromosome inactivation

The process by which one of the two X chromosomes present in female mammals is inactivated.

Gametogenesis

The process by which cells undergo meiosis to form gametes (sperm and eggs).

Numeric abnormalities

Chromosomal abnormalities where the number of chromosomes is altered (e.g., aneuploidy). Mistakes during segregation in meiosis

Structural abnormalities

Chromosomal abnormalities involving changes in the structure of chromosomes (e.g., deletions, duplications).

Polyploidy

A condition in which a cell has more than two complete sets of chromosomes. (anything other than the normal 46 chromosomes)

Triploidy (3n, 69 chromosomes) 69, XXX

Tetraploidy (4n, 92 chromosomes) 92, XXXY

Aneuploidy

A condition in which the number of chromosomes is not an exact multiple of the haploid set.

Aneuploidy arises from faulty segregation of the chromosomes in meiosis or mitosis, nondisjunction. 

Can have autosomal aneuploidy, like Edward syndrome (47,XY,+18) or sex chromosome aneuploidy like Turner Syndrome 45,X (2n-1)

(Turner syndrome is the only chromosomal monosomy syndrome compatible with live birth)

Monosomy: 2n-1

Trisomy: 2n+1

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during cell division.

Trisomy

A chromosomal condition where an individual has three copies of a chromosome instead of two.

Klinefelter syndrome: 47, XXY (2n+1)

Down syndrome: 47, XY, +21

Edward syndrome : 47, XY, +18

Patau syndrome: 47, XY, +13

Monosomy

A chromosomal condition where an individual has only one copy of a chromosome instead of two.

Autosomal monosomy is lethal and nearly always is incompatible with survival to term

Sex chromosome aneupoloidy

Turner syndrome 45, X (2n-1)

Klinefelter syndrome

A genetic condition in males caused by an extra X chromosome (47,XXY) leading to physical and cognitive developmental issues.

Turner syndrome

A chromosomal disorder in females caused by the absence of one X chromosome (45,X), leading to various developmental issues.

Uniparental Disomy (UPD)

A genetic condition where both copies of a chromosome pair come from one parent, and no copies from the other parent. UPD may occur with no apparent impact on the health and development of an individual. UPD can cause health concerns because of the effect of dosage imbalance. 

Maternal UPD: both copies of chromosomes from mother

Paternal UPD: both copies of chromosomes from father

UPD can be

Isodisomy UPD: Inheritance of two identical copies of one parent’s chromosome

Heterodisomy UPD: inheritance of two different copies of the same chromosome from one parent 

Mosaicism

A condition in which a single individual has two or more genetically different cell lines derived from a single zygote.

This type of mosaic is arises after fertilization and during the early cleavage stage of development. 

Usually due to mitotic nondisjunction, post-zygotic nondisjunction 

Triploidy (3n)

accounts for roughly 20% of all chromosome abnormalities identified in spontaneous miscarriages. Survival rates is very small.

There are 2 types of Triploidy

1. Digynic Triploidy - occurs when an egg is a diploid egg (instead of a haploid like its supposed to be)

2. Diandric Triploidy - the most common cause of diandric triploidy is polyspermy, 2 sperms to 1 egg. Another case of occurrence is caused by a diploid sperm to a normal haploid egg.