Immunogenetics: Genes, Cell Cycle, & Genetic Disease

Comprehensive vocabulary flashcards covering immunogenetics, cell cycle regulation, chromosomal abnormalities, and genetic inheritance patterns based on medical lecture notes.

Gene

Sequences of DNA on chromosomes that encode a functional product.

Allele

A form (variant) of a gene located at a particular point (locus) on the chromosome.

Mitosis

The process whereby a cell divides into two daughter cells such that each daughter cell is a clone containing the same number and kind of chromosomes as the parent cell.

Meiosis

The process whereby a cell produces four daughter cells, each with a haploid number of chromosomes (one-half the number possessed by the parent cell).

Crossing over

An event during meiosis where two pairs of sister chromatids exchange genetic information before the first meiotic division.

$G_1$ Checkpoint

A cell cycle control point at the end of the $G_1$ phase that monitors cell size, growth factors, and DNA damage.

$G_2$ Checkpoint

A cell cycle control point at the end of the $G_2$ phase that monitors DNA integrity and DNA replication completion.

Spindle Assembly Checkpoint (SAC)

Also known as the M checkpoint, it monitors correct microtubule attachment to and/or the tension status of each kinetochore during metaphase.

Cyclin D CDK4/CDK6 complex

A protein complex that phosphorylates retinoblastoma protein ($Rb$), which is inhibiting the $E2F$ transcription factor.

Cyclin B CDK1 complex

Also known as the Maturation Promoting Factor ($MPF$), this complex is needed for the cell to enter mitosis.

Proto-oncogenes

Genes involved in signal transduction and cell-cycle progression (e.g., growth factors, Ras, cyclins) that can become oncogenes through gain-of-function mutations.

Tumor Suppressor Genes

Genes whose loss of expression can lead to tumor formation; they contribute to cancer development when both copies (alleles) are inactivated (recessive mechanism).

Loss of Heterozygosity

The loss of the corresponding normal allele in a tumor-suppressor gene, leading to the loss of function and uncontrolled cell proliferation.

$$p53$$

A multifunctional protein that halts the cell cycle to repair damaged DNA in $G_1$ or triggers apoptosis if the DNA cannot be repaired.

$$p21$$

A protein triggered by $p53$ levels that enforces the cell cycle halt by binding to and inhibiting the activity of $CDK$/cyclin complexes.

Familial Retinoblastoma

A condition where an individual inherits one mutated copy of the $RB1$ allele, resulting in a $100\%$ chance of developing retinoblastoma due to the high probability of the second allele mutating.

Sporadic Retinoblastoma

Occurs in individuals who do not inherit mutations in $RB1$ but acquire two specific mutations, one in each $RB1$ allele, during their lifetime.

Cytogenetics

A branch of biology focused on the study of chromosomes and their inheritance, especially as applied to medical genetics.

Autosomes

Chromosomes numbered 1 to 22, generally arranged in biological pairs and numbered roughly in relation to their sizes.

$SRY$ gene

The "sex-determining region of Y" gene found on the Y chromosome that encodes a protein required for male development.

Karyotyping

A chromosome analysis test that evaluates the number and structure of chromosomes to detect genetic disorders or congenital abnormalities.

Aneuploidy

A numerical abnormality in which an individual is either missing one chromosome from a pair (monosomy) or has more than two chromosomes instead of a pair (trisomy, tetrasomy).

Nondisjunction

An unequal chromosome sorting during meiosis I or II that leads to an incorrect number of chromosomes distributed to daughter cells.

Patau syndrome

A chromosomal abnormality characterized by Trisomy 13; features include cleft lip and palate, heart defects, and severe central nervous system anomalies.

Edward syndrome

A chromosomal abnormality characterized by Trisomy 18; features include low birth weight, heart defects, and a small abnormally shaped head.

Down syndrome

A chromosomal abnormality characterized by Trisomy 21; features include hypotonia, characteristic facial features, and developmental delay.

Turner syndrome

A chromosomal abnormality characterized by Monosomy X, occurring in approximately 1 out of $2,500$ live female births.

Klinefelter syndrome

A chromosomal abnormality involving an $XXY$ genotype, characterized by small testes, infertility, and tall stature.

Genotype

The collection of genes of an individual, representing the genetic 'instructions'.

Phenotype

The physical expression of a genotype, representing the individual's 'appearance'.

Silent mutation

A point mutation that alters the code in a triplet without the replacement of the expected amino acid.

Missense mutation

A point mutation that alters the code in a triplet and leads to the replacement of one amino acid by another.

Nonsense mutation

A point mutation that changes an amino acid codon to a stop codon.

Frameshift mutation

A deletion or insertion of a number of nucleotides (not a multiple of 3) that results in an alteration of the reading frame of the DNA strand.

Pleiotropy

A condition where a single gene influences how multiple traits are expressed, such as in sickle cell anemia.

Penetrance

The probability or percentage that a specific genotype will lead to a specific phenotype; for example, $80\%$ for mutations in $BRCA1$ and $BRCA2$ alleles.

Polymorphisms

Allelic variations that occur in $>1\%$ of the population, such as Single Nucleotide Polymorphisms (SNPs) or Short Tandem Repeats (STRPs).