MBG*2040: Basic Principles of Heredity and Pedigree Analysos

gene

The fundamental unit of heredity.

A genetic factor (region of DNA) that helps determine a characteristic. Comes in multiple forms called alleles.

alleles

One of two or more alternative forms of a gene.

locus

Specific place on a chromosome occupied by an allele (location where gene is on a chromosome).

genotype

Set of alleles possessed by an individual organism.

heterozygote

An individual organism possessing two different alleles at a locus.

homozygote

An individual organism possessing two of the same alleles at a locus.

phenotype or trait

The appearance or manifestation of a character.

Law of Segregation

Only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random.

Law of Independent Assortment

The alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

mitosis

Cell division in which cells are duplicated. Chromosomes double into homologues and are subsequently split into two daughter cells with identical information.

meiosis

Cell division that forms sex cells. A source of variation in genes.

null/amorphic alleles

A nonfunctional protein is produced OR no protein is produced.

• Oftentimes a mutation in the promoter region (if a mutation turns transcription off, you don’t get anything)

hypomorphic alleles

A poorly functioning protein is produced OR reduced amounts of a normally functioning protein is produced.

• Some pathways functions well with only 50% of the gene (since we have two copies of each gene, in some cases, one is sufficient to produce the desired effect)

autosomal dominant traits

Reverse of recessive traits! Normal allele cannot override dominant (thus there are no “carriers”, even with one copy of the affected gene, you will show the trait).

bb normal

Bb affected heterozygote

BB affected homozygote

e.g. Huntington Disease

dominant hypermorphic alleles

• Negative phenotypic consequences due to the over-production of a normal protein OR

• Negative phenotypic consequences due to the production of a protein with increased activity levels

  • e.g. Amino acid binds super tightly and results in an overactive cell

Common in promoter regions as it controls how much transcription occurs.

neomorphic alleles

A “new” function of a protein.

• Negative phenotypic consequences due to the presence of an altered protein that has a new function

• Negative phenotypic consequences when the altered protein interferes with the wildtype protein (dominant-negative allele → Huntington Disease)