Biology topic 3

Genome

The complete set of genetic material (DNA) in an organism.

Gene

A segment of DNA that encodes a functional product, usually a protein.

Coding sequence

The portion of a gene that is translated into a protein.

Non-coding sequence

DNA that does not code for proteins but may regulate gene expression or have other functions.

Spontaneous mutations

Mutations that occur naturally without external influence (e.g. errors in DNA replication).

Induced mutations

Mutations caused by external factors such as radiation or chemicals.

Somatic mutations

Mutations that occur in body (non-reproductive) cells; not inherited.

Germ-line mutations

Mutations in reproductive cells that can be passed to offspring.

Point mutation

A mutation affecting a single nucleotide.

Substitution/SNP

A point mutation where one base is replaced by another.

Indel

A mutation involving insertion or deletion of one or more nucleotides.

SSLP/STR

Repeated short DNA sequences used in genetic profiling.

Deletion

Loss of a segment of a chromosome.

Duplication

Repetition of a segment of DNA.

Inversion

A chromosome segment is reversed in orientation.

Translocation

A segment of DNA moves to a different chromosome.

Silent

A mutation that does not change the amino acid sequence.

Missense

A mutation that changes one amino acid in a protein.

Nonsense

A mutation that creates a premature stop codon.

Frameshift

A mutation that shifts the reading frame of a gene (usually due to indels).

No effect on gene function

A mutation that does not alter protein function or phenotype.

Loss of function

A mutation that reduces or eliminates protein activity.

Gain of function

A mutation that gives a protein a new or enhanced activity.

Genotype

The genetic makeup (allele combination) of an organism.

Phenotype

The observable traits of an organism resulting from genotype and environment.

Ploidy

The number of sets of chromosomes in a cell.

Lous/loci

The specific location of a gene on a chromosome.

Haploid

A cell with one set of chromosomes (e.g. gametes).

Diploid

A cell with two sets of chromosomes (e.g. most body cells).

Homologous chromosomes

A pair of chromosomes with the same genes but possibly different alleles.

Sister-chromatids

Identical copies of a chromosome joined together after DNA replication.

Allele

Different versions of the same gene.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Hemizygous

Having only one copy of a gene (e.g. genes on the X chromosome in males).

Dominant

An allele that is expressed even when only one copy is present.

Recessive

An allele that is expressed only when two copies are present.

Incompletely dominant

A pattern where the heterozygote shows an intermediate phenotype.

Co-dominant

A pattern where both alleles are fully expressed in the heterozygote.