Life Sciences Grade 12 - DNA, Meiosis, and Evolution

DNA (Deoxyribonucleic acid)

The molecule that carries the genetic code for protein synthesis and hereditary information.

Nucleotide

The monomer (building block) of nucleic acids, consisting of a phosphate group, a sugar molecule, and a nitrogenous base.

Double Helix

The spiral-ladder shape of DNA consisting of two strands joined by weak hydrogen bonds.

Complementary Base Pairing

In DNA, adenine (A) always links to thymine (T), and guanine (G) always links with cytosine (C).

Nuclear DNA

DNA located within the nucleus of a cell.

Extra-nuclear DNA

DNA found outside the nucleus, such as mitochondrial DNA (mtDNA) or chloroplastic DNA.

RNA (Ribonucleic acid)

A single-stranded nucleic acid containing ribose sugar and the nitrogenous base uracil (U) instead of thymine.

Transcription

The first stage of protein synthesis where a complementary strand of mRNA is formed from a DNA template in the nucleus.

Translation

The second stage of protein synthesis where tRNA brings amino acids to a ribosome to form a protein based on mRNA codons.

DNA Replication

The process occurring during interphase where DNA makes an identical copy of itself to ensure daughter cells have the same genetic information.

DNA Profiling

A technique using unique patterns of DNA bands to identify individuals, crime suspects, or biological parents.

Meiosis

A type of cell division that halves the chromosome number from diploid (2n) to haploid (n) to produce genetically different gametes.

Homologous Chromosomes

A pair of chromosomes of the same size and shape, carrying the same genes at the same loci, one from each parent.

Crossing Over

The exchange of genetic material between chromatids of homologous chromosomes during Prophase I of meiosis, leading to variation.

Non-disjunction

The failure of homologous chromosomes or sister chromatids to separate during meiosis, which can lead to disorders like Down Syndrome (Trisomy 21).

Genotype

The genetic composition of an organism (e.g., TT, Tt, or tt).

Phenotype

The physical appearance or observable traits of an organism (e.g., tall or short).

Allele

Different forms of a gene