3.4.3 Causes of Genetic Diversity

Genetic code

The sequence of base triplets in DNA that codes for proteins.

Genetic diversity

The number of different alleles of genes in a species/population.

Acquired mutations

Mutations that occur after fertilisation and are often caused by mutagenic agents.

Substitution mutation

A base is swapped with another. Can result in silent mutations.

Deletion mutation

One or several bases are removed. Often results in a frame shift.

Addition mutation

One or several bases are added. Often results in a frame shift.

Duplication mutation

One or more bases are repeated.

Inversion of bases mutation

A group of bases becomes separated from the DNA sequence and re-join at the same position but in the inverse order.

Translocation of bases mutation

A group of bases becomes separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of the same or a different chromosome.

Silent mutations (definition)

The genetic code is degenerate - some amino acids are coded for by more than one DNA triplet, which means that often this type of mutation may cause no change in the polypeptide.

Frameshift mutations (definition)

If a base is added to or removed from a gene, it changes the way in which the triplets are read following that mutation.

Protein Function Change

Altered protein structure affects biological activity.

Chromosome

A thread like structure made up of one long DNA molecule wrapped around histone proteins.

Gene

A section of DNA that codes for a particular protein (or functional RNA).

Allele

A version / form of a single gene.

Mutation

A change to the base sequence of DNA.

Homologous chromosomes

A pair of matching chromosomes. Each chromosome contains the same genes at the same positions (loci) but could have different alleles.

Degenerate

One amino acid can be coded for by several different base triplets.

Gene pool

The complete range of alleles present in a population.

Silent mutation

When a mutation doesn't cause a change to the sequence of amino acids in the protein coded for, and function of the protein is not impacted.

Frameshift mutation

A mutation that changes the number of bases in the DNA code, causing a shift in the base triplets that follow, so that the triplet code is read in a different way.

Mutagenic agent

Something that increases the rate of mutations.

Meiosis

A type of nuclear division where a parent cell divides to create 4 genetically different haploid daughter cells.

Haploid

When a cell contains 1 copy of each chromosome. Often these cells are gametes.

Diploid

When a cell contains 2 copies of each chromosome.

Crossing over

When chromatids twist around each other and bits of them swap over during prophase I of meiosis.

Independent segregation

The random division of maternal and paternal chromosomes into daughter cells during meiosis. Occurs in metaphase I.

Genetic diversity (definition)

Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species.

Hereditary mutations

Mutations inherited from your parents that can cause genetic disorders e.g. cystic fibrosis or the cancer causing BRCA1.

Types of gene mutation

There are 6 types of gene mutation: Substitution, Deletion, Addition, Duplication, Inversion of bases, Translocation of bases.

Enzyme

Protein that catalyzes biochemical reactions.

DNA Base Sequence

Order of nucleotides in a DNA molecule.

Primary Structure

Sequence of amino acids in a protein.

Tertiary Structure

3D shape of a protein formed by folding.

Active Site

Region where substrate binds on an enzyme.

Chromosome Mutation

Alteration in chromosome structure or number.

Non-Disjunction

Failure of chromosomes to separate during meiosis.

Down's Syndrome

Genetic disorder caused by an extra chromosome 21.

Mutagenic Agents

Factors that increase mutation rates in DNA.

Ionising Radiation

High-energy radiation that can damage DNA.

Carcinogens

Chemicals that can cause cancer by mutating DNA.

Haploid Number

Half the total chromosome number, n=23 in humans.

Diploid Number

Total chromosome number, 2n restored at fertilization.

Interphase

Phase where DNA replicates before meiosis starts.

Homologous Chromosomes

Matching chromosome pairs with same genes.

Chromatids

Identical copies of a chromosome joined by a centromere.

Meiosis I

First division where homologous chromosomes separate.

Prophase I

Chromosomes visible; crossing over occurs.

Metaphase I

Bivalents align at the cell equator.

Anaphase I

Homologous chromosomes separate, centromeres intact.

Meiosis II

Second division where sister chromatids separate.

Crossing Over

Exchange of genetic material between homologous chromosomes.

Independent Segregation

Random assortment of chromosomes during meiosis.

Genetic Variation

Diversity in alleles and genotypes in offspring.

Fertilization

Union of male and female gametes.

Mitosis vs Meiosis

Mitosis produces 2 identical cells; meiosis produces 4 unique cells.