Human Variation and Evolution

Evolution

The gradual change in the characteristics of a species over generations

Phenotype

The observable characteristics due to alleles (genotype)

Genotype

The combination of alleles for a gene

Population

A group of organisms of the same species living together in a particular place at a particular time.

Gene Pool

sum of all the alleles carried by the members of a population

Allele Frequency

How often each allele of a gene occurs in a population

Mutation

A change in a gene or chromosome leading to new characteristics in an organism

Mutant

an organism with a characteristic resulting from mutation

Gene mutation

changes in a single gene so that the traits normally produced by that gene are changed or destroyed

Chromosomal Mutation

a change in the structure and/or number of chromosomes in an organism

Cause of mutations

occur without any known cause, but agents are known to increase the rate at which they occur.

Mutagenic agents/mutagen

An environmental agent that increases the rate of mutation

Examples of mutagens

• Mustard gas

• Formaldehyde

• Sulfur dioxide

• Some antibiotics

Ionising radiation examples:

• Ultraviolet light

• X - rays

• cosmic rays

• radiation from radioactive waste

• fallout from atomic and nuclear explosions

Albinism

an inherited inability to produce pigment in hair, skin and eyes. Extremely pale skin, whitish blond hair and pinkish eyes. Due to one missing protein.

Induced mutation

A mutation caused by a mutagenic agent

Spontaneous mutation

a mutation that occurs due to an error in a natural process (e.g. mitosis/meiosis

Somatic mutation

a change occurring in a gene in a body cell (cannot be passed on/inherited)

Germinal/germline mutation

a change in the hereditary material in the egg or sperm that becomes incorporated into the DNA of every cell in the body of the offspring (gametes; individual is usually not affected but offspring are).

Phenylketonuria (PKU)

an inherited disease resulting in damage to the growing brain and, thus, extreme intellectual deficiency, a tendency towards epileptic seizures, and failure to produce normal skin pigmentation.

Missense mutations

a mutation that causes a change in an amino acid resulting in a different protein being produced

Nonsense mutations

A mutation that results in a STOP codon, producing a shortened peptide chain

Neutral mutations

a mutation that causes a change in an amino acid; it does not cause an overall change in the protein

Silent mutations

a mutation that does not change the sequence of amino acids

Extent of mutation

Amount of DNA affected; from single base → whole chromosome.

Extent of gene mutation

affects only one single gene

Extent of chromosomal mutation

affects a number of genes; may change structure or number genes. Often course abnormalities so severe that miscarriage often occurs early in the pregnancy

Point mutations

a change in just one of the bases in a DNA molecule

Actions of nucleotide in point mutations

• Inserted - a new nucleotide is added to the DNA strand

• Substituted - an existing nucleotide is replaced with another one, with a different base

• Deleted - a nucleotide is removed from the DNA strand

Frameshift

a mutation involving an insertion or a deletion that results in a change in the way that the sequence is read

Duplication (insertion)

a section of chromosome occurs twice

Deletion

a piece of DNA is removed

inversion

breaks occur in a chromosome and the broken piece joins back in, but the wrong way around.

Translocation

part of a chromosome breaks off and is rejoined to the wrong chromosome

Non - disjunction

during meiosis, a chromosome pair does not separate and so one daughter cell has an extra chromosome, and one daughter cell has one less number.

Aneuploidy

a change in the chromosome number as a result of non - disjunction

Duchenne muscular dystrophy

a genetic disease resulting in wasting of leg muscles, and then arms, shoulders and chest. Occurs through gene mutation. May arise in mother and is inherited by sons or occur in male zygote so that the child develops the disease. Death occurs due to failure to of the respiratory muscles and those affected are unlikely to live more than 20 - 25 years.

Cystic fibrosis

Genetically determined disease, mutation occurs in a huge gene on chromosome 7. Gene codes for 1480 amino acids that make up a protein which regulates the passage of chloride ions across the cell membrane. Symptoms include salty - tasting skin, persistent coughing, wheezing or pneumonia, digestive and other problems. Recessive → must inherit from both parents.

Down syndrome (trisomy 21)

a genetic disorder resulting from an extra copy of chromosome 21 or an extra part of chromosome 21 (3 instead of 2). A chromosomal mutation, symptoms include characteristic facial expression, intellectual disability and weak muscles (can also suffer heart defects or digestive abnormalities)