Mutations

Random assortment of chromosomes during meiosis results in games that have a huge number of possible combinations of the chromosomes that originally came from the male parent and female parent, a pair segregates (goes either north or south of the equator)

Crossing over chromatids during meiosis may result in pieces of chromatids being broken off and attaching to a different chromatid, this results in a changed sequence, or recombination of the alleles along the resulting chromosome

• One or more members of a chromosome pair fail to separate during meiosis • This results in gametes that have more or less than the correct number of chromosomes • If such gametes are involved in fertilisation, the resulting embryo will have the incorrect number of chromosomes. - - Conditions of fault include Monosomy & Trisomy

The differences between members of a species

• Random fertilisation means that because each person will produce a huge number of different sperm or eggs with respect to the alleles each contains • Because any sperm can fertilise any egg there is almost an infinite number of possible combinations of allies in the offspring

• Mutations are a change in a gene or chromosome which leads to new characteristics in an organism which can be beneficial or harmful • If the mutation occurs in a gamete it can be passed on from generation to generation • Mutations can be beneficial such as when they improve an organisms chance of surviving e.g. sickle cell anaemia

A mutant is an organism with a characteristic resulting from a mutation

• Environmental factors that increase the rate at which mutations occur agents • e.g. mustard gas, sulphur dioxide, radiation (UV light, cosmic rays, radioactive waste)

Somatic and Germile Mutations

• DNA changes that take place in body cells • These cannot be passed onto the offspring • Only the individual with the somatic mutation is affected • Each time the mutant body cell decides the mutation is passed onto the daughter cells • The reproductive cells are not affected and once the individual dies the mutation is lost

• DNA change that occur in a sperm or ova • These can be passed onto the offspring • If the reproductive organs are affected the mutation can occur in the gametes and may then be passed onto the next subsequent generation • The individual is not usually affected, but carries the gene, however that individual produces gametes with changed DNA

• Changes in a gene, occur during DNA replication (during interphase before cell division) • This mutation will then be copied each time the new DNA is replicated therefore being passed onto further generations • Include: Point mutations (Substitution, Insertion, Deletion)

• A change of a single nucleotide, includes deletion, insertion or substitution of one nucleotide in a gene • These can alter a protein or ,ay prevent the production of protein, or have no effect at all • 1 abnormal protein can have an enormous effect on the body • e.g. sickle cell anaemia is the result of one nucleotide substitution occurring in the haemoglobin gene

At least one base has been deleted, which will affect the result of the amino acid codon triplet

The exchange of one base for another

An extra base has been added and affects the sequence

• Results from a change in only 1 amino acid • Suffers produce sickle shaped red blood cells, the which do not carry as much oxygen as normal red blood cells and they also stick together and block small blood vessels • Has a heterozygous advantage as it provides resistance to Malaria and therefore it remains in the population as a selective advantage, as a result of natural selection where the environment is such that one genotype is favoured over another

• Most gene mutations produce a recessive allele because they prevent the gene from producing a protein that will be able to function in the body, therefore a person could have a lot of mutation in the genes and be unaware of them • If a person reproduces with a partner who has the same recessive mutation the recessive condition could appear in their offspring • Some recessive mutations are lethal if they are not masked by a dominant normal allele • Lethal recessives cause the death of the embryo or foetus or early death of child e.g. Tay-Sachs Disease (TSD)

• Occurs in the Jewish Community (Ashkenazi jews) • It is a lethal recessive disorder • The disease results in poor lipid metabolism resulting from a missing enzyme, it is the accumulation of a fatty substance in the Nervous System • A baby with two recessive alleles for TSD developed normal for the first few months, then develops mental and physical disability • Death occurs at an early age

• Occurs in part of a chromosome or all of a chromosome and affects several genes, often cause severe abnormalities that miscarriage often occurs • Includes; deletion, duplication, inversion, translocation & Non-disjunction

• A chromosomal mutation of Non-Disjunction, a person will have an extra chromosome e.g. Down Syndrome on Chromosome 21, person will have 3 and Patau Syndrome on Chromosome 13, will have 3, may suffer from mental retardation, a small head, an extra finger

• A person has an extra sex chromosome • e.g. Klinefelter’s Syndrome (XXY) - a person has an extra X chromosome, person will be more feminine, a male will have small testes which do not produce sperm, breasts are enlarged and body hair is sparse, occasionally mental retardation occurs • Jacobs Syndrome (XYY) a person has an extra Y chromosome and considered super male

• A person will have partial deletion of a chromosome e. g. Cri-du-chat Syndrome - a person is missing a proportion of Chromosome 5, it is a rare genetic disorder, there is a problem with the larynx and nervous system, an infant will cry and sound just like meowing kitten

Part of a chromosome is lost during DNA replication