Lesson starter Write down three differences between translation

Lesson starter Write down three differences between translation and transcription

How can mutations affect phenotype (physical appearance) and genotype? Are mutations a good or bad thing?

Learning objectives: Mutations • State that mutations cause changes to the sequence of nucleotides in DNA molecules • Explain how the mutations can have beneficial, neutral or harmful effects on the way a protein functions

The Contribution of Alleles to Phenotypic Variation n Variation between members of the same species is described as intraspecific variation n Phenotypic variation describes the outward physical appearance as a result of genetic variation n Examples of phenotypic variation: q q Morphological Biochemical Physiological Behavioural

The Contribution of Alleles to Phenotypic Variation n Different forms of the same gene are called alleles n Chromosomes are stacks of genes and we get two sets; one from each parent. Each homologous pair of chromosomes contains slightly different genes. E. g. brown eyes vs blue eyes n The genotype of an organism will determine the phenotype (genes determine physical appearance)

Variation n Variation in offspring is essential for life to continue. n Variation is created by: q q q Meiosis (crossing over of portions of chromosomes, random assortment of chromosomes at metaphase) Fertilisation (egg and sperm meet totally at random) Mutations

Mutations are the source of novel genetic variation Germline cell mutation n Mutations in gametes n Potentially can be inherited n Fetus can be spontaneously aborted due to mutation n May result in congenital abnormalities Somatic cell mutation n Only affects daughter cells of mutated cell n All other cells lack mutation n Cancer is an example

Mutations n A mutation is a change in the structure or quantity of an organism’s genetic material. n A gene mutation is a change in one or more nucleotides in a strand of DNA n A chromosome mutation is a change to the structure, such as deletion, inversion or translocation, or a change to the number of chromosomes in a nucleus n Mutations can vary from a small change in DNA or a gene or be a large change in chromosome structure or number

DNA mutations – point mutations n Substitution: one nucleotide is replaced by another with a different base n Inversion: nucleotides change position with each other

DNA mutations – frameshift mutations n Deletion: one nucleotide is removed from the chain and the chain joins up again n Insertion: one extra nucleotide is inserted into the chain

Types of Mutation n Point mutations: these are only minor mutations that will affect the organism only slightly or not at all q q n Substitution Inversion Frameshift mutations: these lead to major changes as large portions of DNA are misread q q Insertion Deletion Remember SIDI for mutations! Substitution, Inversion, Deletion, Insertion http: //www. bbc. co. uk/scotland/education/bitesize/higher/biology/genetics_adaptation/mutations 1 _rev. shtml

Frameshift Mutation n Inserting or deleting one or more nucleotides n Changes the “reading frame” like changing a sentence n Proteins built incorrectly

Frameshift Mutation n Original: q n The fat cat ate the wee rat. Frame Shift (“a” added): q The fat caa tet hew eer at.

Amino Acid Sequence Changed

Deletion – no G Substitution – A for G Insertion – extra C Inversion – bases swapped around

Mini Plenary Framshift mutations result in minor changes to DNA True False

Mini Plenary Point mutations only cause minor effects to changes in DNA True False

Mini Plenary Insertion mutations add an extra amino acid to the sequence True False

Mini Plenary Mutations can affect genes or chromosomes True False

Examples of Mutations n Sickle cell anaemia n Cystic Fibrosis n Protooncogenes in cancer

Frequency of Mutations & Mutagenic Agents n Without external influences, mutations occur randomly and spontaneously n Mutations of this kind are very rare as most mutant genes are recessive. n A person would have to be homozygous to display the mutant trait in their phenotype n Mutagenic agents can increase the rate at which mutations occur q q Mustard gas Types of radiation e. g. gamma rays, X-rays and UV light

Chromosome Mutation Animation

Gene Mutations n Change in the nucleotide sequence of a gene n May only involve a single nucleotide n May be due to copying errors, chemicals, viruses, etc.

Point Mutation n Sickle Cell disease is the result of one nucleotide substitution n Occurs in the hemoglobin gene

Gene Mutation Animation

Cell division n Cell division is tightly controlled by genes, there are two types involved in this q q Tumour suppressor genes – that slow cell division Proto-0 ncogenes - that stimulate cell division These ensure that cells divide at a fairly constant rate, and those cells that are worn out or dead are replaced

Proto oncogenes n These are normally only switched ‘on’ when growth factors are detected by protein receptors on the cell surface membrane. These cause relay proteins in the cytoplasm to switch these genes on.

Oncogenes n A mutation cause proto oncogenes to mutate into oncogenes n This is when these genes are permanently switched on, even in the absence of growth factors that would normally stimulate appropriate cell division q q The receptor on the cell surface membrane could be permanently activated A growth factor is produced in excessive amounts

Tumour Suppressor Genes n n n These inhibit cell division This maintains normal cell division and prevents tumours from developing If these genes become inactivated a tumour can develop

Describing how mutations happen n Study the diagrams below. Using these diagrams to help you, describe the mutation that has occurred and the consequence it has for the protein formed. Sickle cell anaemia Cystic Fibrosis

Describing how mutations happen n Sickle cell anaemia: a result of a point mutation on codon 6 of the gene for the beta polypeptide chain of haemoglobin. n CF: a deletion deleting ONE amino acid out of 1480 in a polypeptide chain

How can mutations affect phenotype (physical appearance) and genotype? Are mutations a good or bad thing?