Small Scale Mutations & Gene Expression. LARGE MUTATIONS & GENETICS Quick Review

Small Scale Mutations&

Gene Expression

LARGE MUTATIONS & GENETICSQuick Review

• Gene: – section of a chromosome coded for a trait

• Example:– Gene 1 codes for your hair color

Review: Genetics

• Allele: different forms of a gene Ex: TACCGTTCAC… = Brown hair or B allele Ex: TAGCGTTCAC… = red hair or b allele

Review: Genetics

• Every organisms receives two alleles for traits• Ex: Genotype: Bb

Review: Genetics

• The interaction of these alleles determines which individual trait will appear

• Example:– Genotype: Bb – Phenotype: Brown Hair

Review: Genetics

• Humans have ~20,000 genes throughout our 23 pairs of chromosomes.

• Example:– Gene 1 codes for:• your hair color

– Gene 2 codes for:• your ear shape

Review: Genetics

Large Scale Mutations

• Any change in chromosome number resulting from errors during gamete formation (meiosis)

Medium Scale Mutations

• Gene mutations: entire sections of DNA change

SMALL MUTATIONS & GENE EXPRESSION

DNA Replication

• For 3.5 b.y. DNA has been copying itself– usually perfectly (parent offspring)

Mutation are Errors

• Sometimes DNA polymerase makes a mistake

• Your DNA has 3-50 nucleotide mutations from your parent’s DNA

You are a mutant!

Most of your DNA is noncoding

Your coding DNA

• Example:– DNA: TACCGTTCAC…– mRNA: AUGGCAAGUG…– Amino acid: met – glu – val…– Protein: Melanin– Trait: Brown hair

Small Scale Mutations

• Any change in the genome (nitrogen base sequence) resulting from errors during DNA replication and environmental conditions.

Point Mutations

• Changes occur in one nucleotide– Missense: wrong amino acid in protein– Silent: no change to amino acid sequence– Nonsense: amino acid codon to STOP codon

Frameshift Mutations

• Deletion: – removal of nucleotide(s)

• Insertion: – addition of nucleotide(s)

Ex: Sickle Cell Anemia

– Missense mutation in the gene that codes for Hgb.• Thymine replaced with adenine• Results in valine instead of glutamine• Hgb folds incorrectly• RBCs become sickle shaped• RBCs cannot carry O2

Ex: Cystic Fibrosis

• Deletion (3 bases) in gene that codes for CFTR– 508th amino acid phenylalanine is removed– Malfunctioning transport protein Cl- ions in

membrane– Causes mucus buildup in lungs, digestive tract

Ex: Huntington’s Disease

• Repetition of a gene that codes for htt– Normal gene: 36 GAC repeats (glutamine)– Mutant htt gene: > 36 GAC repeats– Results in malfunctioning polyglutamine protein– Causes neurons to decay

• Deletion of a gene that codes for CCR5 –Protein is important in immune function–Results in HIV resistance in homozygotes–Delayed onset of HIV infection in heterozygotes –Currently a research study being conducted to

genetically modify T-cells so that they have this mutation

Ex: Beneficial Mutation

• We would not evolve!!!!• We would all be clones!!!• We wouldn’t have the ability to stick to walls!

Without mutations