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BIOLOGY SUMMARY

GENETICS, EVOLUTION AND ECOSYSTEMS

MODULE 6

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MODULE 6Genetics, Evolution and Ecosystems

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TOPIC 1Types of Gene Mutations • Types of gene mutations

○ Substitution – Nucleotide replaced

○ Insertion – Causes frameshift

○ Deletion – Causes frameshift

• Consequences of gene mutations ○ Neutral ○ Harmful ○ Beneficial

• Point mutation ○ Only one base is affected ○ Silent mutation

– No change in amino acid sequence ○ Missense mutation

– 1 amino acid is changed in sequence ○ Nonsense mutation

– Triplet becomes stop codon • Gene expression regulation

○ Some genes constantly expressed ○ Others expressed only when needed

– E.g. lac operon – Presence of lactose and absence of glucose

triggers synthesis of enzymes that break down lactose

• Lac operon = section of E.coli DNA ○ Structural part codes for enzyme ○ Operon part switches structural genes on/off ○ Promoter region = region where RNA polymerase binds to begin transcription

• Lac operon in absence of lactose ○ Regulator gene expressed ○ Repressor protein synthesised and binds operator region

○ RNA polymerase cannot bind promoter region • Lac operon in presence of lactose

○ Lactose changes shape of repressor

○ Repressor breaks away from operator ○ RNA polymerase can bind to promoter

• Homeobox genes ○ Regulate body part development ○ Grouped in hox clusters ○ Precisely conserved due to importance ○ Expressed anterior posterior ○ Determine where limbs branch off

• Apoptosis = programmed cell death in multicellular organisms

○ Enzymes break down cytoskeleton and DNA ○ Remaining parts phagocytosed ○ Controlled by complex cell signals ○ Causes limbs to separate

• Transcription factors ○ Proteins/ noncoding RNA ○ Attach/detach from DNA

• Introns = unexpressed DNA (don’t code for genes) • Exons = expressed DNA

○ Excess amino acids deaminated in liver ○ Converted into ammonia then urea ○ Urea excreted in urine by kidney

TOPIC 2Patterns of Inheritence • Genotype = genetic makeup of an individual • Phenotype = observd/ expressed characteristics of an

individual ○ Result of genotype and environment

• Genetic factors contributing to phenotypic variation ○ Genetic random mutations

– Mutagenic agents – Chromosomal mutations – Aneuploidy/ polyploidy – Variation from sexual reproduction

• Environmental factors contributing to phenotypic variation

○ Environment alone (e.g. limb loss in accident) ○ Environment affecting gene expression ○ Epigenetics

• Genetic diagrams

• Monohybrid = genetic diagram with just 1 gene • Dihybrid = genetic diagram with 2 genes • Linkage = when 2 or more gene loci are on the same

chromosome ○ Autosomal linkage = when the two genes are on non-sex chromosomes

○ Sex linkage = when the two genes are on sex chromosomes

– More likely to be on X chromosome • Epistasis = interaction of non-linked genes where one

masks the other • Recessive epistasis

○ Homozygous recessive alleles mask expression of another allele at different locus

○ E.g. flower colour in Salvia • Codominance = when two different alleles at the same

locus are both expressed ○ E.g. human blood group type

• Chi-squared test ○ Determine whether expected vs observed allele frequency differences are due to chance

○ Use when... – Data variation is discrete – Large sample size

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