Chapter 5 | Genetic Variation

Darwin

Variation => reproductive success

Individuals very in heritable traits, coming from mutations → only heritable traits can be selected

Proteins

• Chains of amino acids

• Primary, secondary, tertiary, quaternary structure determined by amino acid sequence

• Structure impacts function

• Catalysis, signaling, response

DNA

• Nucleic acids/nucleotides

• Structure is a double helix

• Codes for protein — information storage

• Organized into chromosomes

• Stored with redundancy — complementary strand/base pairing & ploidy level (haploid vs. diploid)

Central Dogma

DNA -(transcribed)→ RNA -(translated)→ Protein

Translation

• Ribosomes translate mRNA to protein through genetic code

• Triplet code (codons) translate into different amino acids

Gene expression

• Regulated in many ways that are heritable in the production of that protein

• ex.

  • microRNA blocks translation phase → stops translation, no protein produced

  • microRNA produced from DNA

  • Alters gene expression

  • Splicing post-transcription yields different transcripts

Epigenetics

• Modifications to DNA that don’t change the genetic sequence

• Cell specialization — on/off in different places

• Disease, behavior, environment

Genome

All DNA present in an individual — varies in size & complexity

Pseudogenes

• Duplication event results in nonfunctional copy available for modification

• ex. variation in olfactory receptor genes

Point mutation/SNP

Single nucleotide change

Insertion

Insert extra nucleotides

Deletion

Remove nucleotide(s)

Frame-shift

Shift reading of codons (if <3)

Gene duplication

Duplicates gene or genome level (ex. chromosome to diploid, triploid, etc.)

Inversion

Inverted order of sequence

Chromosome fusion

Chromosomes fuse together or nondisjunction → aneuploidy (n+1 or n-1)

Germline mutations

Heritable

Somatic mutations

Non heritable

Heredity

Offspring resemble parents more than other individuals

Variation

Differences between individuals through genetics & environment

Asexual reproduction

Identical copy produced through mitosis

Sexual reproduction

Gametes produced through meiosis

Somatic cells

Diploid body cells

Homologous pair

23 sets of haploids

Sister chromatid

Two molecules of identical DNA

Sex chromosomes

Non homologous chromosomes

Meiosis

Reduces number of chromosomes from diploid to haploid

Independent assortment

Two equally probably arrangements of chromosomes — 2ⁿ

Crossing over

Homologs share pieces of DNA → recombinants

Random fertilization

Random egg & sperm; 1/8M

Alleles

Versions of genes made up of nucleotides

Locus

Determines the trait

Dominant

Determines the phenotype of a heterozygote

Recessive

No noticeable effect in a heterozygote

Law of Segregation

Homologs pair and separate during gamete formation

Quantitative traits

Continuous variation of phenotypes influenced by many genes and environmental variation

Phenotypic plasticity

Changing phenotypes in response to the environment — produced by a single genotype

Polyphonic trait

Exhibits reproducible bifurcations in multiple distinct outcomes