DNA, Genes, and cell divisionWeek 4(Ch 3)

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DNA StructureStructureDNA is made of complementary chains of stacked nucleotides

Nucleotides structure: composed of a sugar plusa phosphate (sides), and a nitrogenous base (rungs)

Bases: form complementary bonds

Adenine bonds with Thymine

Guanine bonds with Cytosine

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DNA Replication

Process of DNA replication1. Enzymes 'unzip' bases2. Exposed bases attract complementary free-floating nucleotides3. Two parental nucleotide chains are models for growing replicated strands

-the new DNA molecules consist of an original and new strand3

Chapter 3: Biological basis of lifeProteins: perform functions like binding with other molecules

Structural proteins: e.g., collagen

Functional proteins: e.g., hormones, enzymes

Protein composition: amino acid chains

Amino acids: building blocks of proteins-protein function is determined by order and number of amino acids

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Protein synthesis

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Step 1: Transcription (in nucleus)-complementary messenger RNA (mRNA) is produced from DNA strands

mRNA: single-stranded and has Uracil base instead of thymine

Step 2: Translation (at ribosomes)-ribosomes reads mRNA 3-bases at a time (triplets = codons)

Transfer RNA (tRNA) binds codons with one amino acid

GenesGenes: segments of DNA bases coding for specific traits

Human Genome-25,000 genes-90,000 proteins

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Cell divisionChromosomes DNA condenses into sausage-shaped packages visible during cell division

Full complement of genetic material for humans = 46 chromosomes (varies from species to species)

Two types of chromosomesAutosomes: carry genetic information that governs all physical characteristics

Sex chromosomes: governs primary sexX chromosome = femaleY chromosome = male

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Cell division: mitosisMitosis: cell division in somatic cellsOne division:-46 double-stranded chromosomes align at the cell's center -pulled apart at the centromere

Result -two genetically identical daughter cells -46 single-stranded chromosomes

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Cell division: meiosisMeiosis: gamete division

1st division: -46 reduced to 23 double-stranded chromosomes

Recombination: parent genetic material is exchanged

2nd division: -similar to mitosis (pairs are separated)

Result-23 single-stranded chromosomes in each genetically distinct daughter cell

Cell division and evolutionEvolutionary significance of meiosis

Recombination: shuffling of maternal/paternal chromosomes during meiosis

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Cell division and evolutionMutations: change in DNA that creates new genetic material

-necessary fuel for evolutionary change

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Ch 4: Mendel and Modern evolutionary theory

Week 4(Ch 3/4)

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Mendelian principles of inheritanceMendel's principles explains transmission of traits generation to generation

Background: decades of experiments with pea plant hybrids.

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Mendelian principles of inheritance

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Experiments: crossbred pure-bred pea plants

Parent generation:-tall pea plants x short pea plants

F1 generation:

F2 generation:

Mendel's first principle of inheritancePrinciple of segregation: traits are controlled by discrete units which come in pairs and separate into sex cells.

Alleles: variations of a gene at a locus, i.e., allele pairs control trait expression

E.g., pea plant height is controlled by two alleles at one locus

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Mendel's first principle of inheritanceRecessive alleles are masked by the expression of dominant alleles

Homozygous: two copies of an allele

Heterozygous: two different alleles

Genotype: organism's entire genetic makeup

Phenotype: observed physical expression of genotype/genes

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Mendel's second principle of inheritancePrinciple of independent assortment: traits are inherited separately

E.g., pea plant height and seed color are not inherited together

-genes that code for different traits sort out individually during gamete formation

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Punnett square problems1. Identify the different phenotypic and genotypic ratios in F2 generations for a cross of two heterozygous tall plants (tall = dominant trait).

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Punnett square problems2. Hypothetically, B is the allele that causes brachydactyly. If a man with two normal alleles (bb) has average length fingers/toes has kids with a woman with brachydactyly (Bb).

What proportion of their kids will have average length fingers/toes?

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Mendelian geneticsMendelian traits-discrete traits-one gene determines one trait-rarely influenced by environment

Polygenic traits-continuous-multiple genes determine one trait-relationship between genetics/environment heavily influential

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Mitochondrial DNA briefly...Mitochondrial inheritance: mtDNA is transmitted matrilineally-meiosis (and so recombination) doesn't occur because inherited from one parent-only variations between individuals in mtDNA is due to mutations-studying mutation rates to learn more about ancestry, evolutionary relationship between species, etc.

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Synthetic theory of evolutionSynthetic theory of evolution

-modern synthesis of Darwin's theory and genetics now:

Evolution defined: change in allele frequencies of a population from one generation to the next.

Gene pool: the genetic material (alleles) making up a population of organisms

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Synthetic theory of evolutionTwo-stages of evolution involve variation and natural selection

Stage 1: Factors produce and redistribute variation

Stage 2: Natural selection acts on variation

Microevolution: changes from generation to generation

Macroevolution: speciation, changes over time evident in the fossil record

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Factors producing and redistributing variationMutations: any change in alleles-produces new alleles (only source of new genetic material)-only passed on if occurs in gametes

Recombination: chromosome pairs exchange DNA during meiosis shuffling variation for natural selection to act on

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Factors producing and redistributing variationGenetic drift: changes in allele frequencies due to chance

Founder effect: small subpopulation leaves to find new populationE.g., Amish polydactyly

Bottleneck: population shrinks and recoversE.g., Pingelap islanders today are mostly colorblind

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Factors producing and redistributing variationGene flow: (migration) exchange of genes between populationsE.g., significant gene flow between human populations explains the low occurrence of hominin speciation in the past million years

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Variation and natural selectionNatural selection

-directional change relative to environment

-acts on variation

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Mendel - 1860s Monk experimenting with peasRecall: Cross-breeding - artificial selection, farmers...metaphor for natural selection

Missing in Darwin's theory of NS: a mechanism governing how traits were inherited

Background

-Mendel cross-bred pea plants-Observed the traits individual plants possessed over thousands of generations

Inferred the Principles of Inheritance

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