biologie tw4 notities

mendel’s laws

  • character: heritable feature that varies among idv. (eg. flower colour)

    • trait: each variant for character (eg: purple, white)

  • self-fertilization: pollen grains from stamen (sperm)→carpel (egg)

  • cross-fertilization: one plant by pollen to a diff. plant

  • true-breeding: self-fertization→offspring identical to parent

  • hybrid: offspring of 2 diff. var., cross fert.→cross

    • P gen. →F1 gen.→F2 gen.

    • monohybrid cross: parent plants diff. one char. (PP, pp)

      • F2 gen. (F1 x F1)→, ¼ PP, ½ Pp, ¼ pp

      • Phenotypic ratio: 3 purple : 1 white

      • Genotypic ratio: 1 PP: 2 Pp : 1 pp

  • allele: alt. vers. of genes, account for var. in inhr. char. (eg: gene for flower color has two ver.)

    • homozygous: organism has two identical alleles for a gene→homozygote

    • heterozegous: ‘‘ different alleles for that gene→heterozygote

    • dominant allele: allele that determines appearance

    • recessive allele: no noticeable effect on the apperance

    • law of segregation: sperm/egg carries one allele for each inherited char. bc allele pairs segregate during production of gametes

      • P plants gametes: All P & all p; F1 gametes: ½ P & ½ p, F2 gametes: punnett square

  • loci: specific locations of genes

  • dominant phen.→homozyg. genot.(AA)/heterozyg. genot. (Aa)

  • rec. phen.→homozyg. genot. (aa)

    • pedigree = family tree

  • testcross: dom. phen. (RR/Rr) × rec. phen rr:

    • if egg RR: all offspring Rr

    • if egg Rr, F1 ½ rr

  • dihybrid cross: 2 genes

    • homologous chromosones: each gene 2 diff alleles (pprr, ppRr…)

      • homozygous:

        • pprr: 2 rec.

        • PPRR: 2 dom.

      • heterozygous:

        • PrRr

    • dependent assortment: if genes of two characters inherited tgt

      • P (RRYY, rryy) gametes: RY × ry

      • F1 gen.: RrYy gametes: ½ RY ½ ry

      • F2 gen.: phen. ratio 3 : 1

      ½ RY

      ½ ry

      ½ RY

      RRYY

      RrYy

      ½ ry

      RrYy

      rryy

    • law of independent assortment:

      • P gen. (RRYY × rryy) gametes: RY × ry

      • F1 gen. (RrYy) gametes: ¼ RY, ¼ rY, ¼ Ry, ¼ ry

        • 2 char. segregate independently→4 gamete genot.

      • F2 gen. phen. ratio 9 : 3 : 3: 1

      • each pair of alleles segregates independently of other pairs of alleles during gamete formation

  • rule of multiplication:

    • product of probabilities of each independent event

      • F1 (Bb genot.)→egg/sperm: ½ B allele, ½ b allele

      • prob. F2 bb genot.: ½ (b egg) × ½ (b sperm) = ¼

  • rule of addition:

    • prob. of event that can occur in >1 ways→sum of seperate prob.

      • prob. F2 heterozygous: 2 ways that F1 gametes produce Bb

        • B from egg + b from sperm or vice versa (¼ prob. each)

        • thus: ¼ × ¼ = ½

  • 3 diff genes (PYR) on diff. chromosones (indep. assort.), 2 heterozyg. crossed (PpYyRr)

    • prob. offs. rec. monozyg. all genes:

      • pp, yy, rr: ¼ each→(¼)³ = 1/64

  • reccesive disorders:

    • born to heterozygous carrier parents, phen. normal

      • inbreeding: more likely offs. homozygous for rec. traits

  • dominant disorders:

    • lethal dom. disorders < lethal rec. disorders

variations on Mendel’s laws

  • complete dominance: dom. allele same phen. effect→offs. looks like one of the two parental varieties

    • heterozygote same phen. as hetero dom. individuals

  • incomplete dominance: phen. of F1 hybrid is in between 2 parental varities

    • F1 (Rr) phen. of P (RR × rr) (R = red, r = white) is pink

  • pleiotropy: single gene affects many phen. traits, many genes→single character

  • epistasis: expression of 1 gene modigied by the expression of ≥1 genes

    • cc genot.→white rats, brown + black phen. only when C

  • genes ≥ 2 alleles:

    • ABO→3 alleles of single gene

    • various combinations of IA, IB, and i→4 blood groups

      • 6 possible genot., IA + IB dominant to i allele

      • IA + IB are codominant: both alleles are expressed in heterozyg. (AB blood)

        • codominance ≠ incomplete dominance

chromosonal basis of inheritance

  • chromosome theory of inheritance: genes occupy specific loci on chromosones→chromosones undergo segregation and indep. assort. during meiosis→behaviour of chromosomes during meiosis + fertilization that accounts for inheritance patterns

  • linked genes: do not follow law of indep. assort.

    • genes for the two characteristics are on the same chromosone

    • meiosis in the heterozyg. (PpLl)→mostly 2 genot. of gametes (PL + pl)

  • DNA crossover→more genetic variation

  • Recombination frequency:

    • GgLl × ggll

    • further genes→↑ chance of combine→ ↑ recom. freq.

    • Recom. freq. formula: rf = no. of recombinants / total no. of offsp.

sex chromosomes and sex-linked genes

  • male karyotype (46, XY), female karyotype (46, XX)

  • gamete: 1 sex chromosome (X or Y)

    • egg: X, sperm: X or Y

  • on sex chromosomes, the rec. genes goes on the X chromosone are X-chromo

darwin’s theory of evolution

  • artificial selection: modifying species by selecting and breeding idv that have desired traits

  • natural selection:

    • members of pop. vary in traits, most traits inherited from parent to offspring + all species are capable of producing more offs. than envir. can support

    • leads to: idv whose inherited traits give them ↑ probability surviving and reproducing leave tend to leave more offs. than other idv + unequal production of offs. will cause favourable traits to accumulate in pop. over generations

    • occurs through interactions between idv organisms and envir., idv do not evolve

    • can amplify/diminish only heritable traits (acquired traits cannot be passed onto offs.)

    • does not lead to perfectly adapted organisms

  • fossil record: sequence in which fossils appear within layers of sedimentary rocks

    • strata: layers of rock, younger on top of older

    • oldest: prokaryotes

      • fish → amphibians →

  • biogeography: geographic distribution of species

  • comparative anatomy: anatomical similarities between many species → common descent

    • homology: similarity in characteristics that result from common ancestry (divergent evolution)

      • anatomical homology

      • embryological e__?

      • vestigial organs: structures that have little importance, but are remnants of structures that served functions in ancestors (eg appendix)

molecular biology: > sequence diff. between species, > distant last common ancestor; homologies help identify common ancestry

the evolution of populations (13.7-13.10)

  • pop.: group of idv of same species living same place at same time

  • gene pool: total collection of genes in a pop. over time, 2-3 alleles per gene in gene pool usually

    • microevolution: when relative freq. of alleles in pop. change over generations

  • genetic variation: genetic component of variation is relevant to natural selection,

  • Hardy-Weinberg equilibrium:

    • describes gene pool of non-evolving pop.

    • freq. of alleles and genot. constant unless acted upon by agents other than mendelian segregation

    • genot. freq.: p² + 2pq + q²

      • p²: frac. homozyg. dom. idv (RR)

      • 2pq: frac. heterozyg. idv (Rr)

      • q²: frac. homozyg. rec. idv (rr)

    • allele freq: p + q = 1

      • p: # dom allele (R)

      • q: # rec allele (r)

    • assumption: sexual reproduction does not lead to evolution, no. of allele and genot. doesn’t change

    • conditions: very large pop, no gene flow between diff. pop., no mutations, only random mating (no sexual selection of certain characteristics), no natural selection → no pop. irl

  • Natural selection

    • selection for genetic traits that result in survival of a species and ↑ reproduction

    • envir. determines which characteristics are advantageous, so over time pop. adapt to a changing env.

  • Anthropocene

early earth and the origin of life

  • conditions on early Earth:

    • impact of meterorites + compaction by gravity→immense heat

    • molten mass→layers of diff. densities→least dense on surface

    • atmopshere: thick with water vapour

  • stromatolites: layered rocks built up by ancient photosynthetic prokaryotes

  • prokaryortes: 3.5 bil years ago, simpler life form 3.9 bil years ago

  • how simple cells on early earth came to be:

    • 1. the abiotic synthesis of small organic molecules such as amino acids, nucleotides, nitrogenous bases

    • 2. the joining of these small molecules (monomers) into polymers, includ. proteins and nucleic acids

    • 3. the origin of self-replicating molecules that eventually made inheritance possible

    • 4. the packaging of these molecules into “protocells”, droplets with membranes maintained in internal chemistry

  • abiotic synthesis of polymers: by dropping dilute solutions of amino acids or RNA (ribonucleic acid) monomers onto hot sand, clay, rock

    • heat vaporizes the water and concentrates monomers→some may spontaneously bond together in chains

    • waves might have splashed organic monomers onto lava/hot rocks then rinsed polymers back onto sea

  • formation of protocells:

    • vesicles (small membrane-enclosed sacs) form when lipids are mzied with water

    • when EE clay is added, such vesicles form at a faster rate

    • organic molecules become concentrated on the surface of this clay→interact more easily

    • these abiotically created vesicles absorb clay particles to which RNA and other molec. are attached→they can grow and divide

  • self-replicating RNA:

    • short RNA molecules can assemble spontaeneously from nucelotide mononers

    • when RNA is added to an RNA monomer solution→new RNA molec. complementary to parts of starting RNA sometimes assemble

    • 1. RNA monomers adhere to clay particles and become concentrated

    • 2. some monomers spontaeneously join→first small “genes”

    • 3. an RNA chain complementary to one of these genes assembles

    • on EE, some protocells contained self-replicating RNA molecules→natural selection

    • mutations, errors in copying RNA “genes”