Topic 10

• Prophase I


  -chromosomes condense-nuclear envelope breaks down-homologous chromosomes form a bivalent-crossing-over occurs
• Metaphase I


  -spindle fibers from opposing centrosomes connect to bivalents a centromeres and align the bivalents along the cell equator
• Anaphase I


  -spindle fibers contract and split the bivalent-homologous chromosomes move to opposite poles of the cell
• Telophase I


  -chromosomes decondense-nuclear membrane may reform-cell divides (cytokinesis) to form two haploid daughter cells
• Prophase II


  -chromosomes condense-nuclear membrane dissolves-centrosomes move to opposite poles (perpendicular from before)
• Metaphase II


  -spindle fibers from opposing centromeres attach to chromosomes at centromere and align the chromosomes along the cell equator
• Anaphase II


  -spindle fibers contract, separating sister chromatids-chromatids (now called chromosomes) move to opposite poles
• Telophase II


  -chromosomes decondense-nuclear membrane reforms-cells divide (cytokinesis) to form four haploid daughter cells
• Describe the process of crossing over


  -begins with synapsis-DNA molecule of one of the chromatids is cut and a second cut is made at the same point in the DNA of a non-sister chromosome -the DNA of each chromatid is joined up to the DNA of the non-sister chromosome, swapping sections of DNA between chromatids-later in prophase I, the tight pairing of the homologous chromosomes ends, but sister chromatids remain tightly connected→chiasma-results in recombination
• synapsis


  -stage in prophase I-all chromatids of homologous chromosomes become tightly paired up together to form a bivalent
• chiasma


  X-shaped structure formed when each cross-over has occurred
• recombination


  -result of crossing over during prophase I-alleles swapped between two non-sister chromatids
• Mendel's Law of Independent Assortment


  - Inheritance of one trait is independent of any other, as long as the genes are on separate chromosomes-only true for unlinked genes
• genotype


  The alleles that you carry for a gene, e.g. BB, Bb or bb
• Phenotype


  a physical trait of an organism that results from its genetic makeup
• discrete variation


  -grouped into categories with few in-betweens-Ex.) blood groups
• continuous variation


  -variation shows a complete range from one extreme to another-Ex.) height, weight, skin color
• Factors that can influence phenotype


  -environment (ex. sun exposure, burns, scars)-dietary factors (protein content)-diseases
• Common mutations in fruit flies


  -leg length (dominant=long, mutation=short)-wing placement (dominant=normal, mutation=vestigial)-antennae (normal, feathered)
• Differences between male and female fruit flies


  -Male: smaller, rounded/dark back, thick stripe-Female: longer/pointed back, more stripes
• What is the difference between the two types of linkage?

  -Autosomal Gene Linkage: when the genes are on the same autosome-Sex Linkage: genes for trait located on the X chromosome
• Describe how skin color in humans is inherited


  -polygenic inheritance-skin color determined by the amount of melanin that it contains-at least four genes are involved in melanin production-for each gene, one allele codes for melanin production while the other does not-combination of melanin-producing alleles determines the degree of pigmentation, leading to continuous variation
• polygenic inheritance


  -a single characteristic controlled by many genes-alleles can be contributing (add to phenotype) or non-contributing (do not add to phenotype)
• chi square formula


  (O-E)²/E
• Degrees of Freedom


  (# of phenotypes in cross)-1
• fitness


  the likelihood that a genotype/phenotype will be found in the next generation
• speciation


  evolutionary process resulting in the formation of a new species from pre-existing species
• evolution


  the cumulative change in the heritable characteristics of a population over time
• gradualism


  the idea that evolution occurs at a constant pace over time
• genetic equilibrium


  when all members of a population have na equal chance of contributing to the gene pool
• stabilizing selection


  selection pressures act to remove extreme varieties, favoring the intermediate varieties
• example of stabilizing selection


  Human birth weight-babies of low weight lose heat easily and are more susceptible to illnesses-babies of high birth weight are more difficult to be delivered through the pelvis-medium weight babies have lower mortality rates, causing the frequency of medium weight babies to increase
• disruptive selection


  selection pressures act to remove intermediate varieties, favoring extremes
• example of disruptive selection


  Grass-soil close to mine is contaminated with metals-results in two distinct grass populations: slower-growing metal tolerant and faster-growing non-tolerant
• directional selection


  populations changes as one extreme range of variation is better adapted
• example of directional selection


  Beak shape/size in ground finch-during dry years, small seeds are not abundant, so birds with larger beaks are more frequent
• temporal isolation


  two populations differ in their periods of activity or reproductive cycles
• example of temporal isolation


  Leopard frogs and woods frogs mate at different times
• behavioral isolation


  differences in mating/courtship rituals even though the organisms are physically able to interbreed
• example of behavioral isolation


  Satin vs MacGregor's Male Bowerbird decorate their bowers in different colors in order to attract females