Ch7 Part 1 Flashcards
Thomas Hunt
Associated a specific gene with eye colour in flies; however, DNA has proteins and DNA so could not say for certain which carried the hereditary detail.
Frederick Griffith
Used two strains of Streptococcus pneumoniae.
One strain killed mice (S), one did not (R). Heat killed (S) and R, if incubated together would result in the death of mice. Additionally, could extract living S strain from dead mouse.
Still unclear how virulence was being transferred.
Oswald Avery, Colin MacLeod, Maclyn McCarty
systematically destroyed macromolecules in strains of dead (S) strain.
When DNase was added to S strain extracts, virulence could not be transferred.
Although many scientist remained skeptical.
Alfred Hershey and Martha Chase
Model phage T2.
Radiolabeled phosphorous (which is in DNA) and Sulphur (which is in proteins). In separate cultures.
Progeny phases become labeled. Allowed to infect a bacteria.
Cultures (bacteria and phages) were centrifuged. Supernatant contained growth media and phage ghosts (empty capsids). Bacteria cells form at bottom.
Radiation was only seen in the pellet at the bottom of the test tube in the radiolabeled phosphorus.
Other evidence that DNA transfers info
DNA total amount is constant across cells and species. (Erwin Chargaff)
DNA replication is semiconservative, DNA is copied during every cell cycle. (Stahl and Meselson)
In quiescent cells macromolecules like proteins are recylced. DNA remains constant
Mutagens cause mutations in DNA
Human Chromosomes
24 different chromosomes.
22 are autosomes
2 are sex chromosomes
Non-dentical copies of a chromosome are referred to as homologous.
Classical Dominance
Only homozygotes for the recessive gene express the recessive trait.
Meiosis
Cell division that reduces the dumber of copies of genes from 2 to 1.
In males. Spermatogonia undergo meiosis.
In females. oogonia.
Main difference between Mitosis and Meiosis
Two rounds of cell division in meiosis: Meiosis I and Meiosis II
Stages of Meiosis
S - phase before produces 4 copies of the genome.
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase I
Chromosomes condense, nuclear envelope breaks down.
Chromosomes pair with eachother during prophase I in SYNAPSIS - a very specific pairing. In this state chromosomes are called BIVALENT or Tetrad. Allows for crossing over or recombination between homologous chromosomes, not sister chromatids!!
Prophase is the longest stage of meiosis and can take days.
synaptonemal complex (SC)
Mediates the process of synapsis. Forms during prophase.
Functions like a zipper.
SYCP2 and SYCP3 form initial complex between homologous chromatin to be paired. These complexes then connect via SYCP1 with additional proteins.
SC formation and recombination are interdependent.
Metaphase I
Metaphase plate occurs; however, main difference is that in meiosis tetrads line up at center, not sister chromatids.
Anaphase I
Homologous chromosomes separate, but sister chromatids stay together.
Telophase I
Divides into two cells.
Cells are considered haploid at this stage!
Meiosis II
No additional replication of DNA between Telophase I and Meiosis II.
All proceeds the same afterwards, but as haploid cell.
Sister chromatids however, are not identical as a result of recombination.
Non-disjunction
When sister chromatids fail to seperate properly during Meiosis II
Can result in a gamete with either two copies or 0 copies of a given chromosome. Once it bonds with a normal gamete can result in trisomy or monosomy.
Trisomy of Chromosome #21 results in Down Syndrome.
Law of segregation
Two alleles of an individual are separated and passed on to the next generation, singly.
ie. only one allele goes into the gamete
Law of independent assortment
Alleles of one gene will separate into gamete independently of alleles of another gene.
Not true for LINKAGE.
Testcross
When the genotype of an unknown species is crossed with a pure line to determine characteristics.
Progeny are referred to as F1 generation.
Incomplete dominance
phenotype of a heterozygote is blended.
Three phenotypes are possible in this situation if two heterozygotes are cross-bred.
Codominance
Two alleles are both expressed, but are not blended.
Bood type, ie. antigen expression
Note there is another antigen used to determine blood type: Rh (rhesus) factor. Which has a classic dominant pattern.
Pleiotropism
Expression of a gene alters many different, seemingly unrelated phenotypic aspects.
Polygenism
Complex traits influenced by many different genes.
Ex. Height
Penetrance
Likelihood that a specific genotype will provide a specific phenotype.
Penetrance depends on the allele. Can be altered by age, modifiers, environment etc.
Epistasis
Expression of one allele of a gene is dependent upon another gene.
Ex. Can’t have curly hair if you are bald.
Recessive Lethal Alleles
Can be lethal when present in homozygous form.
Can be studied by maintaining a ‘stock’ of heterozygotes in diploid organisms.
Haploids are more difficult to study and require an allele that is inducible.
Recessive X-chromosome genes in Males?
Always expressed.
Linkage
Failure to exhibit independent assortment.
Punnett squares look different for genes on the same allele.
REcombination is the exception to linkage.
Recombination Frequency
proportional to distance between genes on the same chromosome.
RF = #recombinants/#offspring
Autosomal Dominant
Single copy of allele required for expression
Autosomal Recessive
Two copies required for expression
Mitochondrial traits
Haploid genome passed along only by mother.
Kids will have it if mother does. Father will not pass on mitochondrial affects.
Example of hemizigosity - where a diploid organism only has one gene copy (occurs for X or Y genes as well)
Note genes encoded by mitochondria indicated by mt (ex. mt-Ap6)
Sex-linked traits
Odd patterns of inheritance. Father can only pass y-linked traits to sons.
X-linked traits are observed more frequently. Can be recessive or dominant. Note, males always expressive recessive x-linked traits.
ex. hemophilia or red/green colour blindness (X-chromosome recessive)
X-linked dominant traits are harder to spot as Females will express with one or two copies and males will always express. But these traits do not tend to affect men more than women.
Population Genetics
inheritance of traits in population over time.
Note: Population refers to members of a species that mate and reproduce with each other.
Hardy-Weinberg Law
Frequencies of alleles in the gene pool or a population will not change over time.
Assumes:
No mutation
No migration
No natural selection
Random mating
Population is large enough to prevent random drift
Hadry-Weinberg Math
P + Q = 1
Where p is frequency of dominant allele and q is frequency of recessive allele.
P^2 + 2pq + q^2 = 1
predicting proportion of genotypes in a population.
If allele frequencies don’t change over time and genotype frequencies can be calculated from allele frequencies… what happens to phenotype frequencies over time?
Constant. After the first generation that is.
ie. at Hardy-Weinberg Equilibrium
Fitness
How successful an organism is at passing on its alleles to future generations.
Sources of genetic variation in a population
new alleles and a new combination of existing alleles.
Modes of Natural Selection
Directional Selection
Divergent Selection
Stabilizing Selection
Stabilizing Selection
Artificial Selection - human interference
Sexual Selection - sex displays that create non-random selection
Kin Selection - individuals will sacrifice for kin as share alleles
Species
Capable of reproducing together and producing sexually viable children. Morphology is used for asexual species.
Members of a population, can and do reproduce together.
Reproductive Isolation
Keeps existing species separate.
- Prezygotic - prevent formation of a hybrid.
ex. environment, temporal, behavioural, mechanical, gametic
- Postzygotic - prevent survival, development, and reproduction of hybrid individuals.
e. Hybrid inviability (die usually in embryonic stage); hybrid sterility; hybrid breakdown
Cladogenesis
Branching of species. ie. all new species come from old species.
Ex. Allopatric isolation (geographic);
Ex. Sympatric isolation - a species gives rise to another species in the same geographical area by divergent selection
Anagenesis
One species simply becomes another (does not branch).
Homologous Structures
Structures shared by species as a result of a common ancestor.
Analogous Structures
Structures that serve the same purpose but do not arise from a common ancestor.
Convergent Evolution
When two species come to have many analogous structures.
Opposite - divergent selection
Parallel Evolution
Two species go through similar evolutionary processes.
8 principal taxonomic categories
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Dumb King Phil Came Over For Great Sex
Taxonomy General Categories
Pg. 267 Summary table!
Superior
Indicates toward head
or
Cephalad
Inferior
Means toward feet
or caudad
Early earth atmosphere
A reducing environment.
Abiotic Synthesis
Metallic ion mediated spontaneous polymerization of amino acids, carbohydrates, lipids, and ribonucleotides.
Polypeptides made via abiotic synthesis = protenoids.
Microspheres
Droplets formed in water by protenoids.
Liposomes
Lipids in solution surround protenoids.
Coacervate
A complex particle including polypeptides, nucleic acids, and polysaacharides formed during early life development.
Protobionts
Umbrella term for Microspheres; Liposomes; Coacervate
Protobionts Function
Can in a sense replicate (ie. split when too big); can catalyze reactions; have dividing membrane.
Lacked however, form of heredity
