Genetics & Evolution Flashcards
genetics
study of how traits are inherited from one generation to the next
genes
composed of DNA and are located on chromosomes
Mendel’s First Law (law of segregation)
- genes exist in alternative forms, a gene controls a specific trait
- organism has 2 alleles for each trait
- the 2 alleles segregate during meiosis, resulting in gametes that carry 1 allele
- if 2 alleles are different, 1 will be dominant, and the other will be recessive
Mendel’s Law of Dominance
dominant allele is expressed in the phenotype
Mendel’s Second Law (law of independent assortment)
- inheritance of one trait is completely independent of any other
- modern genetics: genes on the same chromosome will not follow this rule and will stay together unless crossing over occurs
incomplete dominance
- progeny phenotypes are blends of parental phenotypes
- heterozygote is an intermediate of the phenotypes of the homozygotes
codominance
- multiple alleles exist for a given gene and more than one of them is dominant
- ex: ABO blood groups, Ia and Ib are codominant and produce IaIb blood type
sex determination
- women have XX, men have XY
- gender of a zygote is determined by the contribution of the male gamete (if sperm carries and X or a Y)
- sex-linked: genes located on the X or Y chromosomes
sex linkage
- recessive genes carried on the X chromosome will produce the recessive phenotypes when they occur in men, ex: hemophilia and color blindness
- sex linked recessives generally affect only men, can be passed from grandfather to grandson via a daughter who is a carrier
nondisjunction
-failure of homologous chromosomes to separate properly during meiosis I or failure of sister chromatids to separate properly during meiosis II
trisomy
3 copies of a chromosome, ex: Down syndrome
monosomy
1 copy of a chromosome
chromosomal breakage
may occur spontaneously or by environmental factors such as mutagenic agents and X-rays
mutagenic agents
- induce mutations
- cosmic rays, X-rays, UV rays, and radioactivity, colchicine, or mustard gas
- sometimes also carcinogenic (cancer-causing)
point mutation
nucleic acid is replaced by another nuclei acid, affects between 1-3 nucleotides
silent mutation
the new codon codes for the same AA and no change is seen
missense mutation
new codon codes for a new AA, may or may not lead to problems in the resulting protein
nonsense mutation
new codon is a stop codon, lethal or severely inhibit the function
frameshift mutation
nucleic acids are deleted or inserted, often lethal bc it throw off entire sequence
examples of genetic disorders
- phenylketonuria (PKU): inability to produce the enzyme for the metabolism of phenylalanine
- sickle cell anemia: RBCs become crescent shaped, substitution of valine for glutamic acid
bacterial genome
- consists of a singular circular chromosome located in the nucleic region of the cell
- also contain smaller rings of DNA called plasmids
episomes
plasmids that are capable of integration into the bacterial genome
replication of bacterial chromosomes
- begins at a unique origin of replication and proceeds in both directions
- DNA is synthesized in the 5’-3’ direction
binary fission
- process by which bacterial cells reproduce
- asexual process
transformation
-a foreign chromosome fragment (plasmid) is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combinations
conjugation
- transfer of genetic material b/w 2 bacteria (that have a sex factor) that are temporarily joined
- genetic material is transferred from the donor male (+) to the recipient female (-)
F factor
- best studied sex factor
- F+ contain this plasmid, F- does not
- F+ replicates its F factor and donates the copy to F-
antibody resistance
genes that code for other characteristics may be found on the plasmids
Hfr cells (high frequency of recombination)
- bacterial chromosome replicates during conjugations and starts to move from donor to recipient
- bridge usually breaks before the entire chromosome is transferred but the bacterial genes that enter the recipient cell can easily recombine with the genes already present
transduction
- bacteriophage infects its host bacterium by injecting its viral DNA into the bacterium
- fragments of bacterial chromosome become packaged into the viral progeny
regulation of transcription
- based on the accessibility of RNA Pol to the genes being transcribed
- directed by an operon, which consists of structural genes, operator region, and a promoter region
operator
sequence of non transcribable DNA that is the repressor binding site
promoter
noncoding sequence of of DNA that serves as the initial binding site for RNA Pol
regulator gene
codes for the synthesis of a repressor molecule that binds to the operator and blocks RNA Pol from transcribing genes
inducible systems
- repressor binds to the operator, forming a barrier that prevents RNA Pol from transcribing structural genes
- for txn to occur, an inducer must bind to the repressor to prevent binding to the operator
repressible systems
- repressor is inactive until it binds with the corepressor
- prevents txn only if a repressor-corepressor complex is formed
constitutive
operons containing mutations that make it incapable of turning off, are always synthesized
Lamarckian evolution
- new organs or changes in existing ones arose because of needs of the organism (disproved theory)
- based on use or disuse
- acquired characteristic, ex: giraffes with long necks bc of excessive use of them
Darwin’s Theory of Natural Selection
- pressures in the environment select for the organism most fit to survive and reproduce
- genes of parents more fit are passed to more offspring and become more prevalent
overpopluation
more offspring produce than can survive
variations
offspring naturally show differences in their characteristics
competition
population must compete for the necessities of life
speciation
- evolution of new species
- genetic variation, changes in environment, migration to new environments, adaptation, natural selection, genetic drift, and isolation lead to speciation
demes
- small, local populations that form within a species
- if deme becomes isolated, speciation may occur
covergent evolution
-when 2 species from different ancestors develop similar traits
parallel evolution
-similar to convergent evolution, but a more recent ancestor can be identified
divergent evolution
-species with shared ancestors develop differing traits die to different environments
adaptive radiation
- emergence of a number of lineages from a single ancestral species
- differences b/w them are those adaptive to a distinct lifestyle or niche
population
all members of a particular species inhabiting a given location
gene pool
sum total of all the alleles for any given trait in the population
gene frequency
decimal fraction representing the presence of an allele for all members of a population that have this particular gene
p
frequency of the dominant allele
q
frequency of the recessive allele
p+q=
1
Hardy-Weinberg principle
ideal conditions: pop is large no mutations mating is random no migration genes are all equally successful at reproducing
p^2+2pq+q^2=1
p^2= dominant homozygous (TT) pq= heterozygote (Tt) q^2= recessive homozygous (tt)
microevolution
- no population stays in the Hardy-Weinberg equilibrium
- agents of microevolutionary change: natural selection, mutation, assortive mating, genetic drift, gene flow
assortive mating
if mates are not randomly chosen but rather selected according to criteria such a phenotype and proximity (sexual selection), the relative genotype ratios will be affected and will depart from the predictions of the Hardy-Weinberg equilibrium
genetic drift
- changes in the composition of the gene pool due to chance
- more profound in small or new populations, founder effect
gene flow
migration of individuals will result in a loss or gain of genes, changing the gene pool
types of fossils
- actual remains: teeth, bones, amber (fossil resin of trees)
- petrification: mineral replace the cells
- imprints: impressions (footprints)
- molds: hollow spaces in rocks
- casts: mineral deposits in mold
homologous structures
same basic anatomical features, similar evolutionary patterns, ex: arms of a human, wings of a bat
analogous structures
similar functions but different evolutionary origins and patterns of development, ex: wings of a fly and wings of a bird
comparative embryology
- stages of development of the embryo resemble the stages of evolutionary history
- earlier the stage at which the development begins to diverge, the more dissimilar the adult organisms will be
comparative biochemistry
-most organisms demonstrate the same basic needs and metabolic processes
-similarity of enzymes involved in these processes mean
all organisms contain some DNA sequences in common
vestigial structures
- have no known function but had some ancestral function
- ex: appendix
geographic barriers
-barriers increase the likelihood of genetic adaptations on either side, each population may evolve specific adaptations for their environment
primordial soup
-theory suggest that life began in a pond or ocean as a result of the combination of chemicals from the atmosphere and some form of energy to make amino acids, the building blocks of proteins, which would then evolve into all the species
coacervate droplets
- cluster of colloidal protein molecules
- small percentage of the droplets with favorable characteristics may have developed into the first primitive cells
development of autotrophs
heterotrophs slowly evolved complex biochemical pathways and anaerobic respiratory processes to convert nutrients into energy
development of aerobic respiration
once molecular oxygen became part of the earths atmosphere, heterotrophs and autotrophs evolved biochemical pathways of aerobic respiration
4 categories of living organisms
- autotrophic anaerobes: chemosynthetic bacteria
- autotrophic aerobes: green plants
- heterotrophic anaerobes : yeasts
- heterotrophic aerobes: humans, earthworms, amoeba
