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FW 104: BIOLOGY BACKGROUND & NATURAL SELECTION (EVOLUTION)
DNA |
The genetic code or Blueprint for life uses 4 "letters" (ATGC) or molecules called bases
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Codon |
A series of 3 base pairs
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Genes |
(a sentence) Use codons that spell out how to construct proteins which produce traits
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Chromosome |
Structure in every cell on which DNA is found
different organisms have distinct number of chromosomal pair
Humans 23
Dogs 78
Goldfish 94
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Locus |
The specific position of the gene sequence on the chromosome
Location on a chromosome where the gene exists
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Diploid |
Pairs of chromosomes
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Alleles |
The different versions of the same genes (two or more alternative forms); code for different versions of the same trait
Heterozygous: different from each parent Rr rR
Homozygous: identical from each parent RR rr
Occupy same locus on a chromosome
Diploid organism- individual inherits one allele from each parent
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How many letters (bases) in the DNA alphabet
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4 Bases (ATGC)
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Alleles refer to DIFFERENT genes on the chromosome
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False; alleles are different versions of the same gene
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Genotype |
An individuals blueprint (genetic makeup)
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Phenotype
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What an individual looks like (characteristics)
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Variation: Can individuals with a different genotype have the same phenotypic trait?
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Yes ; dominant/ recessive traits Rr RR
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Variation: Can individuals with the same genotype have a different phenotype?
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Yes; sometimes genotype + environment = phenotype
(snowshoe hare)
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Genotypic Variation
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Differences in the GENETIC MAKEUP of individuals
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Phenotypic Variation
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Differences in the MORPHOLOGICAL, PHYSIOLOGICAL, OR BEHAVIORAL characteristics
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When you see a person with Brown eyes (dominant trait), do they know the genotype
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No; with a dominant trait the phenotypic expression could be the result of a homozygous allele (BB) or a heterozygous allele (Bb)
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Mutation
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Random changes in the sequence of ATGC or the "blueprint"
original source of genetic variation
Causes: radiation, chemicals, replication errors
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Evolution
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Change in the genetic composition of a population over time ( a change in allele frequency). Can lead to new species if populations are isolated
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Natural Selection
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Environmental factors favor particular inherited traits; process of genetically different individuals with a higher survival potential in a given environment leave more offspring; differential survival and reproduction of organisms based on genetic differences
Critical to understanding and managing populations
Critical to understanding evolutionary change
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Process of Natural Selection
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Genetic Variation
Overproduction of offspring
Struggle for existence
Differential survival and reproduction
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Genetic Variation Summary
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Phenotypic differences among individuals must be the result of genotypic differences
Not all phenotypes blend well with the environment, and thus not all young will survive
Differences in reproductive success or survival are due to genotypic differences between individuals
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Sex |
Shares mutations with offspring and creates new allele combinations
Recombination of chromosomal segments during meiosis into haploid gametes
Then mother/ father chromosomes come together in fertilization
Trillions of possible combinations- chance of having two identical individuals is 1 in trillions unless you have identical twins
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Why Sex?
scientifically speaking........
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Sexual Reproduction randomly creates new genotypes which may be less well adapted.
Sexual Reproduction costly in time and energy
Sexual Reproduction is risky- an adult has to develop from a fertilized egg
Asexual reproduction keeps genotypes intact
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The Red Queen Hypothesis
was named after a character in "Alice and Wonderland"
Is specific to asexual reproduction in fish
states that in order to keep up as a species, the species must continue to evolve
all of the above
A & C
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A & C; The Red Queen Hypothesis was named after a character in Alice & states that in order to keep up as a species, the species must continue to evolve
The Red Queen Hypothesis states that organisms must evolve to maintain their place or become outcompeted, easy prey, etc.
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Genotypes in a Human
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23 pairs of chromosomes so 2^23 combinations = 8,388,608 possible combinations for each egg and sperm before crossing over during recombination
Crossing over rearranges genes increasing variability exponentially (average in humans is 2 crossovers/chromosomes)
Random combinations of egg and sperm during fertilization
In humans we are talking trillions of possible combinations for each new baby!!!!
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Is sexual selection a form of natural selection ?
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YES; sexual selection is a form or subset of natural selection
In peacock example the female choice/mate selections is a selective pressure in the male's environment
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However, all genotypes in existence are not the result of natural selection
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Mutations
Artificial Selection
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Genetic Drift
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Random change in allele frequency in small/ reduced populations
loss of genetic variation
small populations/ endangered species - greater risk!
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mInbreeding
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mating between relatives increases the frequency of homozygous individuals
loss of genetic variation
small populations/ endangered species- greater risk !
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Speciation
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New species are often produced when environments change significantly
Humans and pre-human species originated and diversified during a period of considerable environmental change in tropical Africa.
Similar pressures affected our nearest living relatives (Chimps and Bonobos)
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Evolution occurs at the level of the .......
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POPULATION; New species can form due to isolation of populations. Later, when populations reunite, evolved reproductive barriers prevent viable offspring from developing
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Did natural selection result in the evolution of Bonobos or was it something else?
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YES; changes in the environment resulted in selection pressure for certain traits
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Evolution occurs..
at the individual level
at the population level
at the community level
at the ecosystem level
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at the population level
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Why is the ability to evolve so important?
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Adapt to changing environments
We must maintain variation in natural populations so populations can evolve via natural selection
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Speciation Factors
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long linear change due to environmental changes
splitting into 2 populations through distribution in different areas (geographic isolation)
Reproductive isolation- if geographic isolation is long enough then 2 groups may no longer interbreed and begin to diverge because of different selective pressures until they can't interbreed and produce fertile offspring
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