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Biology-Lecture 2-Modern Evolutionary Theory Sep 18 2008


Course Code
Marcel Danesi

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Modern Evolutionary Theory
y Heredity
y Mendels Experiments
y Gregor Mendel
y Bread several varieties of plea plants and made detailed observations of their offspring
y Ex: (I) tall plants with short plants, (II) yellow with green
y (I) tallness dominated shortness
y (II) green plant disappeared. But then cross seeds from first generation which produced both yellow
and green pea plants in ratio
y The green trait had not been altered or lost; yellow was simply dominant, and green was recessive
y Dominant: the allele of a gene pair that is always phenotypic ally expressed in the heterozygous form
y Recessive: an allele phenotypic ally suppressed in the heterozygous form and expressed only in the
homozygous form
y Genotype: the total complement of inherited traits or genes of an organism
y Phenotype: the observable physical appearance of an organism, which may or may not reflect its
genotype or total genetic constitution
y Genes: The Conveyors of Inherited Traits
y Gene: chemical unit of heredity; occur in pairs for each trait and that offspring inherited one unit from
each parent
y Allele: one member of a pair of genes
y If two genes or alleles for each trait are the same, the organism is homozygous
y Homozygous: possessing two identical genes or alleles in corresponding locations on a pair of
y Heterozygous: possessing different genes or alleles in corresponding locations on a pair on
y Chromosomes: paired rod-shaped structures within a cell nucleus containing the genes that transmit
traits from one generation to the next
y Mitosis: cellular reproduction or growth involving the duplication of chromosome pairs
y Meiosis: the process by which reproductive cells are formed. In this process of division, the number
of chromosomes in the newly formed cells is reduced by half, so that when fertilization occurs the
resulting organism has the normal number of chromosomes appropriate to its species, rather than
double the number
y DNA: carries set of instructions encoded in its chemical structure
y Genome: the complete genetic make-up of an organism
y Messenger RNA (mRNA): a type of ribonucleic acid that is used in the cell to copy the DNA code for
use in protein synthesis
y Ribosome: a structure in the cell used in making proteins
y Sources of Variability
y Genetic Recombination
y Genetic Recombination: a random shuffling of parents genes
y Segregation: the random sorting of chromosomes in meiosis
y Crossing Over: exchange of sections of chromosomes from one another
y Mutation
y A change in the DNA sequence, producing an altered gene
y Result of occasional errors in the chemical bases that make up DNA
y Genetic Drift
y Result of population fission- breaking apart of a previous large pop group into smaller groups
y The various random processes that affect gene frequencies in small relatively isolated populations
y If a particular gene is absent just by chance in the migrant group, the descendents are also likely to lack
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