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GENETICS
• heredity; concerned with how traits are
transmitted from generation to generation.
• analyzing evolutionary processes
• identifying and mapping genes
• analyzing molecular features of genes and
regulation of gene expression.
Heredity
All humans are united by a common set of
traits, or observable characteristics
Characteristics define species
All of these characteristics are inherited
Variation exists
Affects of the environment on characteristics
Milestones in Genetics
• Gregor Mendel analyzed quantitatively the
results of crossing pea plants.
• 1972, Paul Berg constructed first
recombinant DNA in vitro.
• 1973, Boyer and Cohen’s cloning of first
recombinant DNA molecule.
• 1986, Polymerase Chain Reaction (PCR) to
amplify specific gene squences.
Genetics – divided into four branches
• 1) Transmission genetics
– Transmission of genes from generation to generation
• 2) Molecular genetics
– Structure and function of genes at the molecular
level
• 3) Population genetics
– Distribution and behavior of genes within and
between populations
• 4) Quantitative genetics
– Heredity of traits in groups of organisms associated
with multiple traits
Transmission Genetics Basics
• Mendel’s pea experiments (e.g., white &
purple flowers)
• Two copies of each gene, one from each
parent
• Homozygous: same allele; heterozygous:
different alleles
• Dominant, recessive, incompletely
dominant
Phenotype & Genotype
• Phenotype = appearance of an organism (the
expressed characteristics)
• Genotype = genes that influence the
expression of that characteristic (underlying
the phenotype) The specific alleles that the
organism carries for the gene (or genes) that
influence the phenotype in question…
Fig. 10.4 Seven character pairs in the garden pea that Mendel studied
in his breeding
experiments
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
polymorphism
• The existence of naturally occuring
variations in a population of organisms
• The forms can be called “morphs”
DNA, GENES,
CHROMOSOMES
• DNA
(deoxyribonucleic
acid) is the genetic
material for both
prokaryotes and
eukaryotes; viruses
may have RNA
genomes
• DNA has two chains,
each made of
nucleotides composed
of deoxyribose sugar,
a phosphate group,
and a base forming a
double helix (FIG.
1.1)
Fig. 1.1 DNA
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
DNA STRUCTURE
• Four bases of DNA: A (adenine), G (guanine), C
(cytosine) and T (thymine); in RNA U (uracil)
replaces T.
• GENES: specific sequences of nucleotides that
pass traits from parents to offspring.
• CHROMOSOME: is where the genetic material is
organized structurally.
• GENOME: total amount of genetic material in
nuclear chromosomes.
Fig. 1.3 Transcription
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
Population Genetics
• What is the observed level of genetic
variation in populations?
• How allele frequencies change over time?
• What models can explain the change in
allele frequencies?
FORCES OF EVOLUTION
• Mutation: heritable changes in the genetic
material
• Recombination: exchange of genetic
material
• Selection: favoring particular combinations
of genes in a given environment
Quantitative Genetics
• Continuous traits display a range of
phenotypes?
• Is the trait polygenic?
• How much environmental factors influence
the range of trait characters?
• What is the heritability of the trait?
Fig. 1.6 Example of a genetic map, here some of the genes on
chromosome 2 of the fruit fly, Drosophila melanogaster
GENETIC MAP: show
arrangement of genes;
distances between
genes.
LOCUS indicates the
position of the gene on
the map, as well as the
chromosome in which it
is located.
DISTANCE between
genes can be calculated
from the results of the
genetic crosses by
counting the frequency
of recombination.
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
USES OF GENETIC MAPS
-whether genes with related
functions or with similar
expression profiles located in
proximity to each other
-helps in cloning and sequencing
genes of interest or in genome
projects (e.g., Drosophila,
human).