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Chapter
1. Overview of Genetics
Hippocrates 400 B.C.
(Greek Physician) first put forth an explanation for the idea of
hereditary traits.
Suggested seeds were
produced by different parts of the body and passed on to offspring at
conception.
Further hypothesized that
these seeds caused certain traits of the offspring to resemble their
parents.
Pangenesis was accepted by
some for 2000 years until the 17th century.
Microscopes led to the
visualization of sperm.
Many thought they could see
tiny little people in the sperm termed homunculus (little man).
This homunculus was thought
to be a little person waiting to grow in the mothers womb.
Maternal influences on
traits were thought to occur in the womb. However, the ovists thought the egg was totally responsible and the sperm just signaled growth to begin.
Mendels insight into
inheritance was extremely important.
Darwins understanding of
species and its relationship to its environment was also instrumental in
changing the perception of genetics.
Finally in the 20th
century Mendels work was rediscovered and work was being done into the
molecular basis for genetics. 1903 Sutton and Boveri propose chromosomal theory of inheritance.
Not until 1940 that
scientists showed that the genetic material was deoxyribonucleic acid
(DNA).
1950s Watson and Crick
propose structure for DNA.
1960&70s Recombinant
DNA techniques.
Relationship between Genes
and Traits.
Genetics deals with
heredity and variation.
Genetics to a large extent
is the study of genes.
A gene is described as a
unit of heredity.
Genes can often be
described by how they affect traits, the characteristics of an organism.
In humans we discuss genes
that affect hair and eye color or their involvement in disease.
Ex: Sickle cell anemia,
Amyotrophic lateral sclerosis (ALS) or cancer.
Ongoing theme of this
class will be the relationship between genes and traits. Genes provide a blueprint for growth and development, however we will also examine the effect environment has as well.
Living things are composed
of four macromolecules:
Nucleic acids,
proteins, carbohydrates and lipids.
Metabolism
of small molecules (ex: glucose) can provide the energy and starting
material for macromolecule anabolism. Large cellular structures depend on interaction of these macromolecules which allows for the formation of these complex cells.
Cells contain many
proteins that are involved with cellular structure and function.
Ex: movement, cell shape,
protein sorting and ion
transport.
Of particular importance
are enzymes.
Enzymes accelerate
chemical reactions within the cell.
Some are important in
metabolism. »
Catabolic enzymes are
involved in breaking large molecules down to their constituents and for
energy. »
Anabolic enzymes are involved in the synthesis of macromolecules.
DNA stores the information
for protein synthesis.
What does that statement
mean?
Nucleotides contain a
sugar a phosphate and one nitrogenous base. »
Adenine, guanine, cytosine
or thymine.
DNA sequences store
information.
The meaning of individual
sequences can be different.
ATGCGGGTTACTATGA has a
different meaning than ACTGGGTTCTAGATCC. To understand this information you need the genetic code.
The genetic code is
read in three nucleotide groups called codons which specify amino
acids.
EX: ATG GGC CTT AGC is
methionine, glycine, leucine and serine.
Humans have 46 chromosomes »
Each chromosome is an
extremely long piece of double stranded DNA that has over 100 million
nucleotides. »
The genetic information is
contained in small segments called genes. »
A few thousand genes are found per chromosome.
Gene Expression is the
accessing of genetic information.
Gene expression is the
transcription and translation of a gene into a cellular protein.
Central Dogma?
Transcription is the
process of copying the genes DNA into ribonucleic acid (RNA).
The RNA is matured (mRNA)
and translated, with the help of the genetic code, in the cytoplasm into
proteins. »
tRNA and ribosomes are also necessary.
The relationship between
DNA and Protein sequence is important.
Gene Expression within
cells leads to outwardly visible traits.
A trait is a
characteristic an organism displays.
Often the focus is morphological
traits, those that affect organism appearance.
Ex: Flower color and plant height.
Physiological traits:
Traits that affect the ability of an organism to function.
Ex: Metabolism of Glucose.
Genetic observations and
theories span four levels of biological organization:
Molecular level involves
gene expression. »
Transcription, translation
and their regulation.
Cellular level involves the function of the expressed protein.
Organismal level-
Morphological traits are visualized at the organismal level. »
Where do these traits come
from?
Populational level- The
occurrence of a trait within a species is observed at the population
level. »
Often discovered that the
trait is necessary for survival or reproduction. »
Ex: Sickle cell anemia.
Schematic Representation of
the organizational aspect of genetics: Pigmentation in Butterflies.
Molecular level- The gene
(pigmentation gene) can exist in two forms called alleles. »
The protein products of
these genes are enzymes involved in pigment-synthesis. »
The alleles differ
slightly and result in different structure and function of the enzyme.
Cellular level- At this
level the functional differences result in different amounts of pigment. »
Due to function
How?
Schematic
Representation of the organizational aspect of genetics: Pigmentation in
Butterflies continued.
Organismal level- Amount
of pigment made governs the color of the butterfly. »
More pigment darker
color
less pigment lighter color.
Population level- The
population geneticist wants to know why there are two different colored
butterflies in the same species. »
How could this be explained?
Describes trait differences
within a population.
Ex: hair color, eye color,
flower color.
Common?
In fact genetic variation
can be very striking.
Usually occurs when a
species has a wide range of environments that it inhabits.
Dramatic differences in a
species are called morphs.
Ex: garter snakes.
What is the reason for genetic variation?
Variation can occur because
of:
Gene mutation:
small variations in a gene can produce two or more alleles (prev. fig.). »
Can lead to altered
protein function.
Chromosomal
rearrangements and/or
partial deletions: are missing portions of chromosomes or parts of
chromosomes being attached to other chromosomes. »
Ex: Down Syndrome or
modern wheat.
Chromosomal abnormalities usually detrimental in humans.
Traits are also governed
by the environment.
Diet for plants and animals
Sunlight for plants
Ex: Phenylketonuria
(PKU) people who are homozygous recessive for a gene encoding for a
non-functional phenylalanine hydroxylase enzyme cannot
properly metabolize the amino acid phenylalanine.
Accumulation of
phenylalanine is highly toxic.
Leads to: mental
retardation and underdeveloped teeth.
Treated through diet.
Gregor Mendel described
his laws of inheritance and now we know that genes are are passed
from parent to offspring.
We can predict the outcome
of genetic crosses based on his laws of inheritance.
Explained by the behavior
of chromosomes during cell division.
Most sexually reproducing
species are diploid (2N).
Humans have 23 homologous
pairs or 46 chromosomes.
Each pair has the same
kind of genes.
Ex: PHE hydroxylase on
Chromosome 12.
Except?
Gametes are needed for
sexual reproduction.
Enhances genetic
variation.
Genetic composition of a
species can change over time.
This change over many
generations is biological evolution.
Natural selection
is a way for a species to become better adapted to its environment.
Over time this can have a
dramatic effect on a species.
Fields of Genetics:
People from many
disciplines are interested in genetics: physiology, medicine, ecology,
zoology and microbiology.
Classically three main
areas of study: transmission, molecular and population
genetics.
Transmission genetics-
explores the inheritance patterns of traits as they are passed from
parents to offspring.
Fundamental approach is the
genetic cross. Ch. 2-8
Molecular Genetics-
biochemical understanding of the hereditary material.
Detailed analysis of DNA,
RNA and proteins including structure and function.
Biochemistry, cell biology
and biophysics.
Often in cell lines and
model systems (yeast and Drosophila) Ch. 9-19, 23 and 24.
Population Genetics-
concerns the prevalence of alleles within a population and how genes
change over time.
Interested in genetic
variation in a species and how that relates to the environment. Ch. 25-27
Genetics is an
experimental science.
Each chapter in the book
has an experiment dissected this will help with the material along with
required research articles.
Science
is a social discipline discussion of your ideas is critical to learning
and an important part of this class.
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