Kevin Callahan's Lab Notebook Fall 1997
(c) 1997 Kevin L. Callahan
Lab 1 Notes Fall 1997
Lab 2 Notes Fall 1997
Lab 3 Notes Fall 1997
Lab 4 Notes Fall 1997
Lab 5 Notes Fall 1997
Lab 6 Notes Fall 1997
Lab 7 Notes Fall 1997
Lab 8 Notes Fall 1997
Lab 9 Notes Fall 1997
Lab 10 Notes Fall 1997
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Anth. 1101 Human Origins
Lab 3: Genetics and Inheritance
Tips on learning this material
Feel free to ask questions at any time -including during the lecture or lab.
You will be learning definitions and concepts that are interrelated.
If you don’t understand a concept, they all appear in your textbook and the
handouts
The lab will clarify many of these ideas.
The more you hear and work with these terms the clearer they become.
Don’t be overwhelmed!
If you have had genetics before this will seem basic. If you haven’t had any
genetics before it may seem overwhelming to you at first.
Topics
I will (deliberately) repeat many definitions and concepts in the three
contexts of:
Mendel’s genetics,
Watson and Crick’s Molecular genetics, and
Population genetics
Estimates of Important Events in the Evolution of Life
The Big Bang ~15 bya (billion years ago)
Birth of the sun 5 bya and earth 4.5 bya.
Organic molecules formed 4 bya
To create amino acids: add water to chemicals in the Earth’s atmosphere and
lightning (electricity).
Life and the first fossils 3.6 bya
Complex single cells 2 bya
Important events
Free oxygen in the atmosphere: 1.8 bya
multicellular organisms 1.7 bya
40 million years ago (mya) first monkeys
23 mya first apes
4.4 -5 mya first hominids (habitually bipedal)
2.4 mya first stone tools
30-40,000 years ago cave paintings
Genetics
The study of the mechanism of inheritance.
Synthetic Model of Evolution
Modern Genetics is based upon 3 things:
Darwin/ Wallace’s: Natural Selection (1859)
Mendel’s: Principle’s of Inheritance (1866)
Modern Molecular Genetics: Watson, Crick, et al. Discovery of DNA (1962)
Applications of Genetics and Evolutionary Mechanisms
Cloning of sheep. Q: Are humans, extinct hominids, and mammoths next?
The principles of evolution are being applied directly to the problem of
creating artificial intelligence in computers e.g. the Tierra Project and
computer chips that reproduce, mutate and evolve (FPGA’s).
The computers create mutations and rapidly select the options that work better.
General concepts and terms in the reproduction of life
reproduction can be asexual or sexual
sex cells like sperm and eggs are called gametes
a zygote is a fertilized egg before cell division begins
DNA- deoxyribonucleic acid is a 6 foot self-reproducing molecule (the only one
we know of ) that holds the info. to make organisms. It is in some sense "life."
DNA’s Double Helix
Sugars, Phosphates, Bases
Like a twisted ladder
The ladder unzips to replicate or make proteins
Look at the diagram at the back of todays lab exercise (p. 21)
The DNA molecule
Genome
The complete set of instructions for making an organism is called its genome.
It contains the master blueprint for all cellular structures and activities for
the lifetime of the cell or organism. Found in every nucleus of a persons many
trillions of cells, the human genome consists of tightly coiled threads of
deoxyribonucleic acid (DNA) and associated protein molecules, organized into
structures called chromosomes.
Genome
The human genome is 23 chromosome pairs.
One of each pair is from the father and one of each pair is from the mother.
One allele or locus (a location on a DNA molecule that codes for production of
a protein) is from the father and one allele is from the mother.
Cell structure - One more time!
The human body is made up of cells.
Proteins and enzymes make up and run the body’s cells.
Proteins are a chain of amino acids.
Each codon is a 3 letter word for an amino acid coded by the DNA molecule.
Your body- Cells -Proteins-Amino Acids-DNA
The sequence of amino acids determines the protein’s function and structure.
A proteins structure or shape determines a lot about what its function will be
e.g. hair or pollen
Codons
Three DNA bases are called a codon.
Each codon is like a 3 letter word (like "dog") and is the code for a
particular amino acid (the "dog" amino acid).
A sequence of codons puts together a sequence of amino acids - and a sequence
of amino acids is a protein.
Codons code for making proteins.
DNA Codons
Chromosomes
A strand of DNA in the nucleus of a cell that carries genetic information
passed down to subsequent generations.
Generally, the portion of the DNA molecule that codes for a specific trait is
called a "gene" (or "locus").
locus
A locus is the position or location of a particular "gene" and its alleles
(variants of a gene) within the genome.
Alleles
In sexually reproducing organisms chromosomes come in pairs.
One comes from the father and one comes from the mother.
Each genetic locus thus comes in pairs. The two genetic loci can have variants,
called alleles.
allele
Alleles are "genes" whose locus (location on the DNA molecule) is the same, but
which are recognizably distinct
Alternate forms of a gene. In monogenic traits there are 2 alleles per "gene."
There are usually two alleles per gene.
If they are the same they are homozygous.
If they are different they are heterozygous.
homozygous
a zygote (fertilized egg) is HOMOZYGOUS when it has two
indistinguishable (the "same") genes at a particular locus
heterozygous
a zygote is HETEROZYGOUS when it has two recognizably different genes
at a particular locus
genotype
the genes carried by an individual, or the combination of genes that an
individual has at a particular locus
phenotype
an individual’s observable characteristics
Parents and offspring - Review
Each person has two copies of a gene for a trait since chromosomes occur in
homologous pairs; one chromosome of each pair comes from the mother, and one
comes from the father.
If e.g. a person is heterozygous the individual carries two different alleles
for the trait. If e.g. a person is homozygous he or she carries two of the same
alleles for the trait.
General concepts and terms - Review
Chromosomes are found in the nucleus of our cells and are made up of DNA
"Homologous" chromosome pairs carry information for the same traits
a "gene" is generally the portion of the DNA molecule that codes for a specific
trait.
"locus" is now the preferred term (location)
General concepts and terms - Review
an "allele" is a variant of a genetic locus. Most loci (plural) have more than
one allele.
The alleles convey different instructions for development of a certain
"phenotype" which is any physical or chemical trait that can be observed or
measured like blue versus brown eyes or red or black hair, etc.
a mutation is any change in genetic material (e.g.copying error in DNA)
General terms and concepts
a "chromosome" is a strand of DNA in the nucleus of a cell that carries genetic
information passed down to later generations
"somatic cells" e.g. your body cells are "diploid" meaning they have 46
chromosomes (23 pairs)
Your "somatic cells" reproduce through "mitosis" (I.e. they make exact copies)
General terms and concepts
sex cells are said to be "haploid" because they have only 23 single chromosomes
and reproduce through "meiosis" which makes daughter cells with only half the
usual number of chromosomes
The sperm gives 50% of the genetic material and the egg gives 50% of the
genetic material for the new unique individual. Meiosis causes uniqueness.
Meiosis and Mitosis
Meiosis produces the gametes or sex cells (sperm and egg) which have 23
chromosomes. These are "half" or haploid cells.
Mitosis reproduces the cells of the body (somatic cells) with 46 chromosomes
(23 pairs of chromosomes). These are "twice" cells or diploid cells.
Meiosis is sexual reproduction
Meiosis makes you and everyone else unique.
Meiosis creates variation and may be thought of as a mechanism or force of
evolution because it creates unique variation among individuals.
Meiosis and Mitosis
There are good illustrations of the steps involved in mitosis (cell division)
and meiosis (the division of cells that results in sex cells) in the back of
your lab manual on p. 23 and 24)
In meiosis 1 cell with 46 chromosomes becomes 4 sex cells (e.g. sperm) with 23
chromosomes each (the father’s half)
In mitosis 1 cell of the body becomes 2 "daughter" cells.
General terms and concepts - Review
"homozygous" means possessing two of the same alleles in a gene pair e.g. both
parents contribute the same trait. (e.g. AA or aa)
"heterozygous" means possessing two different alleles in a gene pair e.g. the
parents contribute different alleles (e.g. Aa)
If a pair of alleles is different, the one that is expressed is the "dominant"
one.
General terms and concepts
"codominant" alleles occur when neither allele of a gene pair is dominant and
so both are expressed in the organism e.g ABO blood groups
Genotype and Phenotype
an organisms "genotype" just means the alleles possessed by an organism (the
genetic information from both parents)
"phenotype" is any physical or chemical trait that can be observed or measured
like red hair.
co-dominant traits
A co-dominant trait is the situation where both alleles are expressed in the
phenotype of heterozygotes (The expression of two alleles in heterozygotes).
A good example is ABO blood types.
There is a kind of AB type blood where both A &B are EXPRESSED together at the
same time and are co-dominant.
General terms and concepts
Humans have 23 pairs of chromosomes
The first 22 pairs are called "autosomes"
The 23rd pair are the sex chromosomes and they look like an X X(female) or an
X Y (male)
Sex chromosomes
The 23rd pair of chromosomes is XX in females.
The 23rd pair of chromosomes is XY in males.
Sex of offspring
The gametes of females carry X chromosomes.The gametes of males are half X and
half Y.
Whether a given offspring is female or male depends on whether the father’s
sperm happens to have an X or a Y chromosome.
The father controls the sex of the child.
Punnett Squares
Punnett Squares illustrate how 2 alleles from the father and 2 alleles from the
mother combine for their children.
General terms and concepts
The genotype has a relationship to the environment. The wrong genes can be
fatal and selected against. Mutations can occur from radiation, pollution, etc.
Monogenic traits occur at one locus or location on the DNA molecule. They are
like an on/off switch. You either have the trait or you don’t. e.g. tongue
rolling.
Monogenic versus polygenic traits
Monogenic traits are determined by a single gene at a single locus and result
in discontinuous variation within a population. (e.g. yes you have the trait
or no you don’t)
There are distinct categories with no intermediate types.
General terms and concepts - Review
Polygenic traits are controlled by many genes which contribute to a single
effect. Examples include hair and skin color, height and weight which exhibit
continuous variation or shades throughout humankind.
Polygenic = "Many genes" control 1 trait.
Pleiotropy is where one gene has multiple effects.I.e One gene has many effects.
Gregor Mendel
Mendel published his work in 1866. Not until 1900 (16 years after his death)
was his work rediscovered.
Mendel experimented with peas following single, easily visible traits, like
tallness, wrinkles, colors, etc.
Mendel’s experiments
Mendel’s first generation usually showed the traits of only 1 parent (the
dominant gene).
The 2nd generation surprisingly showed 3/4 with the dominant trait and 1/4
with the recessive trait.
Mendel’s conclusion
Traits of the parents were not "blended."
The sex cells (gametes) carried some particular "factor" (later called genes)
that caused progeny to develop traits like color.
Inheritance is "particulate" in nature.
dominant trait
A dominant trait is one that is expressed I.e. phenotypically
A dominant allele is one that masks the effect of another
recessive trait
A recessive trait is one that is expressed only in homozygotes e.g. (aa) as
opposed to (Aa) or (AA).
An allele that is masked is recessive
Mendel’s first law of segregation of unit genes
When a heterozygote (a dominant and a recessive gene) forms its sex cells, the
genes segregate and pass to different gametes (female ovules or male pollen
grains). Equal numbers of gametes, ovules or pollen grains are formed that
contain the genes "D"& "d."
The Punnett square shows why 3/4 will express the dominant trait and 1/4 the
recessive trait.
Punnett Squares
Each pea plant parent has 2 genes for height (tallness or shortness).
If the two genes are alike for tallness we write it DD (capitals are a dominant
trait that is expressed).
This is a homozygote (same genes)
Punnett Squares
If a parent is a dwarf pea plant with a recessive pair of (shortness) genes
we write it "dd"in small letters.
This is also homozygous for the short "dd"genes.
Punnett Squares
A heterozygote parent (different genes) would be written Dd and the tallness
gene (being dominant) would be expressed.
3/4 of the second generation shows or expresses tallness. 1/4 are short.
Mendel’s 2nd law of Independent Assortment
Mendel crossbred varieties with two easily distinguishable traits like yellow
and round seeds (dominant) with green and wrinkled seeds (recessive).
He found that the segregation of the color (A-a) is independent of the
segregation of the trait of seed surface (B-b).
Molecular genetics
Watson and Crick in the 1950’s discovered DNA
Review: Humans on a cellular
and chemical level
Humans are made of cells.
Cells are made of proteins.
Proteins in the form of enzymes are responsible for cell function.
An enzyme is a protein that controls chemical processes.
Humans produce over 100,000 proteins.
Proteins & amino acids
The chief components of proteins are amino acids.
A protein (or enzyme) is a chain of amino acids in a sequence.
The average protein contains 1000 amino acids.
A string of amino acids in the right order is a particular protein.
Proteins
The results of the actions of proteins make up all of the observable chemical
and physical traits of a human.
Hemoglobin in blood, for example, is a protein made up of 2 amino acid chains.
The chemical structure of DNA
The DNA code (information) is a strand of 4 chemical bases: (A) adenine,
(T) thymine, (C) cytosine, and (G) guanine held together with chemical bonds.
The bases are only bonded in A-T or T-A (the reverse) and C-G or G-C pairs.
DNA Replication
DNA makes a copy of itself during cell division by unwinding or unzipping.
Think of a ladder cut in half. The bases are the rungs of the ladder. The
sides are made of sugars and phosphates.
Each half of the ladder is a complementary mirror image of the other.
DNA replication
Each strand with its unpaired bases "hanging out" is in a solution in the cell
with the complementary bases in it.
Only certain types of bases can link together so a mirror image is formed
The ends pick up the proper complementary bases which are in solution.
The free floating amino acids come from the food you eat.
DNA replication
When the loose bases attach there are now two complete DNA molecules.
One DNA moloecule is in each new daughter cell.
(Heat applied to DNA will cause it to unwind).
By the time you are 80 all of your cells will have completely reproduced
themselves.
Protein synthesis (manufacture)
The DNA unzips, as it would in replication, (only a segment unzips though),
exposing the bases.
messenger ribonucleic acid (mRNA) transcribes the code, then moves out of the
nucleus of the cell.
Regular DNA cannot move outside the nucleus which protects it.
Protein synthesis
The mRNA then acts as a template for the translation of the code into a protein.
Transfer ribonucleic acid (tRNA) molecules line up free-floating amino acids
(there are about 20 of them) along the mRNA, the amino acids bond, and a
protein is made.
Population Genetics
Evolution is the change in allele frequencies of a given population over time
General terms and concepts
A species is a group of organisms that can produce fertile offspring among
themselves but not with any other group.
A deme is a genetically isolated population within a species. It is a breeding
population.
a gene pool are all the alleles within a population
Evolution: 3 ways of describing or defining it
1. the change in a group of the same species over a long period of time
through inheritance;
2. the change in allele frequencies in a population over time;
3. the change in the characteristics of a population through time.
EVOLUTIONARY FORCES
MUTATION
GENETIC DRIFT
GENE FLOW
NATURAL SELECTION - 1.ENVIRONMENT, 2.MALTHUS, 3.FITNESS
SEXUAL SELECTION
INDIVIDUALTY FROM MEIOSIS
Main evolutionary processes
Mutation - copying errors in DNA
Genetic drift - random statistical effects and founder effect of small
populations
Gene flow - flow between populations
Natural selection - selects for an advantage
Sexual selection - mating appeal
Meiosis - individual variation from sexual reproduction
mutation
a change in the genetic material, giving rise to a new allele in the
population’s gene pool
some error that happens during the process of cell reproduction. When the DNA
unzips the wrong base might be added resulting in a new protein and allele.
Mutation is the ultimate source of all variation.
Mutation
All variants of genes first arose through mutation.
Each person carries approximately 100,000 genes and on average each person
carries 2 new mutations.
Mutations can be neutral, harmful or advantageous.
genetic drift
an undirected, random change of allele frequencies from generation to
generation
founder effect
radical change in gene frequencies in an isolate, due to sampling
error
gene flow
the movement of genes from one gene pool to another
natural selection
the force of evolution, clarified by Darwin, which acts deterministically
through the differential fitness of genotypes in a population, to produce
adaption
gene pool
the combined genes of a Mendelian population from which are drawn the
genotype of individual population members
population
a breeding group of organisms that tends to choose mates within the
group
The Process of Speciation
Darwinian gradualism versus Punctuated Equilibrium
species
a collection of individuals who can potentially mate and produce
fertile offspring
(it does not mean the same thing as a "population")
Speciation
"allopatric populations" become geographically separated and eventually change
and can no longer interbreed. e.g. monkeys can’t swim and with rising sea
levels were cut off in Borneo.
Reproductive isolating mechanisms & fertility problems
seasonal isolation - mating only during certain times of the year
behavioral isolation - behaviors that preclude reproduction; no recognition
mechanical isolation - e.g. rising water cuts off a population; physical
impossibility
gametic mortality - the gamete dies before fertilization
Reproductive isolating mechanisms
zygote mortality- the fertilized egg dies
hybrid inviability - the offspring does not survive to reproduce.
hybrid infertility - e.g. mules. The offspring are alive but sterile (cannot
reproduce).
Mutations,Phenotype
Macromutations or copying errors can slowly alter the code and cause speciation.
The expression of a genotype- the trait that results in the overall organism-is
the phenotype. Green eyes is a phenotype. brown hair is a phenotype.
Darwinian gradualism
Darwin viewed changes due to natural selection as slow,steady, and gradual
taking a long time to produce a new species.
anagenesis - the rate of change between species was thought to be gradual and
constant.
Punctuated evolution
Developed by Stephen Jay Gould and Niles Eldridge
Long periods of stasis (stability and no change) are interrupted by
environmental change, extinctions, and the opening up of new environmental
niches into which new species fairly suddenly "adaptively radiate" in order to
take advantage of new available food.
Punctuated Equilibrium
Cladogenesis - (punctuated equilibrium)
stasis (no change) is followed by rapid change.
extinction is followed by adaptive radiation and proliferation of closely
related species
Adaptive Radiation - a pop. must be pre-adapted to take advantage of the new
environment e.g. the Galapagos finches
differential fertility
the more fertile individuals contribute more of their traits to the
succeding populations
differential mortality
those who live longer tend to produce more offspring
Todays Lab
1. Work together on the Punnett Square worksheet pp.7-8.
2. Work together on the Monogenic and Polygenic trait problems. Put the data
for the whole classes height on the front chalkboard (and copy it into your
graph on pg. 10.
Outside of Lab
The Analysis of patterns (p.11) you do outside of class and hand them in to
me at the beginning of Tuesday’s lecture. They are due next TUESDAY. They are
individually due. (You can discuss the problem with your lab partners).
Part 3 is the marble exercise and I will give you specific instructions for it
when you get done with part 1 of todays lab exercise.
Lab 1 Notes Fall 1997
Lab 2 Notes Fall 1997
Lab 3 Notes Fall 1997
Lab 4 Notes Fall 1997
Lab 5 Notes Fall 1997
Lab 6 Notes Fall 1997
Lab 7 Notes Fall 1997
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