Genetics Notes: This is a general outline of what you need to know for the section on genetics.
To make the best use of this information, read your text, attend class, take notes and use these
sheets as an outline for key concepts and understandings. The section on genetics can often be a
bit overwhelming at first, but if you follow my recommendations you should do well.
Genetics: the study of how traits are transmitted from one generation to the next. The study of
genetics informs us as to where variation comes from and how inheritance works.
Brief Overview: Humans (along with all other animals and plant life) are made up of cells. Cells
are the basic unit of life in all living organisms. DNA resides in the nucleus of the cell directing cell
replication (for growth and repair) and protein synthesis. DNA contains the genetic code. The four
DNA bases (cytosine-C, guanine-G, adenine-A, and thymine-T), combine in units of three (codons)
to form amino acids, which then code for the tens of thousands of proteins that comprise a human
being. We are basically made up of proteins (enzymes, hormones, collagen, hemoglobin, are all
proteins).
How Genes Work: Once you have read and studied this section you should know;
Where DNA resides _________________________________________________________
The structure or shape of the DNA molecule ______________________________________
How the bases (A, T, C, and G) hook up __________________________________________
How DNA directs cell replication and protein synthesis.
Cell replication: Is a continual process in the body. It involves DNA directing the
unwinding of the DNA molecule, where enzymes cut the base pairs apart, and new bases
are picked up in the cell. The result (if all goes well) is an exact copy or daughter cell. In
this process adenine hooks up with _________________________ and cytosine hooks up
with_____________________.
Protein Synthesis: starts in a similar way as cell replication does, but the DNA molecule
is only partially unwound. Messenger RNA is assembled against one strand of the
unwound DNA. mRNA transcribes the gene by matching complementary bases to the
exposed coding strand of DNA, except that ________________ replaces thymine. mRNA
then leaves the nucleus of the cell and moves to the _______________________. It is in
the _____________________ that the message is decoded and translated into a
_______________________. Transfer RNA reads the three letter code (also called a
_____________). The _________________, or amino ________________ are then
strung together to make a protein.
If we compare DNA to language we can see understand it in the following way:
DNA language has the following 4 letters; ____________________________________________
DNA words are always _________letters long and they form _______________ or ____________
In the DNA language there are ___________________ words (or amino acids).
DNA sentences create ____________________ with a string of amino acids. There are an
estimated _______________ proteins that make us what we are.
All life on earth is made up of these four DNA bases. The different life forms that exist form are in
part the result of the sequence, quantity and coding of the four DNA bases.
From a Gene to a Trait: Genes are portions of the DNA molecule that code for specific traits or
portions of a trait (specifically proteins, or portions of a protein). Humans have some 25,000
genes. Our genes code for some 90,000 proteins. Each gene resides at a specific location on the
chromosome (the locus) and each individual receives two “genes” or alleles at each location, one
from each parent.
Example: The trait of earlobes is coded for by one gene, but there are two possible
________for earlobes, attached and free hanging. Attached earlobes are when the bottom
of the earlobe is attached to the neck, free hanging earlobes are not attached.
Locus _________________________________________________________________________
Alleles________________________________, there are always _________alleles at each locus
Genotype: _____________________________________________________________________
Phenotype ____________________________________________________________________
Homozygous: __________________________________________________________________
Heterozygous: __________________________________________________________________
Alleles come in various forms and this impacts their expression in the individual
Dominant: _____________________________________________________________
Recessive: ______________________________________________________________
co-dominance: ________________________________________, an example is the __________
blood system
incomplete dominance: occurs when a recessive allele has some phenotypic effect, the
recessive allele is not completely “masked” by the dominant allele (tay sachs is an example)
Example: The allele for free hanging earlobes is dominant and the allele for attached earlobes is
recessive. Dominant alleles are shown using capital letters and recessive alleles are shown using
lower case letters. For this trait there are three different genotypes and two possible phenotypes.
Genotype
Phenotype
EE - homozygous dominant
free hanging earlobes
Ee - heterozygous
free hanging earlobes
ee - homozygous recessive
attached earlobes
Genetic Expression: The physical traits that we posses are determined by our genes or a
combination of our genes and the environment.
monogenic traits: __________________________________________________
examplepolygenic traits: ____________________________________________________
examplepleiotropy: __________________________________________________________
exampleHow Inheritance Works: As we learned above, genes (or alleles) come in pairs. When cells
replicate, the result is an exact daughter cell. This process is ______________________. All of
the cells in our body (except the sex cells or gametes) contain all of our genetic information.
Generally our DNA resides in the nucleus of the cell in a long strand but during cell replication and
protein synthesis DNA forms into discrete forms called ________________________________.
We inherit the chromosomes that we posses from our biological parents. Typical humans have 23
_____________ of chromosomes, we get ___________ from each biological parent.
Humans start life as a single cell. With cell division and replication we eventually end up as an
adult human being comprised of some 1,000 billion cells. Cell division and replication of the
somatic cells is responsible for growth and repair of our bodies.
Somatic cells, which comprise the body tissue, muscle, bone, skin, nerves, etc. that make
up our body. Each of our somatic cells contains all _________________pairs of our
chromosomes, for a total of ___________chromosomes.
Mitosis: is cell division of the __________________cells, and the result is two
_______________ daughter cells. Mitosis is an ongoing process in the body.
___________ in the nucleus of the cell, directs this process. Mitosis works for repair and
growth of the nails, hair, bone marrow, etc. which are constantly replaced.
Sex cells or gametes are the cells of reproduction (eggs and sperm). The sex cells
contain only half of our chromosomes (23 total).
Meiosis: is cell division where sex cells are produced (gametes; ___________________&
__________________). During meiosis the cells undergo an extra round of division and
instead of two exact copies being produced as in mitosis, only one set of the twenty-three
chromosomes are left. So, at the end of meiosis the sex cells only contain half of the
individuals chromosomal complement.
Question: Why is it critical that the sex cells undergo another round of division? What role does
this extra round of division play in shuffling existing variation?
Meiosis is a powerful source for genetic diversity. In the production of each gamete or sex cell
there is a _____________chance as to which one of the pair of chromosomes an individual passes
onto to their offspring. Meiosis is a powerful source to reshuffle the existing variation. Each human
has some 8 million possible combinations for their offspring.
Punnett Squares: Show the possibilities for offspring (inheritance). The outside of the punnett
square reflects the ____________________the parents posses for a particular trait. The inside of
the square reflects the possibilities for their offspring’s _______________. During meiosis there is
a __________ possibility as to which allele each parent passes onto their offspring.
Example: A man with attached ear lobes marries a women with free hanging ear lobes
(heterozygous). What are the possibilities for their children? (free hanging alleles are
dominant and attached alleles are recessive). Which alleles represent the male and which
represent the female in this example?
E
e
Ee
ee
e
Ee
ee
e
Offspring: there is a 50% possibility the children will have attached ear lobes and a 50%
possibility they will have free hanging ear lobes
Rules of Inheritence
Segregation: during meiosis chromosomes segregate (and therefore allele pairs segregate)
There is a ___________chance for a parent to pass on either _________________
(this is what is represented in the punnett squares, you are displaying the
_______________chance for what the offspring will receive from their parents)
Independent Assortment: genes on separate chromosomes are inherited ________________. It
is chromosomes that segregate during meiosis not individual genes
Linkage: genes on same chromosome are inherited ___________________, because it is
_______________________________that segregate during meiosis
Crossing Over: exception to linkage, during meiosis portions of chromosome pairs break off and
cross over and are then recombined (recombination)
Variation is increased through: Segregation, independent assortment, crossing over &
recombination
Chromosomes are ____________________________________________________________
that reside in the nucleus of the cell. Generally DNA resides in a long strand inside the cell's
nucleus but as the cell undergoes division the DNA becomes ___________________ and
separates into chromosomes. Each species has a specific number of chromosomes. All typical
humans have 23 pairs of chromosomes, 46 total (23 from each parent).
Autosomes: chromosomes ________to ___________. They contain most all of the
genetic info for our physical characteristics except ___________________determination.
Sex Chromosomes: ______________ & _________________.
 Typical females have an _______& ______ sex chromosomes and thus have a
matching pair for all of their chromosomes. The X chromosome is large and codes for
__________________________ traits.
 Typical males have an__________& __________ sex chromosome. Therefore males
do not have a matching pair for their sex chromosomes. The Y chromosome is small
and for the most part codes for ___________________. Since males do not have a
matching pair of sex chromosomes this makes them more susceptible to traits that
reside on the X chromosome.
Sex linked traits: Sex linked traits reside on either the _______or the ________ chromosome.
Most sex linked traits reside on the ______chromosome (remember it carries many genes and
functions more like an autosome). When you are working to determine the possibilities for
offspring traits on a sex linked trait you need to put the sex chromosomes on the outside of the
punnett square.
Example: Trait under study is red green color blindness which is an X linked recessive
disorder. A male with red green color blindness marries a female who is heterozygous for
the trait. What are the possibilities for their children?
Xr
Y
XR
Xr
XR Xr
XR Y
Xr Xr
Xr Y
Children: There is a 50% probability that their children will be red green colorblind.
Question: Why does the man have only one allele for this trait?
Things to keep in mind
 During meiosis parents pass on 50% of their chromosomal complement
 Punnett squares are used to calculate the possibilities for inheritance. The alleles the parents
posses are on the outside and the possibilities for offspring’s alleles are on the inside.
 Offspring can express traits not expressed in parents (due to recessive alleles)
 Humans have pairs of all autosomes (22 from each parent, 44 total), females have a pair of
sex chromosomes (two X’s, one from each parent), males have one X and one Y chromosome
(males more likely to get conditions passed on X chromosome)
Human Genome: The completion of the Human Genome was an incredible accomplishment. The
race to complete it involved many countries around the world, and also a competition between
public and private interests. The completion of the genome means that we now know the
sequence of the four bases for our species, Homo sapiens. It has lead to many new
understandings and it has also left us with much more to learn. As you read this section make sure
you can answer the following questions;
1. What did the completion of the human genome reveal about junk DNA? Is some
___________% of our DNA actually junk?
2. What is the difference between coding and non-coding DNA?
3. How can humans have 25,000 genes and some 90,000 proteins? What did role does
junk DNA play in this situation?How many genes do we have?
Characteristics of the DNA Code
The Code is universal- The same DNA code is present in all life on earth. Humans share some
200 genes with bacteria, this reflects a common ancestor with bacteria. Some 75% of our genes
are shared with birds, we shared a common ancestor with birds some 310 million years ago. We
share ______________ our DNA code with chimpanzees and bonobo’s.
The Code is triplet- Each amino acid is specified by a sequence of 3 bases
The Code is continuous without pauses- There is no separation from one amino acid (codon) to
another, so if a base is deleted then entire frame is moved, drastically altering the “message”
downstream for other successive codons.
The Code is redundant- There are 20 amino acids, and 4 DNA bases which makes for 64
possible triplets (with 3 stop messages), so there are 61codons specifying 20 amino acids
o Many amino acids are coded for by more than one codon- (valine= UAA, UAG, UGA)
o Redundancy helps if there is a change or mutation in the code it makes it less likely
there will be drastic consequences. Although recent research is showing that a
change in a base may not change the amino acid it may change how the protein is
expressed, how fast a protein is made, etc.
Nature/Nurture Debate
An understanding of the nature/nurture debate requires knowledge of genetics and critical thinking
skills. The nature/nurture debate has been ongoing for millennia. This is a philosophical and
scientific debate with profound, practical, everyday consequences. If we attribute traits solely to
genetics, and we see some traits as problematic (i.e. aggression) than society may work to stop
individuals deemed too aggressive from breeding (the USA had a eugenics program where
individuals deemed unfit were forcibly sterilized from the 1920’s till the 1970’s). If we attribute traits
to our environment or culture than we may work to provide a better environment for individuals (i.e.
fund programs such as Head Start for preschoolers).
What do Genes Do?
Genes code for _________________ or _________________ or portions of a ________________
or a _____________________. Genes give rise to our physical features, although our physical
features are influenced by our ___________________________________ (the food we eat, levels
of exercise, etc). Some genes code for hormones, and hormones affect feelings to a degree (and
the experience of feelings is very much influenced by culture and context). To what degree this
affects behaviors is a matter of debate.
The Nature argument states that our nature, our basic temperament is due to our _____________.
The Nurture argument states that our basic temperament is due to our _____________________.
Most anthropologists see a ___________________________loop between our biology and our
culture. This means, as Park states, we see that we have general potentials from our biology, but
we our not committed to any one path or outcome. One area of debate is over the concept of
instincts. Do humans have any instincts…?
What do you need to evaluate this debate? To critique the nature debate you need to look
at the following.
1. To state that genes lead to behaviors you first need to be able to find the _________________
and draw a direct link between gene and the behavior. This works great with monogenic traits, but
it isn’t as easy with pleotropic and polygenic traits.
2. You need to define the ________________________. Some of the behaviors that have been
labeled genetic include; violence, infidelity, alcoholism, etc. How would you come up with an
operational definition for these behaviors?
3. You would need to rule out the environment as playing a role. The influence of the environment
starts in the ___________________ and continues until the day that we die
To critique the nurture debate you need to look at the same factors. If you state that we are
only a product of our environment you need to draw links between specific cultures and
environments and specific behaviors. You would expect to find fairly divergent behaviors between
different human populations. What do we see in human cultures around the world? How similar or
different are humans in cultures around the world? Take a cultural anthropology class to learn
more….. 