1. Chapter 9 and 12 Important Vocabulary
• Pure- being a purebreed, parent always passes on one trait to the offspring
• Hybrid-being a cross between two purebred parents
• P1 generation-parent or first generation
• F1-filial generation or kids of the parent generation
• F2- grandkids of the parent generation
• Dominant- a trait that always shows up in the F1 generation, it is the strongest
trait and will mask other traits
• Recessive- a trait that is weaker, usually doesn’t appear in F1 generation but
appears in F2 generation
• Mendel discovered that certain traits were dominant and certain ones were
recessive.
• Look in your book for the list of traits.
• An allele is the factor or gene that is passed only; it is a type of gene.
• There may be several alleles for one gene.
• Dominant alleles have capital letters and recessive alleles have lowercase letters.
• Genotype is the actual genetic makeup of the organism or what the genes say.
• Phenotype is the physical look of the organism like color or texture.
• You can see the phenotype but not the genotype.
• The Law of Segregation states that paired factors separate during the formation
of gametes (meiosis)
• Each gamete only receives one factor or trait from each parent.
• The Law of Independent Assortment states that factors for different traits
distribute to gametes independently regardless of the other trait.
• Homozygous means the organism has two of same alleles for a trait.
• Heterozygous means the organism has two different alleles for a trait.
• Heterozygous would automatically have one dominant allele and one recessive
allele.
• Homozygous could have two dominant alleles or two recessive alleles.
• Polygenic traits are controlled by more than one gene.
• Skin color is controlled by at lease six genes which result is a different amount of
pigment produced.
• Eye color is also polygenic as well as height although environment plays a part in
that as well.
• A pedigree is a pictoral representation of a family to show how a trait is passed
along. Circles for women, squares for men. Colored in has the trait. ½ colored in
carriers the trait or is heterozygous for the trait.
OTHER TYPES OF INHERITANCE
Incomplete dominance or intermediate inheritance
• When two or more alleles influence the phenotype, both are expressed so neither
is completely dominant or recessive.
• This results in a third phenotype in addition to the originals.
• The heterozygous genotype is always the new phenotype.

2. Codominance
• This results when two or more alleles are equally dominant and both alleles are
expressed in heterozygous organisms
• Both alleles are expressed equally.
• This is different than incomplete dominance because it isn’t a blended phenotype,
is both expressed.
• Human blood type is an example.
Sex-linked
• Some genes are found only on the X-chromosome.
• Many diseases are X-linked diseases and are more common in males than in
females.
• Males need only one copy of the bad gene while females need two copies of the
bad gene.
• Hemophilia, colorblindness and Duchenne muscular dystrophy are human
diseases associated with this inheritance.
• A carrier is heterozygous for a disease but does not have the disease. It can be
passed on to their children though.
• Sex-influences traits like baldness are influenced by the sex of the person and are
expressed differently even if the gene is the same.
THINKING QUESTIONS-KNOW THE ANSWER TO THESE
1. Who discovered the basic principals and laws of genetics and heredity?
2. Can you do a Punnett Square for each type of heredity?
3. Why are sex-linked traits more common in males?
4. Why is sickle cell anemia more common in African Americans?
5. What types of mutations can result when genes “jump around” or are in the wrong
areas?
6. Can you draw a pedigree properly?
7. Why does a carrier of a genetic disease often not show the symptoms of the
disease?