Download Genetics Notes 2006

Genetics Notes 2007
I. Introduction
A. Genetics – the study of heredity.
B. Heredity – passing of traits from
parents to their young.
C. Gene – a segment of DNA that codes
for a particular protein (modern
definition).
II. Genes and dominance
A. Characters – characteristics that
living things can pass on to their
young. example – eye color
B. Traits-different ways to
express the same character.
example-two traits of
eye color are blue and brown
C. Individual factors control
each trait of a living thing.
These factors are called
genes (Mendel’s definition).
D. Alleles – the different forms
of a gene.
1. dominant- form of a gene
that is expressed even when
present with a contrasting
recessive allele.
2. recessive - form of a gene that is
only expressed when their are two
alleles present for that form.
III. Important Vocabulary
A. Genotype – genetic makeup of an
organism. Examples of genotypes for
eye color include BB, Bb, or bb
B. Phenotype – the physical
characteristics of an organism.
Examples of phenotypes are brown
eyes and blue eyes.
C. Homozygous – organism that has two
identical alleles for a particular trait
1. BB – homozygous dominant
2. bb – homozygous recessive
D. Heterozygous – organism that has
two different alleles for the same trait.
Example – Bb
IV. Mendel’s conclusions
A. There are alternating forms of genes
for particular characters (alleles).
B. An organism has two alleles for each
inherited character (homozygous vs.
heterozygous).
C. Dominant and recessive alleles-what
they are and how they work
D. Segregation-the two alleles for the
same character separate during the
formation of gametes (thus each
gamete carries only one allele for
that character).
E. Independent Assortment-during
meiosis, nonhomologous
chromosomes assort independently.
The genes that are found on
nonhomologous chromosomes
thus assort independently
V. Other forms of inheritance
A. Mendel discovered many of the
importance principles that dictate
some forms of inheritance
B. Mendel’s work did not explain all
of the different kinds of inheritance.
C. Intermediate Inheritance
1. Some characters of
organisms do not have dominant
alleles.
2. The heterozygotes exhibit a
phenotype that is intermediate
between the two homozygotes.
3. Blending hypothesis is not
supported by this pattern
because the parent phenotypes
can reappear in the F2 generation.
4. Andalusian Chicken example-page
215
D. Multiple Alleles
1. Many genes have more than two
alleles
2. This increases the number of
genotypes and phenotypes for
that particular character.
3. Example – blood type (page 216
in book)
4. Codominance-heterozygote
expresses both traits (blood
type AB)
E. Polygenic Inheritance – when
two or more genes affect a
single character.
1. Leads to many variations in
phenotypes
2. Example-height and skin color
in humans
F. Environmental influences
1. All phenotypes are not
determined completely
by genotypes
2. Some traits are determined
more by the environment
than others.
3. Generally speaking the result
of a genotype usually isn’t one
possibility but a range of
possibilities which are influenced
by the environment.
G. Sex-linked traits
1. sex-linked gene-any gene that is
located on a sex chromosome
2. In humans, most sex-linked genes
are found on the X chromosome
3. Sex-linked traits are much more
common in men than women.
4. Examples of human sex-linked
traits - red-green color blindness
and hemophilia
5. Refer to pages 220-221 in the
textbook to see how sex-linked
traits occur.