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Genetics-study of heredity
Heredity- transmission of traits
from parents to offspring
I. You are a unique individual
2 things determine this:
A. Heredity
examples: hair color, eye
color, body build and
features, diseases,
blood type, etc.
B. Environment- your
surroundings
examples: family, friends,
school, community, country,
environmental (sun, climate),
and internal factors (hormones)
C. Heredity and Environment
work together to determine
who you are.
!!! Heredity sets limits but
environment determines if
you reach those limits
Examples:
sun
(tan??)
height (5’4” or 5’8”)
II. Characteristics inherited
A. Species-things that make you
like others
arms with fingers, hair, eyes
B. Individual things that make
you different
length, curly or straight, color
III. Gregor Mendel
“The Father of Genetics”
A. His work 1856-1865 with
garden peas
B. Observed 7 different traits
C. Experimented by breeding
plants
D. Plant anatomy:
1. male anther produces pollen
with sperm cells
2. Female ovary produces the
egg (ovules)
3. Pollination-movement of
pollen from stamen to pistil
a. Self-pollination -same flower
b. Cross-pollination - different
plants
E. Mendel’s Experiment
Mendel controlled the crosses
by removing the stamen
F. Mendel’s results:
Tall + tall = tall
Short + short = short
Short + tall = ?????
IV. Why???
Mendel’s hypothesis:
1. Concept of Unit Characters
- Hereditary
characteristics are
controlled by
factors that occur
in pairs
We call these factors genes, that are
found in the homologous pairs of
chromosomes in our cells
Alleles are different forms of a
gene, often represented by capital
or lowercase letters
Ex: Gene = plant height
- Alleles: tall or short
-Allele for tall = T
- Allele for short = t
Examples:
tall or short
dark hair or red hair
Type A blood or Type B blood
2. Principle of Dominance and
Recessiveness - one factor may
prevent the expression of the
other
Dominant - gene that prevents
the expression of another
characteristic that always appears
in a cross between parents
Recessive- characteristic that
does not appear if a dominant is
present
V. Terms
A. Pure - both genes are the
same
2 dominant, or 2 recessive
- “Purebred”
- TT, tt
B. Hybrid - genes are different;
one dominant one recessive
- “hybrid plants and animals”
- Tt
C. Homozygous- the same
same as pure (TT, tt)
D. Heterozygous- different
same as hybrid (Tt)
F. Genotype - the genes of an
organism; its genetic makeup
- Use of symbols to represent
genes
Ex: TT tt Tt
G. Phenotype - the physical
characteristic or trait of the
organism
- written in words, descriptive
Ex: short or tall
type A blood type
VI. Law of segregation
- a pair of genes separate
during the formation of
sex cells
A. Punnett squarea method used to determine
possible combinations
of genes in offspring
B. Examples
C. Test-cross - crossing an
individual with an unknown
genotype but a known
dominant phenotype
with a recessive to determine
its genotype
VII. Law of Independent
Assortment- chromosomes with
their genes separate
independently of each other
- Genetics cannot be predicted
to an absolute, but we can
determine the probability
Dihybrid cross-crossing
organisms differing in 2
characters