Document 236720

What is Genetics?
What is
A. Gregor Mendel
– Father of Genetics
• Discovered the basic
principles of heredity
from his analysis of
crosses using garden
• He was the first to
integrate science and
What is Genetics?
B. Alleles
= Traits
• Mendel reasoned traits are
controlled by 2 factors known
today as alleles of a gene
• Diploid organisms have two
alleles for every gene
• Alleles are passed sexually &
• Variation arises during sexual
reproduction where offspring
receives different alleles than
either of the parents
What is Genetics?
C. Mendel’s Laws
2. Law of Segregation
• Members of each
pair of alleles
separate when
gametes are formed
• A gamete will
receive one allele or
the other, but not
What is Genetics?
C. Mendel’s Laws 1. Law of Independent
• 2 or more pairs of alleles
segregate independently of
one another during meiosis
gamete formation
• This applies to traits on
different pairs of
chromosomes or ones that
are not close together
What is Genetics?
II. Genes
–History of the
1. Wilhelm Johansen
• Coined the term “gene”
2. Walter Sutton
• Genes on
3. Thomas Morgan
• Verified Sutton’s work
using Drosophilae
(Fruit fly)
What is Genetics?
B. Genes are
segments of DNA
molecules located
on a chromosome
1. Carry instructions for
producing a specific trait
2. Diploid organisms have two
alleles for each gene
• Asexual reproduction:
offspring receives both
alleles from one parent
• Sexual reproduction:
offspring receive one
allele from one parent
and the second allele
from a different parent
What is Genetics?
2. Only one allele of gene
can be expressed in an
a. Dominant allele:
is the allele of a trait
that will be
• Represented by a
capital letter
(Example: “G”)
What is Genetics?
• Incomplete Dominance:
where alleles for a trait are
neither dominant nor
recessive. This causes a
mixing of a trait expression
• Co-dominance: both alleles
are expressed fully
(Example: AB Blood Type)
What is Genetics?
C. Which allele of a
1. Each individual has two
gene is expressed in
factors, or alleles, for
a diploid organism?
each trait, which may or
may not have the same
• Homozygous: the pair
of alleles for a gene
are identical (Example:
GG or gg)
• Heterozygous: the pair
of alleles for a gene
are different (Gg)
What is Genetics?
b. Recessive allele: is
the allele of a trait that
will be hidden unless it
is homozygous
• Represented by a
lower case letter
(Example: “g”)
• This is why you can
be a carrier for a
genetic disorder
and not know it
What is Genetics?
3. Genotype: the actual allele
pair for a gene
• We use symbols to
represent the genotype
• GG – homozygous
• Gg – heterozygous (the
dominant or capital
letter will be expressed)
• gg – homozygous
What is Genetics?
4. Phenotype: the
physical expression
of a trait or the
physical appearance
• GG – Yellow plants
• Gg – Yellow plants
• gg – Green plants
What is Genetics?
D. Mendel’s
Experiments and
Punnet Square
1. P1: (Parent Generation)
• Purple (WW) x
White (ww)
2. F1: 1st Filial Generation
• All offspring were
purple (Ww)
3. F2: 2nd Filial Generation
• 3 plants were purple
and 1 plant was white
What is Genetics?
4. Punnett Squares •
A mathematical model
used to predict the results
of a cross
Steps for a Punnett square:
a. Define what the letters mean
– W = Purple and w = white
b. Tell what is being crossed
– WW x ww
c. Punnett Square
d. Data table
– Genotype % and Phenotype %