• I.History of Genetics
• Genetics - the scientific study of inheritance
• The domestication of dogs is one of the
earliest human experiences with genetics.
• Millions of years ago there were no dogs.
• Today’s domestic dogs are descended from a
wolf ancestors
• Ancient people selected traits to be
passed from generation to generation.
• Trait - a characteristic that can be
passed from parent to offspring
• It has not always been understood how
traits are passed from parent to
offspring.
• For many centuries scientists believed
that traits were blended in offspring,
they would later learn that this idea was
incorrect.
• Review:
• during cell division chromosomes are
replicated and distributed to daughter
cells during meiosis.
• The traits that are passed from parents
to offspring are in these chromosomes
• II.Gregor Mendel
• Clues to
understanding
inheritance came
from an Austrian
monk, Gregor
Mendel, in the
1860’s.
• He used pea plants to study how traits were
passed from one generation to the next.
• Mendel gathered detailed information on
more than 20,000 pea plants over an eight
year period.
• He applied mathematics and statistics to his
findings and found that they did not support
the blending hypothesis.
• III. Mendel’s Experiments
• Mendel chose to work with the pea plant for
several reasons:
1. the structure of
the pea plantthe pea flower petals make
it very easy for the pollen
from the anther from a plant
to fertilize it’s own pistil.
• This produced a purebred offspring.
purebred offspring - receives the
same genetic traits from both parents
• Mendel was also able to transfer pollen
from one plant to another by hand.
This produced a hybrid.
• hybrid offspring - receives different
forms of a genetic trait from each parent
2. Presence of distinctive traits
Mendel studied several traits
Each of the traits had two distinct
forms
ex. pea pods are either yellow or green,
there is no intermediate
3. Rapid reproduction cycle
This allowed Mendel to repeat his
experiments many times to test his
results
• IV. Mendel’s Observations
Mendel began his experiments using
two different groups of inbred plants.
He called this the parents (or P)
generation.
yellow pea x green pea
• He called the offspring of that mating the first
filial generation or F1 generation.
100%yellow pea plants
• Mendel let the F1 plants self fertilize to
produce the F2 generation.
75% of the F2offpsring produced were
yellow while 25% were green.(3:1 ratio)
• V. Mendel’s Conclusions
• Mendel’s experiments showed that the
blending hypothesis was wrong.
• Mendel hypothesized that each trait is
controlled by a distinct “factor”
• We now know that
Mendel’s “factors”
are genes.
• Gene - a section of
a chromosome that
codes for a
particular trait.
• Alleles - different forms of a gene (ex.
yellow, green in peas)
Alleles are represented by letters ex.
Y=yellow, y= green
• dominant allele - form of the gene
that is expressed fully when two
different alleles are present
• recessive allele - form of the gene not
expressed when two different alleles are
present.
• Letters are used to represent alleles:
the dominant traits is represented by an
uppercase letter
ex.Y
• the recessive allele is represented by a
lower case letter
ex.y
• Mendel published his work in 1866, his
work went unrecognized for 37 years.
In 1903, Walter S.Sutton used a
microscope and observed that
chromosomes behaved like Mendel’s
factors.
genes
Chromosome
• VI. Genes Affect Traits
• GENOTYPE - the genetic make up of an
organism. The genotype includes both genes
in a pair of homologous chromosomes.
• genotype of purebred yellow peas is YY
• genotype of hybrid yellow peas is Yy
• genotype of green peas_______
• PHENOTYPE - the outward expression
of a trait
• phenotype for F1 generation of peas is
yellow
Green seeds Yellow seeds
• If the two alleles of the gene are the
same they are called homozygous. ex.
YY, yy
• If the two alleles of the gene are
different they are called heterozygous
ex.Yy
• VII. Mendel’s Laws
• The basic rules of inheritance are called
Mendel’s Laws
• Law of Segregation - each pair of genes
segregates and ends up in gametes during
meiosis
• half an organisms gametes contain one
chromosome from a homologous pair, the
other half contain the other chromosome
• Law of
Independent
Assortment - gene
pairs separate into
gametes randomly
and independently
of one another.
• Law of Dominance - recessive allele
is expressed only when the organism
has no copy of the corresponding
dominant allele
3 types of dominance
complete
incomplete
co-
F1 phenotype=
One parent
neither parent
both parents
• IX. Genetic Interactions
Complete dominance – the dominant
allele masks the recessive allele
Recessive trait : Sugary kernels
shown only when no dominant
allele is present
Dominant trait: Yellow
kernels
• incomplete
dominance - when
two different alleles
for the same trait
combine the
offspring is an
intermediate
ex.red snap dragon x
white snap dragon =
pink snap dragon
• codominance both alleles in the
heterozygote express
themselves fully
ex. blood type
• Polygenic Traits - traits affected by more
than one gene.
ex. eye color, skin color
• X. Probability
• fractions, percentages, or ratios used to
predict the likelihood of an outcome, you are
measuring probability.
• When you flip a coin, you can get either heads
or tails
The probability of getting heads is 1/2, 50%,
1:1
• Scientists can use probability to predict the
outcome of breeding experiments.