Ch. 14: Mendel and the Gene Idea. Introduction A. Heritable traits (brown eyes, green eyes, blue eyes) are passed down from parents to offspring. B. Blending hypothesis: Offspring should have a blend of parental traits. (Yellow + Blue = Green).
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Mendel and the Gene Idea
This blending hypothesis is incorrect.
flowers in the F2 generation were 3:1.
that though the
F1 generation had
no white flowers,
they must have
heritable trait for
white flower color.
was “dominant” and the white color
gene was “recessive.”
Example: Round v. Wrinkled pea seeds
F1 = 100% Round
F2 = 75% Round, 25% Wrinkled
Ex. Purple and
white color genes
to produce a
is to have two
** However, this was not the results of
Their gametes can have four
combinations: YR, Yr, yR, yr
Therefore, the ratios for the F2
F2 = 9 Yellow, Round (Yy, Rr):
3 Yellow, Wrinkled (Yy, rr):
3 Green, Round (yy, Rr):
1 Green, Wrinkled (yy, rr)
** Whenever Mendel did a dihybrid cross,
he always got the 9:3:3:1 ratio. This
can be explained as the result of the
“Law of Independent Assortment.”
P = Red, White
F1 = 100% Pink
F2 = 25% Red
had the same
phenotype. This is
ratio will be
9 black:3 brown:
Norm of reaction:
colors of hydrangea
flowers, range from
blue to pink, depending
on the acidity of soil.
This sickling can cause a number of results.
This sickling has pleiotropic effects.
dominant to the sickle-cell allele.
Heterozygous individuals are carriers
and can suffer some symptoms of
the disease under blood oxygen
stress. Both normal and abnormal
hemoglobins are synthesized.
Individuals that are heterozygous
are also resistant to malaria, a
parasite that spends part of its life
cycle inside RBCs.
-Offspring born to a parent who has
the allele for Huntington’s disease has
a 50% chance of inheriting the
disease and the disorder.
-Molecule geneticists have recently
discovered that the gene for HD is
found on the tip of chromosome #4.
-fetal cells are extracted and karyotyped.
-other disorders can be detected from
chemicals in the amniotic fluid.
-Fetal tissue is extracted from the
chrionic villi of the placenta.
-Both fetoscopy and amniocentesis
cause complications in about 1% of
cases. They can cause maternal
bleeding or fetal death.
-These techniques are usually reserved
for cases in which the risk of a genetic
disorder or other type of birth defect is
the parents must face the difficult decision
of terminating the pregnancy or preparing
to care for a child with a genetic disorder.
-1 in 10,000-15,000 births
-causes a build-up of the amino acid
phenylalanine, and its derivative
phenypyruvate in the blood to toxic
-this build-up can cause mental
-if the genetic test is given at birth, a
child can be given a special diet low in
phenylalanine, which usually promotes