Transcript Genetics - West Ada

• Many of your physical traits resemble
those of your parents. These are
physical or behavioral characteristics
that vary from one individual to
another.
• Heredity can be defined as the passing
of genetic traits from parents to
offspring.
• Before DNA and chromosome
structure were discovered, genetics
was one of the biggest mysteries of
science.
Question: Which one of the
president’s daughters looks more
like their mother?
• Gregor Mendel was an Austrian monk
and a scientist who performed
experiments with garden peas.
• Mendel studied seven pea plant traits,
each with two contrasting characters.
• He crossed plants with each of the seven
contrasting characters and studied their
offspring.
• These experiments led to the
understanding of heredity.
• Genetics is the branch of biology that
focuses on heredity.
• Mendel knew that the male part of
each flower produces pollen
(containing sperm).
• He also knew the female part of the
flower produces egg cells.
• Pea flowers are self-pollinating.
• Sperm cells in pollen fertilize the egg
cells in the same flower.
• The seeds that are produced by selfpollination inherit all of their
characteristics from the single plant
that bore them.
• Mendel wanted to produce seeds
by joining male and female
reproductive cells from two
different plants.
• He cut away the pollen-bearing
male parts of the plant and
dusted the plant’s flower with
pollen from another plant.
• This process is called crosspollination. Crosspollination
produces seeds that have two
different parents. These plants
are called hybrids.
• Each original pair of
plants is the P
(parental) generation.
• The offspring are called
the F1, or “first filial,”
generation.
• The F1 hybrid plants all
had the character of
only one of the
parents.
• Mendel's first conclusion was that
biological inheritance is
determined by factors that are
passed from one generation to
the next.
• He called these factors genes.
• Each of the traits Mendel studied
was controlled by one gene that
occurred in two contrasting forms
that produced different
characters for each trait.
• The different forms of a gene are called alleles.
• Mendel’s second conclusion is called the “Principle of Dominance.”
which states that some alleles are dominant and others are
recessive.
Next, Mendel crossed the new
generation of plants, and he found
the white flowers reappeared in the
next generation.
• True Breeding plants are allowed to
self-fertilize (pollinate) and produce
the P generation (parental).
• F1 Generation results from the
cross-fertilization (pollination) of
the P generation. The dominant
allele masks the recessive allele.
• F2 Generation results from the selffertilization of the F1 generation.
The recessive allele shows up again
in some of the plants. This showed
the alleles had been separated, or
segregated from the dominant trait.
• Mendel suggested that the
alleles segregate from each
other during the formation of
the sex cells, or gametes.
• When each F1 plant flowers and
produces gametes, the two
alleles segregate from each
other so that each gamete
carries only a single copy of each
gene.
• Therefore, each F1 plant
produces two types of
gametes—those with the allele
for purple flowers, and those
with the allele for white.
• Phenotype: the physical characteristics of an organism (what it looks like,
i.e.: tall or short)
• Genotype: The genetic makeup of an organism (TT or Tt) due to the alleles
it has for a trait
• Homozygous: Two alleles of a particular gene that code for the same trait
are the same. Ex PP (dominant purple color) or pp (recessive white flower
color).
• Heterozygous: Two alleles of a particular gene are different for a trait. ex
Pp or Yy
•Genes are passed from parents to their
offspring.
•If two or more forms (alleles) of the gene for
a single trait exist, some forms of the gene
may be dominant and others may be
recessive.
•In most sexually reproducing organisms,
each adult has two copies of each gene.
These genes are segregated from each other
when gametes are formed.
•The alleles for different genes usually
segregate independently of one another.
• Which plant height was dominant in Mendel’s
experiment?
• Which plant height was recessive?
• Mendel found the same results in his experiments,
time and time again.
• The ratio of plants showing the dominant phenotype
(TT or Tt genotype) to those showing the recessive
phenotype(tt genotype) plants is 3:1.
• The predicted ratio showed up in Mendel’s
experiments, indicating that segregation did occur.
• The likelihood that a particular event will occur is called
probability.
• Probability can be used to predict the outcomes of genetic
crosses.
• Punnett squares are diagrams used to predict and compare the
genetic variations that will result from a cross.
To determine the phenotype of an
offspring you must first recognize its
genotype.
• We have discussed two types of alleles,
Dominant (B) and Recessive (b)
• We have also discussed Heterozygous (Bb)
and Homozygous (BB) or (bb) alleles
• Punnett squares provide a means for
determining the phenotypic outcome
resulting from the combination of
gametes
• The basic construction of a simple punnet
square is to the left of this explanation.
List the phenotype and
genotype outcomes for
each cross below using the
Punnett Square.
1. Heterozygous dominant x
Homozygous recessive
• Hh x hh ( H = white, h = green )
2. homozygous recessive x
homozygous recessive
• bb x bb ( B = Black, b = brown)
3. Heterozygous dominant x
homozygous dominant
• Tt x TT ( T = tall, t = short )
• Probabilities predict the
average outcome of a large
number of events.
• Probability cannot predict
the precise outcome of an
individual event.
• In genetics, the larger the
number of offspring, the
closer the resulting numbers
will get to expected values.
•To determine if the
segregation of one pair of
alleles affects the segregation
of another pair of alleles,
Mendel performed a two-factor
cross.
•Mendel crossed true-breeding
plants that produced round
yellow peas (genotype RRYY)
with true-breeding plants that
produced wrinkled green peas
(genotype rryy).
•All of the F1 offspring
produced round yellow peas
(genotype RrYy).
• For a two-factor
F1 hybrid cross,
the Punnett
square predicts a
9 : 3 : 3 : 1 ratio
in the F2
generation.
Some alleles are neither dominant
nor recessive, and many traits are
controlled by multiple alleles or
multiple genes.
• When one allele is not
completely dominant over
another it is called
incomplete dominance.
• In incomplete dominance,
the heterozygous
phenotype is between the
two homozygous
phenotypes.
• A cross between red (RR)
and white (WW) four
o’clock plants produces pink
colored flowers (RW).
In codominance, both alleles
contribute to the phenotype
(like spots!).
• In certain varieties of chicken,
the allele for black feathers is
codominant with the allele for
white feathers.
•Heterozygous chickens are
speckled with both black and
white feathers. The black and
white colors do not blend to
form a new color, but appear
separately.
Genes that are controlled by more than two alleles
are said to have multiple alleles.
•An individual can’t have more than two alleles.
However, more than two possible alleles can exist in a
population.
•A rabbit's coat color is determined by a single gene
that has at least four different alleles.
Traits controlled by two
or more genes are said to
be polygenic traits.
•Skin color in humans is a
polygenic trait controlled
by more than four
different genes. Scientists
do not believe they have
identified all the genes
responsible for eye color.
1. The name of the scientist responsible for forming the
foundations of genetics is __________.
2. Why did this scientist chose garden peas to perform his
experiments?
3. Heredity can be defined as ________
4. Genetics can be defined as _______
5. What is difference between dominant and recessive
traits?
6. Explain the difference between the P, F1 and F2
generations. What type of genetic characteristics can be
observed in each one?
7. The difference between a gene and an allele is?
8. Homozygous is?
9. What is codominance?
10. What is incomplete dominance?