Transcript Chapter 8- Mendel And Heredity

Chapter 8- Mendel And Heredity
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I. The origins of Genetics
A. The passing of traits from parents to
offspring is called heredity.
1. Mendel was a mathematician and
looked at genetics differently than
anyone in the past ever did.
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2. Genetics is the branch of biology that
focuses on heredity.
3. Mendel counted the number of each kind
of offspring and analyzed the data.
4. Quantitative approaches to science-those
that include measuring and counting.
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B. Useful features in peas
1. The garden pea is a good subject for
studying heredity for several reasons.
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a. The garden pea has many traits that
have two clearly different forms that are easy
to tell apart.
b. The mating of the garden pea flowers
can be easily controlled.
c. The garden pea is small, grows easily,
matures quickly and produces many
offspring.
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C. Mendel observed that traits are expressed
as simple ratios
1. Mendel’s initial experiments were
monohybrid crosses. A cross with ONE pair
of contrasting traits.
2. Mendel allowed true breeding or selfpollination to occur.
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3. These true-breeding plants served
as the parental generation in Mendel’s
experiments.
4. The parental generation, or P
generation are the first two individuals
that are crossed.
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5. Mendel crossed the P generation to get
the F1 generation. First generation. He then
examined each F1 plant and recorded the
number of F1 plants and their traits.
6. Mendel then mated the F1 generation to
get a F2 generation. The second generation
and then again examined each of their traits.
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D. Mendel’s results.
1. See page 162 figure 8.4
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II. Mendel’s theory
A. Mendel’s work became a theory of
heredity.
1. The four hypotheses Mendel
developed were based directly on the
result of his experiments.
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a. For each inherited trait, an
individual has two copies of genes- one
from each parent.
b. There are alternative versions of
genes. These are called alleles.
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c. When two different alleles occur
together, one of them bay be completely
expressed, while the other may have no
affect on the appearance. Mendel explained
these to be dominant and recessive.
d. When gametes are formed, the alleles
for each gene in an individual separate
independently of one another.
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B. Mendel’s findings in modern terms
1. If two traits are the same they
are called homozygous.
2. If two traits are different they are
called heterozygous.
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3. Dominant genes are expressed with
capital letters.
4. Recessive genes are expressed with lower
caps.
5. Example Brown is dominant= B, blue is
recessive =b.
6. A set of alleles that an individual has is
called the genotype.
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7. What the individual expresses is called the
phenotype.
8. Example: BB, Bb and bb are genotypes.
9. BB, and Bb would have brown eyes, and
bb would have blue eyes. The colors are the
phenotypes.
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B. Mendel’s Ideas gave rise to the laws
of heredity.
1. The first law, the law of
segregation, states that the two alleles
for a trait segregate or separate when
gametes are formed.
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2. The law of independent assortment
states that the alleles of different genes
separate independently of one another
during gamete formation.
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II. Studying heredity
A. Punnet squares- see
board.
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B. Probability on the
board.
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C. Pedigrees on the
board.
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D. Sex linked traits on
board.
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III. Patterns of Heredity can be
complex
A. Traits influenced by several genes
1. When several genes influence a
trait, the trait is said to be polygenetic.
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2. In some traits there is neither
dominant nor recessive genes. These
are called incomplete dominance.
Example: Red flower RR and a White
WW flower both with incomplete
dominance will have pink flowers.
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3. When two dominant alleles are expressed at
the same time, both forms of the trait are
displayed this is called co dominance.
Example: Coat colors in a horse.
4. Genes with three or more alleles are said
to have multiple alleles. Example blood
groups ABO.
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1. Genotypes
IAIA
IAIo
IBIB
IBIo
IoIo
Phenotypes
AB
A
A
B
BIAIB
O
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5. An individual’s phenotype often depends
on conditions in the environment.
6. Some traits are affected by the
temperature, sunlight or seasons.
7. In humans the environment influences
height. Height is influenced by nutrition, an
internal environment conditions.
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B. Some traits are caused by mutations
1.
Sickle cell anemia is a recessive genetic
disorder caused by a mutated allele that
produces a defected form of the protein
hemoglobin.
2.
Hemophilia is a recessive genetic disorder
that impairs the blood’s body to clot.
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3. Huntington’s disease is a genetic disorder
caused by a DOMINANT allele. The
symptoms do not appear until the victim is in
their 30’s or 40’s. This disease caused
severe mental illness and eventually death.
4. Most genetic disorders cannot be cured,
but progress is being made
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5. There is genetic testing to detect
any bad genes.
6. Gene technology may soon by
replacing defected genes with copies of
healthy ones this is called gene therapy.
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