Download Genetics, Mendel and Units of Heredity

Genetics, Mendel and Units of
Heredity
Gregor Mendel
¾ Austrian monk and
naturalist.
¾ Conducted research
in Brno, Czech
Republic from 18561863
¾ Curious about how
traits were passed
from parents to
offspring.
Mendel’s Peas
¾ Mendel’s pea plant – Pisum sativum
¾ Normally, pea plants self-pollinate and
self-fertilize
¾ Mendel cross-pollinated and crossfertilized
¾ Mendel’s experiments focused on
observable traits or phenotype
¾ Mendel began his experiments using truebreeding lines of peas
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Single Trait Inheritance
¾ Seed color
¾ Initial cross parents
are the parental
generation
¾ Their offspring are
the F1 generation
¾ All offspring
resulted in yellow
seeds
Single Trait Inheritance
¾ F1 seeds allowed to grow
and self-pollinate
¾ Yellow and green seeds
observed in F2 generation
¾ Yellow and green seeds
present in 3:1 ratio
¾ Green color referred to as
recessive
¾ Yellow color referred to as
dominant
¾ Mendel repeated these
experiments with other
traits, yielding similar results
Hereditary Determinants
¾ Mendel’s hypothesis of particulate inheritance
¾ Hereditary determinants are now called genes
¾ Each gene carries DNA, a molecule that encodes the
instructional information
¾ Each gene has two versions or alleles
¾ Alleles found in an individual are its genotype
and have an effect on its phenotype
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The Relationship Between Genotype and
Phenotype
„ Genotype: DNA
„ Carries molecular information (blueprint) of
who and what we are, however, DNA is NOT
the molecule that gives us our appearance.
„ Phenotype: Expression of Proteins
„ DNA encodes the information for making
protein and the resulting expression of the
proteins makes us who and what we are.
Hereditary Determinants
¾ Principle of
segregation
¾ Homozygous
individuals have two
copies of the same
allele for one gene
¾ Heterozygous
individuals have two
different alleles for
the same gene
From: www.prenhall.com/freeman/biology
How to Read a Punnett Square
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Examples of Genetic Inheritance:
Incomplete Dominance
„ Genetic condition
where neither allele is
fully expressed as a
heterozygote (F1
generation).
„ The heterozygote is
expressed as an
intermediate
phenotype.
Examples of Genetic Inheritance:
Codominance
„ Condition where two
alleles have a “shared
dominance”.
„ The I gene yields 4
blood types:
„ A, B, AB, or O
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Examples of Genetic Inheritance: Multiple Alleles
and Polygenic Inheritance
„ Multiple alleles: three or
more alleles of the same
gene existing in a
population.
„
ABO alleles
„ Polygeneic inheritance:
one trait that is
determined by many
genes.
„
Height, weight, hair
color, skin color, etc.
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On To Molecular Biology…
Chromosomes
„
„
„
„
Genetic Material
Seen when cell is about to divide
Contains a particular sequence of genes
Humans have 23 matched pairs of
chromosomes
„ 46 chromosomes total (2n)
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Karyotype
„ A picture of the chromosomes in a cell that is used to
check for abnormalities.
„ A karyotype is created by staining the chromosomes
with dye and photographing them through a
microscope.
„ Chromosomes occur in homologous pairs.
„ Same size, shape, centromere location.
„ Same banding pattern, same genes.
„ Karyotype arranges homologous pairs of
chromosomes from largest to smallest.
„ Some chromosome defects can be detected by
karyotyping.
The Cell Cycle
„ Two main phases in the cycle
„ Interphase (G1, S and G2) – cell growth and
DNA replication
„ Mitotic phase (M) – cell division
„ Four stages of the Mitotic phase
„ Prophase
„ Metaphase
„ Anaphase
„ Telophase and cytokinesis
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Gap 1
cell growth
Mitosis vs. Meiosis
„ Mitosis
„ Growth and repair
„ Final number of cells=2
„ No genetic variation
„ Number of chromosomes=46
„ Meiosis
„ Reproduction
„ Final number of cells=4
„ GENETIC VARIATION
„ Number of chromosomes=23
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X-Linked Inheritance
„ Certain conditions are
called X-linked conditions
because they stem from
dysfunctional genes on the
X chromosome.
„ Men are more likely than
women to suffer from these
types of conditions because
they only have one X
chromosome.
„ X-linked disorders include:
„
„
„
Hemophilia
Duchenne muscular
dystrophy
Red-green color blindness
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Autosomal Genetic Disorders
„ Autosomes: chromosomes other than X and Y
chromosomes.
„ Autosomal recessive disorders:
„
„
„
„
„
„
Albinism
Sickle-cell anemia
Cystic fibrosis
Phenylketonuria
Tay-Sachs disease
Werner syndrome
„ Both parents must have the allele to have a child
born with the condition.
not
Autosomal Genetic Disorders
„ Autosomal dominant disorders:
„ Polydactyly
„ Campodactyly
„ Huntington disease
„ ALS – Lou Gehrig disease
„ Single “faulty” allele causes damage even
with a “good” allele present.
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Tracking Traits with Pedigrees
„ Geneticists can create family tree diagrams
or pedigrees, which can be used to
determine if a disorder is dominant or
recessive, and the probability of future
inheritance.
Let’s Practice!
I
II
III
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Chromosome Abberations
„ Polyploidy
„ Abberations in the number of chromosome
sets.
„ Animals and many plants are normally
diploid.
„ Polyploidy occurs when one or more sets of
chromosomes are added to the genome of a
diploid organism.
„ Lethal condition in humans
„ Some polyploid plants may be more robust (ex:
wheat).
Chromosome Abberations
„ Aneuploidy
„ Abberations in the chromosome number.
„ Aneuploidy is caused by non-disjunction
„ Non-disjunction: The failure of homologous
chromosomes or sister chromatids to separate
during meiosis.
„ Genetic disorders caused by abnormal
chromosome number:
„ Down syndrome (trisomy 21)
„ Turner syndrome
„ Klinefelter syndrome
Down Syndrome
„ Most common form of aneuploidy in
human births.
„ Most trisomy 21 is the result of nondisjunction during egg formation.
„ Detected using karyotype analysis.
„ Frequency of non-disjunction (and Down
syndrome) increases with the age of the
mother.
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Turner Syndrome
„ Abnormal number of sex chromosomes.
„ Women and girls with Turner syndrome
have only one X chromosome
(monosomy).
„ In 75-80% of cases, the single X
chromosome comes from the egg, because
the sperm that fertilized the egg was
missing a sex chromosome.
Klinefelter Syndrome
„ Abnormal number of sex chromosomes.
„ Men and boys with Klinefelter syndrome
have a Y chromosome and 2 X
chromosomes (trisomy).
„ In about half of Klinefelter cases, the extra
X chromosome is from the egg, while in
the other half of cases, the extra X
chromosome is from the sperm.
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