Transcript Mendelian Genetics

Mendelian Genetics
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Genetics
 Genetics:
The study of heredity.
 Trait: A heritable characteristic.
 Gene:
a
portion of DNA that determines a
characteristic
 Composed of nucleotides
 Locus = location on chromosome
 2 per characteristic on autosomes
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Single Gene Inheritance Patterns
 Allele:
 sequence
of genetic material
occupying the same gene
locus on homologous
chromosomes
 Or…alternative forms of the
same gene
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Single Gene Inheritance
 Genome:
set of all genes
necessary to specify an
organism’s characteristics
 Genotype: listing of all genes
present
 Phenotype: the way alleles
express themselves – i.e. what
you see
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Pea Soup?
 Experiments
done by Gregor Mendel
using garden pea plants helped
demonstrate how traits are
inherited.
 A purebred individual receives the
same characteristics from both
parents.
 A hybrid individual receives
different forms of a trait from each
parent.
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Gene Expression
 Dominant
allele: masks effect of other
alleles
 Recessive allele: masked by dominant
alleles
 Homozygous: 2 identical alleles
 Heterozygous: 2 different alleles
Recessive alleles are not less likely to be
inherited, however they must be
homozygous to be expressed.
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Mendel’s Laws of Heredity
 Gregor
Mendel: 1822-1884
 Followed one trait at a time.
 Used highly visible traits; therefore
easy to track his research.
 Since pea plants self-pollinate, may
develop plants that are homozygous
for many traits - Pure Line.
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Mendel Rediscovered
 Mendel’s
work was not recognized
during his life; his unpublished studies
were “resurrected” in the early 1900’s.
 His work is remarkable in that he did not
know anything about genes, much less
chromosomes, yet was able to reason
the existence of alleles through his
careful observations and recording of
data. This is real science.
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Mendel’s observations
 Mendel
observed 7 traits of pea plants,
alone and in various combinations:
Flower Color
 Flower Position
 Pea Color
 Pea Shape
 Pea Pod Color
 Pea Pod Shape
 Height of Pea Plant

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Mendel’s Laws of Heredity
 Mendel artificially pollinated
plants to produce crosses and
documented results.
 All offspring were identical to
parents – unexpected finding.
 Crosses of offspring yielded: 3/4
showed phenotype of dominant
gene.
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Mendel’s Laws of Heredity
Law
of Dominance:
when an organism has 2
different alleles for a given
trait, the allele that is
expressed is considered
dominant. The other
allele is recessive.
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Mendel’s Laws of Heredity
Law
of Segregation: when
gametes are formed by a
diploid organism, the alleles
that control a trait separate
from one another into
different gametes, retaining
their individuality.
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Mendel’s Laws of Heredity
Law
of Independent
Assortment: Members of
one gene pair separate
from each other
independently of the
members of other gene
pairs.
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