Genetics and Heredity
Chapter 8
Mendel Studied 7 Characters in
the Garden Pea (Pisum sativum)
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Flower color.
Flower position.
Seed color.
Seed shape.
Pod color.
Pod shape.
Stem length.
Mendel’s Methods
• Cross-pollination- the
transfer of pollen from one
plant to the stigma of
another.
– Self-pollination
– Artificial cross-pollination
• Monohybrid crosses- an
experimental cross
between individuals that
differ by a single trait.
• First (F1) and second (F2)
generations.
Mendel’s F1 Observations
• One of the traits
could be seen in the
F1 generation=
Dominant
• One of the traits
could not be seen in
the F1 generation=
Recessive
100% Purple
Genetic Terminology
• Phenotype- an organisms
traits.
• Genotype- an organisms
genetic makeup.
• Homozygous- identical
alleles for a gene.
• Heterozygous- two
different alleles for a
gene.
Genetic Terminology #2
• Allele- one of 2 or
more alternative forms
of the same gene.
• Gene- a sequence of
DNA that codes for a
protein.
• Locus- the position on
a chromosome
occupied by a gene.
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Mendel’s F2 Observations
• Flower color
– Purple:white
705:224
3:1
Mendel’s
Dihybrid
Cross
• 315:108:101:32
= 9:3:3:1
Mendel’s Work Yielded
These Genetic Rules
• Alternative versions of genes (different alleles)
account for variations in inherited characters.
• For each character an organism inherits two
alleles, one from each parent.
• If two alleles differ, then one, the dominant allele
is fully expressed in the organism’s appearance.
• The two alleles for each character segregate
during gamete production.
• Alleles of a gene segregate independently of the
alleles of other genes.
Punnett Squares and the Testcross
• Punnett square- a
diagram used to predict
the result of a genetic
cross.
• Testcross- a genetic
experiment used to
determine an organisms
genotype.
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Incomplete Dominance
• Incomplete dominance- type
of inheritance in which the F1
is intermediate in phenotype
between the parents.
• Neither allele is dominant.
• Self-pollination of the F1
yields a 1:2:1 F2 population.
Continuous Variation
• Continuous variation- a gradation in
phenotype; indicates that a trait is controlled
by two or more genes.
– Polygenic inheritance.
Linkage
• Linkage- the tendency for
certain genes to be
inherited together, owing to
the fact that they are
located on the same
chromosome.
• Linked genes- genes that
are inherited together.
Genetically Engineered Rice
Genetically Modified Rice
Genetic Engineering
• Genetic Engineering- the
technique of removing,
modifying, or adding
genes to a DNA molecule.
– Improvements in crops
• Longevity
• Resistance to insects
• Resistance to herbicides
Transgenic Plants
• Tomato with BT
gene and without.
• Transgenic tomatoes
with and without
etr1-1 gene.
• Petunia with and
without etr1-1 gene.
• Tobacco with and
without a cytokinin
gene.
Transfer of Genes
Agrobacterium tumefaciens
Genomics
• Genomics- a field of genetics that attempts to
understand the content, organization, function, and
evolution of genetic information in a whole organism.
Arabidopsis thaliana
Genome
• Genome- all of
the genetic
information of
an organism.