Genetics

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Genetics The study of how characteristics are
passed from one generation to the next. During
the process of fertilization All offspring
get ½ of their genetic information from
their mother ½ of their genetic
information from their father.
(exception self fertilization) It is this
combination of information that leads to
genetic variation
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Structures of genetics Gene A section of
DNA that codes for a specific trait.
Locus The location of a gene on a
chromosome. Allele A form of a gene
A gene locus
A pair of alleles
3 gene pairs
Chromosomes
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History of Genetics First really studied by a
monk Gregor Mendel Looked at pea
plants Cross fertilized different pea
plants with different physical characteristics
(Phenotypes) Noticed that he could
predict the of offspring that would have a
certain Phenotype. Concluded that
each parent must contribute a specific genetic
characteristic (Genotype)
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Cross fertilization
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Punnette Square Mendel was able to predict the
possible offspring using the Punnette Square
method. What did he assume 1. Each trait has
2 possible alleles 2. Each offspring gets 1
allele from each parent 3. All alleles
sort randomly and independent from each
other.
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Punnette Square cont... Some alleles can hide
the trait of its pair, these are said to be
Dominant ( A ) If an alleles trait gets
hidden by another allele, it is said to be
Recessive ( a ) If an organism has the same
alleles, for a trait, they are said to be
Homozygous (AA, aa) If an organism has 2
different alleles for the same trait, they are
said to be Heterozygous (Aa)
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Monohybrid cross
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Trait flower color Pink dominant
Both parents are heterozygous for
the trait White recessive P1
Monohybrid Cross
A
a
a
A
Female parent
Male Parent
Offspring Phenotype ratio 3 pink 1
white Genotype ratio 1 AA 2 Aa 1 aa
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The Punnette square can also be used to look
at more than 1 trait! Why? Because each trait
is independent of the other traits!! A 1
trait cross Monohybrid A 2 trait cross
Dihybrid A 3 trait cross Trihybrid
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AABB purple- flowered tall
aabb white- flowered dwarf
AB
F1 OUTCOME All F1 plants purple-flowered,
tall (AaBb heterozygotes)
AaBb
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