Gregor Mendel 1822-1884 - Weeblymarandoscience.weebly.com/.../gregor_mendel_pwpt_notes.pdf•Mendel...
Transcript of Gregor Mendel 1822-1884 - Weeblymarandoscience.weebly.com/.../gregor_mendel_pwpt_notes.pdf•Mendel...
Gregor Mendel
1822-1884
• Priest who did scientific research
• Father was a farmer, mother was the daughter
of a gardener
• Crossed pea plants
• Had no knowledge of DNA, genes, or
chromosomes
• Described the units of inheritance and how
they pass from one generation to the next
• Not recognized during his lifetime
Why Peas?
• Easy to grow.
• Develop quickly.
• Traits have only two
distinguishable forms.
–Ex- tall or short
• Pea plants use parts of their
flowers to reproduce.
• Male part produces pollen,
female part produces eggs.
• When pollen fertilizes an egg,
a seed for a new plant is
formed.
• The original plants crossed are called the P (parent) generation.
• The offspring are called the F1 (first filial) generation.
–Example: Mendel crosses a tall pea plant with a short pea plant. What do you think the F1 generation will look like?
Monohybrid Cross
Parental generation (P1)
Tall X Short
F1
All Tall
• All of the offspring looked
like only one of the
parents. The
characteristics of the
other parent seemed to
disappear.
–Did it really disappear?
–No! The short trait was
hidden by the tall trait.
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Monohybrid Cross
Parental generation (P1)
Tall X Short
F1
All Tall
F2
1/4 Short : 3/4 TallFigure 4.3
Figure 4.2
• Mendel determined that there is some factor being passed from parent to offspring.
• Scientists now know that these factors are called genes found on chromosomes.
• The different forms of a gene are called alleles.
Principle of Dominance• Some alleles are dominant, some are recessive.
–A dominant allele for a certain trait will always be
expressed over a recessive allele.
–A recessive allele will only be expressed when no
dominant allele is present.
Representation of Dominant and Recessive Alleles
• A capital letter symbolizes
a dominant allele.
• The lower case form of the
same letter symbolizes the
recessive allele.
–Example: The allele for
tallness (T) is dominant and
the allele for shortness (t) is
recessive.
• Genotype- genetic makeup of the organism
–If both alleles acquired by the offspring are the
same, it is said to be homozygous. (ex- TT or tt)
–If both alleles acquired are different, it is said to be
heterozygous or hybrid. (ex- Tt)
• Phenotype- physical appearance of an organism
–Ex- tall or short
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Figure 4.4
Punnett Square
A Punnett square is used to represent possible combinations
of genes in gametes and how they may combine in offspring
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BB
Bb
Bb
bb
25%
25%50%
75%25%
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Bb
Bb
Bb
Bb
B B
b
b
0%
0%100%
100%0%
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Bb
Bb
bb
bb
B b
b
b
0%
50%
50%
50%
50%