The document discusses heritable variation and patterns of inheritance. It describes how traits are usually inherited in particular patterns from parents to offspring. Gregor Mendel performed experiments with pea plants to analyze inheritance patterns and deduce fundamental genetic principles. Through his work, he developed hypotheses about alternative gene forms (alleles), genetic makeup, gamete formation, and dominant and recessive alleles.

1. HERITABLE VARIATION & PATTERNS OF INHERITANCE
•“Wild type” traits are traits most commonly
found in nature
Figure 9.2
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2. • Various traits exist in organisms
x  These traits are usually inherited in particular
patterns
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3. Parents:
X X
Parents:
Wild-type Wild-type Wild-type Sky-blue
First- wild-type
Offspring: All
All Wild-type generation
offspring:
Matings
Second-
generation
(a) Offspring from the mating offspring: 3/4 and /4
1
of two wild-type birds
Wild-type Sky-blue
(b) Two generations of offspring from the
mating of a wild-type with a sky-blue bird
Figure 9.3
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4. Mendelian Genetics
• Gregor Mendel
G  Was the first to
analyze patterns of
inheritance
–  Deduced the
fundamental
principles of
genetics
Figure 9.4
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5. In an Abbey Garden
• Mendel studied
garden peas
e  These plants
are easily
manipulated
–  These plants
can self-fertilize
stamen
Stamen
Carpel
carpel
Figure 9.5
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6. Mendelian White
1 Removed
Genetics stamens from
purple flower
• Mendel
carried out Stamens
some cross- Carpel 2 Transferred pollen
from stamens of
fertilization Parents
(P)
Purple white flower to
carpel of purple
flower
3 Pollinated carpel
matured into pod
4 Planted seeds
from pod
Offspring
(F1)
Figure 9.6
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7. Mendelian Genetics
• He also created true-breeding varieties of
plants
Mendel then crossed two different true-breeding
varieties, creating hybrids
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8. Mendel’s Principles of Segregation
• Mendel performed many experiments
 He tracked several characteristics in pea plants from
which he formulated several hypotheses
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9. Traits in Pea Plants
Dominant Recessive Dominant Recessive
Pod shape Inflated Constricted
Flower color Purple White
Pod Color Green Yellow
Flower position Axial Terminal
Seed color Yellow Green
Stem length Tall Dwarf
Seed shape Round Wrinkled
Figure 9.7
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10. Monohybrid Crosses
P Generation
• A monohybrid (true-breeding
parents)
Purple White
cross is a cross flowers flowers
between parent F1 Generation All plants have
plants that differ purple flowers
in only one among F1
plants
characteristic (F1 × F1)
Fertilization
F2 Generation
1
/4 of
plantsHave
3
/4 of plants have whiteflower
purple flowers s
(a) Mendel’s crosses tracking one
characteristic (flower color) Figure 9.8a
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11. • Mendel developed four hypotheses from the
monohybrid cross:
– 1) There are alternative forms of genes, now
called alleles
– 2) For each characteristic, each organism has
two genes
– 3) Gametes carry only one allele for each
inherited characteristic
– 4) Alleles can be dominant or recessive
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12. Mendel’s Results
Genetic makeup (alleles)
P plants PP PP
• Including a
Gametes All P All p
Punnett
square F1 plants:
(hybrids) All Pp
Gametes 1
/2 P 1
/2 p
Eggs P P Sperm
F2 plants:
p PP p
Phenotypic ratio Pp Pp
3 purple : 1 white
pp
Genotypic ratio
1 PP : 2 Pp : 1 pp
(b) Explanation of the results in part (a) Figure 9.8b
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13. Describing Traits:
• Phenotype
s  An organism’s physical traits
• Genotype
•  An organism’s genetic makeup
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14. Mendel’s Principle of Segregation
 Pairs of alleles segregate (separate) during
gamete formation; the fusion of gametes at
fertilization creates allele pairs again
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15. Genetic Alleles & Homologous
Chromosomes
• Homologous chromosomes:
&  Have genes at specific loci
(locations on the chromosome)
–  Have alleles of a gene at the
same locus
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16. Genetic Alleles & Homologous Chromosomes
Homologous chromosomes:
Gene loci
Dominant
allele
P a B
P a b
Recessive
allele
Genotype: PP aa Bb
Homozygous Homozygous Heterozygous
for the for the
dominant allele recessive allele
Figure 9.9
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17. Genetic Alleles & Homologous
Chromosomes
• Homozygous
s  When an organism has identical alleles for a
gene
• Heterozygous
-  When an organism has different alleles for a
gene
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