- Gregor Mendel conducted genetic experiments with pea plants to study heredity and traits such as plant height, flower color, seed shape and color. He found that traits are determined by discrete factors called genes. - In his experiments, Mendel observed that some traits were dominant over others in hybrid offspring. When he allowed these hybrids to self-pollinate, the recessive traits that had been masked reappeared in a predictable ratio in the next generation. - Mendel's experiments supported the idea that genes assort independently during reproduction, resulting in new combinations of traits in offspring. His findings established foundations of classical genetics and heredity.

1. Genetics

2. The Science of Heredity
• The scientific study of heredity is
called
• GENETICS

3. Gregor Mendel
Pea Plant Experiment
• Gregor Mendel chose pea plants to
conduct genetic experiments
because of their plant life special
properties. For example:
• When pollen fertilizes an egg cell, a
seed for a new plant is formed.
• Pea plants normally reproduce by
self-pollination.

4. Gregor Mendel
Pea Plant Experiment
• What does it mean when pea plants
are described as being true-
breeding?
• If the plants are allowed to self-
pollinate, they would produce
offspring identical to themselves.

5. Gregor Mendel
Pea Plant Experiment
• To perform his experiments, how did
Mendel prevent pea flowers from
self-pollinating and control their
cross-pollination?
• He cut away the pollen-bearing
male parts of a flower and dusted
that flower with pollen from another
plant.

6. Gregor Mendel
Pea Plant Experiment
• Traits - Specific characteristics that
vary from one individual to another
• Hybrids-The offspring of crosses
between parents with different traits
• Genes - Chemical factors that
determine traits
• Alleles - The different forms of a
gene

7. Alleles
State the principle of dominance.
• Some alleles are dominant and
others are recessive.

8. Alleles
• An organism with a recessive allele
for a particular form of a trait will
NOT always exhibit that form.

9. Characteristics of Traits
• In Mendel’s Pea experiment traits
controlled by dominant alleles were
tall plants and the yellow flowering
traits.

10. Characteristics of Traits
• How did Mendel find out whether the
recessive alleles were still present in
the F1 plants?
• He allowed the F1 plants to produce
an F2 generation by self-pollination.

11. Characteristics of Traits
• About one fourth of the F2 plants
from Mendel’s F1 crosses showed
the trait controlled ______ by the
allele.
• recessive

12. Characteristics of Traits
• Mendel assumed that a dominant
allele had masked the corresponding
recessive allele in the F1 generation.

13. Characteristics of Traits
• At some point, the allele for
shortness was segregated, or
separated, from the allele
for tallness.

14. Characteristics of Traits
• What are gametes?
• They are the sex cells.

15. In the diagram above, the dominant allele is
represented by ___and the recessive allele is
represented by __ .

16. Probability and Punnett
Squares

17. Probability
The likelihood that a particular event
will occur is called_______.
• Probability

18. Probability
Circle the letter of the probability that a
single coin flip will come up heads.
• a. 100 percent
• b. 75 percent
• c. 50 percent
• d. 25 percent

19. Probability
• Is the following sentence true or
false?
• The past outcomes of coin flips
greatly affect the outcomes of future
coin flips.
• False

20. Probability
• Why can the principles of probability
be used to predict the outcomes of
genetic crosses?
• The way in which the alleles
segregate is completely random, like
a coin flip.

21. Punnett Squares
• How do geneticists use Punnett
squares?
• Punnett squares can be used to
predict and compare the genetic
variations that will result from a
cross.

22. Punnett Square
Complete the Punnett square to show
the possible gene combinations for the
F2 offspring.

23. Allele Types
• Homo - Same
• Hetero - Opposite
• Pheno – Physical
• Geno - Genetic

24. Allele Types
Definitions
• Organisms that have two identical alleles
• particular trait (TT or tt) Homozygous
• Organisms that have two different alleles
• same trait (Tt) Heterozygous
• Physical characteristic of an organism
Phenotype
• Genetic makeup of an organism (Tt)
Genotype

25. Gene Expression
Are the following sentences true or
false?
- Homozygous organisms are true
breeding for a particular trait.
• False
- Plants with the same phenotype
always have the same genotype.
• False

26. Probability and Segregation
• b. The F2 ratio of tall plants to short
plants produced in a cross between
two hybrid tall pea plants (Tt) is 3 tall
plants for every 1 short plant.
• c. Mendel observed that about 3⁄4 of
the F2 offspring showed the
dominant trait.
• d. Segregation occurs according to
Mendel’s model.

27. Probability
• In Mendel’s model of segregation,
what was the ratio of tall plants to
short plants in the F2 generation?
• The ratio was 3 : 1.

28. Probability
• Is the following sentence true or
false?
• Probabilities predict the precise
outcome of an individual event.
• False

29. Probability
• How can you be sure of getting the
expected 50 : 50 ratio from flipping a
coin?
• You must flip the coin many times.

30. Probability
17. The _____ number of offspring
from a genetic cross, the closer the
resulting numbers will get to
expected values.
• Larger

31. Probability
Is the following sentence true or false?
• The ratios of an F1 generation are
more likely to match Mendelian
predicted ratios if the F1 generation
contains hundreds or thousands of
individuals.
• True

32. Exploring Mendelian
Genetics

33. Independent Assortment
• In a two-factor cross, Mendel
followed______ different genes as
they passed from one generation to
the next.
• 2

34. Independent Assortment
• Write the genotypes of the true-
breeding plants that Mendel used in
his two-factor cross.
• Phenotype Genotype
a. round yellow peas __RRYY_
b. wrinkled green peas __rryy_

35. Independent Assortment
• Heterozygous dominant with round
yellow peas, best describes the F1
offspring of Mendel’s two-factor
cross.

36. Independent Assortment
• Is the following sentence true or
false?
• The genotypes of the F1 offspring
indicated to Mendel that genes
assort independently.
• False

37. Independent Assortment
How did Mendel produce the F2
offspring?
• He crossed F1 plants to each other.

38. Independent Assortment
• Circle the letter of the phenotypes
that Mendel would expect to see if
genes segregated independently.
• a. round and yellow
• b. wrinkled and green
• c. round and green
• d. wrinkled and yellow

39. • What did Mendel observe in the F2
offspring that showed him that the
alleles for seed shape segregate
independently of those for seed
color?
• He observed F2 offspring that had
combinations of phenotypes—and
therefore combinations of alleles—
not found in either parent.

40. Exceptions to Mendel´s
principles
• Incomplete Dominance
• One gene, many traits
• Many genes, one trait
• Environment influences

41. INCOMPLETE
DOMINANCE
• When each allele has its own degree
of influence.
• A cross of red snapdragon flower
with a white snapdragon flower
produces only pink snapdragon
flowers

42. SNAPDRAGON PUNNET
SQUARE

43. ONE GENE, MANY TRAITS
• One gene can influence more than
one trait.
• Example: The white tiger has one
gene for its white fur, which also
influence the blue eyes color.

44. Many Genes, One trait
• Some traits, such as the
color of your skin, hair,
and eyes, are influenced
by several genes acting
together.
• Example: different eye
color shades of blue or
different skin color.

45. Environment Influence

46. Environment Influence
• A polymorphism in the monoamine oxidase
gene promoter can moderate the association
between early life trauma and increased risk
for violence and antisocial behavior. Low
MAOA activity is a significant risk factor for
aggressive and antisocial behavior in adults
who report victimization as children.