1. Principles of Heredity

2. Genetics
The study of heredity, how traits are passed from one generation to the next

3. Gregor Mendel ~ Father of Genetics
Mini Biography Video

4. Gregor Mendel Discovered the Basic Principles of Heredity
19th century monk and teacher
Predicted how traits are transferred from one generation to next

5. Mendel designed experiments using pea plants in the
Mendel designed experiments using pea plants in the
monastery garden

6. Male part of flower makes Female part of flower makes
pollen (sperm cells)
Female part of flower makes
ovaries (egg cells)

7. In pea plants, the pollen normally joins with an egg from the same plant (= self-pollinating) so seeds have “one parent”

8. MENDEL’S PEA EXPERIMENTS
Mendel started his experiments with peas that were true breeding
if allowed to
self-pollinate
they would produce
offspring identical
to themselves.

9. MENDEL’S PEA EXPERIMENTS
Mendel cross-bred plants by removing pollen
making parts from one plant and adding pollen
from another plant

10. MENDEL’S PEA EXPERIMENTS
This allowed him to
experiment with plants
having different
characteristics and
study the results

11. A specific characteristic is called a trait
Mendel studied 7 traits in peas
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12. Parental generation (P1)
MENDEL’S EXPERIMENTS
Parental generation (P1)
Filial generation
(F1 = offspring)

13. Mendel Successes
Successful b/c studied only one trait at a time to control variables
Analyzed his data mathematically

20. What’s going on? The white flower trait had reappeared.
Mendel repeated for other traits and in every case he found that one trait seemed to disappear in the 1st generation only to reappear unchanged in ¼ of the 2nd generation.

21. one factor must be able to HIDE the other
Mendel decided that there must be a pair of factors that control each trait and that
one factor must be able to HIDE the other

22. We now know that Mendel’s “factors” are genes carried on
the pair of homologous chromosomes

23. gene (trait) are called alleles
Different versions
for a
gene (trait) are called alleles

24. Alleles = green, brown, blue
Trait = eye color
Alleles = green, brown, blue

25. Mendel’s Law of Dominance
Some alleles are dominant (trait is expressed)
Other alleles are recessive (only expressed if dominant allele is absent)
Ex: Purple & white flowers

26. All F1 plants received a purple allele for color and a white allele
All F1 plants received a purple allele for color and a white allele. Which allele is dominant?

27. Why did the recessive trait disappear in the F1 generation and reappear in the F2?

28. The pattern corresponds
to the movement of
chromosomes during
MEIOSIS
Image modified from:

29. Homologous chromosomes
REMEMBER…
Homologous chromosomes
separate during
ANAPHASE I
= SEGREGRATION
Image modified from:

30. EXPLAINING Mendel’s Results LAW OF SEGREGRATION:
alleles are separated
when the P1 plants made gametes
Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

31. EXPLAINING Mendel’s Results
F1 offspring received an allele for purple color from their purple parent and an allele for white color from their white parent.
The F1 plants ALL look purple but are carrying an
allele for white color
Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

32. EXPLAINING Mendel’s Results
When these gametes combined to make the F2 generation, the trait reappears in ¼ of the offspring
Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006

33. How would you answer?

34. Which of these are genetically identical?
A) Homologous chromosomes B) Sister Chromatids C) Neither

35. Which of these will pair up to form chromosomes during meiosis?
A) Homologous chromosomes B) Sister chromatids C) Chromatids pair at random, so it’s impossible to predict

36. An allele is:
a) another word for a gene b) a homozygous genotype c) a heterozygous genotype d) one of several possible forms of a gene

37. DOMINANT/RECESSIVE
Dominant allele is represented by a capital letter. (usually the first letter of the trait)
Recessive allele is represented by the SAME letter except in lower-case.
EX: (Trait: height)
Tall = T
Short = t; not s for short

38. Misconceptions About Dominant Alleles

39. The genetic makeup (set of 2 alleles) of an organism is its genotype
Genotype & Phenotype
The genetic makeup (set of 2 alleles) of an organism is its genotype
The physical appearance of an organism is its phenotype

40. Genotype vs. Phenotype

41. Talk to a Partner: Determine the genotype and phenotype of each flower

42. HOMOZYGOUS & HETEROZYGOUS
When both alleles in the pair are the same, the organism is homozygous (purebred)
EX: TT or tt
When both alleles in the pair are different, the organism is heterozygous (hybrid or carrier)
Ex: Tt

43. Which chromosome set is heterozygous?

44. Cornell Summary