1. Chapter
11
Introduction to
Genetics

2. 11- 1 The Work of Gregor Mendel
• Every living thing – plant or animal,
microbe or human being – has a set
of characteristics inherited from its
parents
• Since the beginning of recorded
history, people have wanted to
understand how that inheritance is
passed from generation to generation

3. Genetics
• The scientific study of heredity

4. Gregor Mendel
• Austrian Monk
• Born 1822 in Czech
Republic
• Worked at monastery
and taught high school
• Tended the monastery
garden
• Grew peas and became
interested in the traits
that were expressed in
different generations of
peas

5. True breeding
• If allowed to self pollinate they
would produce offspring identical
to themselves
• He was also able to cross breed
peas for different traits

7. Genes and Dominance
• Mendel studied seven different
pea plant traits
• Each trait he studied had a
contrasting form

8. Pea Plant Traits

9. Genes and Dominance
• The offspring of crosses between
parents with different traits are called
Hybrids
• When Mendel crossed plants with
different traits he expected them to
blend, but that’s not what happened at
all.
• All of the offspring had the character of
only one of the parents

11. Mendel drew two conclusions
1. Inheritance is determined by
factors that are passed from
generation to generation – today
we call these factors genes

12. Alleles
• Different forms of a gene

13. Mendel’s 2 conclusion
nd
2. The Principal of Dominance
• Some alleles are dominant and
some are recessive

14. dominant
• Covers up the recessive form
Ex.) T = tall

15. recessive
• Gets covered up in the presence
of a dominant allele
Ex.) t = short

16. Segregation
• Mendel wanted to answer another
question
Q: Had the recessive alleles
disappeared? Or where they still
present in the F1 plants?
• To answer this he allowed the F1
plants to produce an F2 generation
by self pollination

17. P1 Parental F1 F2
Tall Short All Tall 3 tall : 1 short
75% tall
25% short

18. The F1 Cross
• The recessive traits reappeared!
• Roughly 1/4 of the F2 plants
showed a recessive trait

19. Explanation of the F1 Cross
• The reappearance indicated that at some point
the allele for shortness had been separated from
the allele for tallness
• Mendel suggested that the alleles for tallness
and shortness in the F1 plants were segregated
from each other during the formation of sex cells
or gametes
• When each F1 plant flowers, the two alleles
segregate from each other so that each gamete
carries only a single copy of each gene.
Therefore, each F1 plant produces two types of
gametes – those with the allele for tallness and
those with the allele for shortness

21. 11-2 Probability and Punnett
Squares
• Mendel kept obtaining similar
results, he soon realized that the
principals of probability could be
used to explain the results of
genetic crosses

22. Probability
• The likelihood that a particular
event will occur
• The way in which alleles
segregate is random like a coin
flip

23. Punnett Square Vocab
If you do not know the
following vocabulary words
you will fail miserably

24. Punnett Square
• Diagram used to determine
genetic crosses

25. Homozygous
• Organisms that have 2 identicle
alleles for a trait
Ex.) TT , tt

26. Heterozygous
• Have two different alleles for a
trait
Ex.) Tt

27. Phenotype
• Physical characteristics – (words)
Ex.) tall

28. Genotype
• Genetic make-up - (letters)
Ex.) Tt, TT, tt

29. 11-3 Exploring
Mendelian Genetics

30. • Mendel wondered if alleles segregate
during the formation of gametes
independently
• Does the segregation of one pair of alleles
affect the segregation of another pair of
alleles?
• For example, does the gene that
determines whether round or wrinkled in
shape have anything to do with the gene
for color?
• Must a round seed also be yellow?

31. All heterozygous 9:3:3:1 Ratio

32. Independent Assortment
• Genes that segregate
independently do not influence
each others inheritance

33. A Summary of Mendel’s Principles
• The inheritance of biological
characteristics is determined by
individual units known as
_______________. In organisms
Genes
that reproduce sexually,
_______________ are passed
Genes
from parents to offspring

34. A Summary of Mendel’s Principles
• In cases in which 2 or more forms of a
gene are present, some forms of the gene
may be _______________________ or
dominant
___________________________
recessive
• In most sexually reproducing organisms,
each adult has two copies of each gene –
one from each parent. These genes are
segregated from each other when
gametes are formed
• The alleles for different genes usually
segregate independently of one another

35. Incomplete Dominance
• When one allele is not dominant
over another
• Four o’clock flowers
• The heterozygous phenotype is
somewhat in-between the two
homozygous phenotypes

37. Codominance
• When both alleles contribute to
the phenotype of an organism
Ex.) Speckled Chickens

38. Multiple Alleles
• When more than two possible
alleles exist in a population
Ex.) blood type
• IA
Dominant
• IB
•i Recessive

39. Human Blood Types
Phenotype Genotype
A IAIA or IAi
B IBIB or IBi
AB IA I B
O ii

40. Polygenic Traits
• Traits controlled by two or more
genes
Ex.) eye color, skin color

41. Genetics and the Environment
• The characteristics of any organism,
is not only determined by the genes it
inherits
• Characteristics are determined by
interactions between genes and the
environment
• Ex.) genes may affect a plants height
but the same characteristic is
influenced by climate, soil conditions
and availability of water

42. Do Now
• Human hair is inherited by
incomplete dominance. Human
hair may be curly (CC) or straight
(cc). The heterozygous genotype
(Cc) produces wavy hair. Show a
cross between two parents with
wavy hair

43. Do Now
• A man is suing his wife on grounds of
infidelity. The man claims that the
child is blood type O and therefore
must be fathered by someone else.
Can he use this evidence in court if
he and his wife both have
heterozygous B genotypes?
• Show the cross of the two parents

44. 11 – 4 Meiosis

45. Objectives
• What happens during the events
of meiosis?
• What is the difference between
mitosis and meiosis?

46. Meiosis
• Gregor Mendel did not know
where the genes he had
discovered were located in the
cell
• Genes are located on
chromosomes
______________________ in the
cell ______________
nucleus

47. Mendel’s principles of genetics
require at least 2 things
1. Each organism must inherit… a
single copy of every gene from each
of its parents
2. When an organism produces its own
gametes… these two sets of genes
must be separated from each other
so that each gamete contains just
one set of genes

48. Chromosome Number
Ex.) fruit fly 8 chromosomes
• 4 from mom, 4 from dad
Ex.) Humans 46 chromosomes
• 23 from mom, 23 from dad

49. Homologous
• Chromosomes that each have a
corresponding chromosome from
the opposite sex parent

50. Diploid
• A cell that contains both sets
of homologous chromosomes
(2N)
–Body cells

51. Haploid
• A cell that contains only a single
set of chromosomes (1N)
– Sex cells (gametes)

52. Meiosis
• A process of reduction division
in which the number of
chromosomes per cell is cut in
half through the separation of
homologous chromosomes in
a diploid cell
–Makes sex cells

57. Meiosis usually involves 2 divisions
• Meiosis I
• Meiosis II

58. Meiosis I
• prior to meiosis I, each
chromosome is replicated
• The cells then begin to divide
similar to mitosis

59. Prophase I
• Each chromosome pairs with its
corresponding homologous
chromosome to form a structure
called a
Tetrad
_____________________ - has 4
chromatids

60. Crossing over
• When chromosomes exchange
portions of their chromatids and
results in the exchange of alleles

62. Crossing over
• Leads to new combinations of alleles
• The homologous chromosomes separate,
and 2 new cells are formed
• Although each cell now has 4 chromatids
something is different. Because each pair
of homologous chromosomes was
separated, neither of the daughter cells
has two complete sets of chromosomes
that it would have in a diploid cell
• The two sets have been shuffled

63. Meiosis II
• The two cells produced by
meiosis I now enter a second
meiotic division
• Unlike the 1st division, no
chromosomes are replicated
• Each cell’s chromosomes has 2
chromatids

64. Metaphase II
• 2 chromosomes line up in the
center of each cell

65. Anaphase II
• The paired chromatids separate

66. Telophase II
• Forms 4 daughter cells each with
2 chromatids
• These 4 daughter cells are now
haploid (N) – just 2 chromosomes
each

67. Gamete Formation
• In male animals, the haploid
gametes produced by meiosis are
called sperm
• In some plants they are called
pollen

68. Spermatogenesis

69. Gamete Formation
• In females, generally only one of
the cells produced by meiosis is
involved in reproduction
• This female gamete is called an
egg
• The other 3 cells that do not
receive as much cytoplasm as the
egg are called polar bodies

70. oogenisis

71. Comparing Mitosis and Meiosis
• Mitosis results in the production of
two genetically identical diploid
cells, whereas meiosis produces
four genetically different haploid
cells

72. Comparing Mitosis and Meiosis
Mitosis Meiosis
46 46
46 46 23 23 23 23

73. 11-5 Linkage and
Gene Maps

74. Gene Linkage
• When genes are located on the
same chromosome they are
inherited together (Linkage)
• It’s the chromosomes that assort
independently not individual
genes

75. • When genes are formed on the same
chromosome, this does not mean that
they are linked forever
• Crossing over during meiosis
sometimes separates genes that had
been on the same chromosome onto
homologous chromosomes
• Cross over events occasionally
separate and exchange linked genes
and produce new combinations of
alleles

76. Q: Why is this good?
A: Generates genetic diversity

77. Gene Maps
• 1911 Alfred Sturtevant
• hypothesized that the further apart
genes were, the more likely they were
to be separated by a crossover in
meiosis
• the rate at which linked genes were
separated and recombined could then
be used to produce a “map” of
distances between genes

78. Gene map
• Shows the location of each gene