Mendelian

1
Mendelian Genetics
2
What is Genetics?
3
A. Devoted to understanding how characteristics
are transmitted from parents to offspring.
1. Founded with the work of Gregor Johann Mendel
a. An Austrian monk
b. Conducted research on heredity
i. heredity-the transmission of characteristics
from parents to offspring
c. Most famous for his experiments with garden
peas
4
Mendels Garden Peas
5
A. Observed 7 characteristics of pea plants
1. Each characteristic occurred in 2 contrasting
traits (a total of 14 individual traits)
a. Traits-a specific characteristic that varies
from one individual to another
i. plant height (long or short stem)
ii. flower position along stem (axial or
terminal)
iii. pod color (green or yellow)
iv. pod appearance (inflated or constricted)
v. seed texture (smooth or wrinkled)
vi. seed color (green or yellow)
vii. flower color (purple or white)
b. Mendel only observed 1 trait at a time!
6
(No Transcript)
7
B. Collected seeds and carefully recorded
characteristics of the plant the seeds came from.
C. Planted new seeds and recorded characteristics
D. Wanted to find explanations for variations
from generation to generation
1. Example Plants w/ purple flowers usually
produced plants with purple flowers but
sometimes they produced plants w/ white flowers.
2. Example Tall plants usually produced tall
plants but sometimes short plants
8
E. Controlled how plants were pollinated
1. Pollination-occurs when pollen produced in
the male reproductive parts of the flower
(called anthers) are transferred to the female
reproductive part of the flower (called stigma)
9
(No Transcript)
10
a. Self-Pollination
i. occurs when pollen is transferred from the
anthers of a flower to the stigma of either the
same flower or a flower on the same plant
ii. pea plants usually undergo self-pollination
b. Cross-Pollination
i. occurs when flowers of 2 separate plants
pollinate
11
2. Mendel started with plants pure for a trait
a. Always produced offspring with that trait
b. Allowed plants to self-pollinate for several
generations
c. Ended up with 14 strains of pea plants, 1 for
each of the observable traits
i. called these plants P1 generation
3. Once he had pure strains for each trait, he
cross- pollinated them
a. Cross-pollinated plants with contrasting
traits (green pods or yellow pods, etc.)
b. He actively prevented self-pollination by
manually transferring the anthers of one flower
to the stigma of another flower on a different
plant
12
i. removed anthers from the plant in which you
want to cross-pollinate so that the plant
cannot "accidently self-pollinate -crossing
yellow pod plants with green pod plants
remove anthers from the green-podded plant
flowers, added pollen (from anthers) of
yellow- podded plant flowers to green pod plant
flowers
c. When new plants matured, he recorded the of
each type of offspring by each P1 plant
(remember, 2 plants 2 P1 plants)
i. first generation plants are called F1
generation (first filial)
13
d. Allowed F1 generation plants to
self-pollinate and collected the seeds
i. second generation plants are called F2
generation (second filial)
e. Example
P1 generation green-podded plants x
yellow-podded plants F1 generation all
green-podded plants F2 generation 3/4
green-podded plants 1/4 yellow-podded
plants
14
e. Example
P1 Generation
F1 Generation
¾ green-podded plants ¼ yellow-podded plants
F2 Generation
15
(No Transcript)
16
Mendel's Results Conclusions
17
A. Observations lead him to hypothesize that
something within the pea plants controlled the
characteristics
1. Called these controls factors
a. Hypothesized each trait was inherited by
means of a separate factor
b. Since characteristics had 2 alternative
forms, he believed there must be a pair of
factors for each controlling trait dominant
and recessive
i. dominant factor-controlled the outcome of the
F1 generation by masking or "dominating" the
other possible trait
Example all green-podded plants in the F1
generation dominant factor
18
ii. recessive factor-did not show up again until
the F2 generation and showed no observable
effect on an organism's appearance when it was
paired with a trait controlled by a dominant
factor
Example yellow-podded plants in the F2
generation
iii. Be aware that dominant alleles
-do NOT subdue a recessive allele (is no
interaction of the alleles themselves)
-Dominant alleles are not necessarily more
common
19
c. Paired factors (alleles) separate during the
formation of gametes (reproductive cells) due
to the Law of Segregation (see separation
below in punnett squares)
i. gametes receive only 1 factor from each pair
ii. when gametes combine during fertilization,
the offspring will have 2 factors controlling a
specific trait
20
d. Mendel also crossed plants that had 2
different characteristics
i. Genes that occur separately do not influence
each others inheritance
ii. The Law of Independent Assortment states
that genes for different traits can segregate
independently during the formation of gametes
Example pea pod color and pod shape are
separate genes that occur independently from
one another. You can have a green pea pod that
is constricted or inflated or vice-versa.
21
What is Molecular Genetics?
22
A. Study of the structure and function of
chromosomes and genes.
1. Genes-the segment of DNA on a chromosome that
controls a particular hereditary trait occur
in pairs
a. Alternate forms (of the pair) are called an
allele (Mendel's "factors")
i. allele's are represented by letters dominate
allele's are capital letters, recessive
allele's are lower case letters -green pod
color is a dominant allele G -yellow pod color
is a recessive allele g

ii. remember that when gametes combine, the
offspring receives 1 allele (a factor for a
particular trait) from each parent
23
B. Genetic makeup of an organism
1. Consists of the alleles that the organism
inherits from its parents (1 from each parent)
a. Green pod plant-GG (2 dominant alleles) or Gg
(1 dominant, 1 recessive)
i. also known as complete dominance because the
dominant trait always masks over the recessive
trait
b. Yellow pod plant can be represented as gg (2
recessive alleles)

C. The appearance of an organism as a result of
its genotype
1. What the organism actually looks like (called
phenotype)
a. Example GG or Gg green-podded plant gg
yellow-podded plant
24
Green-podded plant Yellow-podded plant
GG or Gg
gg
25
D. Hybrids are offspring generated by crossing
parents with different traits
26
What is the Difference Between Homozygous and
Heterozygous?
27
A. Homozygous
1. Both alleles of a pair are alike
a. Example GG or gg for pod color
B. Heterozygous
2. Both alleles of a pair are different
a. Example Gg for pod color

28
How are Monohybrid Crosses Predicted?
29
A. A monohybrid cross occurs between individuals
that involves one pair of contrasting traits
(green pods vs yellow pods)
1. ExamplePure green-podded plant crossed with
a pure yellow-podded plant
a. Remember, those are P1 generation plants
2. Punnett Squares are used to help predict the
probability that certain traits will be
inherited by the offspring

a. Example of a P1 generation fertilizing to
produce F1 generation organisms
30
Punnett Square
The offspring genotypes are shown inside the 4
squares.
The parent alleles are shown outside of the
squares
31
B. Homozygous x Homozygous cross
1. Example GG x gg
32
Green-podded plant
Yellow-podded plant
33

• 100 probability of creating a heterozygous
  genotype (Gg) plants
• 100 probability of creating a phenotype of
  green-podded plants

34
C. Homozygous x Heterozygous cross
1. Example GG x Gg
35
Green-podded plant
Green-podded plant
36

• 50 probability of creating a homozygous dominate
  genotype (GG)
• 50 probability of creating a heterozygous
  genotype (Gg) plants
• 100 probability of creating a phenotype of
  green-podded plants

37
D. Heterozygous x Heterozygous cross
1. Example Gg x Gg
38
Green-podded plant
Green-podded plant
39

• 50 probability of creating a heterozygous
  genotype (Gg),
• 25 probability of creating a homozygous dominant
  genotype (GG)
• 25 probability of creating a homozygous
  recessive genotype (gg) plants
• 75 probability of creating a phenotype of
  green-podded plants
• 25 probability of creating a phenotype of
  yellow-podded plants

40
E. Testcross
1. An individual of unknown genotype is crossed
with a homozygous recessive individual
2. Can determine the genotype of any individual
whose phenotype is dominant
41
F. Incomplete Dominance
1. Occurs when 2 alleles influence the
phenotype, resulting in an appearance in
between the dominant and recessive trait.
a. Neither allele is dominant over the other so
a different looking phenotype appears
i. certain red flowering plants cross-pollinated
with certain white flowering plants produce
pink flowering plants two nuclei
G. Codominance
1. Occurs when both alleles for a gene are
expressed in a heterozygous offspring
a. Neither allele is dominate or recessive and
allele's don't blend
42
i. example ABO blood types A and B allele's
are codominate with the O being a recessive
allele.
43
ABO Blood Typing
44
H. Pleiotrophy
1. The phenomenon of one gene being responsible
for or affecting more than one phenotypic
characteristic
a. Most genes have MULTIPLE phenotypic effects
b. Ability of a gene to affect an organism in
many ways is called PLEIOTROPHY
Example Sickle-cell anemia
45
(No Transcript)
46
I. Epistasis
1. The production of a phenotype is often
(usually) controlled by more than one gene.
Example For example, in mice there is a gene
that codes for the presence or absence of
pigmentation in fur. A second gene codes for the
color of the fur. If the first gene codes for the
absence of pigmentation, the mouse will have
white fur regardless of the color the second gene
codes for.
47
(No Transcript)
48
J. Polygenic Inheirtance
1. Additive effect of two or more genes on a
single phenotypic character
2. Controlled by multiple genes that are
inherited independently
Examples height, weight, body shape, skin
color, behavior, and intelligence
49
(No Transcript)
50
How are Dihybrid Crosses Predicted?
51
A. A dihybrid cross occurs between individuals
that involves 2 pairs of contrasting traits
1. More possible combinations of alleles due to
the 2 pairs of contrasting traits
a. Punnett squares contain 16 possible outcomes
rather than 4
52
A. A dihybrid cross occurs between individuals
that involves 2 pairs of contrasting traits
1. More possible combinations of alleles due to
the 2 pairs of contrasting traits
a. Punnett squares contain 16 possible outcomes
rather than 4
B. Homozygous x Homozygous cross
1. Example GGII x ggii
53
Green, Inflated Pods
Yellow, Constricted Pods
54

• 100 probability of creating a pea plant with a
  heterozygous genotype (GgIi)
• 100 probability of creating a pea plant with a
  phenotype of green, inflated

55
C. Heterozygous x Heterozygous cross
1. Example GgIi x GgIi
56
Green, Inflated Pods
Possible combinations from a GgFf genotype GF,
Gf, gF, or gf
Green, Inflated Pods
57

• 9 out of 16 (9/16) of the plants will have
  phenotypes of green, inflated pods with possible
  genotypes of GGII, GGIi, GgII, and GgIi
• 3 out of 16 (3/16) of the plants will have
  phenotypes of green, constricted pods with
  possible genotypes of GGii and Ggii
• 3 out of 16 (3/16) of the plants will have
  phenotypes of yellow, inflated pods with possible
  genotypes of ggII and ggIi
• 1 out of 16 (1/16) of the plants will have
  phenotypes of yellow, constricted pods with a
  genotype of ggii

58
D. Homozygous x Heterozygous cross
1. Example ggii x GgIi
59
Yellow, Constricted Pods
Green, Inflated Pods
60

• 25 probability (or 4/16) of creating green,
  inflated pods (GgIi)
• 25 probability (or 4/16) of creating green,
  constricted pods (Ggii)
• 25 probability (or 4/16) of creating yellow,
  inflated pods (ggIi)
• 25 probability of creating yellow, constricted
  pods (ggii)