Basic Genetics

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Basic Genetics

The Father of Genetics
Gregor Mendel
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Gregor Mendel
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Objectives

• To distinguish between heredity and inheritance
• To define pollination
• To identify the major parts of a flowering plant
• To describe Mendels experiments in heredity

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Heredity transmission of traits from parents to
their offspring
Inheritance passing of traits by heredity
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Mendels experiments used pea plants
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Pollination transfer of pollen from anthers to
stigma in flowers

• 1) self pollination occurs within the same
  flower or same plant
• 2) cross pollination occurs between different
  plants

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Receptical
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Mendels Crosses with Pea Plants
X
Pure tall plants
Pure short plants
parental generation
P1
Cross Pollination
All Tall plants
first filial generation
F1
Self Pollination
second filial generation
787 tall plants, 277 short plants
F2
3 to 1 ratio
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Objective

• To describe Mendels 3 principles of inheritance

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1) Principle of Dominance and Recessiveness

• Each trait is controlled by 2 factors, one factor
  (dominant ) may mask the other factor (recessive
  ) preventing it from having an effect.

F1
F2
P1
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2) Principle of Segregation

• The two factors for a characteristic separate
  during the formation of eggs and sperm.

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3) Principle of Independent Assortment

• Factors for different characteristics are
  distributed to reproductive cells independently.

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Objectives

• To define gene
• To define allele

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Gene segment of DNA on a chromosome that
codes for a particular protein

• genes occur in pairs

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Allele alternative form of a gene
Dominant capital letter
T tall
t short
G green pods
g yellow pods
Recessive Lowercase letter
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Objectives

• To define genotype and phenotype
• To distinguish between homozygous and
  heterozygous
• To define multiple alleles

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Genotype genetic makeup of an
organism (genes)
(internal information)
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Phenotype physical characteristics of an
organism
(external appearance)
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What does Phenotypes come form
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Example of Genotype and Phenotype
Tall
TT
genotype
phenotype
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Homozygous when both alleles
of a pair are the
same
homozygous dominant
TT
homozygous recessive
tt
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Heterozygous when both alleles
of a pair are not
the same
heterozygous (tall)
Tt
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Multiple alleles 3 or more alleles
that control a trait

• Example blood type (IA,IB,io)

GENOTYPES IAIA IAio RESULTING PHENOTYPES Type A Type A
IBIB IBio Type B Type B
IAIB Type AB
ioio Type O
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Objectives

• To define probability
• To predict the results of monohybrid crosses by
  using a Punnett square

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Probability likelihood that a particular event
will occur
number of times a particular event occurs
Probability
number of opportunities for the event to occur
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Example 1 Flipping a Coin
½
Chances of coming up heads

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Example 2 Rolling Dice
1
1
1
x

6
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6
probability of rolling a six on 1 dice
probability of rolling a six on 2 dice
probability of rolling a six on 1 dice
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monohybrid cross
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Objectives

• To define test cross
• To define incomplete dominance
• To define codominance

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Test cross an individual with unknown genotype
is crossed with a homozygous recessive
individual

• used to determine the genotype of any individual
  whose phenotype is dominant

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In rabbits, black fur color is dominant over
brown fur color
B black fur
b brown fur
bb
BB
or
Bb
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Incomplete Dominance

• when 2 or more alleles influence the phenotype

• results in a trait intermediate between the
  dominant and recessive traits

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Incomplete Dominance
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Codominance condition in which both alleles of
a gene are expressed

• example roan coat in horses
• white hair (HW) is codominant with red hair (HR)
• horses with genotype (HRHW) have coats with a
  mixture of red and white hairs (roan)

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Roan Coat
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Objectives

• To predict the results of dihybrid crosses by
  using a Punnett square

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dihybrid cross cross between individuals that
involves two pair of contrasting traits