Transcript Chapter Opener Slide

Chapter 3 Lecture
Concepts of Genetics
Tenth Edition
Mendelian Genetics
Mendel and his peas
• Mendel put forth the basic principles of
inheritance, publishing his findings in
1866. The significance of his work did not
become widely known until 1900.
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Monohybrid Crosses Reveal:
• Mendel's first three postulates
• Unit factors in pairs
– Genetic characters are controlled by unit factors
existing in pairs in individual organisms
• Dominance/Recessiveness
– In the pair of unit factors for a single characteristic
in an individual, one unit factor is dominant and
the other is recessive
• Segregation
– The paired unit factors segregate (separate)
independently during gamete formation
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• A Punnett square allows the genotypes
and phenotypes resulting from a cross to
be visualized easily
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Figure 3.3
Now Solve This: 3-1 pg 47
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• The test cross: One character
• A testcross is a way to determine whether
an individual displaying the dominant
phenotype is homozygous or
heterozygous for that trait
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Figure 3.4
Probability as a tool in genetics
• Express the likelihood of the occurrence of a particular
event
• Have to know something about how the vent takes place
or how often it takes place.
• The multiplication rule – probability of two or more
independent events taking place together is calculated
by multiplying their independent probabilities
– Ex: Roll of the die two fours 1/6 x 1/6 “AND”
• The addition rule – probability of any one or two or
more mutually exclusive events is calculated by adding
the probabilities of these events
– Ex: want either a three or a four 1/6 + 1/6 = 2/6 = 1/3
• EITHER and OR
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Application of probability to genetics
• Cross between two pea plants
heterozygous for height locus Tt x Tt
• ½ T and ½ t gametes by each plant
– TT
– Tt
– tT
– tt
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½x½
½x½
½x½
½x½
tall
tall
tall
short
Solve the problem:
• What is the probability of rolling two six
sided dice and obtaining the following
numbers?
• A) 2 and 3
• B) 6 and 6
• C) at least one 6
• D) Two of the same number ( two 2’s etc)
• E) An even number on both dice
• F) An even number on at least one die
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Answers
•
•
•
•
•
•
A) 1/18
B) 1/36
C) 11/36
D) 1/6
E) ¼
F) ¾
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Dihybrid Crosses
• Crossed peas that differed in two
characteristics – two factor cross
• Generated a unique F2 ratio
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Figure 3.5
• The product law can be used to predict the
frequency with which two independent
events will occur simultaneously
Dihybrid crosses are basically two
monohybrid crosses conducted
separately.
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© 2012 Pearson Education, Inc.
Figure 3.6
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• Mendel's fourth postulate: Independent
assortment
– states that:
– traits assort independently during gamete
formation
– all possible combinations of gametes will form
with equal frequency
– Due to the independent separation of
homologous pairs of chromosomes in meiosis
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Now Solve This
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Answer
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The Trihybrid Cross Demonstrates That
Mendel's Principles Apply to Inheritance
of Multiple Traits
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• The Trihybrid cross demonstrates that
Mendel's principles apply to inheritance of
multiple traits
• Trihybrid crosses involving three
independent traits show that Mendel's
rules apply to any number of traits
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• The forked-line method, or branch diagram
• The forked-line (branched diagram)
method is easier to use than a Punnett
square for analysis of inheritance of larger
number of traits
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Figure 3.9
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Table 3.1
Chi-Square Analysis Evaluates the
Influence of Chance on Genetic Data
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• Chi-Square analysis evaluates the
influence of chance on genetic data
• Chance deviation from an expected
outcome is diminished by larger sample
size
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• Chi-Square Calculations and Null
Hypothesis
• When we assume that data will fit a given
ratio, we establish what is called the null
hypothesis—so named because it
assumes that there is no real difference
between the measured values (or ratio)
and the predicted values (or ratio)
• The apparent difference can be attributed
purely to chance
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• Chi-square (2) analysis is used to test
how well the data fit the null hypothesis
• Table 3.3 shows the steps in 2
calculations for the F2 generation of a
monohybrid cross
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Table 3.3
• Chi-square analysis requires that the
degree of freedom (df) be taken into
account, since more deviation is expected
with a higher degree of freedom (Figure
3.11)
• The degree of freedom is equal to n – 1,
where n is the number of different
categories into which each datum point
may fall
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Figure 3.11
• Once the number of degrees of freedom is
determined, the 2 value can be
interpreted in terms of a corresponding
probability value (p)
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Now Solve This:
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Pedigrees Reveal Patterns of
Inheritance of Human Traits
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• Pedigrees reveal patterns of inheritance of
human traits
• A pedigree shows a family tree with
respect to a given trait. Pedigree analysis
reveals patterns of inheritance
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Figure 3.12
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Figure 3.13
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© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Table 3.4
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