313
Lecture Biology 6
Sept 2, 2011
Madrid, Spain
(2011): What
is this person
doing?
Problems (Ch 3 Complete: Edition 4)
Concept Checks: 1- 7
Worked Problems: 1-4
Comprehension Questions 1 11
Application Questions /Problems: 13,
14, 16, 17, 20, 22, 24, 25, 27, 28, 30, 31,
34, 38
Vocabulary for Wednesday (Sept 7)
Hermaphroditism
Monoecious organism
Dioecious organism
Drosophila
Chapter 3 Basic Principles of Heredity
1. Mendel
2. Monohybrid Crosses: Mendels First
Law, the Law of Segregation
3. Punnett Square & Probability
4. Dihybrid Crosses: Mendels Second
Law, the Law of Independent Assortment
5. Chi-square test
Law of Independent Assortment
Different genetic factors (alleles)
assort randomly into gametes
independently from one another
(separation occurs at Anaphase I)
An example of the 2nd
Law from Chapter 2
(Figure 2-17) : random
distribution of
chromosomes at
Anaphase I produces
genetic variation
m = maternal
p = paternal
How predict progeny for multiple traits?
Branching method: an easier, faster way
to predict progeny of crosses than
Punnett Square, especially for more than
two traits
Independent assortment applies so can
apply the multiplication rule
Branching method for Dihybrid Cross: Phenotype
Prediction
Consider each gene
(chromosome)
separately
Yy x Yy
First trait
Second trait
Both traits
How to work a genetics problem?
See p. 59 (Worked Problem)
(Good tips)
Chapter 3 Basic Principles of Heredity
1. Mendel
2. Monohybrid Crosses: Mendels First
Law, the Law of Segregation
3. Punnett Square & Probability
4. Dihybrid Crosses: Mendels Second
Law, the Law of Independent Assortment
5. Chi-square test
Goodness-of-fit chi-square test
When two (or more!) genes segregate
independently, do we expect to see
exactly the ratios predicted by rules of
probability?
NO !!!!!!!!
Why is there deviation between an
observed outcome and the expected
outcome?
chi-square test
To Elmo
chi-square test
2 steps:
1. Determine 2 value
2 = (observed-expected)2/expected
2. Use the calculation of 2 to determine a
probability (p-value)
Degrees of freedom (df) = one less than number
of independent variables (for us, this is one
less than the number of progeny classes)
Consider the testcross: Rr Yy x rr yy
Hypothesis: F1 progeny are expected to have 1:1:1:1
genotypic and phenotypic ratios
(null hypothesis = chance alone explains differences
between observed and expected results)
2 test:
genotype
Rr Yy
Rr yy
rr Yy
rr yy
Total
observed
55
expected
51.75
(obs-exp)2/exp
0.204
51
49
52
51.75
51.75
51.75
0.011
0.146
0.001
207
207.00
0.362 = 2
Determine p-value
Degrees of freedom (df) = 4 -1 = 3
df = one less than the number of
progeny classes
2
> 0.05 Accept null hypothesis:
chance explains the deviation of the
observed from the expected
< 0.05: Reject null
hypothesis:
something else
explains the deviation
of the observed from
the expected
Step 1: Find df = 3
Step 2: Read over to 2 = 0.362
Step 3: Read up to p-value = >0.9)
0.362
p-value > 0.9 (i.e., a deviation between observed and
expected due to chance is likely, thus accept the null
hypothesis
How many female scientists
in Chapters 2 and 3?
A good Honors topic!!!!!
END OF CHAPTER students 3
ISU study Marine Biology in Spain:
Mediterranean Sea (summer 2010)
Chapter 4:
Sex determination & sex-linked
characteristics
1. Mechanisms of sex determination
A. Chromosomal
B. Genic
C. Environmental
D. Human sex determination
Problems (Ch 4 : Edition 4)
Concept Checks:
Worked Problems:
Comprehension Questions
Application Questions /Problems:
Vocabulary for Wednesday (Sept 7)
Autosome
Heterogametic sex
Homogametic sex
Barr Body
Chapter 4:
Sex determination & sex-linked
characteristics
1. Mechanisms of sex determination
A. Chromosomal
B. Genic
C. Environmental
D. Human sex determination
Sex Determination: Definitions
Sex = sexual phenotype (male,
female)
Male produces small gametes
Female produces large
gametes
Sex Determination: Definitions
Monoecious: both male and female
reproductive structures in the same
organism
-- called Hermaphroditism
Dioecious: either male or female
reproductive structures in one
organism
Sex determination = mechanism by
which sex is established
Sex Determination: 3 Mechanisms
Chromosomal
Genic
Environmental
(To Elmo)
Chapter 4:
Sex determination & sex-linked
characteristics
1. Mechanisms of sex determination
A. Chromosomal
B. Genic
C. Environmental
D. Human sex determination
Genic Sex Determination
Sex is determined by genes at one or
more loci, but there are no obvious
differences in the chromosomes of
males and females
-occurs in some plants, fungae,
protozoa
Environmental Sex Determination
Sex is determined fully or in part by
environmental factors
e.g, temperature that occurs during embryonic
development determines whether a turtle
will be male or female (warm temps, a
female; cool temps, a male), REGARDLESS
of what sex chromosomes are present
Environmental Sex Determination
Called temperature-dependent sex
determination (TSD)
Hypothesis (still being tested): temp
influences enzyme activity and/or controls
the production of steroid hormones that
act as a signal to control the expression
of sex-determining genes
Chapter 4:
Sex determination & sex-linked
characteristics
1. Mechanisms of sex determination
A. Chromosomal
B. Genic
C. Environmental
D. Human sex determination
Human sex
determination
Male is
heterogametic
Female is
homogametic
X and Y form a homologous pair
Most genes on the human X and Y are
different, but X and Y form a
homologous pair (and synapse at
Prophase I of meiosis) because they
have short regions of homology, called
pseudoautosomal regions (PARs), that
have the same genes
Pseudoautosomal regions on X and Y
What is
odd about
this human
karyotype?
Sex Determination in Humans XX-XY
Turner syndrome: XO; a female
-1/3000 female births
-Underdeveloped sex characteristics
-Sterile
Is anything odd about this human
karyotype?
Sex Determination in Humans XX-XY
Klinefelter syndrome: XXY, or XXXY, or
XXXXY, or XXYY; a male
- 1/1000 male births
- Underdeveloped sex characteristics
- Sterile
Sex Determination in Humans XX-XY
00
--Lethal (embryo); spontaneously aborted
Poly-X females (triplo-X syndrome):
- 1/1000 female births
- XXX has normal intelligence, but as
increase the # of X, mental retardation
appears
Conclusions from cytology
To Elmo
END OF LECTURE, Friday Sept 2