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Infomercial
• True or false: if I miss more than two labs,
it only counts off my lab grade.
Infomercial
• True or false: if I miss more than two labs,
it only counts off my lab grade.
– False. Automatic F for the course if more than
two labs are missed.
Infomercial
• True or false: if I miss more than two labs,
it only counts off my lab grade.
– False. Automatic F for the course if more than
two labs are missed.
• Where are the study guides/outlines for
each lecture and exam?
Infomercial
• True or false: if I miss more than two labs,
it only counts off my lab grade.
– False. Automatic F for the course if more than
two labs are missed.
• Where are the study guides/outlines for
each lecture and exam?
– The study guides/outlines can be found at the
beginning of the slides for lecture.
Broad Course Objectives for Principles of Heredity
Students should be able to:
• Explain Mendel’s principles of inheritance and apply these to problems of
inheritance
• Describe the different forms of inheritance patterns and identify these in
genetic data
• Use and interpret probabilities and statistics in the gathering, predicting, and
analysis of genetic data
• Describe various types of genetic crosses and indicate when/why they would
be used by a geneticist
• Explain more complex modes of inheritance and how sex influences the
inheritance and expression of genes; use this information in predicting
genetic outcomes and the analysis of genetic data
Necessary for understanding future material on:
• Phenotypic and statistical differences between traits that assort
independently vs. two traits that co-segregate
• Setting up genetic crosses for gene characterization and mapping, including
Virtual Flylab.
• Pedigree analysis in Human Genetics.
Ch 3-Mendelian Genetics-Outline and Study Guide
Review terms: true-breeding, homozygous dominant, Homozygous recessive,
Heterozygous, genotype, phenotype
Mendel’s discovery of genetic principles
Monohybrid crosses—studying one gene
•
Mendel discovers genetic principles using true-breeding pea plants
•
Mendel continually sees a 3:1 ratio of the dominant : recessive phenotypes
•
Genetic symbols for dominant and recessive, for genetic crosses
•
Predicting haploid gamete genotypes from the diploid parent
•
Using Punnett squares for predicting results of genetic matings (crosses)
•
Mendel’s Principle of Segregation
•
Cellular basis of Principle of Segregation (meiosis and creation of haploid
gametes)
Dihybrid crosses-studying two genes on different chromosomes
•
Genetic symbols for dihybrid crosses
•
Predicting haploid gamete genotypes from the diploid parent
•
Law of Independent Assortment
•
Cellular event in meiosis that is the basis of the Law of Independent Assortment
•
Difference between a monohybrid cross and a dihybrid cross?
Test Cross—how is a genetic test cross used to determine the genotype of an individual
by looking at his/her children?
Ch 3—Outline and Study Guide, cont.
Using simple probability to predict inheritance
•
Branch and Fork method
•
Multiplicative probability—how often will two conditions
(e.g. blonde hair and blue eyes, or homozygous
recessive) coincide in the same individual?
•
Additive probability – how many total progeny will share
this trait? (e.g. how many progeny will have blond hair?)
•
Predicting frequency of phenotypes and genotypes from
specific crosses
e.g.
AaBb x AaBb
aabb X AABB
AABB x AaBB
•
Using the chi-square distribution to determine if the
observed data “fit” a particular hypothesis or prediction.
Gregor Mendel
Culver Pictures
The garden of the Augustinian Convent in Brno. This view is looking towards the entrance to
the garden, with Mendlovonamesti, Mendel Square, beyond. In the shadows in front of the tree
can just be seen part of the foundations of the greenhouse that Mendel used. His peas were
planted in the beds against the building on the left. A MENDEL PHOTO-ESSAY –simonmawer.com
Traits of Pea Plant Studied by Mendel
Review of Genetic Terms
•
•
•
•
•
•
•
•
•
•
•
True-breeding-Genotype-Phenotype-Gene—
Allele—
Diploid-Haploid—
Dominant-Recessive—
Homozygous—
Heterozygous—
Mendel observes that the recessive trait “disappears” in the
2nd generation and reappears in the next
Mendel observes that the recessive trait “disappears” in the
2nd generation and reappears in the next
Mendel observes that the recessive trait “disappears” in the
2nd generation and reappears in the next
Studying different genes gave Mendel the same 3 to 1 ratio
705:224
3.15 to 1
651:207
3.14 to 1
6022:2001
3.01 to 1
5474:850
2.96 to 1
Adding genetic symbols to Mendel’s crosses
Mendel’s 1st Law—Principle of Segregation
Each physical trait of a diploid organism is determined by
two factors. These two factors separate between the
generations (meiosis and gametogenesis) and re-unite in
the next generation (fertilization of egg and sperm).
Observation: the F2 generation shows all traits from the P0, even
though the F1 parents do not show all traits.
Conclusion: the F1 must receive something that causes the
“hidden” trait revealed in the F2, in addition to the trait that the F1
show. Therefore
Using Punnett Squares to predict the progeny from
genetic crosses
Principle of
Segregation is due to
diploid organisms
creating haploid
gametes
Heterozygous (Yy ) (yellow seed plant )
Meiosis I
Prophase
y
Metaphase
y
Y
y
Y
Principle of
Segregation:
chromosome
view
Y
Anaphase
Telophase
y
y
Y
Principle of Segregation is due to
diploid organisms creating
haploid gametes
Y
Meiosis II
y
y
Y
Y
Haploid gametes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig 3.11, Brooker
Studying two genes on different
chromosomes
Gene 1—seed shape, 5p19.2
Alleles:
Gene 2—seed color, 7q22.1
Alleles:
Mendel’s 2nd Law—Principle of
Independent Assortment
Genes for different traits (e.g. eye color
vs. hair color) segregate
independently of one another during
gametogenesis.
Exception—when genes are closely linked on the
same chromosome, then original alleles tend to
segregate together in next generation.
Chromosome basis for a dihybrid individual
Gene 1—seed shape, 5p19.2
Gene 2—seed color, 7q22.1
Draw diploid karyotype for an RrYy individual:
Draw haploid genotypes for the
gametes coming from this
individual:
Draw haploid karyotypes for the
gametes coming from this
individual:
Chromosome Basis of Principle of
Independent Assortment
YyRr
y
genotype
r
y
R R
y Y
Large chromosome
and small c’some
segregate
independently of
one another:
Y
r
Y
“Big Red” can cosegregate with “little
red”
Y
y
Meiosis I
(two possible
arrangements
in metaphase)
r
OR
R
r
R
“Big Red” can cosegregate with“little
blue”
y
r
y
Y
Y
R
R
r
y
y
Y
Y
R
r
r
R
Meiosis II
y
y
Y
R
r
r
2 ry
:
y
Y
R
y
R
2 RY
Y
R
2 Ry
Y
r
:
r
2 rY
Fig 3.12, Brooker
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
From the cross Aa x Aa:
• What is the probability that a child will
be Aa or aA?
• What is the probability that a child will
have at least one allele a?
• Assume that A codes for the “wildtype”
phenotype. What is the probability that
a child will be wildtype?
Branch and Fork Method
Practice predicting the genotypes of the
progeny
• Assume that the gene with the alleles R/r
(R=round, r=wrinkled) is on a different
chromosome than the gene with the alleles
for Y/y (Y= yellow, y = green)
• Use Punnett Squares or the Branch and
Fork method if you need to
• Give proportions of each genotype
• Give associated phenotype
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
RR x rr
Rr x rr
Rr x Rr
RR x Rr
RRyy x rrYY
RrYy x RrYy
RRYy x RrYy
RrYy x rrYy
Which one is the monohybrid
cross? The dihybrid cross?
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
RR x rr
Rr x rr
Rr x Rr
RR x Rr
RRyy x rrYY
RrYy x RrYy
RRYy x RrYy
RrYy x rrYy
Use the Branch and Fork
method to determine the
genotypic ratios of the
progeny from crosses 6-8
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
RR x rr
Rr x rr
Rr x Rr
RR x Rr
RRyy x rrYY
RrYy x RrYy
RRYy x RrYy
RrYy x rrYy
What is the probability of
getting a progeny of “RrYY”
from each of crosses 5 -8?
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
RR x rr
Rr x rr
Rr x Rr
RR x Rr
RRyy x rrYY
RrYy x RrYy
RRYy x RrYy
RrYy x rrYy
What is the probability of
getting yellow progeny from
crosses 5-8?
5.)
6.)
7.)
8.)
RRyy x rrYY—100% yellow progeny
RrYy x RrYy—75% yellow progeny
RRYy x RrYy—75% yellow progeny
RrYy x rrYy –75% yellow progeny
What is the probability of
getting a yellow progeny from
crosses 5-8?
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
RR x rr
Rr x rr
Rr x Rr
RR x Rr
RRyy x rrYY
RrYy x RrYy
RRYy x RrYy
RrYy x rrYy
What is the probability of
getting wrinkled, yellow
progeny from crosses 5-8?
Short hair in rabbits (S) is dominant over long
hair (s). The following crosses are carried out,
producing the progeny shown. Give all
possible genotypes of parents in each cross.
a.) P0--short x short
F1--4 short and 2 long
b.) P0--Short x long F1--12 short
c.) P0--Short x long F1--3 short and 1 long,
d.) P0--long and long F1--2 long.
Test Cross
You are given a pea plant with smooth
seeds that are yellow.
You know that smooth is dominant to
wrinkled, and yellow is dominant to
green. How can you determine the
exact genotype of this pea plant?
Hairlessness in American rat terriers is recessive to the
presence of hair. Suppose that you have 3 rat terriers
with hair. You perform test crosses on these dogs and
get the following among their puppies:
Dog 1
Dog 2
Dog 3
3 hairless
1 hairless
0 hairless
4 hair
4 hair
6 hair
What are the genotype of the test-crossed dogs with hair?
Dog 1: Hh; Dog 2: Hh, Dog 3: most likely HH [technically need to see 30 of its progeny for definitive answer]
Round is dominant to
wrinkled; yellow is
dominant to green.
Individuals of the Round Yellow phenotype were test
crossed. Give the expected phenotype ratios of progeny for
each of the possible individuals:
1.) RrYy x rryy
2.) RRYy x rryy
3.) RrYY x rryy
4.) RRYY x rryy
1.) RrYy x rryy 1:1:1:1
2.) RRYy x rryy ½ round yellow, ½ round green
3.) RrYY x rryy ½ round yellow, ½ wrinkled yellow
4.) RRYY x rryy all round yellow