Transcript Gene Mapping

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Seminar Agenda
 Review of Course Information
 Review of Genetic Linkage and Genetic
Mapping
 Seminar Discussion Questions
 Questions & Answers
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Review of Course Information:
Assignments
 First Assignment due this week (at end of Unit 3).
 You will prepare a 1-2 page project report discussing Genetic
Mapping and Chromosomes. Choose a topic discussed in
the textbook.
 Some guidelines:
 Use Microsoft Word
 Be sure to complete all parts of the assignment
 Use clear and concise language and proofread your work.

Your work should be free of spelling and grammatical
errors.
 Cite source of information (reference list).
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Final Project
 For your Final Project you will complete a report and
create an essay that integrates what you have learned
about genetics and biotechnology. The topic can
address any area to be covered in this course. The
project will be completed in three parts. Please submit
parts I and II of the project in the “Outreach”
Dropboxes for Units 3 and 7.
 Project Part 1
 By the end of Unit 3, you will need to turn in the
genetics topic you are choosing for your report. This
topic needs to be a genetic or biomedical issue that is
relevant to this course.
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Final Project
 Project Part 2
 By the end of Unit 7, you will turn in your report outline, along with a list
of references.
 In a properly formatted document, submit an outline. In general, an
outline is used to organize your thoughts for your final paper. You will
roughly organize your thoughts to produce an outline that will give you
direction in your reading and note-taking. The outline should be at least
one and ½ pages and will address, at a minimum, the following points:
 I. Introduction
 II. Discuss the genetic or biomedical issue you have chosen
 III. Reason for this selecting this issue
 IV. Description of this issue
 V. Background factors contributing to this issue
 VI. Local data available
 VII. Possible problem solving approaches
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 VIII.Conclusion
Final Project
 Project Part 3
 By the end of Unit 9, you will turn in your report. Using
Internet resources and/or textbooks, produce and
submit a report that provides the following information
in an APA-style five-page paper. Make sure you report
contains the following information:
 Discuss the genetic or biomedical issue you have chosen
 Description of this issue
 Background factors contributing to this issue
 Local data available
 Possible problem solving approaches
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Review of Course Information
 A few tips…
 Read directions very carefully
 Work early in the week JUST IN CASE there is
something unexpected that comes up at the end of the
week
 Follow and then EXCEED all of the requirements for
each assignment
 Proofread your work multiple times prior to submission.
 Something to keep in mind when checking your grades:
 Kaplan instructors have 5 days to grade after the due
date.
 I try to keep up with the submissions, but may not. So, I
often need the 5 days.
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Any questions?
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Gene Linkage and
Genetic Mapping
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Mendel’s Laws: Chromosomes
• Locus = physical location of a gene on a chromosome
• Homologous pairs of chromosomes often contain
alternative forms of a given gene = alleles
• Different alleles of the same gene segregate at meiosis I
• Alleles of different genes assort independently in
gametes
• Genes on the same chromosome exhibit linkage:
inherited together
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The stages of meiosis I and II
Interphase
Prophase I
Prophase II
Telophase I
(and cytokinesis)
Metaphase I Anaphase I
Metaphase II
Anaphase II
Telophase II
(and cytokinesis)
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The Stages of Meiosis I
Interphase
Prophase I
Metaphase I
Anaphase I
The chromosomes
replicate. It is
similar to
chromosome
replication of
mitosis. Two
identical sister
chromatids are held
together by a
centromere.
Chromosomes
shorten and thicken.
Each chromosome
pairs with its
corresponding
homologous
chromosome to form
a tetrad. There are 4
chromatids in a
tetrad.
Tetrads line up
at the center
of the cell.
The tetrads break
apart and the pairs
move to opposite
sides of the cell.
Sister chromatids
remain attached at
their centromeres.
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The Stages of Meiosis II
Telophase I
(and cytokinesis)
The cell
separates into
two cells.
Meiosis I results
in 2 haploid (1N)
daughter cells
Each daughter cell has
half the number of
chromosomes as the
original cell.
Prophase II
Metaphase II
Anaphase II
Telophase II
The pairs of
sister
chromatids
start
toward the
center.
Pairs of
sister
chromatids
line up at
the center.
The pairs of
sister
chromatids
separate
and move
to opposite
sides of the
cell.
(and cytokinesis)
Results in 4
new cells
that are 1N.
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Gene Mapping: Crossing Over
• Two exchanges taking place
between genes, and both
involving the same pair of
chromatids, result in a
nonrecombinant
chromosomes
Fig. 4.13
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Gene Mapping
• Gene mapping determines the order of genes and the relative
distances between them in map units
• Gene mapping methods use recombination
frequencies between alleles in order to determine the relative
distances between them
• Recombination frequencies between genes are inversely
proportional to their distance apart
• Distance measurement: 1 map unit = 1 percent recombination (true
for short distances)
• 1 map unit = 1 cM (centimorgan)
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Fig. 4.6
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Gene Mapping
• Genes with recombination frequencies less than 50 percent
are on the same chromosome = linked)
• Linkage group = all known genes on a chromosome
• Two genes that undergo independent assortment have
recombination frequency of 50 percent and are located on
nonhomologous chromosomes or far apart on the same
chromosome = unlinked
Fig. 4.7
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Genetic Mapping
• The map distance (cM) between two genes equals
one half the average number of crossovers in that
region per meiotic cell
• The recombination frequency between two genes
indicates how much recombination is actually
observed in a particular experiment; it is a measure
of recombination
• Over an interval so short that multiple crossovers
are precluded (~ 10 percent recombination or less),
the map distance equals the recombination
frequency because all crossovers result in
recombinant gametes.
• Genetic map = linkage map = chromosome map 18
Discussion Question 1:
 A gene in Neurospora, a fungus with
ordered tetrads, shows 10% seconddivision segregation. What is the map
distance between the gene and the
centromere?
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Fig. 4.26
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Tetrad Analysis: Ordered Tetrads
• Homologous centromeres of parental chromosomes
separate at the first meiotic division
• The centromeres of sister chromatids separate at the
second meiotic division
• When there is no crossover between the gene and
centromere, the alleles segregate in meiosis I
• A crossover between the gene and the centromere
delays segregation alleles until meiosis II
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Tetrad Analysis: Ordered Tetrads
• The map distance between the gene and its
centromere equals
• 1/2 x (Number of asci with second division
segregation/ Total number of asci) x 100
• This formula is valid when the gene is close
enough to the centromere and there are no
multiple crossovers
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Fig. 4.27 top
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Fig. 4.27 bottom
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Discussion Question 1:
 A gene in Neurospora, a fungus with ordered tetrads,
shows 10% second-division segregation. What is the
map distance between the gene and the centromere?
 Map distance =
½
X
Number of asci with second
division segregation
Total number of asci
X 100
 10% recombination frequency X 1/2 = 5 cM
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