1. Welcome to Genetics: Unit 3 Seminar!
Please feel free to chat amongst yourselves
until we begin at the top of the hour.

2. Seminar Agenda Review of Course Information
Review of Genetic Linkage and Genetic Mapping
Seminar Discussion Questions
Questions & Answers

3. 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).

4. 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.

5. 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
VIII.Conclusion

6. 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

7. 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.

8. Any questions?

9. 4 Gene Linkage and Genetic Mapping

10. 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

11. The stages of meiosis I and II
Let’s first label each stage.
Interphase
Prophase I
Metaphase I
Anaphase I
Prophase II
Metaphase II
Anaphase II
Telophase II
(and cytokinesis)
Telophase I
(and cytokinesis)

12. 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.

13. The Stages of Meiosis II
Telophase I
(and cytokinesis)
The cell separates into two cells.
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)
Meiosis I results in 2 haploid (1N) daughter cells
Results in 4 new cells that are 1N.
Each daughter cell has half the number of chromosomes as the original cell.

14. 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

15. 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)

16. Fig. 4.6

17. 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

18. 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

19. 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?

20. Fig. 4.26

21. 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

22. 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

23. Fig top

24. Fig bottom

25. Discussion Question 1: ½ X X 100
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 =
10% recombination frequency X 1/2 = 5 cM
Number of asci with second
division segregation
Total number of asci
½ X X 100