1. Linked Genes, Down Syndrome, and Non-disjunction
Describe what is meant by a linked gene and explain how linked genes can separate.
What is down syndrome and what causes down syndrome.
Aneuploidy
Trisomy, Monosomy
Polyploidy
Test on Thursday.
Study Outline Due on Exam Day. (Extra Credit)
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Take out homework. Which two questions were the easiest? …the hardest?

2. Chromosome Theory of Inheritance
Mendelian genes have specific loci along chromosomes, and it’s the chromosomes that undergo segregation and independent assortment.

3. Thomas Hunt Morgan
1933 – Nobel Prize Winner for Chromosomal Heredity (Columbia University)
First to associate a specific gene with a specific chromosome
Drosophila melanogaster = fruit fly

4. Alfred Henry Sturtevant
Sturtevant was always interested in inheritance and genetics.
One of Sturtevant's earliest publications was a pedigree analysis of horses owned by his father.
In 1909, while an undergraduate at Columbia University, Sturtevant attended a lecture given by Thomas Hunt Morgan.
It was one of the few undergraduate classes that Morgan ever taught.
Morgan's passion for science and discovery interested Sturtevant so much that he approached Morgan about working for him. Sturtevant became one of Morgan's first students in the "Fly room" to work on Drosophila melanogaster.

5. body color and wing shape are usually inherited together because their genes are on the same chromosome

8. linkage map
used recombination frequencies from fruit fly crosses to map the relative position of genes along chromosomes
frequency of recombinant offspring reflected the distances between genes on a chromosome

9. map units
One map unit is equivalent to a 1% recombination frequency

10. “Disorders” Examples Duchenne muscular dystrophy Hemophilia
Absence of an X-linked gene for a key muscle protein, called dystrophin
Characterized by a progressive weakening of the muscles and loss of coordination
Hemophilia
Absence of one or more clotting factors
Prolonged bleeding because clots form slowly

11. Linked Genes, Down Syndrome, and Non-disjunction
What is down syndrome and what causes down syndrome.
Aneuploidy
Trisomy, Monosomy
Polyploidy
Chromosomal Mutations
Test on Thursday.
Study Outline Due on Exam Day. (Extra Credit)
Do Now
What is a linked gene?
How can linked genes be “unlinked”?
How do we measure the frequency of genes becoming unlinked?

12. Sex Linked Genes Heterozygous females will be carriers
Any male receiving the recessive allele from his mother will express the trait

13. What information does this karyotype give us?
Down syndrome
3 copies of chromosome 21
affects 1 in 700 children born in the US

14. Nondisjunction
Problems with the meiotic spindle cause errors in daughter cells

15. Aneuploidy
Trisomic cells  three copies of a particular chromosome type
2n + 1 total chromosomes
Monosomic cells  only one copy of a particular chromosome type
2n - 1 chromosomes

16. Polyploidy Organisms with more than two complete sets of chromosomes
Relatively common among plants and much less common among animals
fishes and amphibians have polyploid species

17. Aneuploidy vs. Polypoidy
Aneuploidy – ONE OR MORE EXTRA CHROMOSOMES
Polyploidy – AN EXTRA SET OF CHROMOSOMES

18. Chromosomal Mutations Barr Bodies
Describe four different types of chromosomal mutations.
Describe what a barr body is and why it only occurs in females.
Test on Friday.
Study Outline Due on Exam Day. (Extra Credit)
Do Now
What is down syndrome? What process causes down syndrome and when does this process occur?

19. Sex Chromosome Disorders
Klinefelter’s syndrome
XXY male
Occurs 1 in every 2000 live births
have male sex organs, but are sterile
Turner’s syndrome
XO female (monosomy)
occurs 1 in every 5000 births
produces phenotypic, but immature females

20. changes in chromosome structure
deletion  a chromosome fragment lacking a centromere is lost during cell division
duplication  a fragment becomes attached as an extra segment to a sister chromatid

21. changes in chromosome structure
inversion  a chromosomal fragment reattaches to the original chromosome in the reverse orientation
translocation  a chromosomal fragment joins a nonhomologous chromosome

22. Barr body
During female development, one X chromosome per cell condenses into a compact barr body
This inactivates most of its genes
Reactivated in ovarian cells that produce ova
Females consist of a mosaic of cells
some with an active paternal X
others with an active maternal X