Chromosomes and Inheritance

1. Chromosomes and Inheritance Since genes are carried on chromosomes, knowledge of chromosome number and structure has far-reaching implications for basic genetics, human health, and evolution. A normal human male karyotype.

2. X-linked Inheritance – When Men and Woman Play by Different Rules Behind the 8-ball? Colorblindness is an X-linked recessive trait.

3. X-linked Inheritance There are many X-linked recessive traits.

4. Pedigree Analysis is a Key Tool in Human Genetics Analyzing a pedigree is like puzzle-building – you try things (assigning potential genotypes) until the pieces fit (you’re as certain as you can be about genotypes and modes of transmission (autosomal vs. X-linked; dominant vs. recessive).

5. A Pedigree of a Recessive Human Trait Note that the trait can appear in offspring of parents without the trait. Heterozygotes who do not show the trait are termed carriers.

6. A Pedigree of a Dominant Human Trait Note that the trait appears in every generation and ½ the offspring of an affected heterozygote are expected to show the trait.

7. Down syndrome is caused by a change in chromosome number. Changes in Chromosome Number and Structure Changes in chromosome number and structure are important for health and evolution.

8. Aneuploidy Aneuploidy occurs when one of the chromosomes is present inan abnormal number of copies. Trisomy and monosomy are two forms of aneuploidy.

9. Down Syndrome is Caused by Trisomy for Chromosome 21 Aneuploidy is remarkably common, causing termination of at least 25% of human conceptions. Aneuploidy is also a driving force in cancer progression (virtually all cancer cells are aneuploid).

10. Chromosome Non-Disjunction in Meiosis Causes Aneuploidy

11. The Frequency of Chromosome Non-Disjunction And Down Syndrome Rises Sharply with Maternal Age The phenomenon is clear – the explanation isn’t.

12. Klinefelter syndrome Sex Chromosome Aneuploid Conditions are Common

13. Polyploidy Polyploidy occurs when all the chromosomes are present inthree or more copies. Polyploidy is common in plants and rare in animals.

14. Polyploids Are Created When Chromosome Number Doubles A common way for this to occur is for the mitotic spindle to fail, leaving all chromosomes in one cell.

15. Polyploidy is a Major Force in Plant Evolution Roughly 35% of flowering plants (the most familiar plant species) arose through polyploidization.

16. Most Crop Species are Polyploid Polyploids, like the one on the left, are larger than their diploid progenitors (strawberry on right).

17. Chromosome Structural Changes There are 4 types of chromosome structural change – all of them associated with human disorders

18. A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder Caused by Chromosome Deletion

19. Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy of Chromosome 5

20. In Burkitt’s lymphoma, a chromosome translocation causes a cell cycle-promoting gene to always beactive. Translocations Lead to a Number of Human Cancers

21. Searching for Chromosomal Defects - Amniocentesis and Chorionic Villus Sampling Many new techniques for learning about individual genes rather than whole chromosomes are available or under development.

22. Removing a cell for diagnosis from a human embryo. Searching for Chromosome and Gene Defects – Pre-Implantation Genetic Diagnosis (PGD) The diagnosis: trisomy 21 (Down syndrome).