1. Chapter 2: Genes and Medical Genetics

2. Introduction So far, it’s been all about the cell.So far, it’s been all about the cell. Last lecture we examined how cells divide. A process which facilitates life.Last lecture we examined how cells divide. A process which facilitates life. This time we’ll consider genetic and there impact on how we “look,” and what potential pitfalls may occur when cell division and replication don’t “give us what we wanted.”This time we’ll consider genetic and there impact on how we “look,” and what potential pitfalls may occur when cell division and replication don’t “give us what we wanted.”

3. Introduction As always we have several new terms.As always we have several new terms. Genotype: genes of the individual. Your genetic makeup, if you will.Genotype: genes of the individual. Your genetic makeup, if you will. Phenotype: What you look like, or more precisely, what physical manifestations are observed.Phenotype: What you look like, or more precisely, what physical manifestations are observed. Allele: Alternate forms of a gene which are located in the same position on a pair of chromosomes.Allele: Alternate forms of a gene which are located in the same position on a pair of chromosomes.

4. Fig. 02-01 Three paths: Three paths: Two results?? Two results?? Not really! Not really! Again, new terms… Again, new terms… Dominant allele Dominant allele (capital letter) (capital letter) Recessive Allele Recessive Allele (lower case letter) (lower case letter)

5. As you can see during As you can see during meiotic cell division, alleles meiotic cell division, alleles are isolated within each are isolated within each gamete. gamete.

6. How do alleles (genes) get mixed up?? How do alleles (genes) get mixed up?? Rem: Meiosis? Crossing over?? Rem: Meiosis? Crossing over?? Alleles are spread around in an amazing way during sexual reproduction. Alleles are spread around in an amazing way during sexual reproduction. As we will see, this leads us to some interesting results which don’t always seem logical. As we will see, this leads us to some interesting results which don’t always seem logical.

7. Alleles on autosomes Alleles on autosomes Basic Mendelian Genetics Basic Mendelian Genetics and the Punnett Square and the Punnett Square If we “cross multiply,” it If we “cross multiply,” it becomes evident that not becomes evident that not all genotypes result in the all genotypes result in the same phenotype. same phenotype. The example at the left is a The example at the left is a single-trait cross. single-trait cross. Notice the expected Notice the expected phenotypic ratio (3:1). phenotypic ratio (3:1). This will become important This will become important later. later.

8. What happens if we What happens if we mix it up a bit?? mix it up a bit?? Same method, different Same method, different results. results. Now the phenotypic Now the phenotypic ratio is 50:50 (Better odds ratio is 50:50 (Better odds than you’d get in Vegas!) than you’d get in Vegas!)

9. Okay, Emiril, let’s…Okay, Emiril, let’s… “Kick it up a notch!!” Dihybrid crossesDihybrid crosses (and beyond) are (and beyond) are handled similarly. handled similarly. You must be carefulYou must be careful to transfer all your to transfer all your alleles though!! alleles though!! Once this is done,Once this is done, figuring out what figuring out what you have can be you have can be challenging. challenging.

10. Genetic Disorders Most of the time, genes are expressed and individual live quiet lives.Most of the time, genes are expressed and individual live quiet lives. Sometimes two alleles get together that shouldn’t!Sometimes two alleles get together that shouldn’t! Many are autosomal dominant and expressed with alarming frequency.Many are autosomal dominant and expressed with alarming frequency. In the case of autosomal dominance, even heterozygotes express the phentype.In the case of autosomal dominance, even heterozygotes express the phentype.

11. Genetic Disorders: Autosomal Dominant Disease OccurenceSymptoms Disease OccurenceSymptoms Neurofibromatosis 1/3500 Dark Spots Huntington ??Neuopathy Polycystic KidneyNephretic cysts/ hypertension renal failure

12. Genetic Disorders: Autosomal Recessive DiseaseOccurenceSymptoms DiseaseOccurenceSymptoms Cystic Fibrosis1/2500bronchial mucus clogged pancreatic ducts Phenylketonuria1/5000high urinary phenylalanine concentration Tay-Sachs??Blindness, paralysis, death

14. Polygenic Inheritance: Height, skin color, etc. Height, skin color, etc. The absolute reason for The absolute reason for expression of some traits expression of some traits such as a persons height such as a persons height can be nebulous. can be nebulous. Many alleles dictate the Many alleles dictate the height of an individual, so height of an individual, so just because your dad just because your dad was 7’ doesn’t mean you was 7’ doesn’t mean you will be (though it doesn’t will be (though it doesn’t hurt either). hurt either).

15. Some traits share an additional genetic component, despite differing environmental factors

16. Multiple Allelic Traits Multiple Allelic Traits Blood types are coded Blood types are coded for by three different for by three different alleles. alleles. Codominance exists Codominance exists because A and B are because A and B are dominant over O. dominant over O.

17. Incomplete dominance Incomplete dominance Paul Mitchell aside, Paul Mitchell aside, hair curls, or lack of hair curls, or lack of them are expressed them are expressed as a mixture of straight as a mixture of straight vs. curly locks. vs. curly locks. What can result is a What can result is a continuum of hair curls, continuum of hair curls, waves and looks. waves and looks.

18. Incomplete dominance is also observed in Incomplete dominance is also observed in Sickle-cell Disease. Here homozygotes (HH) are normal, Sickle-cell Disease. Here homozygotes (HH) are normal, heterozygotes (Hh s )are carriers, and recessives (h s h s ) heterozygotes (Hh s )are carriers, and recessives (h s h s ) have the disease. Oddly enough, carriers are superior in have the disease. Oddly enough, carriers are superior in certain environments due to Malaria resistance conferred certain environments due to Malaria resistance conferred by the Sickle-cell trait. by the Sickle-cell trait.

19. Sex-linked traits Sex-linked traits Occur when alleles are Occur when alleles are located on sex chromosomes. located on sex chromosomes. Sex-linked traits can be harsh. Sex-linked traits can be harsh. Ex.: Muscular distrophy & Hemophilia Hemophilia

20. Fig. 02-14 Muscular Distrophy

21. Fig. 02-15 Sex-Influence Traits

22. Fig. 2D

23. Fig. 2C