Deciphering Human Genetics: Chromosomes, Traits & Diseases

1. Unit 4 Genetics Ch. 14 The Human Genome

2. Human Chromosomes • To analyze chromosomes, biologists photograph cells in mitosis • They then cut out the chromosomes from the photograph, & group them together in pairs

3. Human Chromosomes • Karyotype - a picture of chromosomes arranged in pairs

4. Human Chromosomes • Sex chromosomes - 2 of the 46 chromosomes, that determine an individual’s sex • Females: XX • Males: XY • Autosomes - remaining 44 chromosomes

5. Human Traits • Pedigree - chart that shows the relationships within a family

6. Human Traits • Remember that the phenotype of an organism is determined by its genotype • Also, that environmental effects on gene expression are not inherited, genes are

7. Human Genes • The human genome, our complete set of genetic information, includes 10’s of 1000’s of genes • The DNA sequences on these genes carry information for specifying many characteristics

8. Human Genes • Many genetic disorders are caused by autosomal recessive alleles

9. Human Genes • However, some genetic disorders may be caused by a dominant allele • Ex.) Dwarfism, Huntington’s Disease (loss of muscle control, & mental function until death occurs)

10. From Gene to Molecule • In cystic fibrosis, & sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

11. From Gene to Molecule • Cystic fibrosis is caused by the deletion of 3 bases in the DNA of a single gene • As a result, the body does not produce a protein needed to transport chloride ions • CF causes serious digestive & respiratory problems

12. Cystic Fibrosis

13. From Gene to Molecule • Sickle cell disease is common in African Americans • It is characterized by the bent & twisted shape of the red blood cells • The cells get stuck in the capillaries, damaging cells, tissues, & organs • It causes physical weakness, & damage to the brain, heart, & spleen (may be fatal)

14. Human Genes & Chromosomes • Genes located close together on the same chromosome are linked, so they tend to be inherited together • Linked genes may be separated, however, during crossing-over

15. Sex-Linked Genes • Sex-linked genes - genes located on the sex chromosomes • Males have 1 X chromosome, therefore, all X-linked alleles are expressed in males, even if they are recessive

16. Sex-Linked Genes • Ex. of sex-linked disorders: colorblindness, hemophilia, muscular dystrophy

17. Chromosomal Disorders • Nondisjunction - when homologous chromosomes fail to separate during meiosis • If it occurs, abnormal #’s of chromosomes could find their way into gametes, & a disorder of chromosome #’s may result

18. Chromosomal Disorders • Down Syndrome results when there is an error on chromosome 21

19. Human DNA Analysis • DNA Fingerprinting - (Gel Electrophoresis), analyzes sections of DNA that vary from 1 individual to another

20. DNA Fingerprinting

21. The Human Genome Project • The Human Genome Project is an ongoing effort to analyze the human DNA sequence • Biotechnology companies are rushing to find genetic info. that may be used in developing new drugs & treatments for diseases

22. Gene Therapy • In gene therapy, an absent or faulty gene is replaced by a normal, working gene • Viruses are often used because they can enter cells so easily

23. Ethical Issues in Human Genetics • The goal of biology is to gain a better understanding of the nature of life • As our knowledge increases, so does our ability to change the genetics of living things, including humans • What will happen to the human species if we design our bodies?