Honors Biology- Chapter 14

The Human Genome Project  Completed in 2003  13 year project  discovered all the estimated 20,000-25,000 human genes  determined the complete sequence of the 3 billion DNA bases in the human genome  used the bacterium E.coli to help with the project

14.1 Human Chromosomes A. Background Info 1. We can view a person’s genome on a karyotype. a. this will allow us to see the number of chromosomes a person has and the person’s gender 2. Transmission of Human Traits a. dominant & recessive alleles b. Codominant & Multiple alleles c. sex linked inheritance

3. Mammals only need the genes on one X chromosome. a. in females, one of the X chromosomes is inactivated creating something called a Barr Body

B. Pedigrees 1. Used to study inheritance patterns 2. How to read pedigrees a. = male, = female b. Colored shapes = individual shows the trait c. Parents are connected with horizontal lines d. Their children are underneath them 3. Most of the genotypes can be determined by looking at the patterns - Pg. 397

14.2. Human Genetic Disorders A. Non-separation of chromosomes 1. During meiosis chromosomes may not separate correctly producing the wrong number of chromosomes in the cell a. Called nondisjunction 2. this could leave a sex cell with an extra copy of a chromosome or without a copy 3. can happen in meiosis I or II 4. Nondisjunction is more likely to occur in a female’s sex cell as she gets older. a. The longer the egg cell is stopped in the middle of meiosis, the more likely it is to complete the process incorrectly.

B. Down Syndrome 1. Genetic disease that results in a duplication of the 21 st chromosome in the egg or sperm 2. Called Trisomy 21 because the person has 3 copies of the 21 st chromosome 3. The person has 47 chromosomes instead of Affects 1 out of 700 children born in the US 5. Most embryos with an abnormal chromosome number do not survive, but Trisomy 21 embryos can survive

C. Recessive Inherited Diseases 1. Most of the time children who inherit a recessive disease, have parents that are carriers a. Carriers are heterozygous for the recessive disease and do not show any symptoms b. Punnett squares can be used to determine the possibility of inheriting a recessive disease c. Ex. Albinism, deafness, Tay-Sachs, Cystic Fibrosis

D. Dominant Inherited Traits 1. Affect the heterozygous individual 2. usually being homozygous dominant is lethal 3. Huntington’s Disease is a dominant disorder that doesn’t cause death until adulthood, so it affects multiple generations in a family.

E. Sex linked Disorders 1. Most sex linked disorders are located on the X chromosome 2. A male only needs one recessive allele to be affected but females need 2 recessive alleles to be affected 3. Ex. Color blindness

F. Predicting and Treating Genetic Diseases 1. Genetic counselors help a couple with a questionable family history determine the risk of a genetic disease being passed down to their child a. Perform karyotypes on the child and can test the fluid in the sac surrounding the baby for chemical abnormalities 2. Tests are also performed right after birth at the hospital regardless of family history. a. This helps prevent side effects from the disease going untreated