Genetics CH5 SEC

Transcription

1 Genetics CH5 SEC

2 Sex Chromosomes Sex chromosomes carry genes that determine sex. In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). During meiosis in females, each cell will receive an X chromosome. In males, the new cells will either receive an X or a Y chromosome. Therefore, male sperm determine the sex of the offspring.

3 Sex-linked Disorders Since females have 2 copies of the X chromosome, they always have a backup of each gene in case one becomes damaged. The Y chromosome does not carry all of the genes of an X chromosome, and they do not have an extra X chromosome. The genes for some disorders are carried on the X chromosome, making males more susceptible to the disorder. Colorblindness is one such sex-linked disorder. About 8 % of males are color blind while only 0.5 % of females are color blind. Red/Green color blindness is the most common form.

4 Genetic Disorders Down Syndrome Caused by the presence of all or part of a third copy of chromosome 21 It is typically associated with physical growth delays, characteristic facial features and mild to moderate intellectual disability.

5 Achondroplasia A form of dwarfism that can be inherited or the result of a mutated gene. It is genetically dominant. If one parent has the gene, then the offspring has a 50% chance of inheriting the disorder. If BOTH parents have the disorder, the offspring will not likely survive.

6 Hemophilia Inherited from one's parents through an X chromosome with a nonfunctional gene. Inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. Klinefelter Syndrome A set of symptoms that result from two or more X chromosomes in males resulting in 47 rather than 46 chromosomes. Males with this condition are sterile. Other symptoms are weaker muscles, greater height, poor coordination, less body hair, smaller genitals, and breast growth.

7 Prader-Willi Syndrome A genetic disorder due to loss of function of specific genes on chromosome 15 Symptoms include weak muscles, constant hunger, intellectual impairment and behavior problems. Often the forehead is narrow, hands and feet small, height is short, skin is light in color, and they are unable to have children Sickle-Cell Disease A blood disorder in which a person inherits two abnormal copies of the hemoglobin gene, one from each parent. Red blood cells are rigid, sickle shaped. A number of health problems may develop, such as attacks of pain, anemia, bacterial infections, and stroke. Long term pain may develop as people get older. The average life expectancy in the developed world is 40 to 60 years.

8 Genetic Counseling Genetic counselors help people learn about genetic disorders and their chance of being affected or passing a condition on to offspring. A Pedigree is a tool used by genetic counselors to trace genetic conditions though a family tree. A pedigree can help predict whether a person is a carrier of a hereditary disorder.

9 Selective Breeding The practice of selecting organisms with desirable traits for breeding. A pug A Beagle A Puggle

10 How have humans changed fruits and vegetables over time through selective breeding? COM/HERE -S-WHAT -FRUITS-AND- VEGETA BLES-LOOKED-LIKE-BEFORE -WE-DOMESTICATED-THEM

11 Review 1. What gender is a person with XY sex chromosomes? Male 2. If a couple has 3 male children, what is the chance that their 4 th child will be female? 50% (every time) 3. Why are more males color-blind than females? It is a sex-linked disorder. Males do not have an extra X chromosome. 4. Is it possible to predict some genetic conditions? Yes, through genetic counseling, tests, pedigrees 5. Name a genetic disorder 6. Why do humans use selective breeding? To increase desirable traits.