Chapter 2: Genes and Heredity

1. Chapter 2: Genes and Heredity How Traits and Genetic Abnormalities are Inherited By Kati Tumaneng (for Drs. Cook & Cook)

2. Dominant-Recessive Traits • Dominant-Recessive Relationship is a relationship between genes where the dominant allele will govern a particular trait, and the recessive allele will be repressed. To express a recessive trait, the individual needs to inherit two recessive alleles – one on each chromosome.

3. Dominant-Recessive Traits • Dominant Gene Diseases • Huntington Disease is the most common example. • Symptoms do not usually appear until after 30, causes progressive damage to brain and nervous system and involuntary movements

4. Dominant-Recessive Traits

5. Dominant-Recessive Traits • Recessive Gene Diseases • Less common because two recessive alleles need to be inherited before the individual shows the condition • Cystic fibrosis most common among Caucasians; nearly 1 in 22 carry gene • Sickle cell disease most common in those of African or Hispanic descent • Tay-Sachs diseasefatal in childhood

6. Dominant-Recessive Traits

7. Dominant-Recessive Traits • X-Linked (Sex-Linked) Traits • Differences in males and females caused by dominant and recessive alleles on the X and Y chromosomes. • Y chromosome small; contains little genetic material. • Since many genes on X chromosome do not have counterpart on Y, males (XY) more likely to suffer recessive disease traits. • Hemophilia, Duchenne muscular dystrophy, and color blindness – more likely in males.

8. Dominant-Recessive Traits • X-Linked (Sex-Linked) Traits (cont.) • Dominant disease alleles on X chromosomes are very rare. • Females are two times more likely to have these types of diseases than males. • Vitamin D-resistant rickets • Rett syndrome

9. Chromosome Abnormalities • 1 in every 160 live births • Account for majority of miscarriages • Errors occur that cause sperm or egg to have a missing or extra chromosome • Down Syndrome – extra 21st chromosome

10. Down Syndrome

11. Chromosome Abnormalities

12. Prenatal Screening and Genetic Testing

13. Prenatal Screening and Genetic Testing • Ultrasonography (ultrasound) – Images, produced by sound waves, of the fetus inside the mother’s womb. Help physicians monitor fetal growth and detect physical defects. • Amniocentesis – Procedure used to detect chromosomal and genetic abnormalities in the fetus. A needle is inserted through the mother’s abdomen and uterus and into the amniotic sac, and fetal cells are withdrawn from the amniotic fluid. • Chorionic Villus Sampling (CVS) – Procedure used to detect chromosomal and genetic abnormalities in the fetus. A catheter (tube) is inserted into the uterus and cells are taken from the chorionic layer of the placenta around the fetus. Chromosomes are removed to conduct genetic tests. National Society of Genetic Counselors www.nsgc.org

14. Prenatal Screening and Genetic Testing

15. Dominant Disease Alleles on Slide 4: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 57). Boston: Allyn and Bacon. • Recessive Disease Alleles on Slide 6: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 58). Boston: Allyn and Bacon. • Chart on Slide 10: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 61). Boston: Allyn and Bacon. • Ultrasound on Slide 12: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 63). Boston: Allyn and Bacon. • Image on Slide 14: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 64). Boston: Allyn and Bacon. • All other images retrieved from Microsoft PowerPoint Clip Art.