Understanding Genes, Heredity, and Human Reproduction: The Four-Letter Code

1. Chapter 2: Genes and Heredity Genes and Human Reproduction By Kati Tumaneng (for Drs. Cook & Cook)

2. Genes and the Magical Four-Letter Code • Chromosomes – Strands of deoxyribonucleic acid (DNA) that contain genetic codes. • Human body has 23 pairs of chromosomes. • One pair are sex chromosomes – XX for females, XY for males. • DNA – two strands that twist around each other like a spiral staircase. Connect by a series of nucleotide bases (Adenine, Thymine, Guanine, and Cytosine).

3. Genes and the Magical Four-Letter Code • Gene – a segment of DNA that provides an instruction for a particular structure, function, or trait. • 30,000 genes alignedalong 46 chromosomes; each gene may contain many thousands of base pairs. • Estimated 3 billion base pairs in human genome. • Only approximately 10% of base pairs provide active instructions.

5. Genes and the Magical Four-Letter Code • Human Genome Project – multinational effort by governments and scientist to map the 3 billion nucleotide bases and 30,000 genes contained in human chromosomes. • Working draft of human genomecompleted in 2000; full genome reported in 2003. • Still need to determine meaning of base sequences and function of genes located. • When complete, scientist will know the genetic markers for every trait & disease that can be inherited. Human Genome Project http://www.genome.gov/10001772

6. Genes and the Magical Four-Letter Code • Could potentially escape devastating effects of many genetically determined diseases, but where do we draw the line?

7. Human Reproduction and Cell Division • Alleles – an alternate version of a gene; determine the unique traits of each individual. • Except for mutations, errors in cell divisions, and sex cells, every cell contains copy of chromosomes that originated at conception.

8. Human Reproduction and Cell Division: Mitosis • Mitosis – “copy division,” the type of cell division that occurs when chromosomes are copied into each new cell. • Weak base pair bonds “unzip.” • Each half forms new DNA strand to link back up with old strand. • Occurs throughout body as it forms and grows.

9. Mitosis

10. Human Reproduction and Cell Division: Meiosis • Meiosis – “reduction division,” the type of cell division that occurs during the formation of gametes (sperm and eggs). • Process reduces chromosomes to 23 in each gamete so fertilized egg has 46. • Ensures diversity in gene pool by allowing crossing-over of genetic material across pairs and random distribution of chromosomes among gametes.

11. Meiosis

12. Meiosis

13. Human Reproduction and Cell Division: Meiosis • Identical twins are the one exception because they do have the same genetic codes. • Monozygotic (MZ) Twins – identical twins; come from same fertilized egg (zygote). • Dizygotic (DZ) Twins – nonidentical twins; form when two eggs are fertilized by two different sperm cells.

14. Human Reproduction and Cell Division • Sex Chromosomes – the 23rd pair of chromosomes (in humans), specialized to determine the sex of the child and other characteristics. • Sex chromosomes consist of two types – X and Y. • Males are XY and Females are XX. • When sperm cells form, half have X and half have Y chromosomes. • Sex of offspring determined by which type of sperm fertilizes egg.

16. Figure 2.2 on Slide 4: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p.44). Boston: Allyn and Bacon. • Mitosis on Slide 9: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p.51). Boston: Allyn and Bacon. • Meiosis on Slide 11: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 52). Boston: Allyn and Bacon. • Meiosis on Slide 12: from Cook, J. L., & Cook, G. (2005). Child development: Principles and perspectives (1st ed.) (p. 53). Boston: Allyn and Bacon. • All other images retrieved from Microsoft PowerPoint Clip Art.