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 aligned along 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 genome completed 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

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)
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.