1. Chromosomes and Cell Reproduction Chromosome structure and role in development and reproduction

2. What allows a few cells to grow into a human being?

3. During cell division, what allows each cell to receive the proper genes?

4. Objectives Identify examples of cell division in prokaryotes and eukaryotes Distinguish between a gene, a DNA molecule, a chromosome, and a chromatid Differentiate between homologous chromosomes, autosomes, and sex chromosomes Compare haploid and diploid cells Predict how changes in chromosomes can affect development

5. Why cell division? Growth Tissue repair Replace worn out cells Asexual reproduction

6. Why are we interested in chromosomes? Vitally important that each new cell receives the proper set of chromosomes to function properly Each organism has a characteristic number of chromosomes We need to understand the structure of chromosomes and the role of chromosomes in the cell

7. Different types of cell division – all involve passing on DNA Bacterial cell division – Binary Fission Division of body cells in eukaryotes - Mitosis Formation of gametes (reproductive cells) in eukaryotes - Meiosis

8. Prokaryotic Cell Division Called Binary Fission Form of asexual reproduction Single parent passes on exact copies of all DNA to offspring First stage = single circular DNA molecule is copied Second stage = Cell divides

9. Eukaryotic Cell Division Much more complicated process due to larger amount of genetic information (genes) Genes = segment of DNA that codes for a protein or RNA molecule When genes being used, DNA (chromatin – DNA and its associated proteins) is stretched out Before cell division, DNA must divide and then coil up into chromosomes

10. Chromatids and Centromere Chromatids will become separated during cell division 1 Chromatid will be placed into each new cell This ensures that each new cell will have the same genetic material as the original cell

11. Chromosome Number and Structure Each human body cell (excluding sperm and egg cells) has 2 copies of 23 different chromosomes Total chromosomes = 46 Each chromosome contains thousands of genes Genes play important role in how person’s body develops and function

12. Homologous Chromosomes Each pair of chromosomes = homologous chromosomes Chromosomes similar in size, shape and genetic content Each homologue comes from one of the two parents One set = Ma One set = Pa

13. Somatic Vs Sex Cells = Diploid Vs Haploid Body cells (non-sex cells) = somatic cells A cell that contains 2 sets of chromosomes (i.e. a somatic cell) = diploid or 2n A cell that contains only one set of chromosomes (i.e. a sex cell or gamete) = haploid or n For humans n = 23. That is how many chromosomes our gametes have. 2n = 46. That is how many chromosomes our somatic cells have

14. Zygote Fusion of two haploid gametes = fertilization Diploid zygote formed by fertilization = first cell of a new individual

15. Different Types of Chromosomes AutosomesSex Chromosomes Chromosomes that are not directly involved in determining the sex (gender) of an individual One of the 23 pairs of chromosomes in humans Determine the sex of the individual Humans and many other animals - X and Y chromosomes Anyone with a Y chromosome is male. Female = XX; Male = XY Female can only give an X, so sex of offspring determined by father

16. Change in chromosome number Genes help determine how body develops and functions All 46 chromosomes must be present for normal development/function Too many or too few chromosomes leads to problems Abnormalities in chromosome number detected by a karyotype - a photo of chromosomes in dividing cell - shows chromosomes arranged by size

17. Down Syndrome – Trisomy 21 Extra copy of chromosome 21 Short stature, round face, mental retardation Occurs more frequently in older mothers Mothers younger than 30 – 1 in 1500 births Mothers over 45 – 1 in 46 births

18. How does someone end up with an extra chromosome? When sperm and egg cells form (during meiosis) each homologous pair separates (disjunction) If chromosomes fail to separate (non-disjunction) one gamete ends up with both chromosomes and the other gamete gets none Trisomy – gamete with both chromosomes fuses with normal gamete

19. Changes in chromosome structure Mutations = changes in chromosome structure Chromosome breakage  4 types of mutations Duplication = chromosome fragment attaches to homologous chromosome (which then carries 2 copies of set of genes) Inversion = chromosome fragment reattaches to original chromosome but in reverse order Translocation = chromosome fragment reattaches to non-homologous chromosome Deletion = a piece of a chromosome breaks off

20. Types of mutations InversionTranslocation

21. Types of Mutations DeletionDuplication