Cellular and Organismal Reproduction

1. Cellular and Organismal Reproduction Set numbers of chromosomes are copied exactly and distributed during cell division.

2. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

3. Bacteria divide in a simple form of reproduction called Binary Fission. • A bacterium has a single circular chromosome. • This single chromosome is duplicated. • The cell pinches together and forms 2 new cells, each containing exactly the same genetic information. • This is much simpler than the division that eukaryotes, like humans, use.

4. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

5. A chromosome is a combination of DNAwrapped around proteinsthat help it to keep its shape. Chromosomes are... • stretched out very thin while being used. • broken up into thousands of different sections of information called genes. Eachgene is responsible for the production of one type of protein.

6. Before division, each chromosome must be copied and condensed to facilitate movement. • The replication of a chromosome, results in two identical sister chromatids bound at a region called the centromere. • Each of the sister chromatids is ½ of the old DNA strand, and ½ newly formed nucleotides. Replication

7. The copying of DNA is known as replication. • The two strands of DNA are pulled apart by the enzyme DNA Helicase. • Nucleotides with the matching bases are attached to each open spot by the enzyme DNA Polymerase.

8. Sexually reproducing organisms always have an even number of chromosomes. Pairs = X 2 2 x 2 = 4 3 x 2 = 6 13 x 2 = 26 ETC… • Each chromosome is part of a homologous pair, that are identical in size, shape and gene types (23 pairs = 46 total in humans). • Each of an organism’s parents contributed one member to the homologous pair. • Homologous pairs contain the same genes, but perhaps in different variations. (e.g. blue eyes or brown eyes for the eye color gene)

9. Chromatids versus Homologues Resulting from fertilization Resulting from replication

10. A karyotype shows each of an organism’s chromosomes aligned with its homologous partner. Sex Chromosomes of a male

11. Some cells have half the normal number of chromosomes. • Normal body cells are called Somatic cells and sex cells (sperm and egg) are called Gametes. • “n” represents the number of chromosome types in an organism. • Somatic cells are called diploid (2n), since they always contain pairs of homologous chromosomes (23 pairs = 46). • Gametes are called haploid (n), since they always contain one of each type of chromosome (23 individual chromosomes). • Fertilization of a haploid (n) egg by a haploid (n) sperm yields a diploid (2n) Zygote(n + n = 2n).

12. One of the pairs of chromosomes controls the gender of the individual. • Most chromosome are called Autosomes, and play no part in gender determination (in humans = Chromosome pairs # 1-22). • The Y chromosome holds all the genes that cause an embryo to become male. • Females have two X chromosomes (XX). • If an embryo has one Y chromosome, it becomes a male (XY). • Therefore, males always determine the sex of the offspring.

13. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

14. The Cell Cycle describes the life of a Eukaryotic cell. • The Cell Cycle (5 stages) is a repeating sequence of growth and division. • A cell spends 90% of its life in the first 3 phases of the cell cycle (collectively called Interphase). • The cell will only enter the second stage of the cycle if it is going to divide. • Eukaryotic cells must divide the contents of the nucleus as well as the contents of the cytoplasm. • Average time for this process is about 24 hours.

15. As checkpoints are met, signals are sent that prepare a cell to move forward.

16. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

17. Mitosis Mitosisoccurs in 4 very recognizable steps. Interphase (prior to Mitosis) • Prophase • Metaphase • Anaphase • Telophase “IPMAT” helps you to remember the order of events: Interphase, Prophase, Metaphase, Anaphase, Telophase

18. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

19. The purposes of mitosis and meiosis differ. • Mitosis is cell division that... • Allows unicellular organisms to reproduce. • Allows multicellular to organisms grow and develop. • Meiosisis cell division that… • produces cells with a reduced chromosome number. • allows sexually producing organisms to produce gametes for fertilization.

20. Meiosis

21. In Asexual reproductiona single parent passes copies of ALL of its genes to each of its offspring. • There is no fusion of haploid cells in asexual reproduction, instead, genetically identical clonesare created. • Asexual reproduction can happen in one of three ways: • Binary fission • Fragmentation • Budding

22. There are some advantages and disadvantages to asexual reproduction. • Advantage: In a stable environment, many offspring can be formed with very little energy used. (no gamete production or courtship). • Disadvantage: In a changing environment, there is little chance for evolutionary change, since new combinations of genes are only formed through mutations.

23. Sexual reproduction may have evolved as a way to repair damaged chromosomes. • Advantage: The constant recombining of genetic information causes muchvariation, keeping the species strong. • Disadvantage: An increase in the complexities of life (courtship, mating, child rearing) and the time it takes to produce the next generation.

24. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

25. An abnormal chromosome number can cause serious problems to a developing embryo. • Examination of a fetus's karyotypecan reveal chromosomal abnormalities. • Down syndrome is characterized by Trisomy of chromosome 21 (3 instead of 2 homologues). • This is caused by non-disjunction(abnormal separation). • Disjunctionis the normal separation of chromosomes during cell division.

26. Nondisjunction in Meiosis