Cell Division and Genetics

1. Cell Division and Genetics Table 4, 3rd Period Lindsay Keare, Flint Mitchell, Chris Scherm, Wendy Wang

2. The Cell Cycle • Unicellular organisms reproduce and eventually form multi-cellular organisms with specialized cells via cell division • Bacteria do binary fission: the chromosomes replicate, then daughter chromosomes move apart and pinch off

3. Categories of Cells in Humans • Sex cells a.k.a. gametes • sperm and eggs • Do meiosis, involved in reproduction • Somaticcells-all other cells • Neurons, blood cells, muscle cells, etc. • Do mitosis, not involved in reproduction

4. DNA and Cell Division • Cells replicate their DNA before dividing, causing chromosomes—the genetic material of the cell—to consist of two sister chromatids joined together by a centromere • Chromosomes are made up of chromatin—DNA and its proteins

5. Mitosis: The Process by which Eukaryotic Cells Divide

6. Mitosis (Cont.) • When a cell is not dividing, it is in interphase • The three phases of interphase are G1, S1, and G2 • DNA replication occurs during the synthesis phase (S-Phase)

7. Mitosis (Cont.) • Cyclin: activates protein kinases, enzymes that activate or inactivate other proteins and thus prompt the cell to being certain phases • MPF-”maturation-promoting factor,” triggers the start of the M-phase

9. Mitosis (Cont.) http://www.youtube.com/watch?v=HYKesI9jL8c

10. Mitosis (Cont.) • Mitosis and cytokinesis—division of cytoplasm after telophase—occur during the mitotic phase (M-phase)

11. During cytokinesis, animal cells (and certain types of Plantae like algae) form a cleavage furrow and pinch apart; plant cells form a cell plate

12. Meiosis and Sexual Life Cycles • Offspring inherit genes from their parents • Genes exist at a specific locus on a chromosome • Sexual reproduction consists of two sets of genes from two different parents and creates genetically diverse offspring • In asexual reproduction, one parent produces genetically identical offspring by mitosis

13. Meiosis • When an egg and a sperm unite, they form a zygote: a single-celled diploid that develops into a multi-cellular organism • Meiosis creates 4 haploid cells from one diploid cell • Consists of meiosis I and meiosis II

16. Meiosis in Humans • Human somatic cells contain 46 chromosomes, 23 from each parent, and thus are diploid because they have two complete sets of chromosomes • The 23rd pair are called the sex chromosomes; they determine a person’s gender • Haploid (one only set of chromosomes) gametes are formed by meiosis; thus, each gamete contains only 23 chromosomes

17. Genetic Variation in Reproduction • Independent assortment of chromosomes during meiosis, crossing over in meiosis I, and random fertilization of eggs by sperm allow for genetic variation, as these vents result in recombinant chromosomes • Mutations are at the root of genetic variation and allow for new combinations of genes

18. Mendel and the Gene Idea • In the 1860s, German monk Gregor Mendel experimented with the idea of inheritance by doing experiments with garden peas

19. Mendel’s Ideas • Law of Segregation: genes have alternative forms (alleles); each organism receives one allele from each parent • For each heritable characteristic, the two alleles segregate during gamete formation, so they end up in different cells

20. Alleles • Most alleles are either dominant or recessive • Heterozygous: contains two different alleles, shows dominant trait • Homozygous dominant: contains two dominant alleles, shows dominant trait • Homozygous recessive: contains two recessive alleles, shows recessive trait

22. Genotypes and Phenotypes • An organism’s genotype is its set of alleles • An organism’s phenotype is affected by both its genotype and its environment

23. Genetic Variability • Law of Independent Assortment: Pairs of alleles segregate independently of one another during meiosis • Allows for genetic variation among offspring

24. The Chromosomal Basis of Inheritance • The Chromosomal Theory of Inheritance: “Genes are located on chromosomes… and the behavior of chromosomes during meiosis accounts for Mendel’s Laws of Segregation and Independent Assortment”

25. Sex-linked Genes • Sex is determined by whether an organism has a Y chromosome (which makes it a male) • Sex-linked genes are found on sex chromosomes and can thus make it more likely for a certain gender to inherit a certain allele • In mammalian females, one of the X chromosomes is inactivated, forming a Barr body

26. Variability at the Chromosomal Level • Genes that are located near each other on the same chromosome tend to be inherited together • Chromosome breakage, such as deletion, duplication, inversion, and translocation can have a drastically negative effect or no effect at all

27. Credits Data and diagrams: Campbell Biology, Ninth Edition, AP Edition Title Slide Photo: http://publications.nigms.nih.gov/insidethecell/inside-the-cell_backdrop.jpg?cachebuster=0.575484572444111&timestamp=1229904000020 Mitosis Video: http://www.youtube.com/watch?v=HYKesI9jL8 Cleavage Furrow: http://plantphys.info/plant_physiology/cellcycle.shtml DNA: http://www.teenjury.com/can-a-company-patent-your-genes/ Peas: http://www.davislifemagazine.com/2011/04/peas-please/ Mendel: http://www.csmonitor.com/Innovation/2011/0720/Why-you-should-care-about-Gregor-Mendel