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Cell Division and Genetics

Table 4, 3rd Period

Lindsay Keare, Flint Mitchell, Chris Scherm, Wendy Wang

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

Categories of Cells in Humans• Sex cells a.k.a. gametes

– sperm and eggs– Do meiosis, involved in reproduction

• Somatic cells-all other cells– Neurons, blood cells, muscle cells, etc.– Do mitosis, not involved in reproduction

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

Mitosis: The Process by which Eukaryotic Cells Divide

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)

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

Mitosis (Cont.)

http://www.youtube.com/watch?v=HYKesI9jL8c

Mitosis (Cont.)

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

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

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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

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

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

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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

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Mendel and the Gene Idea

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

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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

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

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

Genetic Variability

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

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”

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

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

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