genetics--nuclear division & inheritance
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Genetics--Nuclear Division & Inheritance. Mitosis & Meiosis. Introduction. What is Genetics? What level of organization is being examined? molecular, cellular, species, or population What is the purpose of this lab?. Somatic versus Reproductive Cells. Somatic cells : - PowerPoint PPT PresentationTRANSCRIPT
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Genetics--Nuclear Division & Inheritance
Mitosis & Meiosis
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Introduction
• What is Genetics?
• What level of organization is being examined?– molecular, cellular, species, or population
• What is the purpose of this lab?
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Somatic versus Reproductive Cells
• Somatic cells:– all except the reproductive
cells
– 2 copies of each chromosome
– diploid
– example: in humans, the diploid number is 46
• Reproductive or sex cells:– haploid
– 1 copy of each chromosome
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Nuclear Division
• Mitosis– prior to mitosis chromosomes are duplicated– nuclear division in somatic cells– genetic info from “parent” to daughters– cancer: uncontrolled cell division
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Nuclear Division
• Meiosis– prior to meiosis: chromosomes are duplicated– nuclear division in the sex cells– genetic diversity
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Cytokinesis
• division of the cytoplasm• occurs at the end of mitosis• occurs at the end of meiosis I• occurs at the end of meiosis II
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Interphase
Mitosis
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Interphase
• no nuclear or cell division
• DNA replication, chromosome duplication, and cell growth
• “chromosomes,” not visible inside nucleus
• but can see nucleolus inside nucleus
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Mitosis
• Four phases of mitosis:
– prophase
– metaphase
– anaphase
– telophase
• End result of mitosis: 2 daughter cells
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Prophase
• Duplicated chromosomes condense and become visible as sister chromatids joined at the centromere
• nuclear membrane disintegrates; neither the nucleus nor the nucleolus is distinct
• spindle apparatus of the cell is formed
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Early prophase
Prophase
Prophase
• Chromatin condenses into discrete chromosomes– two identical “sister
chromatids”
– joined at the centromere
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Metaphase
• Chromosomes are aligned along the cell’s equator at their centromeres
• spindle fibers are visible
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MetaphaseChromosomes convene on the metaphase plate, an imaginary “equator” located between the two poles of the spindle. Centromeres are aligned, and sister chromatids of each chromosome straddle the metaphase plate.
Metaphase plate
Spindle fibers
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Anaphase
• Migration of the chromosomes: – centromeres split – move along the spindle fibers towards opposite
poles – pulling the sister chromatid
• Each chromatid -- a chromosome
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AnaphaseThe sister chromatids separate from each other and move along the spindle fibers towards opposite poles. Each chromatid is now considered a chromosome.
Early anaphase
Anaphase
Spindle poles
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Anaphase
Late anaphase
By the end of anaphase, each pole has an equivalent and complete set of chromosomes.
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Telophase
• Chromosomes are aggregated at the poles and begin to thin out and extend in length
• new nuclear membrane forms; nucleolus and nucleus begin to reappear
• spindle disintegrates
• cytoplasm divides (cytokinesis occurs); daughter cells begin to form
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Telophase
Late telophase
Cytokinesis begins, separating the cytoplasm into 2 “daughter cells”.
Telophase
• The “daughter” nuclei begin to form at the two poles
• Nuclear membranes begin to form
• chromosomes lose their distinct appearance.
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Daughter Cells
Telophase
• formation of 2 daughter cells
• Each daughter cell has same genetic material as parent
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Meiosis: Reproductive or Sex Cells• Gametes
– female gametes: “eggs” or “ova” (ovum, singular)
– male gametes: “sperm”
– HAPLOID, have 1 copy of each chromosome (i.e., 1/2 as many chromosomes as somatic cells)
– example, in humans, the haploid number is 23.
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Meiosis in the Lily Anther
• Lily anther:
– male reproductive organ in flowering plants.
– meiosis takes place
– result: haploid pollen grains
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Meiosis in the Lily Anther• A very thin cross-section of a lily anther
• stain it
• examine with a compound light microscope:
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Meiosis in the Lily AntherEach anther contains 4 pollen sacs where meiosis takes place.
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Meiosis in the Lily Anther
• Study the various phases of meiosis in prepared slides of the lily anther.
• look at the cells inside the pollen sacs
• locate the different phases.
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Stages of Meiosis
Meiosis consists of meiosis I and meiosis II and both have 4 stages leading up to the actual cell division.
Meiosis I: Meiosis II:
Prophase I Prophase II
Metaphase I Metaphase II
Anaphase I Anaphase II
Telophase I Telophase II
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Meiosis: Prophase I
Chromatin condenses into discrete chromosomes. Chromosome is actually composed of 2 sister chromatids.
Homologous chromosomes come together as pairs.
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Meiosis: Metaphase I
Metaphase plate
Spindle fibers
• Chromosomes are arranged on the metaphase plate, still in homologous pairs.
• Spindle fibers from each pole attach to one chromosome of each pair of the homologue.
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Meiosis: Anaphase I
• each homologous pair of chromosomes separate and move toward opposite poles.
• each chromosome still consists of 2 sister chromatids joined together at the centromere.
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Meiosis: Telophase I
Haploid
Haploid
• Chromosomes have moved to opposite poles.
• Cytokinesis separates the cytoplasm into 2 daughter cells.
• Each cell is now haploid.
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Meiosis: Prophase IIIn prophase II, the chromatin again condenses so the chromosomes have a distinct shape.
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Meiosis: Metaphase II
In metaphase II, chromosomes align on the metaphase plate.
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Meiosis: Anaphase II
• sister chromatids separate, and move towards opposite poles
• sister chromatids are now individual chromosomes.
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Meiosis: Telophase II
Haploid
Haploid Haploid
Haploid
• nuclei begin to form at opposite poles, and cytokinesis occurs
• 4 daughter cells, each with the haploid number of chromosomes.
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Meiosis I: Review
Prophase I Metaphase I
Telophase IAnaphase I
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Review: Meiosis II
Prophase II Metaphase II
Anaphase II Telophase II
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Chromosomes and Genes• one long strand of
DNA• associated proteins
– “chromatin”
• thousands of genes• gene
– discrete unit of heredity
• locus– physical location of a
gene
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Homologous Chromosomes, Genes, and Alleles
• Chromosome pair:– “homologous
chromosomes”
• pair has genes at the same loci– “alleles”
– may be the same or different
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Human Genetics
• Genotype– heterozygous– homozygous
• Phenotype
• Observe traits and identify which form you possess
• Make a table
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Extra 21st chromosome
Heredity and Genetic Disorders
• Video, “Healthy, Heredity, and Genetic Disorders”
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Mechanics of Mitosis
• Answer questions– use instructional materials available
• video: Mechanics of Mitosis
• posters
• Photo Atlas of Biology
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Mitosis in the Onion Root Tip
• Today’s lab exercises
– examine the tip of an onion root
– find and identify the 4 different phases of mitosis.
• Root tips are useful material because the cells are frequently dividing as the root grows.
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Growth and Mitosis in Onion Root Tips
A) Examine onion (Allium) root tip under low power objective (10x)– answer questions
B) Examine same slide under high power objective (40x)– follow instructions
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Meiosis: The basis of Genetic Inheritance and Sexual
Reproduction
• Mechanics of Meiosis– Answer questions
• use instructional materials available– video: Mechanics of Meiosis
– posters
– Photo Atlas of Biology
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Meiosis and Gamete Formation in Lily Anthers
• Observe first and second meiotic division in demonstration slides
Note:
•DO NOT move the slides out of position
•Use only FINE focus