Genetics--Nuclear Division

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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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Prophase

• Chromatin condenses into discrete chromosomes
• two identical sister chromatids
• joined at the centromere

Early prophase
Prophase
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Metaphase

• Chromosomes are aligned along the cells equator
  at their centromeres
• spindle fibers are visible

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Metaphase
Chromosomes 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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Anaphase
The sister chromatids separate from each other
and move along the spindle fibers towards
opposite poles. Each chromatid is now considered
a chromosome.
Spindle poles
Early anaphase
Anaphase
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Anaphase
By the end of anaphase, each pole has an
equivalent and complete set of chromosomes.
Late anaphase
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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

• The daughter nuclei begin to form at the two
  poles
• Nuclear membranes begin to form
• chromosomes lose their distinct appearance.

Telophase
Cytokinesis begins, separating the cytoplasm into
2 daughter cells.
Late telophase
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Telophase

• formation of 2 daughter cells
• Each daughter cell has same genetic material as
  parent

Daughter Cells
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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 Anther
Each 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

• 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.

Spindle fibers
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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

• Chromosomes have moved to opposite poles.
• Cytokinesis separates the cytoplasm into 2
  daughter cells.
• Each cell is now haploid.

Haploid
Haploid
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Meiosis Prophase II
In 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

• nuclei begin to form at opposite poles, and
  cytokinesis occurs
• 4 daughter cells, each with the haploid number of
  chromosomes.

Haploid
Haploid
Haploid
Haploid
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Meiosis I Review
Prophase I
Metaphase I
Telophase I
Anaphase 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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Heredity and Genetic Disorders

• Video, Healthy, Heredity, and Genetic Disorders

Extra 21st chromosome
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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

• Todays 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