Meiosis & Variation Notes

Meiosis & Variation NotesObj. 1: Define Meiosis and explain its benefits.

Obj. 3: Describe 2 ways meiosis causes genetic variation in organisms.

Obj. 4: Explain the importance of genetic variation.MeiosisMeiosis: a special kind of cell division that forms 4 sex cells (gametes), each with half the number of chromosomes as the parent cell.Benefits of MeiosisVariationKeep number of chromosomes constant after fertilization.Terms to Know:1. Gamete: sex cells (egg or sperm)2. Diploid: any cell that contains 2 complete sets of chromosomes (body cells; 2n=46)3. Haploid: any cell that contains 1 complete set of chromosomes (gametes; n=23)4. Homologous chromosomes: a pair of chromosomes, each with the same type and number of genes; one is maternal, one is paternal5. Phenotype: physical characteristics

If meiosis did not occur, the number of chromosomes would double with each new generation.VariationVariation: Differences among members of the same population.Examples: height, color of hair, length of beaks, etc.VariationKey to a populations survival in a changing environment.

As the degree of variation in a population increases, so does the likelihood that the species will survive.Diversity (Variety) = Stability

Organisms that reproduce sexually have much more variation than those that reproduce asexually.2 Ways that Meiosis Causes Genetic Variation Crossing Over:Occurs at the Prophase I of Meiosis I.Genes are exchanged between pairs of homologous chromosomes.

2 Ways that Meiosis Causes Genetic Variation 2. Independent Assortment:Occurs during Metaphase I of Meiosis I, when the chromosomes line up in the middle. Maternal and paternal chromosomes line up randomly and independently of each other.

9Phases of MeiosisObjective 2: Describe and order major events of meiosis. InterphaseNormal Cell ActivitiesDNA replicationProphase 1 of Meiosis 1Homologous (duplicated) chromosomes condense and pair upNuclear membrane dissolvesCrossing over occurs

Metaphase 1 of Meiosis 1Homologous chromosomes line up in the middle of the cell next to their pairRandom/Independent assortment

Anaphase 1 of Meiosis 1Homologous Chromosomes separate and move to opposite sides of the cell

Telophase 1 of Meiosis 1Membrane pinches in and Cytokenesis occurs forming 2 haploid cells

Prophase 2 of Meiosis 2Duplicated chromosomes re-condense

Metaphase 2 of Meiosis 2Duplicated chromosomes line up in the middle of the cell.

Anaphase 2 of Meiosis 2Duplicated chromosomes split and move to opposite sides of the cell.

Telophase 2 of Meiosis 2Membrane pinches in and Cytokenesis occurs forming 4 haploid cells

Summary of Divisions

Cytokinesis: Division of cytoplam, forming 4 haploid cells

1 Diploid Cell 2 Haploid Cells 4 Haploid Cells

*DNA replication DOES NOT occur between Meiosis I and Meiosis II!

20Mitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits / Purpose1. Growth2. Repair & Maintenance3. Reproduction Number of cells producedType of cells producedMitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits of each type of division1. Growth 2. Repair & Maintenance3. Reproduction 1. Variation2. Same # of chromosomes after fertilizationNumber of cells producedType of cells producedMitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits of each type of division1. Growth 2. Repair & Maintenance3. Reproduction 1. Variation2. Same # of chromosomes after fertilizationNumber of cells produced2Type of cells producedMitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits of each type of division1. Growth 2. Repair & Maintenance3. Reproduction 1. Variation2. Same # of chromosomes after fertilizationNumber of cells produced24Type of cells producedMitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits of each type of division1. Growth 2. Repair & Maintenance3. Reproduction 1. Variation2. Same # of chromosomes after fertilizationNumber of cells produced24Type of cells producedBody CellsMitosis vs Meiosis: The ShowdownMitosisMeiosisBenefits / Purpose1. Growth 2. Repair & Maintenance3. Reproduction 1. Variation2. Same # of chromosomes after fertilizationNumber of cells produced24Type of cells producedBody CellsGametesMitosis vs Meiosis(continued)MitosisMeiosisNumber of chromosomes in resulting cellsNumber of DivisionsGenetic Variation in Daughter Cells(Yes or No)Mitosis vs MeiosisMitosisMeiosisNumber of chromosomes in resulting cellsDiploid(46 in Humans)Number of Divisions

Genetic Variation in Daughter Cells(Yes or No)Mitosis vs MeiosisMitosisMeiosisNumber of chromosomes in resulting cellsDiploid(46 in Humans)Haploid(23 in Humans)

Number of Divisions

Genetic Variation in Daughter Cells(Yes or No)Mitosis vs MeiosisMitosisMeiosisNumber of chromosomes in resulting cellsDiploid(46 in Humans)Haploid(23 in Humans)

Number of Divisions

1Genetic Variation in Daughter Cells(Yes or No)Mitosis vs MeiosisMitosisMeiosisNumber of chromosomes in resulting cellsDiploid(46 in Humans)Haploid(23 in Humans)

Number of Divisions

12Genetic Variation in Daughter Cells(Yes or No)NoMitosis vs MeiosisMitosisMeiosisNumber of chromosomes in resulting cellsDiploid(46 in Humans)Haploid(23 in Humans)

Number of Divisions

12Genetic Variation in Daughter Cells(Yes or No)NoYesNOTES: Human Chromosome Abnormalities & Karyotyping

Chromosome numbers

35All even, as all are diploid, contain pairs of chromosomes.ChromosomesKaryotype: ordered display of an individuals chromosomes.Collection of chromosomes from mitotic cells.Staining can reveal visible band patterns, gross anomalies.36

37

38Karyotyping

39

Types of Chromosomal Disorders

Changes in structure: large segments of chromosomes changed Deletions, Duplications, Inversions, Additions, Translocations

Changes in number: too many or too few of a certain chromosome

Monosomy (1), Trisomy(3)

Can involve autosomes OR Sex Chromosomes

Chromosomal Abnormalities:42Chromosomal Abnormalities: Changes in structure

Deletion= piece missing

Cri du chat Syndrome. Partial deletion of short arm of chromosome 5.

Duplication

= doubled piece

Addition= piece of extra DNA (viral or other) added

Inversion

= sections reversedTranslocation

pieces exchanged between2 different chromosomesTranslocation:

A Type of Leukemia

Chromosomal Abnormalities: Changes in number

Nondisjunction: at either meiosis I or II

Usually a zygote with amissing or extra chromosome DOES NOT SURVIVEResult of change in number?There are some exceptions:Exceptions =Down Syndrome1/900 births

Cause: Trisomy-21, 47 XX/XY +21

Effect: distinctive features mentally impaired

Down's Syndrome59

Turner Syndrome 1/3000 femalesCause: 45 X0 (0 symbol used only as a placeholder) missing one sex chromosomeEffect: short femalenormal intelligenceno functional ovaries = sterilewebs of skin from neck to shoulders (can be removed surgically)

Turners syndrome

Klinefelter Syndrome 1/500 malesCause: 47 XXY, extra X

Effect: Male with small testesdelayed secondary sex char. sparse body hair higher than usual voice usually unable to reproducegenerally no effect on IQKleinfelters syndrome

Other Chromosomal disorders that survive for a timePatau Syndrome (Trisomy 13)Multiple facial abnormalities, brain abnormalities

Other Chromosomal disorders that survive for a time

Edward's Syndrome Trisomy 18

Meiosis Iamniocentesis a prenatal test that gathers information about a baby's health and development from a sample of amniotic fluid (the fluid that surrounds a baby in the uterus). AmniocentesisThis test is usually carried out between 11 - 20 weeks of pregnancy

The amniotic fluid contains the baby's cells that have shed naturally.

These cells will be analyzed in your laboratory.

Amniocentesis

Inoculating a Culture.

7-14 Days Later

Culture shows Cell GrowthPlace Cells into Vial

Centrifuge

Place on Slide then Stain

Add a fixativePhotomicroscope

View Under Microscope

Objective 7: Describe how the phenotype (physical characteristics) of an organism may be affected by the environment. Genes and the Environment Some obvious human traits are almost impossible to associate with single genes.

Traits, such as the shape of your eyes or ears, are polygenic, meaning they are controlled by many genes.

Many of your personal traits are only partly governed by genetics.

Important Terms:

Polygenic: Many genes are involved in the determination of a phenotypeExamples: Height, weight, hair color, skin color, eye color

Multifactorial: Many factors (not just genes) are involved in determining a phenotypeExamples: Height, weight, hair color, skin color

Examples of Environmental Factors that Influence Humans:

Prenatal Health very important development timeNutritionExerciseChildhood Development behavior of mother toward offspring can program gene expression in adulthoodExposure to infection, radiation, smoke, sun,Social Environment as Adults (human behavior)

Key Task for Scientists: To Prevent Disease

First, scientists must figure out if the diseases are specifically genetic or multifactorial.If a disease is multifactorial, they must figure out how genes and related factors are associated.Then, they must use the information about the relationship to find ways to prevent the disease.

Factors that influence how a gene is expressed include:

The information on the gene itselfOther genesEnvironmental factors (external and internal)