What Are The Odds?

What Are The Odds?

Non-Fatal InjuriesZipper: 1: 2,600Toilet: 1: 6,500Alarm Clock: 1: 350,000Bed: 1: 400

Fatal Injuries 1Snake Bite: 1: 36,000,000Dog Bite: 1: 20,000,000

Fatal Injuries 2Ebola: 1: 14,000,000Appendicitis: 1: 700

Fatal Injuries 3Earth Destroyed By Meteor: 1: 20,000You Alone Are Killed By Meteor: 1: 150,000,000,000

What Are The Odds That There Is An Exact Duplicate of YOU?

Unlikely3.2 billion nucleotides in human genome97% of this is intron (non-coding), dropping the number of coding base pairs to 210,000Two parents = 2^210,0001 chance in 10^63,000

However, only ~108 billion humans have EVER been born.

Probability and GeneticsProbability: The determination of certain outcomes based upon the number and type of possible outcomesGenetics: The determination of heritable outcomes due to the passage of DNA

If the central dogma dictates that DNA is copied in its entirety, and mitosis ensures that each daughter cell gets the same information as the previous, why do organisms need to be different?

Genetic VarietyGenetic variety ensures that populations/species continue to survive despite changes in their ecosystemsPopulations that do not change genetically must have environments that rarely change

Sources of Genetic VarietyMutationsPoint Mutations (Single Nucleotide Polymorphisms)Frameshift/Nonsense MutationsChromosomal Mutations

7 Billion Individuals v. 3 Million SNPsHow Is Such Variety Possible If 99.9% of our Genes are identical?Sources of Genetic Variety v 2.0

Sexual Reproduction Builds In Genetic Variety

Sexual v. Asexual Reproduction

Asexual ReproductionDef: Reproduction requiring only one parent/genetic sourcei.e. binary fission, parthenogenesis, buddingPRO: Quick, Fast, Low RequirementsCON: Low Genetic Variety

Sexual ReproductionDef: Reproduction requiring two parents/genetic sourcesi.e. conjugation, fertilizationPRO: Genetic VarietyCON: Need water, partners and GAMETES

GAMETESDef: Specialized reproductive cells (i.e. sperm, ovum)Gametes contain half the genetic content of other cells in the organism (yet still contain all of the genes)To produce another generation, gametes must be fused together to produce a ZYGOTE

Diploid v. HaploidSomatic (body) cells are DIPLOID (two sets of chromosomes)In each diploid cell, there are pairs of homologous chromosomes containing the same number and type of genes but NOT necessarily coding for identical proteinsGAMETES are HAPLOID (only one set of chromosomes)

How does a cell go from diploid to haploid and yet retain all of the genes necessary for the organism?

MeiosisTo develop gametes, a cell must undergo MEIOTIC DIVISION (i.e. MEIOSIS)

How is meiotic division different from mitotic division?

Mitosis v. MeiosisMitosis occurs in somatic (body) cellsOne diploid cell produces two diploid cellsDaughter cell is genetically identical to parent cellMeiotic division only occurs in ovary or testes cellsMeiosis contains two sets of steps/divisionsOne diploid cell produces four haploid cellsAll resultant cells have half the genetic material as the original cellMeiotic Cell Division

What Is The Significance of The Differences In Prophase?

Tetrads/Bivalents

NON-SISTER HOMOLOGOUS CHROMOSOMES move next to each other, forming groups of four called TETRADS or BIVALENTSSYNAPSISThe non-sister homologous chromosomes, pressed together as tetrads, may swap genes between their NON-SISTER HOMOLOGOUS CHROMOSOMESCreates hybrid chromosomes carrying the same traits but different versions

What Is The Significance of The Differences In Metaphase?

Meiotic Metaphase 1Unlike meiosis, the centromeres of the sister chromatids are not lined up directly on the equatorial planeHomologous pairs are arranged side by side on either side of the equator, with one spindle fiber attaching to each centromere.Because they are not on the equator, there are two ways to place the homologous pairs

Meiotic Anaphase (1)Homologous pairs separate, but the sister chromatids DO NOT.

Meiotic Telophase & InterkinesisSame actions as mitotic telophaseHowever, after cell has divided into two diploid cells, DNA REPLICATION STOPSThis period of time is called INTERKINESIS

Why is the lack of DNA replication during interkinesis essential in the formation of gametes?

Meiosis II = Mitosis

Prophase II

Metaphase IIAs in mitotic division, the sister chromatids line up above each other with the centromeres directly on top of the equator

Anaphase IINow that spindle fibers have been attached to each side of the centromere, the retraction of the spindle fibers caused the centromere to break

MEIOSIS

Telophase II & CytokinesisFour cells are created by the second anaphase divisionResultant cells have less cytoplasm but also half the genetic material (HAPLOID))

Oogenesis v. SpermatogenesisThe meiotic division of testes cells produces four viable spermatidsThe meiotic division of an ovary cell/ovum is unequal in terms of cytokinesisOnly one of four egg cells is viable

Why does the double division of meiosis actually increase genetic diversity?

Lab: Modeling Meiotic DivisionWith your lab partner(s), build two sets of homologous chromosomes, The first pair of homologues should contain 10 genes (i.e. beads), 5 on each side of the centromere.The second pair of homologues should contain 6 genes, 3 on each side of the centromereUse two different colors to differentiate between the homologues. Replicate both homologues, connecting each to its sister chromosome with a magnetic centromere. You should have 8 total chromosomes at this pointLab: Modeling Meiotic Division Part 2Move the homologous chromosomes & their attached sister chromatids through the various steps of meiotic divisionInclude synapsis of two genes in the first homologous pair and one gene in the second homologous pair as part of Prophase 1Your lab group will be checked for understanding. One step of the processes (mitosis AND meiosis) will be selectedComplete the analysis questions #1-10Modeling Meiosis Analysis Questions1) How does meiosis accurately resemble the old adage, The more things change, the more they stay the same? Be specific in what is changing and what is continuous2) Why is a consistency of chromosome number an important prerequisite of successful sexual reproduction?3) Spores are cells produced by meiosis that can independently grow into a new plant. If spores are produced by meiosis, why is the new generation not the product of sexual reproduction?Modeling Meiosis Analysis Questions cont.4) Why is sexual reproduction the most efficient way of bringing genetic variety to a population?5) The ovaries and testes of pre-pubescent humans must grow and develop, yet do not produce sperm or eggs. How is cellular division different during these years than post-puberty?6) Monera and Protista are both single celled organisms, yet while there are 20,000 different Monera, there are 100,000 different Protista. Why?Modeling Meiosis Analysis Questions cont.7) How does the fact that horses and donkeys have different numbers of chromosomes (48 and 50) explain why mules are sterile?8) Why is there no synapsis during mitotic division?9) Why is there no synapsis between sister chromatids?10) Patau Syndrome is a fatal genetic condition caused by three copies of chromosome 15. Explain how this condition occurs in every cell of the fetus, while neither parent has the condition.