2. Introduction to Genetics: Meiosis
Ch. 11
Adams
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3. 11.1 The Work of Mendel
Heredity: basically just the passing on of genetic traits from parents to offspring.
Gregor Mendel: demonstrated that inheritance followed particular patterns
Every organism inherits a single copy of every gene from each of its “parents.”
Offspring acquire genes from parents by inheriting chromosomes
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4. 11.1 The Work of Mendel Genes and Dominance
Inheritance is possible because:
Sperm and ova carrying each parent’s genes are combined in the nucleus of the fertilized egg
True Breeding: (sometimes also called a purebred), is an organism that always passes down certain physically expressed traits (purebred German Shepard)
Hybrids: also known as cross breed, is the result of mixing, through sexual reproduction, two animals or plants of different breeds, varieties, species (German shepherd basset hound)
True Breed
Hybrid
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5. 11.1 The Work of Mendel Genes and Dominance
Simplifying Genetics:
So we've all got chromosomes, which are the form that our DNA takes in order to get passed on from parent to child.
Human cells have 23 pairs of chromosomes
Gene: a section of DNA in a specific location on a chromosome that contains information that determines a trait. (hair color)
Allele: specific gene, version of a gene (brown hair color)
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6. 11.1 The Work of Mendel Genes and Dominance
Simplifying Genetics:
So we've all got chromosomes, which are the form that our DNA takes in
Physical trait: a reflection of a bunch of different genes working together
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7. 11.1 The Work of Mendel Genes and Dominance
Simplifying Genetics:
Polygenic trait: are those traits that are controlled by more than one gene (hair color, eye color, height…)
Pleiotropic. : is single gene can influence how multiple traits are going to be expressed
Gamete is the male or female reproductive cell that contains half the genetic material of the organism.
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8. 11.1 The Work of Mendel Mendel’s Two Conclusions: 1st Conclusion:
Biological inheritance is determined by factor that are passed down from one generation to the next
Factors are now called genes
Each trait he studied was controlled by one gene in two forms producing different contrasting forms
These different forms called alleles
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9. 11.1 The Work of Mendel 2nd Conclusion: Mendel’s Two Conclusions:
Principle Of Dominance
Some alleles are dominant and some are recessive
Dominant traits will always show in offspring
Recessive only show when the dominant trait is not present
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10. 11.1 The Work of Mendel

11. 11.1 Segregation Pearson Prentice Hall Biology
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12. 11.1 Segregation Genotypes: 25% = TT 50% = Tt 25% = tt
What happens to the recessive alleles?
~25% the recessive genes reappeared in Mendel’s experiments
T-> dominant (TT; Tt) dominant trait will show (75%)
T-> recessive (tt) only recessive trait will show (25%)
Genotypes: 25% = TT
50% = Tt
25% = tt
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13. 11.2 Probability and Punnett Squares
Mendel used the laws of probability to help predict results in plant succession
Probability: how likely something is going to happen
Relate to Genetics:
Alleles segregation is random but the laws of probability can be used to predict outcomes
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14. 11.2 Punnett Squares Drawings used to help predict genetic outcomes
Below: Brown eyes are dominant (B); blue eyes are recessive (b).
Both “parents” heterozygous for eye color
Meaning that they carry the allele for both brown and blue eyes
This cross shows that 75% of the time offspring will have brown eyes but 25% they will have blue
Phenotype: Brown eyes or blue eyes (phenotype is the physical characteristics)
Genotype: 50% heterozygous
25% homozygous dominant
25% homozygous recessive
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15. 11.2 Punnett Squares Drawings used to help predict genetic outcomes
Here we have one homologous recessive and one heterozygous W w
50% homozygous
50% heterozygous
50% dominant
50% recessive Ww ww w Ww ww w
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16. Drawings used to help predict genetic outcomes
Below: Red flowers dominant(F); pink flowers recessive(f).
Both “parents” homozygous for petal color
Meaning that they carry the allele for either red or white only
This cross shows that 100% of the time offspring will have red petals but will be carriers for both
Genotype: the genotype for this cross is Rr. The genetic make up (it’s the letters)
The phenotype is red petals
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17. 11.2 Punnett Squares Probability and segregation
25% of the time recessive genes that were segregated will reappear
Probability and predict averages
Higher your population of study the closer your averages are
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18. Mendel’s Conclusions Pearson Prentice Hall Biology
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19. 11.3 Exploring Mendelian Genetics
Independent Assortment
Alleles can separate independently during the formation of gametes
Any one pair can combine with any other pair independently during construction
This gives different traits equal opportunities to be expressed in offspring
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20. 11.3 Independent Assortment
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21. 11.3 Independent Assortment
HOMOZYGOUS
HOMOZYGOUS
TWO-FACTOR CROSS
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22. 11.3 Summary Mendel
Biological inheritance is determined by individual genes
In organisms that reproduce sexually, genes are passed from parent to offspring
In cases of two or more forms of the gene for a single trait exist, some genes will exhibit over others
Dominance and recessive
In most sexually reproducing organisms each offspring has two copies of a trait, one from each parent
These traits can be segregated and reformed in new gametes
Alleles for different genes will mostly segregate independently of one another
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23. 11.3 Beyond Dominant and Recessive
Mendel's Principles have two major exceptions
Not all genes show simple patterns of dominant or recessive
Many traits are controlled by one or more gene
Majority of genes have more than one allele
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24. 11.3 Incomplete Dominance Incomplete Dominance:
intermediate inheritance where one allele for a specific trait is not entirely expressed over its paired allele.
Results: in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.
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25. 11.3 Codominance Codominance:
Both alleles contribute to the phenotype.
This results in offspring with a phenotype that is neither dominant nor recessive.
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26. 11.3 Multiple Alleles Multiple Alleles
Genes that have more than two alleles
More than two possible alleles can exist
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27. 11.3 Polygenetic Other examples: Fingerprints Eye color height
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28. 11.3 Polygenetic Pearson Prentice Hall Biology
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29. 11.4 Meiosis Key terms: Homologous Chromosome pairs: similar relation
½ of chromosomes come from mom/other ½ from dad
Each of the chromosomes from dad have a corresponding pair from mom
Diploid: meaning two sets of chromosomes (one inherited from each parent)
Not identical
Haploid: meaning one set
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30. 11.4 Meiosis Chromosome Number
The gametes (sex cells) haploid
Meiosis: Not exact copies of parent
Somatic cells (body cells) are diploid
Mitosis: Clones of parents
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31. Human Life Cycle Sex chromosomes: determine gender (XX; XY)
Each human somatic cell (body cell) has 46 chromosomes or 23 matching pairs (diploid)
Sex chromosomes:
determine gender (XX; XY)
Autosomes: non-sex chromosomes (somatic)
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33. Review
Chromosome: location of genetic information in the form of genes
Chromatid: Each strand of a chromosome that divides longwise during cell division. 
Centromere: What connects the chromatids
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34. Phases of Meiosis Phases of Meiosis
Mixture of chromosomes from both parental chromosomes
Meiosis involves two divisions, meiosis I and meiosis II.
By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells.
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35. Phases of Meiosis I
Major differences in Prophase I (meiosis) and Prophase (mitosis)
Crossover
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
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36. Interphase I
Cells undergo a round of DNA replication, forming duplicate chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad
Tetrad is formed: structure of 4 chromatid
Like Mitosis: cells undergo a round of DNA replication, forming duplicate chromosomes.
Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes.
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37. Prophase I: Different from Mitosis
Pairs of homologous chromosomes now will intertwine
Crossover occurs
Chromosomes swap genetic info
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38. Cross Over
When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.
Crossing-over produces new combinations of alleles.
Crossing-over occurs during meiosis.
Homologous chromosomes form a tetrad.
Chromatids cross over one another.
The crossed sections of the chromatids are exchanged.
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39. Metaphase I: Like Mitosis
Spindle fibers attach to the chromosomes.
Chromosomes line up in the middle (just like mitosis)
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40. Anaphase I: Like Mitosis
The fibers pull the homologous chromosomes toward opposite ends of the cell.
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41. Telophase I Nuclear membrane reforms, Nucleoli form within
Chromosomes unwind into chromatin
Crease forms
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42. End of Round 1
We now have two haploid cells with 23 chromosomes each with unique combinations
But we want to have 4 cells so we go for Round 2. Which is the same process but with different goal
Instead of duplicating chromosomes we want to pull them apart into separate single strand chromosomes
Unlike meiosis I, neither cell goes through chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.
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43. Meiosis II
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.

44. Prophase II
Prophase II is where the nuclear membrane will again break down and the spindle fibers are formed. 
The chromosomes condense again after a interphase but this time there is NO DNA replication
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45. Metaphase II The chromosomes line up in the center of cell.
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46. Anaphase II
The sister chromatids separate and move toward opposite ends of the cell.
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47. Telophase II Meiosis II results in four haploid (N) daughter cells.
Cytokinesis when they finally separate
MEIOSIS II Telophase II and Cytokinesis - Meiosis II results in four haploid (N) daughter cells.
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48. Comparing Mitosis and Meiosis
Mitosis results in the production of two genetically identical diploid cells.
Meiosis produces four genetically different haploid cells.
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49. Comparing Mitosis and Meiosis
Cells produced by mitosis have the same number of chromosomes and alleles as the original cell.
Mitosis allows an organism to grow and replace cells.
Some organisms reproduce asexually by mitosis.
NO change in number of chromosomes in daughter parent as parent cell.
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50. Comparing Mitosis and Meiosis
Cells produced by meiosis have half the number of chromosomes as the parent cell.
These cells are genetically different from the diploid cell and from each other.
Meiosis is how sexually-reproducing organisms produce gametes.
Number of chromosomes are reduced to half of the number of the parent
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51. Meiosis Mitosis Similar but not exact Exact copy Gametes Somatic cells
Creates 4 cells
Two rounds of division
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase/Cytokinesis I
Interphase II
Prophase II
Metaphase II
Anaphase II
Telophase/Cytokinesis II
Mitosis
Exact copy
Somatic cells
Creates two cells
One round of cell division
Interphase
Prophase
Metaphase
Anaphase
Telophase/Cytokinesis