BIOLOGY CHAPTER 6 &7  Meiosis and Mendelian Genetics
6.1 & 6.2 CHROMOSOMES AND MEIOSIS 6.6 MEIOSIS AND GENETIC VARIATIONMitosisSomatic cells undergo mitosisOne diploid cell ...
MeiosisGerm cells produce gametes (sex cells) during meiosisOne diploid cell produces 4 genetically different haploid ce...
Homologous ChromosomesHalf of an organism’s chromosomes come from the mother, and half from the father. The chromosomes p...
All humans have 23 total pairs of chromosomes, for a total of 46 chromosomes.22 of the pairs are autosomes (body chromos...
Meiosis ISame steps as mitosis, except during Prophase I crossing over can occur(see below),during Metaphase I homologou...
Crossing OverHomologous chromosomes exchange genesThis results in a new combination of genes (called recombination)Gene...
6.3 MENDEL AND HEREDITYGregor MendelAn Austrian monk who is known as the “father of genetics”He discovered that traits (...
WHY PEA PLANTS?They reproduce quicklyThey can both self-pollinate(creating purebreds) and cross-pollinate(creating a mix...
MENDEL’S CONCLUSIONSMendel’s Law of Segregation: Organisms inherit two copies of each gene, one from each parentOrganism...
6.4 TRAITS, GENES, AND ALLELES6.5 TRAITS AND PROBABILITIESGenesEach gene has a specific locus, or place on the chromosome...
Letters are used to represent different alleles. There are two alleles per trait (one from mother, one from father)Domin...
EXAMPLE: P= purple flowers         p= white flowersPP=purple flowers (homozygous)pp= white flowers (homozygous)Pp= purple ...
PUNNET SQUARESPunnet squares are used to predict the outcome of genotypes when crossing two organismsMonohybrid cross- c...
CHAPTER 7EXTENDING MENDELIAN GENETICSComplex Patterns of InheritanceIncomplete Dominance—the trait is in betweenthe domina...
Polygenic Traits—when two or moregenes influence a traitEx. Human eye color(at least 3 different genes), human skin color...
SEX-LINKED TRAITS—TRAITS CAUSED BY GENES LOCATED ON THE SEX CHROMOSOMES  The X contains many genes  The Y only determine...
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Biology chapter 6 & 7

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Biology chapter 6 & 7

  1. 1. BIOLOGY CHAPTER 6 &7 Meiosis and Mendelian Genetics
  2. 2. 6.1 & 6.2 CHROMOSOMES AND MEIOSIS 6.6 MEIOSIS AND GENETIC VARIATIONMitosisSomatic cells undergo mitosisOne diploid cell produces 2 genetically identical, diploid cellsThere are 4 stages (prophase, metaphase, anaphase, telophase)DNA is copied once and divided onceMitosis is used for development, growth, and repair
  3. 3. MeiosisGerm cells produce gametes (sex cells) during meiosisOne diploid cell produces 4 genetically different haploid cellsThere are 8 stages (prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II)DNA is copied once and divided twice
  4. 4. Homologous ChromosomesHalf of an organism’s chromosomes come from the mother, and half from the father. The chromosomes pair up to form homologous chromosomesHomologous chromosomes are two chromosomes with the same length, general appearance, and the same type of genesThe pairing of the genes on the homologous chromosomes are what code for all of an organism’s traits (see examples in section 6.4)
  5. 5. All humans have 23 total pairs of chromosomes, for a total of 46 chromosomes.22 of the pairs are autosomes (body chromosomes)1 pair is the sex chromosomes (XX= female, XY=male)
  6. 6. Meiosis ISame steps as mitosis, except during Prophase I crossing over can occur(see below),during Metaphase I homologous chromosomes pair up in the middle andduring Anaphase I, the sister chromatids DO NOT separateBy the end of Meiosis I, there are 2 haploid cells
  7. 7. Crossing OverHomologous chromosomes exchange genesThis results in a new combination of genes (called recombination)Genes that are located near each other on a chromosome are more likely to be moved (or crossed over) together. This is called genetic linkage (refer to page 191)Meiosis IIThis is exactly the same as mitosis
  8. 8. 6.3 MENDEL AND HEREDITYGregor MendelAn Austrian monk who is known as the “father of genetics”He discovered that traits (genes) are inherited from parents by working with pea plantsHe made both purebred plants and crossed plants to see what the results would be.
  9. 9. WHY PEA PLANTS?They reproduce quicklyThey can both self-pollinate(creating purebreds) and cross-pollinate(creating a mix of traits)They have “either-or” traits (the traits do not mix to make a 3rd trait, ex. The purple flowers and white flowers don’t mix to make a pink flower)(refer to page 179 to see the traits and results of Mendel’s experiment)
  10. 10. MENDEL’S CONCLUSIONSMendel’s Law of Segregation: Organisms inherit two copies of each gene, one from each parentOrganisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation (Law of Independent Assortment)In other words, the Law of Ind. Assortment is saying that traits are inherited separately.
  11. 11. 6.4 TRAITS, GENES, AND ALLELES6.5 TRAITS AND PROBABILITIESGenesEach gene has a specific locus, or place on the chromosomeA gene is a piece of DNA that provides a set of instructions to make a certain protein. The proteins then code for traits.Each trait is represented by alleles.
  12. 12. Letters are used to represent different alleles. There are two alleles per trait (one from mother, one from father)Dominant alleles are represented by capital letters and Recessive alleles are represented by lowercase lettersDominant alleles will always overpower the recessive alleles.
  13. 13. EXAMPLE: P= purple flowers p= white flowersPP=purple flowers (homozygous)pp= white flowers (homozygous)Pp= purple flowers (heterozygous)Genotype-the alleles/genetic code (PP or Pp)Phenotype-the physical trait (purple or white)
  14. 14. PUNNET SQUARESPunnet squares are used to predict the outcome of genotypes when crossing two organismsMonohybrid cross- crosses one trait (always yields a 3:1 phenotypic ratio)Dihybrid cross- crosses two traits (always yield 9:3:3:1 phenotypic ratio)
  15. 15. CHAPTER 7EXTENDING MENDELIAN GENETICSComplex Patterns of InheritanceIncomplete Dominance—the trait is in betweenthe dominant and recessive Ex. RR=red rr=white Rr=pinkCodominance—both traits are expressed at thesame time Ex. RR=red rr=white Rr= both red and white
  16. 16. Polygenic Traits—when two or moregenes influence a traitEx. Human eye color(at least 3 different genes), human skin color (4 different genes)Environmental factors—when theenvironment plays a role in geneexpressionEx. Sea turtle eggs become female in warmer temps and male in colder temps
  17. 17. SEX-LINKED TRAITS—TRAITS CAUSED BY GENES LOCATED ON THE SEX CHROMOSOMES The X contains many genes The Y only determines sex (male) A male is XY, so all of the alleles on the X are expressed in a male, even the recessive ones A female is XX, so dominant alleles can mask the recessive onesCarriers—those who carry a recessive genetic disorder, but do not express the phenotype. They can pass on the disorder to their offspring

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