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Genetics Genetics Presentation Transcript

  • Genetics
  • Mendel Is known as the  Mendel worked with pea Father of Heredity for plants his study of heredity (how traits are passed from parent  His work is considered to offspring) good science because *many trials The study of heredity *many different traits is known as *excellent record keeping genetics *results are repeatable
  • Mendel‟s Law of Dominance Prior to Mendel‟s work, it was believed that a baby inherited all of its factors (now called genes) from one parent Mendel‟s experiment proved that offspring inherit two alleles for each trait, one from each parent His Law of Dominance: of these two inherited alleles, one masks the expression of the other and is known as dominant. The masked gene is called recessive
  • Mendel‟s Experiment Mendel crossed two  His prediction was homozygous pea based on the plants (one dominant, assumption at the one recessive) time that offspring All of the members of only inherited genes the F1 generation from one parent (not were tall from both parents as Mendel predicted that we now know to be all generations from true) then on would also be tall
  • Mendel‟s Experiment Instead, he found that 25% of the F2 generation were short This meant that either the trait magically reappeared, or that it was always present, just hidden This led to the idea of recessive and dominant genes
  • Vocabulary to Know Gene: a section of  Allele: a version of a DNA located on a gene chromosome that contains directions  Your parents will each (codes for) a trait give you an eye color gene, but the allele For example, a gene you receive from each for eye color could be different (brown vs. blue)
  • Vocabulary to Know Genotype: the two  Phenotype: the trait that letter combination that results from this genotype represents the two  Bb= phenotype brown alleles you have (pheno= physical expression) inherited from your parents. Ex: Bb Dominant: only one  Recessive: two recessive dominant allele is alleles are needed to show required to show the the recessive phenotype. dominant phenotype The presence of one dominant allele will mask the expression of the recessive trait
  • Vocabulary to Know Homozygous: a  Heterozygous: a genotype that genotype that contains two of the contains two different same alleles alleles For example, BB or bb  For example, Bb You can differentiate by saying homozygous dominant (BB) or homozygous recessive (bb)
  • Punnett Squares Punnett squares are used to predict the outcome of genetic crosses Monohybrid crosses show the inheritance of one trait Dihybrid crosses show the inheritance of two traits
  • Punnett Squares Are based on Mendel‟s principle of segregation, which says that during meiosis, alleles separate so that each gamete carries only one allele (original cell had two) This relates to our last chapter: segregation happens during anaphase, and the products of meiosis are haploid (one copy of each chromosome)
  • Patterns of Inheritance Mendelian Genetics (regular dominance) One allele is dominant over the other Results in two phenotypes only Dominance Ex: pea plants Tall (TT or Tt) & short (tt)
  • Patterns of Inheritance Incomplete dominance aka intermediate inheritance The dominant gene does not completely mask the recessive gene, resulting in a phenotype midway between the two Results in three phenotypes For example: Red + white = pink
  • Patterns of Inheritance Codominance is when two alleles cannot mask each other and are both expressed Seen often in the form of stripes or polka dots in flowers Results in multiple phenotypes Ex: Red + white= red and white stripes, red and white polka dots Ex: blood groups/blood types
  • Patterns of Inheritance Multiple Alleles In these cases, the gene has more than two forms (alleles) Blood groups/blood types Results in multiple phenotypes
  • Patterns of Inheritance Sex linked genes, aka X linked genes Are located only on the X chromosome Females receive two X‟s while males only receive one X For this reason, males are more susceptible to recessive diseases located on the X chromosome as they only have one chance to get the protective dominant gene
  • Patterns of Inheritance Polygenic traits are phenotypes that are expressed due to a combination of different genes Eye color, skin color, hair color, height Results in a large range of phenotypes
  • Patterns of Inheritance SummaryName ExampleMendelian Dominance Rr= redIncomplete Dominance Rr=pink (not red)Codominance Rr=red and white stripes or polka dots, type AB bloodMultiple Alleles Blood type alleles: A, B, OSex Linked Carried on the X only Hemophilia, colorblindness, male pattern baldnessPolygenic Many genes impact pheno. Height, Hair, skin, eye color
  • Environmental factors Many genes are  In humans, affected by environmental factors environmental include: conditions that can turn genes „on‟ or „off‟ nutrition In animals, exercise temperature impacts many genes (ex: exposure to sunlight arctic fox fur color) infection altitude
  • In summary… “The product of a genotype is generally not a single, rigidly defined phenotype, but a range of possibilities influenced by the environment” P. 217, Biology: Exploring Life
  • Pedigrees A pedigree is a genetic family tree It is used by genetic counselors to analyze the probability of a disease by using known phenotypes to predict genotypes
  • Common Genetic Disorders Symptoms DefectCystic Mucus clogs lungs, liver, Failure of Cl ionFibrosis pancreas transport mechanismSickle Cell Painful, poor blood Abnormal hemoglobinAnemia circulation, clotsTay Sachs Deterioration of CNS in Defective enzyme infancy hexosaminidase APKU Failure of brain to Defective enzyme develop in infancy phenylalanine hydroxylaseHuntington‟s Gradual brain function Production of brain loss metabolism inhibitorMD Wasting away of muscles Muscles fibers degenerate and atrophy
  • Chromosomal Mutations  Other chromosomal mutations include: Down Syndrome is caused by a trisomy  Duplication of chromosome #21  Deletion (part of This is due to a chromosome breaks off) nondisjunction of Inversion (breaks off, sister chromatids  reattaches upside down) during anaphase of meiosis when they  Translocation (breaks are supposed to off, reattaches on separate another chromosome)
  • Diagnosis An amniocentesis takes cells from the developing fetus (dead skin cells floating in the amniotic fluid) A picture of the chromosomes called a karyotype is taken Chromosomal abnormalities can be seen (not individual genes)
  • Karyotypes