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Week 14 - Heredity.pptx

  1. 88% Elementary Teacher Education GENETICS & INHERITANCE
  2. The passing of physical characteristics from characteristics from parents to offspring What is heredity? What is genetics? • The study of how traits are passed from parent to offspring by looking at genes • Genes are small sections of DNA on a chromosomes that has information about a trait What is trait? Physical characteristics of an organism
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  4. Sex cells have 23 chromosomes and the two sex cells combine to form a zygote with 46 chromosomes During fertilization the offspring receives half of its genetic information from its mother and the other half from its father.
  5. • The sex chromosomes carry genes that determine whether a person is male or female. • also carry genes that determine other traits. XX = female XY = male
  6. • Gregor Mendel (1822-1884) laid down the basic principles of heredity. • He explored the ways physical traits could be expressed in plant hybrids. • A hybrid is the offspring of individuals that differ with regard to certain traits or certain aspects of genetic makeup.
  7. Phenotype: the observed traits of an organism. Example: hair color Genotype: the genetic makeup of an organism. Example: the gene that says what your hair color will be. Gene: a region of DNA that describes a trait of an organism. Example: eye color gene Allele: a different form of a gene Example: brown eye color allele, blue eye color allele
  8. Dominant allele: Traits that mask the effect of other traits Recessive allele: Traits that are masked by dominant traits Examples of dominant and recessive traits Heterozygous: the organism has one dominant allele and one recessive allele. Example: Bb Homozygous: the organism has either 2 dominant alleles or 2 recessive alleles. Example: BB or bb
  9. Monohybrid cross • Parents differ by a single trait. • Crossing two pea plants that differ in stem size, one tall one short T = allele for Tall t = allele for dwarf TT = homozygous tall plant t t = homozygous dwarf plant T T  t t
  10. Monohybrid cross for stem length: T T  t t (tall) (dwarf) P = parentals true breeding, homozygous plants: F1 generation is heterozygous: T t (all tall plants)
  11. • A useful tool to do genetic crosses • For a monohybrid cross, you need a square divided by four…. • Looks like a window pane… We use the Punnett square to predict the genotypes and phenotypes of the offspring.
  12. Using a Punnett Square STEPS: 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a p-square Parent genotypes: TT and t t Cross T T  t t
  13. Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the p-square 5. determine the possible genotypes of the offspring by filling in the p-square 6. summarize results (genotypes & phenotypes of offspring) T t T t T t T t T T t t Genotypes: 100% T t Phenotypes: 100% Tall plants T T  t t T T t t The gametes are:
  14. Monohybrid cross: F2 generation • If you let the F1 generation self-fertilize, the next monohybrid cross would be: T t  T t (tall) (tall) T T T t T t t t T t T t Genotypes: 1 TT= Tall 2 Tt = Tall 1 tt = dwarf Genotypic ratio= 1:2:1 Phenotype: 3 Tall 1 dwarf Phenotypic ratio= 3:1
  15. A man who is heterozygous for brown eyes marries a woman who is homozygous recessive for blue eyes. What are the phenotypes, genotypes of their 4 children?
  16.  Geneticist use pedigrees to follow a human trait to learn how the trait was inherited  A pedigree is a chart or “family tree” that tracks the members of a family that have a certain trait
  17. The chart below follows hemophilia in a family. Hemophilia is a genetic disorder that does not allow the blood to clot normally. How many males have hemophilia?
  18. Blood type is determined by a single gene with three alleles.