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Genetics

Genetics. 7 th Grade Science e. Genetics is…. the science of genes, heredity, and the variation of organisms. Chromosomes and DNA. Our genes are on our chromosomes . Chromosomes are made up of a chemical called DNA . Chromosomes.

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Genetics

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  1. Genetics 7th Grade Science e

  2. Genetics is… the science of genes, heredity, and the variation of organisms

  3. Chromosomes and DNA • Our genes are on our chromosomes. • Chromosomes are made up of a chemical called DNA.

  4. Chromosomes • Chromosomes are structures found in the nucleusof cells • Chromosomes carry all of our genes, and therefore all of our genetic information • Humans have 46 chromosomes, or 23 pairs, to carry our approximately 25,000 genes • The 23rd pair are the sex chromosomesthis pair will either be XX or XY

  5. DNA is often called the blueprint of life. • In simple terms, DNA contains the instructions for making proteins within the cell.

  6. DNA • Each cell has about 2 m of DNA • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun • DNA has a diameter of only 0.000000002 m.

  7. Every cell in your body has the same DNA!

  8. There are a few important vocabulary terms

  9. GENOTYPE = the genes present in the DNA of an organism • We use a pair of letters (ex: Tt or YY or ss, etc.) to represent genotypes for one particular trait. • There are always two letters in the genotype because (as a result of sexual reproduction) one code for the trait comes from mama organism & the other comes from papa organism, so every offspring gets two codes (two letters).

  10. there are three possible GENOTYPES • two big letters (like "TT") • one of each ("Tt") • or two lowercase letters ("tt")

  11. TT or tt HOMOZYGOUS("homo" means "the same").  Sometimes the term “PURE“ is used instead of homozygous.

  12. Tt HETEROZYGOUS ("hetero" means "other") a heterozygous genotype can also be referred to as HYBRID

  13. Genotype = genes present in an organism(usually abbreviated as two letters) TT = homozygous = pure Tt = heterozygous = hybrid tt = homozygous = pure

  14. Phenotype=how the trait physically shows up in the organism The simplest way to determine an organism's phenotype is to look at it.  Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers.

  15. ALLELES= alternative forms of the same gene.  Alleles for a trait are located at corresponding positions on homologous chromosomes. Remember that "one code (letter) comes from ma & one code (letter) comes from pa"? "allele" is a fancy word for codes.

  16. Which of the following is a possible abbreviation for a genotype? A. BCB. PpC. TyD. fg

  17. What is the best way to determine the phenotype of the feathers on a bird? A. analyze the bird's DNA (genes)B. look at the bird's feathersC. look at the bird's beakd. examine the bird's droppings

  18. Which of the following pairs is notcorrect? A. kk = hybridB. hybrid = heterozygousC. heterozygous = HhD. homozygous = RR

  19. The genes present in an organism represent the organism's __________. A. genotypeB. phenotypeC. physical traits

  20. Which choice represents a possible pair of alleles? A. k & tB. K & TC. K & kD. K & t

  21. How many alleles for one trait are normally found in the genotype of an organism? A. 1B. 2C. 3D. 4

  22. Which statement is not true? A. genotype determines phenotype B. phenotype determines genotype C. a phenotype is the physical appearance ofa trait in an organism D. alleles are different forms of the same gene

  23. That’s it for today……more to come tomorrow!

  24. Genetics Notes……continued

  25. Mendel’s Laws

  26. Gregor Johann Mendel (1822-1884)“The Father of Genetics” Augustinian monk who cross-bred pea plants with different characteristics Observations led to laws regarding the transmission of hereditary characteristics from generation to generation Many of the concepts from his observations still hold true today!

  27. Mendal’s Laws • the Law of Dominance 2. the Law of Segregation 3. the Law of Independent Assortment

  28. Mendel's First LawThe Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

  29. In other words, the phenotype is… Homozygous dominant (BB)= dominant phenotype Hybrid (Bb) = dominant phenotype Homozygous recessive (bb)= recessive phenotype

  30. Example:

  31. Hybrids always show the dominant trait in their phenotype

  32. The PUNNETT SQUARE (P-Square for short) • Used to illustrate Mendel’s Law of Dominance. • Uses symbols instead of words • Shows ALL possible outcomes

  33. F1 GenerationTall x Short t t T T T t T t T t T t

  34. Summary of F1 Generation

  35. Mendel’s 2nd LawThe Law of Segregation • During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

  36. F2 GenerationTall x Tall T t T t T T T t T t t t

  37. Summary of F2 Generation Any time two parents have the same phenotype for a trait but some of their offspring look different with respect to that trait, the parents must be hybrid for that trait.

  38. Mendel’s 3rd LawLaw of Independent Assortment • Alleles for different traits are distributed to sex cells (& offspring) independently of one another. • In other words, being tall didn't automatically mean the plants had to have green pods, nor did green pods have to be filled only with wrinkled seeds, the different traits seem to be inherited INDEPENDENTLY.

  39. Which cross would best illustrate Mendel's Law of Segregation? A. TT x ttB. Hh x hhC. Bb x BbD. rr x rr

  40. In the cross YyxYy, what percent  of offspring would have the same phenotype as the parents? • 25% B. 50% C. 75%D. 100%

  41. In a certain plant, purple flowers are dominant to red flowers.  If the cross of two purple-flowered plants produces some some purple-flowered and some red-flowered plants, what is the genotype of the parent plants? A. PP x PpB. Pp x PpC. pp x PP D. pp x pp

  42. Information adapted from: http://www.hobart.k12.in.us/jkousen/Biology/mendel.htm

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