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  1. Biology Principles of Heredity Part II

  2. Learning Objectives 1. Explain other types of relationships between alleles and how to determine the probable outcome of these relationships. 2. Explain how to determine the genotype of an unknown individual. 3. Demonstrate how the probability is determined for dihybrid crosses. 4. List four examples of mutations and explain how mutations can change the genetic make-up of an organism. 5. Explain how humans have manipulated the genetic make-up of organisms.

  3. Albinism Chromosome mutation Codominance Deletion Dihybrid cross Diploids Frameshift mutation Gene mutation Haploids Heterosis Hybridization Hybrid vigor Incomplete dominance Inversion Lethal mutation Multiple alleles Mutation Nondisjunction Point mutation Terms

  4. Polygenic traits Polyploidy Selection Testcross Tissue culture Transgenic plant Translocation Terms Agricultural Research Service, USDA

  5. I. What are other types of relationships between alleles? In genetics there are relatively few examples of complete dominance relationships among alleles. • There is a great degree of genetic variation between alleles.

  6. A. Incomplete dominance 1. a relationship where the heterozygous individual will have a phenotype in between the parents 2. Japanese Four O’Clock flowers a. In this type of a plant a homozygous dominant (RR) flower is red, a heterozygous (Rr) flower is pink, and a homozygous recessive (rr) flower is white

  7. Incomplete Dominance in Four O’Clock Flowers RR Section 11-3 R R r rr r

  8. Incomplete Dominance in Four O’Clock Flowers RR Section 11-3 R R r rr Rr Rr r Rr Rr

  9. B. Codominance 1. when a heterozygous offspring will express both alleles for a gene 2. For example, roan coat color in shorthorn cattle and in horses - the animals have red hairs and white hairs present in their coat a. RR = red, RR’ = roan, and R’R’ = white

  10. C. Multiple alleles 1. genes that have more than two different alleles that trait 2. example - blood types in humans have three different alleles—IA, IB, and i a. these three alleles form six different genotypes 3. coat color in rabbits

  11. Figure 14-4 Blood Groups Section 14-1 Safe Transfusions Antigen on Red Blood Cell Phenotype (Blood Type Genotype From To

  12. D. Epistasis 1. when a gene alters the genetic expression of another gene 2. examples a. albinism gene hides genes for hair color b. gene for baldness hides genes for Widow’s Peak

  13. E. Polygenic Traits 1. traits governed by more than one gene 2. most traits (hair color, skin color, eye color, height, weight, metabolism) 3. The phenotype that is observed is a result of all the genotypes for that trait that are present

  14. 4. Skin color in humans (many genes) a. simple version – 3 genes - AaBbCc Person 1 – AABBCC = dark skin Person 2 – aabbcc = light skin Person 3 – AaBbCc = medium skin 5. Bell curve

  15. II. How is the genotype of an unknown individual determined? A. testcross 1. a procedure that scientists use to determine the genotype of an unknown individual 2. If an organism possesses the dominant phenotype, its genotype could be homozygous dominant or heterozygous 3. scientists cross the unknown with a homozygous recessive

  16. 4. For example, a purple flowered pea plant could be PP (homozygous dominant) or heterozygous (Pp) a. The purple flowered plant is crossed with a white flowered plant (pp) to determine the genotype of the first pea plant

  17. b. If 100% of the offspring have purple flowers, then the unknown is homozygous dominant or PP c. If half of the offspring have purple flowers and half have white flowers, then the unknown is heterozygous or Pp;;

  18. 5. If the unknown is crossed with anything other than a homozygous recessive, the results could be inconclusive a. An unknown purple flowered pea plant crossed with another purple flowered pea plant could result in offspring that all have purple flowers, but that does not guarantee that they both are homozygous dominant

  19. B. Test crosses are performed in parent seed research departments to ensure that plants are pure for particular traits 1. Only pure strains can be used to develop hybrid crops

  20. III. How is the probability determined when considering two different sets of traits? A. A dihybrid cross is one where two different sets of traits are considered 1. Example - round versus wrinkled seeds and yellow versus green seeds in peas 2. 16 square punnett square 3. Each trait is distributed independently

  21. Section 11-3

  22. Genotypes 1/16 RRYY 2/16 RRYy 1/16 RRyy 2/16 RrYY 4/16 RrYy 2/16 Rryy 1/16 rrYY 2/16 rrYy 1/16 rryy Phenotypes 9/16 round and yellow 3/16 round and green 3/16 wrinkled and yellow 1/16 wrinkled and green Section 11-3

  23. IV. How can a mutation change the genetic code of an organism? A. Selection is the process of breeding plants that are selected for a particular characteristic 1. This leads to the dominance of certain genetic traits 2. Producers can select the traits that they want and may select for traits that are a result of a mutation

  24. B. mutation is when the DNA is changed or varies in an organism 1. results in the development of a new trait that did not exist in the parents

  25. 2. Natural mutations have been found in the “Gala” apple resulting in new varieties called “Royal Gala” and “Imperial Gala” 3. Mutations cannot be predicted

  26. C. Types of Mutations 1. Gene mutations involve changes in the gene and not in the entire chromosome a. Point mutations involve the substitution of one nucleotide for another nucleotide on the DNA molecule 1) For example, GTATCC becomes GGATCC

  27. b. Frameshift mutations result from either the insertion or deletion of a nucleotide in the DNA sequence 1) DNA is read as a series of condons (a sequence of three nucleotides) 2) this changes the DNA sequence from that point forward 3) For example, GTATCC becomes GTTATC or GATCC

  28. 2. Chromosome Mutations a. mutation in all or part of a chromosome b. Deletion - when a piece of a chromosome breaks off losing part of the genetic information

  29. c. Inversion - a piece of the chromosome breaks off and reattaches itself to the same chromosome d. Translocation - a piece of a chromosome breaks off and reattaches itself to a different chromosome

  30. e. Nondisjunction - when a chromosome does not separate from its homologue (one of a pair of chromosomes) during meiosis 1) results in one gamete receiving two copies of the chromosome and the other receiving none of this particular chromosome 2) In humans, Down Syndrome is a result of the offspring receiving three copies of chromosome 21 3) Turner’s Syndrome is a result of the offspring receiving only one sex (number 23) chromosome

  31. Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

  32. D. germ-cell mutation - When a mutation occurs in a gamete (egg or sperm) 1) this mutation can be passed to the offspring E. When non-reproductive cells mutate, the change will only affect that organism; it cannot be passed on their offspring F. Lethal mutations result in death 1. A plant or part of a plant lacking chlorophyll is called an albino 2. Albinism - usually lethal in higher plants

  33. G. Some mutations are beneficial and result in the change of a species causing evolution to occur 1. Horned Hereford cattle were crossed 2. allele for polled is dominant and is a result of a mutation

  34. H. Mutations can be caused by radiation (x-ray or nuclear), chemicals, environment, or by accident

  35. V. How have humans manipulated the genetic make-up of organisms? A. Hybridization 1. the breeding of two pure lines resulting in offspring that possess the best characteristics of the two parent strains 2. Hybridization has been used for the past century and results in hybrid vigor

  36. 3. Examples of hybrid vigor or heterosis include faster growth, greater vigor, increased disease resistance, and other beneficial characteristics 4. Hybrid seed corn is probably the most visible example of hybridization 5. If the offspring of a hybrid cross are allowed to reproduce, the hybrid vigor will probably be lost

  37. B. Tissue culture 1. asexual reproduction 2. method used by plant researchers to produce large numbers of offspring by using a few cells from the parent

  38. 3. A small slice of cells (explant) is cut off of the parent, placed in a growing medium that contains proper nutrients and hormones, and the cells develop into an entirely new plant 4. The new plant is a clone of the parent 5. This is beneficial for creating a large number of plants in a short amount of time when the plant is unique in nature

  39. 6. For example, a blue rose was developed through years of research a. tissue culture allowed the blue rose to be mass produced rather than trying to use traditional breeding techniques which would require an enormous amount of time

  40. C. Transgenic organism 1. organism that has been produced through the process of genetic engineering 2. Genetic engineering takes DNA from one organism and inserts it into the DNA or another organism

  41. 3. Canola is an example of a transgenic plant a. A variety of canola contains DNA from a flounder which allows the canola to be grown in colder regions stretching the growing season an additional month

  42. D. Copies of Chromosomes 1. Haploids - cells that contain one copy of each chromosome in the nucleus a. egg and sperm cells b. referred to as 1n where n represents the number of different chromosomes

  43. 2. Diploid cells a. cells that contain two copies of each chromosome in the nucleus b. In animals all cells except the sex cells are diploids c. referred to as 2n d. Animals that possess more or less than the diploid number of chromosomes are considered mutations e. Corn and cultivated barley

  44. 3. Polyploidy a. cells that have more than two copies of each chromosome b. Over 1/3 of plant species are estimated to be polyploidy

  45. c. examples 1) Apples and bananas can be either 2n or 3n 2) Alfalfa, potatoes, and cotton are tetraploid or have four copies of each chromosome 3) Wheat is hexaploid; it has six copies of each chromosome 4) Strawberries contain 8 copies and boysenberries contain 7 copies of each chromosome

  46. d. Polyploidy can be caused by nondisjunction during meiosis (the chromosomes did not separate during cellular division) or by artificial means

  47. 1) Scientists have learned that the application of colchicine (comes from the root of the Autumn crocus) can be applied to seeds or seedlings to cause the doubling of chromosomes 2) Irradiation and chemicals can also cause polyploidy