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IAN PAGE 91 Dominant & Recessive Alleles

IAN PAGE 91 Dominant & Recessive Alleles. MAIN IDEAS Genotype Phenotype Dominant Allele Recessive Allele Homozygous Dominant Homozygous Recessive Heterozygous . Objective: Identify some of the basic components of Heredity using notes, collaboration and worksheets.

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IAN PAGE 91 Dominant & Recessive Alleles

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  1. IAN PAGE 91Dominant & Recessive Alleles MAIN IDEAS • Genotype • Phenotype • Dominant Allele • Recessive Allele • Homozygous Dominant • Homozygous Recessive • Heterozygous Objective: Identify some of the basic components of Heredity using notes, collaboration and worksheets

  2. I. Gregor Mendel & Heredity A. FATHER OF GENETICS! B. Study inheritance traits in Pea Plants (Height, Flower color, Seed shape) C. Concluded “factors” responsible for traits = ALLELES!!

  3. Definitions • Allele- discrete version of the same gene • Genotype- the genes of an organism for one specific trait • Phenotype- the physical appearance of a trait in an organism

  4. II. Combinations of Alleles interact to produce an organism’s phenotype and genotype A. 2 types of Alleles 1. Dominant – expressed in the phenotype. (TT or Tt) 2. Recessive – expressed in the phenotype. (tt) We use letters to represent the genotype: Capital Letter = Dominant Lower Case Letter = Recessive

  5. SO… WW Wwww (Homozygous (Heterozygous) (Homozygous Dominant) Recessive) Dominant Allele Dominant Allele Recessive Allele Expressed ExpressedExpressed Both Alleles are Dominant Different Alleles Both Alleles are Recessive

  6. Genetics Using Punnett SquaresIAN pg 90

  7. Punnett Squares • The Punnett square is the standard way of working out what the possible offspring of two parents will be. • It is a helpful tool to show allelic combinations and predict offspring ratios.

  8. Next, put the genotype of one parent across the top and the other along the left side. For this example lets consider a genotype of BB crossed with bb. B B • Notice only one letter goes above each box • It does not matter which parent’s genotype goes on either side. b b

  9. R r r r Red throats (R) are dominant over white (r) throats in Goonie birds. Make a cross between a PURE RECESSIVE and a HETEROZYGOUS Goonie bird. Rr rr Rr rr What are the possible phenotypes of their offspring? (% and color) 50% red throats 50% white throats

  10. B b B b Black eyes (B) are dominant over red eyes (b) in rats. Make a cross between two HETEROZYGOUS rats. BB Bb Bb bb What are the possible phenotypes of their offspring? (% and color) 75 % black eyes 25% red eyes

  11. W w Usually write the capital letter first W W W w W Lets say: W- dominant white w- recessive violet w W w w w Parents in this cross are heterozygous(Ww). Note: Make sure I can tell your capital letters from lowercase letters. What percentage of the offspring will have violet flowers? ANSWER: 25% (homozygous recessive)

  12. Let’s try some more… In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. T t What are the percentage of phenotypes? t t 50% tall 50% short

  13. Black eyes (R) is dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. R R What is the possibility of a red eye off springs? r r 0% 

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