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Genetics A study of inheritance Thanks to Mr. Byman, MMHS Biology 12/05/05.

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Presentation on theme: "Genetics A study of inheritance Thanks to Mr. Byman, MMHS Biology 12/05/05."— Presentation transcript:

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2 Genetics A study of inheritance Thanks to Mr. Byman, MMHS Biology 12/05/05

3 Gregor Mendel Father of modern genetics

4 Gregor Mendel Father of modern genetics Researched with pea plants

5 Gregor Mendel Father of modern genetics Researched with pea plants Developed ideas of dominance and trait segregation

6 Phenotype –Physical characteristics

7 Genotype Phenotype –Physical characteristics Genotype –Genes we inherit from our parents

8 Phenotype –Facial structure Notice the similarities:

9 Phenotype –Facial structure –Eyes Notice the similarities:

10 Phenotype –Facial structure –Eyes –Smile Notice the similarities:

11 Phenotype –Facial structure –Eyes –Smile –Ears Notice the similarities:

12 Phenotype –Facial structure –Eyes –Smile –Ears –Nose Notice the similarities:

13 Phenotype –Facial structure –Eyes –Smile –Ears –Nose –Neck Notice the similarities:

14 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL

15 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW

16 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND

17 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY

18 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH

19 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN

20 Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

21 Mendelian Genetics We will work the following three: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

22 Predicting Inheritance To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes. UPPERCASE letters are used to represent dominant genes. lowercase letters are used to represent recessive genes.

23 Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait!

24 Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! Mendels’ Principle of Dominance Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.

25 Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F 1 generation. TT x tt TT tt

26 Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F 1 generation. TT x tt TT tt Mendels’ “Law” of Segregation Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait.

27 Punnett Squares TtTtTt The genes from one parent go here. The genes from the other parent go here.

28 Punnett Squares TT tTtTtTt t P1 P2

29 Punnett Squares TT tTtTtTt tTtTt

30 Punnett Squares TT tTtTtTtTt tTtTtTtTt

31 TT tTt tTtTtTtTt

32 Punnett Squares TT tTt t

33 Punnett Squares TT tTt t F 1 generation

34 Interpreting the Results The genotype for all the offspring is Tt. The genotype ratio is: Tt - 4/4 The phenotype for all the offspring is tall. The phenotype ratio is: tall - 4/4

35 Punnett Squares Tt T?? t Your Turn!!

36 Punnett Squares Tt TTTTt t tt F 2 generation

37 Punnett Squares Tt TTTTt t tt Next, give the genotype and phenotype ratios of the offspring (F 2 generation).

38 Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1

39 Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2

40 Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1

41 Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3

42 Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3, short - 1

43 Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant.

44 Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant. Tomorrow we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape. two

45 Homework - Punnett Squares Tt TTTTt t tt Questions 1 & 2 on Rats Practice Problems and question 1 on Foxes and Watermelons Practice Problems.


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