Chapter 2: Traits and How They Change

Transcription

1 Chapter 2: Traits and How They Change Section 2: Genetics Heredity x Genetics Mendel s experiments Punnett Square For the test: study the powerpoint and textbook

2 1)What is Heredity? 2)What is genetics? Heredity is the passing of traits from parents to offspring. ** Genetics is the branch of Biology that studies genes, heredity, and the variation of inherited traits in living organisms.

3 Mendel Austrian monk, lived in the 1800s The Father of Genetics He was the first to describe the inheritance of traits in an offspring, by studying pea plants. Why pea plants?

4 Pea plants reproduce quickly, so the inheritance of traits can be observed in a short period of time

5 As a result of his observations, Mendel developed 3 basic principles of genetics

6 Read pages Mendel s Principles of Heredity 1 st Principle of Dominance 2 nd Principle of Segregation 3 rd Principle of Independent Assortment

7 1st Principle Mendel s Principle of Dominance Traits are determined by different factors. Each trait is determined by at least two factors. One factor is dominant over the other Today we call factors genes and alleles

8 What are dominant and recessive alleles? Dominant alleles will show their effect on the phenotype whenever they are present in the genotype. Recessive alleles will show their effect on the phenotype only when two of them are present in the genotype.

9 2 nd Principle: Mendel s Principle of Segregation Mendel also concluded that for each trait: Organisms receive ONE allele from the father and ONE from the mother. This allows for many different allele combinations AND explains why variation exists among the offspring of the same parents.

10 Mendel s 3 rd principle : Law of Independent assortment Alleles for one trait have no effect on the inheritance of alleles of another trait

11 Vocabulary not in the book! Homozygous or Purebred an organism that has two identical alleles for a trait Heterozygous or Hybrid an organism that have two different alleles for a trait

12 **Representing alleles Letters are used to represent alleles Capital letters are used for dominant alleles and lowercase letters are used for recessive alleles Ex: short and tall tall is dominant and short is recessive we always use the first letter of the dominant trait TT homozygous or purebred = organism is tall tt homozygous or purebred = organism is short Tt heterozygous or hybrid = organism is tall (it has the dominant allele, that will always show in the phenotype)

13 Punnett Square Tool to predict the genotype and phenotype of an offspring Ex: cross a pink flower with a white flower. Pink is dominant Steps: 1) Represent alleles 2) Do the Punnet square 3) Interpret the results in % for the genotypes and phenotypes

14 More examples: Mendel s experiments : Mendel named: P - Parental generation F1 generation - the result of 1 st crossing F2 generation - result of the 2nd crossing ****IMP: No matter what trait he was working with, Mendel observed that there was a pattern in the inheritance of traits.

15 Discovering the Patterns: EX: Tall and short plants tall is dominant -Cross two homozygous for the dominant trait -Cross two homozygous for the recessive trait -Cross two heterozygous

16 Discovering the Patterns: RESULTS BELOW ARE ALWAYS THE SAME NO MATTER THE TRAIT -Cross two homozygous for the dominant trait = 100% with the dominant trait -Cross two homozygous for the recessive trait = 100% with the recessive trait -Cross two heterozygous = 75% with the dominant trait and 25% with the recessive trait

17 Practicing Punnett Square - Pea plants with different seed color Dominant yellow seed what is the genotype? Recessive green seed what is the genotype? 1)Homozygous yellow x homozygous green 2)Heterozygous yellow x heterozygous yellow 3)green x green 4)Heterozygous yellow x green 5)Homozygous yellow x homozygous yellow Identify Genotypes and phenotypes for all crosses Page 47 Applying math

18 Non-Mendelian Inheritance not in the book use powerpoint to study

19 The inheritance of traits not always follows Mendel's rules Mendel studied traits determined by one gene with 2 pair of alleles and one allele is always completely dominant over the other This type of inheritance is called Complete Dominance

20 Nowadays we know that there are other types of inheritance: Incomplete Dominance Codominance Multiple Alleles Polygenic Inheritance Sex-Linked Traits

21 Incomplete dominance- Snapdragon traits determined by genes with alleles that are neither dominant nor recessive. The offspring show a phenotype that is a blend of the parents phenotype (pink flower)

22 Snapdragons: A plant that is homozygous for the red allele will have red flowers A plant that is homozygous for the white allele will have white flowers A plant that is heterozygous will have pink flowers Neither the red nor the white alleles are dominant, so the phenotype of the offspring is a blend of the two parents.

23 Incomplete dominance- Snapdragon Representing the alleles: use the upper case letter of the trait = color C R C R red C W C W white C R C W pink

24 Incomplete dominance- Snapdragon Punnett Square : C R C R red versus C W C W white C R C W pink versus pink

25 Incomplete Dominance in horses - color of the fur C C C C C W C W C C C W - Chestnut homozygous - White homozygous - Palomino heterozygous

26 Incomplete Dominance in horses C C C C C W C W C C C W - Chestnut - homozygous - White homozygous - Palomino heterozygous Do a Punnett Square to cross: Palomino with Palomino Palomino with Chestnut

27 Incomplete dominance in humans Wavy hair inherit curly hair from a parent and straight hair from another parent

28 Codominance Codominance is a type of incomplete dominance. Codominance would show both alleles equally. It is not a blend of the traits as is seen in incomplete dominance. alleles are represented as in Incomplete Dominance

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30 Blood Type AB in humans is a case of Codominance Blood types are: A,B,AB,O Blood AB: A and B are proteins called antigens, present in the blood In Blood AB - both proteins are present in the phenotype. (not a blend) worksheet

31 Multiple Alleles: another type of inheritance The trait is determined by a gene that has more than 2 alleles. Blood type is an example There are: 2 dominant alleles: alleles for type A and alleles for type B One recessive for type O

32 Blood type alleles and how to represent them: i recessive I A and I B are Codominant (when present, both will show in the phenotype Type AB)

33 Cross type AB with Type O 50% A heterozygous 50% B heterozygous Cross heterozygous A with heterozygous B Cross heterozygous A with recessive O

34 Polygenic Inheritance When traits are determined by more than one gene. EX: height, eye color, skin color More difficult to study because of the wide variety of phenotypes (range) that the different gene combinations can produce

35 SKIN COLOR: 3 Genes and 6 Alleles the skin gets lighter when more recessive alleles are present in the genotype

36 Different genotypes and phenotypes

37 Sex-Liked traits - Remember X and Y chromosomes determine the sex Remember, if you have: 2 chromosomes X female (XX) 1 chromosome X and one Y male (XY)

38 What are Sex-Liked traits? are traits linked with the X or Y chromosomes linked means that the chromosome has the allele for that trait, so the trait is inherited with the X or Y chromosome Sex linked traits are usually X-linked Y-linked traits very rare Ex of sex-linked traits: Color-blindness, hemophilia both recessive traits

39 Sex-Linked traits to the X chromosome: Conditions for the recessive trait to show in the phenotype: Females need to be homozygous to have the disease, males have to have only one chromosome to be affected by the disease.

40 The alleles in the Sex-linked traits EX: Hemophilia bleeding disorder that slows the blood clotting process it is recessive To be hemophilic women need two lower case h and man needs one lower case h

41 The alleles in the Sex-linked traits EX: Colorblindness - it is recessive to be color blind woman needs 2 lower case c and male needs 1 lower case c.

42 What is a carrier? Is an organism that carries the allele for a certain trait but does not have the trait expressed in the phenotype.

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