Chapter 14 Part I: Mendel and Chapter 14 Part I: Mendel and the Gene Ideathe Gene Idea

• This chapter details Mendel’s discovery of general laws of heredity as well as monohybrid dihybrid genetic crosses.

A. Gregor MendelA. Gregor Mendel

1 Austrian Monk

2 Formulated two laws of inheritance in 1860s.

3 Previously studied math and science at University of Vienna.

B. Blending Concepts of B. Blending Concepts of InheritanceInheritance

1 Theory stated that offspring would possess traits intermediate between those of different parents.

2 Red and White flowers make Pink flowers.

3 Darwin wanted to develop a theory of evolution based on Mendel’s heredity principles.

C. Mendel’s Experimental C. Mendel’s Experimental ProcedureProcedure

1 Mendel did a statistical study

2 Prepared experiments carefullyA . Garden PeaB . 22 true-breeding varietiesC . Simple traits were studied

3 Mendel traced inheritance of individual traits.

4 Principles of probability used for interpretation.

11.2 Monohybrid Inheritance11.2 Monohybrid Inheritance

A . Cross-pollination Monohybrid Crosses1 A hybrid is result of 2 true-breeding parents2 A monohybrid cross is between two true-breeding parents for two distinct

forms of a trait.3 Mendel tracked 2 generations

A . P GenerationB . F1 GenerationC . F2 Generation

B. Mendel’s ResultsB. Mendel’s Results

1 Contrary results to predictions

2 F1 resembled one parent

3 1/4 of F2 resembled one parent; 3/4 resembled other parent like F1 generation.

4 3:1 ratio resultsA . Dominant/recessive shown in F2.B . Factors separated when gametes were formed.C . Random fusion upon fertilization.

B. Mendel’s Results ContinuedB. Mendel’s Results Continued

5 Mendel’s First Law of Inheritance: Law of SegregationA. Each organism contains 2 factors for each

trait; factors segregate in formation of gametes; each gamete contains one factor for each trait.

B . Factors passed from generation to generation

C. As Viewed by Modern C. As Viewed by Modern Genetics Genetics

1 Traits controlled by two alleles, alternate forms of trait found at the same gene locus.

2 Gene locus is a specific location on a gene

3 Homozygous is two identical alleles for a trait.A . Homozygous dominant - 2 dominant allelesB . Homozygous recessive - 2 recessive alleles

4 After cross-pollination, all F1 are heterozygous genotypes.

D. Genotype Vs. PhenotypeD. Genotype Vs. Phenotype1 2 organisms with different allele combinations can

have same outward appearance (TT & Tt)

2 Genotype refers to alleles at fertilization.

3 Phenotype refers to physical appearance.

E. Laws of ProbabilityE. Laws of Probability

1 Probability is the likely outcome a given event will occur from random chance.

2 Multiplicative law of probability = chance of 2 or more independent events occurring together is the product of the probability of the events occurring separately

3 Additive law of probability = probability of an event that occurs in 2 or more independent ways.

F. The Punnet SquareF. The Punnet Square

1 Provides simple method to calculate probable results of genetic cross.

2 Sperm cells lined up vertically; egg cells lined up horizontally.

3 Larger sample sizes give better outcomes for predicted ratios.

4 Humans use phenotypic rations for predictions.

G. One-Trait TestcrossG. One-Trait Testcross1 Mendel performed testcrosses by crossing F1 to

homozygous recessive.2 Results indicated recessive factor in F1.3 Testcross = dominant phenotypic individual crossed with

recessive individual.

11.3 Dihybrid Inheritance11.3 Dihybrid InheritanceA . Dihybrid Crosses1 Dihybrid cross is an experimental

cross between 2 true-breeding parents for 2 different traits.

B . Plants Self-Pollinate1 Mendel observed 4 phenotypes among

F2.2 This gave him Second Law of Heredity:

law of independent assortment.A . Members assort independently of

each other.

C. Dihybrid Genetics ProblemsC. Dihybrid Genetics Problems

1 Laws of probability indicate a 9:3:3:1 phenotypic ratio of F2.A. 9/16 dominant for both traitsB . 3/16 dominant for 1 trait, recessive for otherC . 3/16 dominant/recessive opposite of previousD. 1/16 recessive for both traits

2 9:3:3:1 ratio expected when heterozygous for 2 traits are crossed.

D. Two-Trait Test CrossD. Two-Trait Test Cross

1 Dihybrid Test Cross - homozygous dominant traits or heterozygous.

2 Dihybrid genetic problems: 4 alleles for 2 traits.

END OF CHAPTER 11