Objectives:1) Explain the principle of

independent assortment.2) Describe the inheritance

patterns that exist aside from simple dominance.

3) Explain how Mendel’s principles apply to all organisms.

11-3EXPLORING MENDELIAN GENETICS

Independent Assortment•Mendel completed experiments with pea plants to determine if the segregation of one pair of alleles affected the segregation of another pair of alleles•2-factor cross

The 2-Factor Cross: F1

1) Cross true-breeding plants that make only round yellow peas (RRYY) with plants that make wrinkled green peas (rryy)

2) Every F1 genotype was RrYy

The 2-Factor Cross: F2

• F1 plants were heterozygous (RrYy)

1) Cross the F1 plants with each other to determine if the segregation of one pair of alleles affected the segregation of another pair of alleles

2) Made the F2 Generation

The 2-Factor Cross: F2 Cont’d• Discovered the principle of independent

assortment• Genes for different traits can segregate

independently during the formation of gametes

• Helps account for the many genetic variations observed in plants, animals, and other organisms

Dog Breeds

A Summary of Mendel’s Principles•Form the basis of the modern science of genetics1)Inheritance of

biological characteristics is determined by genes

A) Passed from parents to their offspring

A Summary of Mendel’s Principles Cont’d2) Sometimes 2 or more forms of the gene (alleles)

for a single trait existA)May be dominant or recessive

3)In most sexually reproducing organisms, each adult has 2 copies of each gene (1 from each parent)

A) Segregated from each other when gametes are formed

A Summary of Mendel’s Principles Cont’d4) Alleles for different genes usually segregate independently of 1 another

Beyond Dominant and Recessive Alleles• Important exceptions to most of Mendel’s principles1)Not all genes are in patterns of dominant and

recessive alleles2)Majority of genes have more than 2 allelesA)Many important traits are controlled by more than 1

gene*Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

Incomplete Dominance• Incomplete dominance: in which 1 allele is not completely dominant over another•The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes

Codominance• Codominance: both alleles

contribute to the phenotype• Both are dominant

• Both show up

Multiple Alleles• Multiple alleles: many genes have more than 2 alleles for

combinations• Can only have 2 alleles (1 from mom and 1 from dad)

• More than 2 possible alleles exist in a population

Polygenic Traits• Polygenic traits: traits

controlled by 2 or more genes• Hint: 2 Allelesgenetrait

• Often show a wide range of phenotypes

Blue Ticket Question• What are multiple alleles?

Blue Ticket Answer• Genes have more than 2

alleles for combinations

Applying Mendel’s Principles• 1900’s• American geneticist• Thomas Hunt Morgan• Experimented with genetics

of fruit flies• Morgan and other biologists

had tested each of Mendel’s principles and learned that they applied to other organisms too• Mendelian genetics can be

used to• Study the inheritance of human

traits

• Calculate the probability of certain traits in the next generation

Genetics and the Environment• Characteristics of an

organism is determined by genes and environment• Genes provide a plan for

development, but how that plan unfolds also depends on the environment

11-3 Exit Ticket• Answer the following

questions.• Use complete sentences.• You may NOT use your book.• You MAY use your notes.• This is a quiz grade.

1) What is the principle of independent assortment?

2) What are the inheritance patterns that exist aside from simple dominance?

3) How does Mendel’s principles apply to all organisms?