Mendel and Genetics

I. Mendel’s Investigations

I. Mendel’s Investigations

A. Prior theory's

1. Blending Theory of Inheritance

a. offspring of two parents "blend" the traits of both parents

I. Mendel’s Investigations

2. Particulate Theory of Inheritance

a. traits are inherited as "particles", offspring receive a "particle" from each parent

I. Mendel’s Investigations

B. Some stuff about Mendel

1. parents were farmers

2. he became ordained as a priest

3. studied science and mathematics at the University of Vienna

I. Mendel’s Investigations

C. Why study pea plants?

1. they are fast growing and easy to raise

2. They also have several visible characteristics that may vary (purple vs white flowers, tall vs short stems, round vs wrinkled seeds)

I. Mendel’s Investigations

D. Mendel’s laws

1. law of segregation

a. It states that there are two factors controlling a given characteristic, one of which dominates the other

b. these factors separate and go to different gametes when a parent reproduces.

I. Mendel’s Investigations

2. law of independent assortment

a. It states that factors controlling different characteristics are inherited independently of each other

I. Mendel’s Investigations

E. Genetics of inheritance

1. Characteristics of organisms are controlled by genes on chromosomes at a locus

I. Mendel’s Investigations

2. In sexually reproducing organisms, each individual has two copies of the same gene, one copy comes from each parent

I. Mendel’s Investigations

3. The gene for a characteristic may have different versions called alleles

I. Mendel’s Investigations

F. Genes and expression

1. Genotype

a. is the alleles an individual inherits

b. The two alleles may be the same (homozygote) or different (heterozygote)

I. Mendel’s Investigations

2. Phenotype

a. The phenotype refers to the organism’s characteristics or the expression of the genotype

Mendel and Genetics

II. Mendelian Inheritance

II. Mendelian Inheritance

A. Punnett square

1. is a chart that allows you to easily determine the expected percents of different genotypes in the offspring of two parents

II. Mendelian Inheritance

Ex) both parents are heterozygous for flower color (Bb)

II. Mendelian Inheritance

B. Non-Mendelian Inheritance

1. Codominance

A. Occurs when both alleles are expressed equally in the

phenotype of the

heterozygote

II. Mendelian Inheritance

2. Incomplete dominance

a. Occurs when the dominant allele is not completely dominant

b. Expression of the dominant allele is influenced by the

recessive allele, and an

intermediate

phenotype results

II. Mendelian Inheritance

3. Multiple Alleles

a. Many genes have multiple (more than two) alleles

b. An example is ABO blood type in humans, there are three common alleles for the gene that controls this

A, B, O

II. Mendelian Inheritance

4. Polygenic Characteristics

a. Controlled by more than one gene, and each gene may have two or more alleles

b. The genes may be on the same chromosome or on nonhomologous chromosomes

II. Mendelian Inheritance

C. Effects of Environment on Phenotype

1. Genes play an important role in determining an organism’s characteristics.

2. However, for many characteristics, the individual’s phenotype is influenced by the environment

a. If you have genes for great height but a poor diet you will not reach your full potential