Mendel and his Peas

Chapter 5 Lesson 1

Chapter 5: Genetics

How are traits passed from parents to offspring?

Mendel and his Peas

• Why did Mendel perform cross-pollination experiments?

• What did Mendel conclude about inherited traits?

• How do dominant and recessive factors interact?

Gregor Mendel

the father of genetics

Geneti

csthe study of how traits are

passed from parents to offspring

(the study of inheritance)

Heredity

the passing of traits from parents to offspring

Trait: a genetically determined characteristic or condition

Gregor Mendel

Mendel's work was done about 140 yrs. ago, but even now much of what we know about genetics is based on Mendel's work and illustrated by it.

Gregor Mendelwas born in 1822 on a farm in Heinzendorf, AustriaAt age 21 entered the Augustinian order of the Roman Catholic ChurchAs a monk he - studied science at the University of Vienna and became an excellent mathematician

Gregor MendelAs a school teacher - he engaged in many scientific activitiesAt a monastery - he began a program of selective breeding of peas. After 8 yrs. of raising 30,000 pea plants and recording and classifying many pages of notes, he wrote a paper with his conclusions called Mendelian Genetics (1865).

Mendel’s Experimental Methods

Mendel studied genetics by doing controlled breeding experiments with

pea plants.

There are two types of pollination:• self-pollination• cross-pollination

Self-Pollenation

Mendel’s Experimental Methods

When a true-breeding (purebred) plant self-pollinates, it always produces offspring with traits that match the parent.

Mendel cross-

pollinated pea

plants himself

and recorded

the traits that

appeared.

Cross-Pollenation

Mendel’s Experimental Methods

Why did Mendel perform cross-pollination experiments?

Mendel’s Results

Once Mendel had enough true-breeding plants for a trait he wanted to test, he cross-pollinated selected plants.

Plants are called hybrids if they come from true-breeding parent plants with different forms of the same trait.

First-Generation Crosses

Mendel’s Results

hybridScience Use the offspring of two animals or plants with different forms of the same traitCommon Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor

Mendel’s ResultsMendel also cross-pollinated hybrid plants.

He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.

Second-Generation (hybrid) Crosses

Mendel’s ResultsMendel recorded traits of offspring from many hybrid crosses.

Mendelian Genetics

His paper was the first recorded study of how traits pass from one generation to the next. Mendel also was the first to use the mathematics of probability to explain heredity.

Mendelian Genetics

When Mendel's paper was published, in 1865, it received little attention, and was rarely cited by botanists or biologists during the next 34 years. In 1900, Mendel's work was cited by three botanists, writing in different parts of Europe: Hugo de Vries, in Amsterdam; Carl Correns, in Tübingen; and Eric Von Tcshermak, in Esslingen, Austria.

Mendel's Theories

the concept of unit characteristics

the concept of dominant and recessive

the concept of segregation

the concept of unit characteristics

Mendel concluded that two factors, one from the sperm and one from the ovum,

control each inherited trait.

if factors were the same - purebred TT (tall) tt (short)

if factors were not the same - hybrid Tt (tall)

The Concept of Dominant and Recessive

Dominant trait - a genetic factor that blocks another genetic factor.

Recessive trait - a genetic factor that is blocked by the presence of a dominant factor.

The dominant allele (factor) completely masks the presence of the recessive allele (factor).

the concept of segregation

Mendel reasoned that when a cell forms gametes, the genes separate (segregate) so that there is only 1 gene for each characteristic in each gamete.

Principles of Heredity

1. Traits are controlled by alleles on chromosomes.

2. An allele’s effect is dominant or recessive.

3. When a pair of chromosomes separates during meiosis the different alleles for a trait move into separate sex cells.