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Lesson 13

The Work of Gregor Mendel
by

Lori Richardson

on 27 February 2015

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Transcript of Lesson 13

Lesson 13
Mendel's Mystery
Think About It!
What is an inheritance?
The delivery of characteristics from parent to offspring is called
heredity.

The scientific study of heredity, known as
genetics,
is the key to understanding what makes each organism unique.

The modern science of genetics was founded by an Austrian monk named
Gregor Mendel
.

Mendel carried out his work with ordinary garden peas, partly because peas are small and easy to grow.
Experiments
The male part of each flower makes pollen, which contains
sperm
—the plant’s male reproductive cells.

The female portion of each flower produces reproductive cells called
eggs
.

During
sexual reproduction
, male and female reproductive cells join in a process known as fertilization to produce a new cell.
The Role of Fertilization
Mendel’s garden had several stocks of pea plants that were “
true-breeding
,” meaning that they were self-pollinating, and would produce offspring with identical traits to themselves.

A
trait
is a specific characteristic of an individual, such as seed color or plant height, and may vary from one individual to another.

Mendel decided to “cross” his stocks of true-breeding plants—he caused one plant to reproduce with another plant.
The Role of Fertilization
This process, known as
cross-pollination
, produces a plant that has two different parents.

Cross-pollination allowed Mendel to breed plants with traits different from those of their parents and then study the results.

Mendel crossed plants with each of the seven contrasting characteristics and then studied their offspring.

The offspring of crosses between parents with different traits are called
hybrids.
The Role of Fertilization
When doing genetic crosses, we call the original pair of plants the
P
, or parental, generation.

Their offspring are called the
F1
, or “first filial,” generation.

For each trait studied in Mendel’s experiments, all the offspring had the characteristics of only one of their parents.

In each cross, the nature of the other parent, with regard to each trait, seemed to have disappeared
Genes and Alleles
An individual’s characteristics are determined by factors that are passed from one parental generation to the next.

Scientists call the factors that are passed from parent to offspring genes.

Gene variations produced different expressions, or forms, of each trait.

The different forms of a gene are called
alleles.
Genes and Alleles
Some alleles are dominant and others are recessive.

An organism with at least one dominant allele for a particular form of a trait will exhibit that form of the trait.

An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele for the trait is not present.
Dominance
Every individual possesses a pair of alleles for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring
Law of Segregation of Characteristics
Separate genes for separate traits are passed independently of one another from parents to offspring
Law of
Independent Assortment
Full transcript