The Work of Gregor MendelThe Work of Gregor Mendel

Think About It!Think About It!

What is an inheritance?What is an inheritance?– It is something we each receive from our It is something we each receive from our

parents – a contribution that determines blood parents – a contribution that determines blood type, hair color, and much more.type, hair color, and much more.

Every living thing has a set of Every living thing has a set of characteristics that are inherited from its characteristics that are inherited from its parent or parents.parent or parents.

HeredityHeredity is the delivery of characteristics is the delivery of characteristics from parent to offspring.from parent to offspring.

Think About It!Think About It!

Genetics Genetics is the is the scientific study of scientific study of heredity.heredity.– It is the key to It is the key to

understanding what understanding what makes each organism makes each organism unique.unique.

– Was founded by an Was founded by an Austrian monk named Austrian monk named Gregor Mendel.Gregor Mendel.

Experiments of Gregor MendelExperiments of Gregor Mendel

MendelMendel– Performed his work in Performed his work in

a monastery garden.a monastery garden.– Carried out his work Carried out his work

with ordinary garden with ordinary garden peas, because peas peas, because peas are small and easy to are small and easy to grow.grow.

These peas These peas represented a represented a “model system”“model system”

Experiments of Gregor MendelExperiments of Gregor Mendel

Mendel was able to Mendel was able to carry out experiments carry out experiments that would have been that would have been impossible or taken impossible or taken years to do.years to do.

Experiments of Gregor MendelExperiments of Gregor Mendel

Studied seven different pea plant traits. Each Studied seven different pea plant traits. Each trait had two contrasting characteristics. trait had two contrasting characteristics.

Pea Plant Traits, Contd.Pea Plant Traits, Contd.

The Role of FertilizationThe Role of Fertilization

Fertilization is a process that produces a new Fertilization is a process that produces a new cell when male and female reproductive cells cell when male and female reproductive cells join.join.– Male reproductive cells are called sperm.Male reproductive cells are called sperm.– Female reproductive cells are called eggs.Female reproductive cells are called eggs.

The Role of Fertilization The Role of Fertilization

In seed plants, In seed plants, fertilization occurs fertilization occurs through self- or cross-through self- or cross-pollination.pollination.Pollination transfers Pollination transfers pollen (sperm) from pollen (sperm) from the male the male reproductive organ to reproductive organ to the female the female reproductive organ reproductive organ (stigma).(stigma).

The Role of FertilizationThe Role of Fertilization

In self-pollination, sperm In self-pollination, sperm cells fertilize eggs cells cells fertilize eggs cells from within the same from within the same flower. flower. – Peas flowers are self-Peas flowers are self-

pollinating, because of pollinating, because of this theythis they

Produce a seed that Produce a seed that inherits all of the inherits all of the characteristics characteristics (traits) of its parents.(traits) of its parents.Are “true breeding” Are “true breeding” because they because they produce offspring produce offspring with identical traits.with identical traits.

The Role of Fertilization The Role of Fertilization

In cross-pollination, pollen from the anther of a In cross-pollination, pollen from the anther of a flower goes to the stigma of a different flower.flower goes to the stigma of a different flower.– Mendel utilized this process to learn more about Mendel utilized this process to learn more about traits.traits.

A trait is a specific characteristic of an individual that may vary A trait is a specific characteristic of an individual that may vary from one individual to another.from one individual to another.

The Role of Fertilization The Role of Fertilization (Cross-Pollination, Continued)(Cross-Pollination, Continued)– First, Mendel prevented self-pollination by First, Mendel prevented self-pollination by

removing the male part of a flower.removing the male part of a flower.– Then, Mendel dusted the female part of the Then, Mendel dusted the female part of the

flower with pollen from a different plant.flower with pollen from a different plant.– These plants produced a seed that inherited These plants produced a seed that inherited

different characteristics of its parent.different characteristics of its parent.

The offspring of these plants are called The offspring of these plants are called hybrids.hybrids.

Mendel’s Conclusions Mendel’s Conclusions

An individualsAn individuals

characteristics are characteristics are determined by genes determined by genes that are passed from that are passed from parent to offspring.parent to offspring.

– Genes are Genes are

segments of DNA segments of DNA that determine a that determine a trait.trait.

Mendel’s Conclusions Mendel’s Conclusions

– Each individual has Each individual has two factors for each two factors for each trait, one from each trait, one from each parent.parent.

– Alleles are forms of a Alleles are forms of a gene for a specific gene for a specific trait.trait.

They are a single They are a single member of a pair of member of a pair of genes, responsible for a genes, responsible for a single trait.single trait.

Mendel’s ConclusionsMendel’s Conclusions

Some alleles are dominant and others are Some alleles are dominant and others are recessive.recessive.– This is called the principle of dominance.This is called the principle of dominance.

Mendel’s ConclusionsMendel’s Conclusions

An organism with one dominant allele for a An organism with one dominant allele for a particular trait will exhibit the trait. particular trait will exhibit the trait. – A dominant allele is represented by a capital A dominant allele is represented by a capital

letter.letter.

An organism with a recessive allele for a An organism with a recessive allele for a particular trait will exhibit the trait when the particular trait will exhibit the trait when the dominant allele is not present.dominant allele is not present.– A recessive allele is represented by a A recessive allele is represented by a

lowercase letter.lowercase letter.

SegregationSegregation

Mendel assumed Mendel assumed thatthat– A dominant allele A dominant allele

masks a recessive masks a recessive allele in an Fallele in an F1 1

generation.generation.

Segregation

In F2 generations the recessive trait reappeared indicating that the dominant and recessive alleles had separated.

- Segregation explains how this occurred.

Segregation

Is the separation of alleles during gamete formation.

– Gametes are sex cells

– When gametes are formed, allele pairs separate leaving each cell with a single allele for each trait.

– When fertilization occurs alleles randomly unite to form a gene for a specific trait

Practice Quiz for Mendel's GeneticsPractice Quiz for Mendel's Genetics

http:/http://anthro.palomar.edu/mendel/quizzes/mend/anthro.palomar.edu/mendel/quizzes/mendqui1.htmqui1.htm