JIGSAW• You will have five minutes to master your set of

notes as YOU will be teaching the class your set!

• Take paper with you to your station so you can read, summarize and record the notes from your section.

• We will then come together as a class to discuss MENDELIAN GENETICS as understood by YOU!!

• Best teaching group will receive bonus points on their lowest daily grade…..

Mendelian Genetics

The Work of Gregor Mendel

Chapter 11.1

What is Inheritance?

• Every living thing has a set of characteristics passed on to them from their parents – genes!

• Genetics: The scientific study of heredity

Gregor Mendel

• 19th century Austrian monk

• Worked in monastery garden with pea plants

“Father of Genetics”

Some terms to know…

• Fertilization: male and female reproductive cells join to form a new cell – diploid embryo

• Self-pollinating plants: sperm cells (in pollen) fertilize the egg cells in the same flower

• True-breeding: if plant self-pollinates, offspring produced is identical to itself

Mendel’s Work

• Prior Knowledge– Part of each flower produces pollen (male

sperm) and part produces egg cells (female)– Pea flowers are normally self-pollinating– His peas were true-breeding (tall plants

produce tall plants, short plants produce short plants, green seeds produce green seeds…etc)

Mendel’s Work• Mendel’s Plan:

– To produce seeds by joining male and female reproductive cells from two different plants

– To do this, self-pollination needed to be prevented– So, he cut away pollen parts from one plant and

dusted them on a different flower (Cross-pollination)

NOW, seeds produced have two different parents:He could now cross-breed plants with different

characteristics and study the results…

Traits

• Mendel studied seven different pea plant traits

• Trait: Specific characteristic that varies from one individual to anotherEx. Seed color or plant

height

Mendel’s F1 Crosses on Pea Plants

• P (Parental generation)– Original pair of plants• F (Filial generation)– Offspring - “filia” means son/daughter

– F1 is the first generation of offspring (from P generation parents)

• Hybrid = offspring of crosses between parents with different traits

Examples of hybrid crosses

• When one parent’s pod color was green and the other parent’s pod color was yellow, the offspring was…green.

• When one parent was round and one parent’s seed was wrinkled, the offspring was…round.

Did the characteristics of the parent plants blend in the offspring?

• NOT AT ALL!

• ***Each offspring carried on the character of only ONE parent!• Green parent x Yellow parent = Green offspring• Round parent x Wrinkled parent = Round offspring

WHY?

• What conclusions can you make?

Mendel’s Principles

• Principle of Biological Inheritance (unit characters)

• Principle of Dominance

• Principle of Segregation

• Principle of Independent Assortment

KNOW THESE FROM PAGE 272!!!!!!!!!!!

Mendel’s 1st Conclusion

• Biological inheritance is determined by factors that are passed from one generation to the next– GENES - chemical factors that determine traits– ALLELES - different forms of a gene

• Ex: The gene for plant height occurs in one form that produces tall plants and in another, short plants – twp alleles

Mendel’s 2nd Conclusion

• Principle of DOMINANCE– States that some alleles are dominant and

some are recessive

– Let’s look at our example: • When one parent’s pod color was green

and the other parent’s pod color was yellow, the offspring was…green.

Which color is DOMINANT?

Dominance

• An organism with a dominant allele for a form of a trait will always exhibit that form of the trait

• An organism with a recessive allele for a form of a trait will only exhibit that form when the dominant allele is not present

Gene Expression• Each form of the particular gene is an

allele.

• Alleles can be either 1. Dominant – always show trait - T

2. Recessive – only see if dominant trait absent – t

• In order to see the trait expressed, 2 alleles must be paired together (one from mom and one from dad)

T t+ Tt

Mendel’s 3rd Conclusion• Had the recessive alleles totally disappeared or

were they still present in the offspring?P: Green parent x Yellow parent

F1: Green offspring do they still have recessive alleles?

• Mendel allowed the F1 hybrid plants to self-pollinate– He crossed the F1 generation with itself to produce

the F2

F1: Green offspring x Green offspring

F2: ???

Results….• Instead of all green…he saw YELLOW too!

Gg Gg

G g G g

GG Gg Gg gg

Segregation

F1

F2

gametes

Even though the plants are both green, they can have a yellow baby because

the allele is still present!

Results of F1 Cross

• Mendel assumed dominant masked the recessive allele

• But, recessive alleles reappeared in F2!Example – P: Green parent x Yellow parent

F1: Green offspring x itself

F2: Green offspring and Yellow offspring

• Somehow the alleles for green and yellow had separated – Segregation!!!!!– Occurs during formation of gametes

Principle of Segregation

As gametes form, gene pairs (homologous chromosomes) separate. Each gamete contains one gene for the

trait.

When do gametes form? So when does segregation occur?

“Mendel’s Principle of Segregation”:

• Recessive characters hidden in the F1 progeny of two true-breeding strains, reappear in a specific proportion of the F2 progeny.

Segregation

Segregation

Homologous pairs separate!ANAPHASE!!

Principle of Independent Assortment

As gametes form, gene pairs separate

independently of each other.

Alignment of one chromosome pair during metaphase, does not affect

alignment of another pair. Random arrangement creates

independent assortment = VARIATION!

Independent Assortment

Genetic variation results since gametes carry different genes.

Independent Assortment

• Each plant in the F1 generation was formed by the fusion of a gamete carrying the dominant alleles (RY) with another gamete carrying the recessive (ry) alleles.

• Does this mean the two dominant alleles would always stay together?

• Or would they “segregate independently” so that any combination of alleles was possible?

Principle of Independent Assortment

Genes for different traits can segregate independently during the formation of

gametes.

Example: genes for seed shape segregate independently of those for seed color