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 19 th 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 another Ex. Seed color or plant height

Mendel’s F 1 Crosses on Pea Plants P (Parental generation) –Original pair of plants F (Filial generation) –Offspring - “filia” means son/daughter –F 1 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 1 st 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 2 nd 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 3 rd Conclusion Had the recessive alleles totally disappeared or were they still present in the offspring? P: Green parent x Yellow parent F 1 : Green offspring  do they still have recessive alleles? Mendel allowed the F 1 hybrid plants to self- pollinate –He crossed the F 1 generation with itself to produce the F 2 F 1 : Green offspring x Green offspring F 2 : ???

Results…. Instead of all green…he saw YELLOW too! Gg GgGg GGGg gg  Segregation F1F1 F2F2 gametes Even though the plants are both green, they can have a yellow baby because the allele is still present!

Results of F 1 Cross Mendel assumed dominant masked the recessive allele But, recessive alleles reappeared in F 2 ! Example – P: Green parent x Yellow parent F 1 : Green offspring x itself F 2 : 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 F 1 progeny of two true-breeding strains, reappear in a specific proportion of the F 2 progeny. 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