INTRODUCTION TO GENETICS: THE WORK OF GREGOR MENDEL

BiologyUnit 6 / Chapter 11Powerpoint #1Mr. Velekei

VOCABULARY

1. Allele2. Cross pollination3. Gene4. Genetics5. Hybrid6. Self pollination7. Trait8. True breeding

•Gregor Mendel was born in 1822 in the Czech Republic

•Studied Science and Mathematics at the University of Vienna

•Spent the next 14 years teaching high school and working at a monastery in the garden

Mendel noticed that the SAME type of plant could have VARIATIONS, or differences, these are the

variations he noticed:

Seed Shape Seed Color Seed Coat Color

Round Yellow Gray

Wrinkled Green White

Pod Shape Pod Color Flower Position Plant Height

Smooth Green Axial Tall

Constricted Yellow Terminal Short

AFTER MENDEL NOTICED THESE VARIATIONS HE DECIDED TO DO AN

EXPERIMENT OF HIS OWN. Mendel wanted to breed the pea plants

together in different combinations to see what the offspring (seedlings) would look like.

used experimental method

used quantitative analysis collected data & counted them

excellent example of scientific method

TERMINOLOGY

Genetics: study of heredity (how traits pass from one generation to the next)

True-breeding: if allowed to self-pollinate, produce offspring identical to self

Self-pollination: pollen from one flower fertilizes egg cells in same flower

Cross-pollination: pollen from one flower fertilizes egg cells in a different flower

Pollen transferred from white flower to stigma of purple flower

anthersremoved

all purple flowers result

MENDEL’S WORK

F1

P

F2

self-pollinate

Bred pea plants cross-pollinate

true breeding parents (P) P = parental

raised seed & then observed traits (F1) F = filial

allowed offspring to self-pollinate & observed next generation (F2)

TECHNIQUES OF MENDEL

Describe how Mendel prevented self-pollination and controlled cross-pollination in pea plants: He cut off the male parts (anthers) of one flower, then dusted the stigma with pollen from a second flower.

Why did he want to do this? He wanted plants with specific traits to breed with one another.

F2generation

3:175%purple-flower peas

25%white-flower peas

LOOKING CLOSER AT MENDEL’S WORK

P

100%F1generation(hybrids)

100%purple-flower peas

Xtrue-breedingpurple-flower peas

true-breeding white-flower peas

self-pollinate

Where didthe whiteflowers go?

Whiteflowers cameback!

WHAT DID MENDEL’S FINDINGS MEAN?

Traits come in alternative versions purple vs. white flower color alleles

different alleles vary in the sequence of nucleotides at the specific locus of a gene

some difference in sequence of A, T, C, G

purple-flower allele & white-flower allele are two DNA variations at flower-color locus

different versions of gene at same location on homologous chromosomes

TRAITS ARE INHERITED AS DISCRETE UNITS

For each characteristic, an organism inherits 2 alleles, 1 from each parent diploid organism

inherits 2 sets of chromosomes, 1 from each parent

homologous chromosomes like having 2 editions of encyclopedia

Encyclopedia Britannica Encyclopedia AmericanaWhat are the

advantages ofbeing diploid?

WHAT DID MENDEL’S FINDINGS MEAN?

Some traits mask others purple & white flower colors are

separate traits that do not blend purple x white ≠ light purple purple masked white

dominant allele functional protein masks other alleles

recessive allele allele makes a

malfunctioning protein masked by the dominant allele

homologouschromosomes

I’ll speak for both of us!

wild typeallele producingfunctional protein

mutantallele producingmalfunctioningprotein

Principle of dominance: dominant trait is always seen when dominant allele is present; recessive trait is only seen when no dominant allele is present

MENDEL’S OBSERVATIONS

• 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics?

• 2. How do the characteristics of the second generation compare to the characteristics of the first generation?

• 3. How do we know the recessive allele did not disappear?

Parents

Long stems short stems

Red flowers white flowers

Green pods yellow pods

Round seeds wrinkled seeds

Yellow seeds green seeds

First Generation

All long

All red

All green

All round

All yellow

Second Generation

787 long: 277 short

705 red: 224 white

428 green: 152 yellow

5474 round: 1850 wrinkled

6022 yellow: 2001 green