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