Transcript Intro to genetics

INTRODUCTION TO GENETICS:
THE WORK OF GREGOR MENDEL
Biology
Unit 6 / Chapter 11
Powerpoint #1
VOCABULARY
1.
2.
3.
4.
5.
6.
7.
8.
Allele
Cross pollination
Gene
Genetics
Hybrid
Self pollination
Trait
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
MENDEL’S WORK

Bred pea plants
Pollen transferred from white flower
to stigma of purple flower
P
 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)
anthers
removed
all purple flowers result
F1
self-pollinate
F2
TECHNIQUES OF MENDEL
Describe how Mendel prevented selfpollination 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.
LOOKING CLOSER AT MENDEL’S WORK
P
F1
true-breeding
purple-flower peas
X
true-breeding
white-flower peas
100%
purple-flower peas
Where did
the white
flowers go?
100%
generation
(hybrids)
self-pollinate
F2
generation
75%
purple-flower peas
White
flowers came
back!
25%
white-flower peas
3:1
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 Americana
What are the
advantages of
being diploid?
WHAT DID MENDEL’S FINDINGS MEAN?

Some traits mask others
 purple
& white flower colors are separate
I’ll speak for
both of us!
traits that do not blend
 purple
x white ≠ light purple
 purple masked white
 dominant
allele
 functional
protein
 masks other alleles
 recessive
allele
makes a
malfunctioning protein
 masked by the dominant allele
wild type
allele producing
functional protein
mutant
allele producing
malfunctioning
protein
 allele
homologous
chromosomes
PRINCIPLE OF DOMINANCE
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
Parents
First Generation
Second Generation
Long stems  short stems
All long
787 long: 277 short
Red flowers  white flowers
All red
705 red: 224 white
Green pods  yellow pods
All green
428 green: 152 yellow
Round seeds  wrinkled seeds All round
5474 round: 1850 wrinkled
Yellow seeds  green seeds
6022 yellow: 2001 green
All yellow
• 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?