Transcript Mendel and Meiosis ppt.

Gregor Mendel was an
Austrian Monk who is
famous for his work
with garden peas and
his contribution to the
study of heredity.
Mendel noticed that sometimes the seeds of tall pea
plants produced short offspring plants, and that
sometimes the seeds of purple flowered plants
produced white flowered offspring….
He wondered why???!!!!.... And decided to search for
the answer.
Seed Flower Flower
Seed color
color position
shape
Pod
color
Pod
Plant
shape height
green
inflated
tall
yellow
constricted
short
Dominant
trait
round yellow
purple
axial
(side)
Recessive
trait
wrinkled
green
white
terminal
(tips)
When he wanted to
breed, or cross,
one plant with
another, Mendel
opened the petals
Remove
of a flower and
male parts
removed the male
organs.
He then dusted the female organ with pollen
from the plant he wished to cross it with.
Pollen
grains
Transfer pollen
Female
part
Male
parts
Cross-pollination
1. Mendel produced pure strains of pea plants by allowing
the plants to self pollinate for many generations.
 These pure strains are called the
parental or P1 generation.
2. He crossed the P1’s to get the
first filial or F1 generation.
Ex: Tall x Short = 100% Tall
(P1) x (P1) = (F1)
3. He then crossed the F1’s with
each other to get the second
filial or
F2 generation.
P1
F1
Ex: Tall x Tall = 75% Tall, 25% short (F1)
x (F1) = (F2)
F2
1. The Rule of Unit Factors:
Each plant had 2 factors controlling the expression
of traits (One factor from each parent).
2. The Rule of Dominance
Some “factors” cover, or mask, others.
Dominant- masks another factor- ex. Tall
Recessive- the factor that is masked- ex. Short.
3. The Law of Segregation- Pairs of factors segregate,
or separate during gamete (egg or sperm) formation.
Ex:
Tall Plant
TT (dominant)
T
T
x
x
Short Plant
tt (recessive)
T
t
T
t
t
t
Meiosis- the process of making gametes (egg or sperm).
When the gametes combine to form a zygote
(fertilized egg), the offspring will have received
one factor from each parent.
t
T
This zygote will
become a tall pea
plant.
T
t

In 1900, Walter Sutton proposed The
Chromosome Theory, which linked
chromosomes and meiosis to Mendel’s Laws.
Today, instead of factors, we study genes.

A gene is a segment of DNA on a
chromosome that controls a particular
hereditary trait. Because chromosomes occur
in pairs, genes occur in pairs.
Alternative traits of a
gene are called
alleles (Mendel’s
factors).
Gene- eye color
Allele- blue, brown
Genotype
The genetic makeup
of an organism.
TT
Tt
tt
Phenotype
The appearance
of an organism.
Tall
Short
Homozygous
When both alleles
are the same
(called pure).
TT- tall
tt- short
Heterozygous
When a pair a
alleles are not
the same (called
hybrids).
Tt- tall
Probability - the likelihood that an event will occur.
- # of times an event is expected______
# of times the event actually happens
Ex. What is the probability that a coin toss will result
in heads?
½
or
50%
or
1:1
fraction
percentage
ratio
A Monohybrid Cross- is a cross involving 1 pair
of contrasting traits.
Ex. What are the expected genotypic and
phenotypic ratios resulting from the cross of a
pure (homozygous) tall plant with a hybrid
(heterozygous) tall plant?
1.
Write possible genotypes and phenotypes.
TT- tall
Tt- tall
tt- short
2.
Determine parent genotypes and separate
alleles (because 1 allele goes to each gamete)
homozygous tall (TT) x heterozygous (Tt) tall
T
T
T
t
3. Draw a Punnett Square with 4 boxes and put
the alleles from one parent on one side and the
alleles form the other parent on other side.
T
T
T
t

4. Report results:


Genotypic Ratio- 2 TT: 2Tt (1TT: 1Tt)
Phenotypic Ratio- 4 Tall: 1 short (1 tall: 0 short)