Download Mendel`s Work PPT.

Chapter 5 section 1
What is heredity?
Heredity is…
the passing of traits from
parents to offspring.
Who first studied
heredity?
 born in 1822
 Served as a monk
(a type of religious life)
 Known as the “father of
genetics”
Worked as
 A Gardener in a monastery
 Experimented with pea
plants to understand the
process of
heredity
Unraveling a Mystery
 Mendel was interested in how traits
(physical characteristics) were passed
down from parents to offspring
 He saw that sometimes a trait would
show up in one generation but not the
next.
 He decided to study these patterns in
pea plants.
Used pea plants
 Grow quickly and have a
fast life cycle (from seed
to offspring)
 Could self-pollinate and
cross-pollinate
Pea Plants
 Come in many varieties (round
vs. wrinkled seed, purple vs.
white flowers)
 Each characteristic had 2 forms
Mendel’s Experiments
 Cross-pollinated plants with
contrasting traits. (Ex: tall plant x short
plant)
 Had to start with two purebred plants
(true-breeding) plants – plants that are
the result of many generations of the
same trait. (Example: purebred short
plants always come from short parent
plants)
Mendel’s Experiments
 Had to control
cross-pollination:
 Anthers of flower
are removed from
one plant.
 Pollen from another
plant with
contrasting trait is
used to fertilize the
plant with no
anthers
Mendel’s 1st Experiment
 Mendel crossed two purebred plants with one
contrasting trait. This was the parental
generation (P generation)
 Example: purebred tall plant x purebred short
plant
 Result: All offspring were tall. (F1 generation)
X
Parent Tall
P generation
Parent Short
P generation
All Offspring Tall
F1 generation
Conclusion
 There are two forms of
each trait. One is dominant
the other recessive.
 Dominant trait – the trait
that was present in the F1
generation.
Conclusion
 Recessive trait - the trait that
seemed to disappear
 Mendel performed a second
experiment to find out what
happened to this trait
Mendel’s 2nd Experiment
 Mendel allowed the F1 generation to selfpollinate.
 Result: ¾ of the offspring were tall, ¼ were
short (F2 generation)
 The recessive trait reappeared in the F2
generation.
 Always occurred in the above ratio, didn’t
matter what trait it was (plant height, flower
color, seed shape, etc…)
.
Parent Plants
Offspring
X
Tall
F1 generation
3⁄4 Tall & 1⁄4 Short
F2 generation
Mendel’s Conclusion
 Each parent donates one set of
instructions to the offspring.
 These instructions are now
known as GENES
What are genes?
 Sections of DNA
 Genes are represented by
a letter
 Sometimes, one gene
controls a trait
Genes Have Two Forms
 There are two forms of each gene called alleles.
 Organisms inherit one allele from each
parent
 Some alleles are dominant over others.
The dominant allele “masks” the presence
of the recessive allele.
 If the recessive form of the trait shows,
then the organism must have 2 recessive
alleles.
Alleles
 Dominant alleles are symbolized
with capital letters (T, B, X, C)
 Recessive alleles are symbolized
with lowercase letters (t, b, x c)
 An organism can be purebred
dominant (TT), purebred recessive
(tt), or hybrid (Tt) for a trait
 A hybrid individual will show the
dominant trait.
Genes and Mendel’s
Experiments
 Parent Generation: tall x short
TT x tt
 F1 Generation: All hybrids
All Tt = All Tall
 F2 Generation:
 ¾ inherited at least 1 dominant allele
(T) = Tall
 ¼ inherited 2 recessive alleles (t) =
short
Mendel’s 1st experiment: Tall is dominant, short recessive
X
Tall parent
Short parent
TT
tt
All Offspring Tall
F1 generation
Tt
Mendel’s 2nd experiment: Tall is dominant, short recessive
X
Tall
F1 generation
F2 generation
Tt
¾ TT or Tt and ¼ tt