Download The Principle of Segregation

How are
characteristics passed
down through
generations?
• Inheritance –
characteristics are passed
through generations by
genetic material (traits)
How Do We Know?
Gregor Mendel - discovered
the pattern of inheritance by
studying pea plants.
What did Mendel
discover?
The Principle of Segregation
1) Inherited traits are
determined by distinct units
named genes
2) Each gene carries two
factors, one inherited from
each parent (alleles)
3) The two alleles separate
from each other and end up
in gametes during meiosis.
Largest Size
NUCLEUS
Contains
CHROMOSOMES
Contains
GENES
Interaction
between two
ALLELES
Made of
DNA
SMALLEST size
Largest Structure:
• In each of our cells
(except or gametes)
we have 23 pairs of
chromosomes
• One member of the
chromosome pair
comes from our
father, the other from
our mother.
Karotype
How are genes arranged
on chromosomes?
• Genes are regions of
DNA within the
chromosome pair that
code for a particular
trait.
• Each gene is made up
of two factors, one from
each chromosome pair.
• These factors are called
alleles
Are an individual's alleles the
same?
homozygous
• The two alleles that make
up each gene may be the
same or different.
• If the alleles are the same
they are called
homozygous
• If the alleles are different
they are called
heterozygous
heterozygous
How do alleles
determine the trait
of an individual?
• Each trait is determined
by the interaction
between the two alleles of
a gene and several
interactions are possible.
• The genetic make up of a
trait= genotype
• The physical appearance
of a trait= phenotype
1. Complete Dominance – when one allele completely
masks the other.
Dominant Alleles – only one allele needed to express trait.
Recessive Alleles – need two recessive alleles for trait to be
expressed.
Ex: Y = yellow
y= sugary
Recessive trait :
Sugary kernels are
recessive
Dominant trait:
Genotype=
Genotype=
Phenotype=
Phenotype=
Yellow kernels
2. Incomplete dominance
When the alleles are
blended and the
offspring have a mix of
their parent traits.
ex. Snap Dragons
R = red
r = white
Offspring can be pink!
Heterozygous genotype
3. Codominance – in
this case both
alleles are
expressed.
BB= black corn
YY= yellow corn
BY = black and yellow
corn
Genotype codes for
phenotype
• GENOTYPE - the two letters that
represent the alleles of a gene
EX. RR, Rr, rr
• Phenotype - the outward appearance of an
organism (what it looks like)
Ex. If a farmer has a red flower (RR)
- the genotype is RR
- the phenotype is red
1. A brown dog (bb)
bb
the genotype ________
brown
the phenotype _______
2. A long haired cat (Hh)
the genotype _______
Hh
Long haired
the phenotype _______
3. A spotted owl (SS)
SS
the genotype _____
spotted
the phenotype _____
(Review)
• Remember The
Principle of
Segregation?
• Mendel learned that
the alleles of each
individual seperate
and end up in
gametes (meiosis)
• Ex. A female pure brown dog (bb)
bb
b
b
PRACTICE
1. A hybrid male yellow canary (Yy)
Yy
2. A pure female white flower (rr)
rr
If a male red flower (Rr) and a pure white
flower from above got their gametes
together (fertilization )
what kind of combinations could be formed?
X
• Male red flower (Rr)
• Female white flower
Rr
Sperm 1
rr
Sperm 2
Egg 1
Egg 2
Genotype
+
1
=
1
+
1
2
2
2
+
=
=
1
+
2
=
Phenotype