Transcript Genetics - Ms. Pass's Biology Web Page

GENETICS
Ch. 11
Gregor Mendel
 Genetics is the
study of heredity.
 Gregor Mendel
(1860’s) discovered
the fundamental
principles of
genetics by
breeding garden
peas.
2. Mendel
crosspollinated
pea plants
 He cut away
the male
parts of one
flower, then
dusted it with
pollen from
another
3. What did Mendel
conclude?
 He concluded that factors are passed
from one generation to the next.
eye color locus
b = blue eyes
eye color locus
B = brown eyes
4. The
Principle of
Dominance
The Principle of
Dominance – some
alleles are
dominant and other
are recessive.
Paternal Maternal
 Alleles
1. Alternative forms of genes.
2. Units that determine
heritable traits.
5. Dominant and
Recessive alleles
Dominant alleles – upper-case
a. homozygous dominant
(BB – Brown eyes)
Recessive alleles – lower case
a. homozygous recessive
(bb – blue eyes)
b. Heterozygous (Bb – Brown eyes)
Phenotype vs. Genotype
 Outward appearance
 Physical
characteristics
 Examples:
1.Brown eyes
2.blue eyes
 Arrangement of
genes that
produces the
phenotype
 Example:
1. TT, Tt
2. tt
6. Segregation
Alleles separate during meiosis
7. Recessive traits show
th
up about 1/4 of the time.
 Because there is
only a 25% chance
that two recessive
alleles will be
paired together.
9. Punnett square
 A Punnett square is
used to show the
possible
combinations of
gametes.
 Monohybrid Cross
Monohybrid Cross
 Example:
Cross between two heterozygotes
for brown eyes (Bb)
BB = brown eyes
Bb = brown eyes
bb = blue eyes
B
b
B
Bb x Bb
b
female gametes
male
gametes
Monohybrid Cross
B
b
B
BB
Bb
b
Bb
bb
Bb x Bb
1/4 = BB - brown eyed
1/2 = Bb - brown eyed
1/4 = bb - blue eyed
1:2:1 genotype
3:1 phenotype
Dihybrid Cross
Dihybrid Cross
RY
RY
Ry
rY
ry
Ry
rY
ry
Dihybrid Cross
RY
RY RRYY
Ry RRYy
Ry
RRYy
RRyy
rY
RrYY
RrYy
ry
RrYy
Round/Yellow:
9
Round/green:
3
Rryy
wrinkled/Yellow: 3
rY RrYY
RrYy
rrYY
rrYy
wrinkled/green:
ry
Rryy
rrYy
rryy
9:3:3:1 phenotypic ratio
RrYy
1
Dihybrid Cross
 Example:
R
r
Y
y
= round
= wrinkled
= yellow
= green
cross between round and yellow
heterozygous pea seeds.
RrYy x RrYy
RY Ry rY ry x RY Ry rY ry
possible gametes produced
10. Independent
Assortment
 Chromosomes separate
independently of
eachother Bb
B
Ff
This means all
gametes will be
different!
B
B
F
b
f
sperm
B
Bb
Bb
Ff
B
Bb
diploid (2n)
f
b
b
Ff
B
b
meiosis I
meiosis II
F
haploid (n)
Independent Assortment
 Genes for different traits can segretate
independently during the formation of
gametes without influencing eachother
 Question: How many gametes will be produced
for the following allele arrangements?
 Remember:
1.
2.
3.
2n (n = # of heterozygotes)
RrYy
AaBbCCDd
MmNnOoPPQQRrssTtQq
Answer:
1. RrYy: 2n = 22 = 4 gametes
RY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gametes
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64
gametes
11. Incomplete
Dominance
 One allele is not
completely dominant
over another
R
R
r
Rr
Rr
produces the
F1 generation
r
Rr
Rr
All Rr = pink
(heterozygous pink)
11. Codominance
 Both alleles are
expressed
 Example: blood
1.
type A
2.
type B
3.
4.
type AB
type O
Black cow + white cow =
spotted cow
= IAIA
or IAi
= IBIB
or IBi
= IAIB
= ii
12. Which shows more
genetic variation. (more
combos?)
 Male CC with female
Cc
C
 Male cc with female
Cc
C
c
C
C
c
c
c
Genetic Engineering
Gene
Therapy
Is cloning a
possibility?
 Is it right to use
cloning to create an
entirely new human
being?

Is it ethical to create
an embryonic copy of
John Doe to supply
cells to keep John
alive?

Does a multicellular
ball of tissue -- an
embryo -- have the
same rights and
status as a human
being?
How does Mendel’s
principles apply to
organisms
 The basic principals
can be applied to
humans as well as
any other living
organism.
And now it’s time for….
 Spongebob
Genetics!!!!!