Transcript Genetics Chapter 3 1

Genetics
Chapter 3
1
Gregor Mendel
Mendelian genetics (Mendel
is the father of genetics)
• Heredity is the
passing of
characteristics from
parent to offspring.
– Get 50% of
characteristics
from each
biological parent.
(fertilization occurs
when the egg &
sperm meet)
– Some traits
appear and others
are hidden.
2
Traits
• Each different characteristic is
called a trait.
3
Punnett Square
•
Crossing traits
– Purebred
organisms have
the same trait. (TT
or tt)
– Hybrid organisms
have two different
alleles for a trait.
(Tt)
– P generation is the
parent generation.
– F1 is the first filial.
– F2 is the second
filial.
4
Alleles
•
– A gene is the
factor that controls
a trait.
– Alleles are
different forms of a
gene.
– Some alleles are
dominant.
– Some alleles are
recessive.
In Mendel’s experiment, only
one trait appeared in the F1
generation, but in the F2
generation, the lost form of
the trait always reappeared
in 25% of the plants.
5
Probability
–
Probability and Heredity
• Probability is the
chance that a
particular outcome will
occur.
• Punnett squares are
used to predict that a
particular trait will
show.
• In a genetic cross, the
allele each parent
passes on to the next
generation offspring is
dependent on
probability.
6
What is an adaptation?
A change in DNA.
An over production of
offspring.
A competition between two
members of the same
species.
A modification in a species
for survival.
3
4
21
22
23
24
5
6
7
8
9
10
11
12
13
14
s.
..
e.
.
a
tw
in
n
tio
fic
a
m
co
od
i
m
pe
tit
io
n
be
tio
n
uc
A
2
A
1
of
...
A.
N
D
A
n
ov
er
A
ch
pr
od
an
4.
0% 0% 0% 0%
in
3.
ge
1.
2.
:10
15
16
17
18
19
20
7
Which of the following is true about
the rate of evolution?
:10
1. Evolution can occur
over a weekend.
2. Evolution occurs in
several months.
3. Evolution occurs
over hundreds of
years.
4. Evolution occurs
over millions of
years.
1
2
3
4
21
22
23
24
5
6
7
8
9
0% 0% 0% 0%
Ev
10
11
12
n
io
ut
l
o
n
ca
13
c
oc
E
...
ur
n
tio
lu
o
v
14
c
oc
s
ur
E
in
...
n
tio
lu
o
v
15
c
oc
s
ur
Ev
e
ov
...
n
io
ut
l
o
16
c
oc
s
ur
ov
17
..
e.
18
19
20
8
:10
If tree grew taller over time, what physical
characteristics of a giraffe would allow them to
survive?
1
2
3
4
21
22
23
24
5
6
7
9
10
11
12
13
14
or
tn
ec
ck
.
16
Sh
Lo
ng
ne
te
e
15
0%
k.
0%
th
.
0%
or
e
Th
in
ne
c
ne
c
ic
k
8
0%
k.
k.
0%
M
Thick neck.
Thin neck.
More teeth.
Long neck.
Short neck.
Th
1.
2.
3.
4.
5.
17
18
19
20
9
Which of the following is a result of adaptations
over a long period of time?
:10
1. Species are very
diverse.
2. Species are very
similar.
3. Species quickly
become extinct.
4. I don’t know.
0% 0% 0% 0%
S
1
2
3
4
21
22
23
24
5
6
7
8
9
10
11
c
pe
12
s
ie
e
ar
ry
ve
S
ve
di
c
pe
13
...
s
ie
e
ar
ry
ve
S
14
m
si
c
pe
r
ila
s
ie
.
k
ic
qu
15
ly
c.
be
..
Id
16
o
w
no
t’ k
n
.
17
18
19
20
10
Codominance
•
Codominance is when the
allele is neither dominant nor
recessive; both alleles are
expressed in the offspring.
11
Problem #1
•
•
•
•
•
•
•
Cross:
B is dominant brown eyes
b is recessive blue eyes
BB x bb
Bb x Bb
Bb x bb
Show phenotype and
genotype
12
Phenotype vs. Genotype
•
•
•
•
The phenotype is the
physical appearance
of the organism.
The genotype is the
genetic makeup of the
organism or the allele
combination.
Homozygous is when
the organism has two
identical alleles for a
trait.
Heterozygous is when
the organism has two
different alleles for a
trait.
13
Problem #2
•
•
•
•
•
•
Cross:
T is dominant tall pea plant
t is recessive short pea plant
TT x tt
TT x Tt
Tt x tt
14
What type of allele prevent other
alleles from being shown?
0%
no
es
cl
si
v
e
ue
!
0%
e
H
el
p!
Ih
C
av
R
D
om
in
a
nt
in
a
od
0%
nt
0%
ec
Codominant
Dominant
Recessive
Help! I have no
clue!
om
1.
2.
3.
4.
1
2
3
4
21
22
23
24
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
15
What is the phenotype of the offspring if a blue
eyed parent (bb) is crossed with a brown eyed
parent (Bb)?
1. 25% blue eyed, 75%
brown eyed
2. 50% blue eyed, 50
% brown eyed
3. 75 % blue eyed, 25
% brown eyed
4. 100% brown eyed
3
4
21
22
23
24
5
6
7
8
9
10
12
13
14
15
ed
ey
br
ow
n
25
ey
e
%
bl
10
ue
0%
d,
,5
ed
ey
bl
ue
%
...
%
...
0
5%
...
,7
ed
ey
bl
ue
%
25
11
75
2
50
1
0% 0% 0% 0%
16
17
18
19
20
16
Chromosomes
– The Cell and
Inheritance
•
•
Sutton explored
chromosomes through
the study of the
grasshopper.
According through the
chromosome theory of
inheritance, genes are
carried from parents to
their offspring on
chromosomes.
17
Meiosis
•
•
Meiosis is the process by
which the number of
chromosomes is reduced
by half to form sex cells
(sperm and eggs)
During meiosis, the
chromosome pairs
separate and are
distributed to two
different cells. The
resulting sex cells have
only half as many
chromosomes as the
other cells in the
organism.
18
Human Genome
•
•
•
A Punnett square
shows the events that
occur at meiosis.
Chromosomes are
made up of many
genes joined together
like beads on a string.
Humans have 23
chromosome pairs
19
Deoxyribonucleic Acid
– DNA
•
•
•
•
Genes control the
production of proteins.
Proteins determine the
traits of an organism.
Chromosomes are
composed of DNA.
Chromosomes have
four nitrogen bases.
–
–
–
–
adenine
thymine
guanine
cytosine
20
Protein Synthesis
•
The arrangement of
the nitrogen bases
along a gene
determines the type of
protein produced.
– Proteins are made of
amino acids.
– Three-base code
determines the
amino acid used in
the making of
proteins.
21
Amino Acids
•
During protein
synthesis, cells use
the information from a
gene on the
chromosome to
produce a specific
protein.
– Protein synthesis
takes place in the
ribosome of a cell.
22
Ribonucleic Acid
•
RNA is a single helix.
– Contains uracil
instead of thymine.
– mRNA copies the
coded message from
the DNA in the
nucleus, and carries
the message to the
ribosome in the
cytoplasm.
– tRNA carries the
amino acid to the
ribosome and adds
the amino acid to the
protein chain.
23
Producing Proteins
•
Steps in Protein
Synthesis
– First step: DNA
molecule unzips and
one strand directs
the production of
mRNA. Cytosine
pairs with guanine
and uracil pairs with
adenine.
– Second step: mRNA
enters cytoplasm
and attaches to the
ribosome. mRNA
provides the code to
produce the protein.
24
Transcription
– Third step: tRNA
attaches to the
mRNA to attaché
a specific amino
acid to the protein.
The order of the
amino acid
determines the
type of protein.
– Protein chain
grows longer. The
tRNA releases into
the cytoplasm to
get another amino
acid.
25
Mutations
•
Mutations cause a cell
to produce an
incorrect protein that
may lead to a different
phenotype.
– One type of
mutation may
occur when a
nitrogen base is
changed during
DNA replication.
26
Helpful or Harmful?
– Another mutation
may occur when
chromosomes do
not separate
correctly during
meiosis.
– Mutations are
helpful if they
increase an
organism’s chance
for survival and
are harmful if they
decrease an
organism’s chance
for survival.
27