Download MULTIPLE ALLELES Multiple alleles -

MULTIPLE ALLELES
Multiple alleles -
three ore more contrasting genes affecting the expression
(phenotypes) of one character (detail of structure); however,
only two of these genes may occur in a genotype and only
one is transmitted in a gamete.
Character
Phenotypes
Genes
1. Color of fur
Agouti
C*
CC, Ccch, Cch, Cc
Chinchilla
cch
cchcch, cchch, cchc
Himalayan
ch
chch, chc
Albino
c
cc
(rabbits)
*Genes are listed in order of dominance.
Genotypes
COLOR OF FUR IN RABBITS
P
Females
P
Males
AGOUTI
CC
C
CHINCHILLA
cchcch
cch
HIMALAYAN
chch
ch
AGOUTI
CC
C
AGOUTI
CC
F1 AGOUTI
Ccch
½ C ½ cch
F2 3 AGOUTI
1 CC 2 Ccch
1 CHINCHILLA
1 cchcch
F1 AGOUTI
Cch
½ C ½ ch
F2 3 AGOUTI
1 CC 2 Cch
1 HIMALAYAN
1 chch
CHINCHILLA
cchcch
F1 CHINCHILLA
cchch
½ cch ½ ch
F2 3 CHINCHILLA
1 cchcch 2 cchch
1 HIMALAYAN
1 chch
HIMALAYAN
chch
CHINCHILLA
cchcch
cch
HIMALAYAN
chch
ch
ALBINO
cc
c
ALBINO
cc
c
F1 AGOUTI
Cc
½C ½c
F2 3 AGOUTI
1 CC 2 Cc
1 ALBINO
1 cc
F1 CHINCHILLA
cchc
½ cch ½ c
F2 3 CHINCHILLA
1 cchcch 2 cchc
1 ALBINO
1 cc
F1 HIMALAYAN
chc
½ ch ½ c
F2 3 HIMALAYAN
1 chch 2 chc
1 ALBINO
1 cc
ALBINO
cc
Codominant genes - alleles, each of which produces an independent
effect when heterozygous.
Genotypes
2. ABO blood group
(humans)
Percent
0
IO IO
aa
45
A
IA IA, IA IO
AA, Aa
41
B
IB IB, IB IO
ABAB, ABa
10
AB
IA IB
AAB
4
Genes
IO, a - does not produce antigen, allows A and B antibodies to be produced.
IA, A - produces antigen A, inhibits production of antibody A.
IB, AB - produces antigen B, inhibits production of antibody B.
268
Antigen - A substance present on the red blood cells.
Antigen A, antigen B.
Antibody - A substance present in the serum of the blood.
Antibody A, antibody B.
Antiserum - A serum that contains a known antibody.
Antiserum A, antiserum B.
Antigen-antibody-reaction - When an antigen (Antigen A) and its
corresponding antibody (Antibody A) are brought
together.
If n = number of alleles of a gene, then the number of different genotypes
possible = [n(n + 1)]/2. Therefore, for 2, 3, 4, and 5 alleles (n), the number of
possible genotypes = 3, 6, 10, and 15, respectively.
269
BLOOD TYPING – SHOWING AGGLUTINATION OF CELLS OF THE
DIFFERENT BLOOD TYPES WITH ANTI-A AND ANTI-B AGGLUTININS
Red Blood
Cell Types
O
A
B
AB
Sera
Anti-A
+
+
Anti-B
+
+
Type A blood has A agglutinogens and therefore agglutinates with anti-A
agglutinins. Type B blood has B agglutinogens and agglutinates with anti-B
serum. Type AB blood has both A and B agglutinogens and agglutinates with
both types of serum.
Codominant genes- Alleles, each of which produces an
independent effect when heterozygous
DETERMINATION OF ABO BLOOD TYPES (PHENOTYPES)
REACTIONS OF ANTIGEN(S)
BLOOD WITH
ON RBCs
ANTISERUM
A
B
none
A
+
B
+
+
A and B
+
ANTIBODY(S)
IN
SERUM
None, A and/or B
None or B
None or A
None
BLOOD
TYPE
PERCENT OF
EACH BLOOD
TYPE
O
A
B
45
41
10
4
AB
INHERITANCE OF ABO BLOOD GROUP
O
A
B
AB
O
O
A
O
A
O
A
B
O
B
O
A
B
AB
O
B
AB
A
B
A
B
AB
A
B
AB
A
B
AB
BLOOD TYPES ARE:
1. Used in making blood transfusions,
2. Used in legal cases involving disputed parentage,
3. Used in genetic counseling.
BLOOD TRANSFUSIONS
Donor
O (Universal Donor)
A
B
AB (Universal Recipient)
Rh+
Rh-
Recipient
O, A, B, AB
A, AB
B, AB
AB
Rh+
Rh+, Rh-
An Rh- female should have the Rh vaccine if she has an Rh+ baby if (1) she has
not had an Rh+ blood transfusion, if (2) she has not had an Rh+ baby without
having had the Rh vaccine. Give Rh vaccine within 3 days after Rh+ birth.
WHERE DO WE GET Rh VACCINE?
1. From Rh- females who have had Rh+ children if the Rh- female did not
have vaccine.
2 From Rh- males who have had Rh+ antigen
HOW AN RH-DISEASE BABY IS PRODUCED
1. CHILD received from FATHER
an “Rh-positive” gene and begins
to produce Rh-positive blood,
shown by symbol.
2. MOTHER’S blood is Rh-negative.
shown by symbol.
3. Some of the CHILD’S Rh-positive blood *
substance travels through placenta into
MOTHER.
4. MOTHER’S blood begins producing
antibodies to attack hostile substances
from baby. *
*
If Rh-negative mother has had previous Rh-positive pregnancies, or
transfusions with Rh-positive blood, antibodies already are present.
5. Antibodies from MOTHER enter CHILD
and begin destroying its blood cells.
Quantitative Traits
Quantitative traits may be governed by many genes (perhaps
10-100 or more), each contributing such a small amount to the
phenotype that their individual effects cannot be detected by Mendelian
methods. Genes of this nature are called polygenes. Thus, more than
one gene may contribute to a given trait. This is where we get the
polygene concept as defined at the back of your workbook.
As a means by which we may determine the number of genes
that interact to control a quantitative trait, use the formula 2n + 1 to
calculate "n", which is the number of different genes interacting.
For example: Plants may be 10, 20, 30, 40, 50, 60, or 70 cm high where plant
height is under polygenic control. A true-breeding plant that is 10 cm is
crossed to another true-breeding plant that is 50 cm high. How many gene
pairs are involved? What F1 and F2 results can be predicted?
Answer: Since there are seven groups of phenotypes, using our 2n + 1 rule,
we can propose that there are three pairs of genes that control height
additively. Each additive allele adds 10 cm to a base of 10 cm. The 10 cm
plant contains no additive alleles. The 50 cm plant, since it is true-breeding,
must be homozygous for additive alleles at two of the three gene sites:
P: aabbcc x AABBcc
F1: All AaBbcc (30 cm)
It is simplest to determine the F2 ratio by using the forked-line method.
Since each allele influences plant height additively, we must compute the
genotypic ratio. All F2 plants will be cc, so we can add the c alleles to the B
group:
# Additive
Height
Alleles
F2:
1/4 BB cc
1/16 AA BB cc
4
50
1/4 AA 2/4 Bb cc
2/16 AA Bb cc
3
40
1/4 bb cc
1/16 AA bb cc
2
30
1/4 BB cc
2/16 Aa BB cc
3
40
2/4 Aa
2/4 Bb cc
4/16 Aa Bb cc
2
30
1/4 bb cc
2/16 Aa bb cc
1
20
1/4 BB cc
1/16 aa BB cc
2
30
1/4 aa
2/4 Bb cc
2/16 aa Bb cc
1
20
1/4 bb cc
1/16 aa bb cc
0
10
Final ratio: 1/16
4/16
6/16
4/16
1/16
10 cm
20 cm
30 cm
40 cm
50 cm
271