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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