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Lab – 5 -
Multiple Alleles An allele is a gene type which affects certain characteristics of an organism; each gene usually have only two possible alleles dominant or recessive (A and a). Multiple alleles therefore are more than three alleles contained in one gene (A, a, A1, A2, A', etc.). A good examples of multiple alleles are the blood groups in human and rabbit fur color which are determined by a single gene with a series of alleles, each resulting in different trait.
1- Blood groups and Rhesus factor (Rh) in human
The discovery of human blood groups was reported by Dr. Karl Landsteiner in 1900.Landsteiner's work led to the establishment of the Abo system used to group human blood into different types, based on the presence or absence of certain markers on the surface of red blood cells. The four main blood types are A, B, O, and AB. The basis for the four blood groups is the presence of naturally occuring antigens and antibodies in the blood of individuals in various combinations. In the ABO blood groups the factors that determine the antigens and antibodies are inherited, the antigen appearing in the progeny only if present in at least one parent. The two antigens that were discovered by Landsteiner are called A and B and are found on the surface of the erythrocytes. The antibodies are found in the serum and they are known as anti-A and anti-B. The antigens determining the four blood groups are the result of the expression of three alleles A, B and O; the first two being dominant to O.
The blood group A and B show the codominance inheritance which means that both the A allele and the B allele are equally expressed. Thus only four phenotypes (A, B, AB, and O) can be recognized, although six genotypes occur as illustrated in this table.
genotype Phenotype
IAIA^ IAi A
IBIB^ IBi B
IAIB AB
ii O
**** Which is the Universal donor? What is the condition required to be a universal donor?** Blood group O is considered as Universal donor.The condition required is that the blood group is without any antigens on RBC to react with antibodies of plasma of other blood groups.O group is without any antigens on RBC, so it is considered as universal donor.
There are many other blood grouping systems known in addition to the ABO series; for example the N and M series and the well known Rh+ and Rh- groups.
EXAPLE/ What is the probability that a couple whose blood types are AB and O will have a type A child?
I A^ I B^ X ii
IA^ I B^ i
I A^ i 50% , I Bi 50%
Rhesus factor (Rh)
Rh is a type of antigen. It was first detected in the RBC of Rhesus monkey and later in man. Rh antigen (D) is present in the persons who are considered as Rh positive. Rh antigen is absent in the persons who are considered as Rh negative. Reaction Ab Ag genotype phenotype with Ab
IA^ IB i
MN blood system The MN blood system is a third (in addition to the ABO and the Rh) system of blood antigens also related to proteins of the red blood cell plasma membrane. The inheritance pattern of the MN blood system is autosomal with codominance, a type of lack of dominance in which the heterozygous manifests a phenotype totally distinct from the homozygous. The possible phenotypical forms are three blood types:
type M blood (MM)
type N blood (NN)
type MN blood (MN)
EXAMPLE/ What happens when you cross a dark gray (Cc) and a white rabbit?
genotype ratio: ________________________________
phenotype ratio: ________________________________
EXAMPLE/ A chinchilla rabbit is mated with a Himilayan. Some offspring are white.What are the parent genotypes?
genotype ratio: ________________________________
phenotype ratio: ________________________________
EXAMPLE/ Would it be possible to obtain white rabbits if one rabbit is white and the other is chinchilla?
genotype ratio: ________________________________
phenotype ratio: ________________________________
EXAMPLE/ Would it be possible to obtain Himilaya rabbits if one rabbit is Ccch^ and the other is c h^ c?
genotype ratio: ________________________________
phenotype ratio: ________________________________
EXAMPLE/ A type B woman whose mother was type O marries a type O man. What are the possible phenotypic ratios of their offspring?
EXAMPLE/ A type A woman whose father was type B marries a type B man whose mother was type A. What are the possible phenotypes of their offspring?
EXAPLE/ What is the probability that a couple whose blood types are AB and O will have a type A child?
EXAMPLE/ A woman who has heterozygous type A blood has a baby with type O blood. The man she claims is the father of the child says he is not. If he has type AB blood, could he be the father of the child? Prove your answer.
EXAMPLE/ What are the possible blood types of a child whose parents are both heterozygous for B blood type? The possible blood types of a child is : B blood type = 3 ; O blood type = 1
EXAMPLE / What are the chance of a woman with type AB and a man with type A having a childwithtype O? No chance for the blood type O in progeny
EXAMPLE / Determine the possible genotypes and phenotypes with respect to blood type for acouple who’s blood types are homozygous A and heterozygous B. Male is I AI A, Female is I Bi. Both are crossed, thenThe possible genotype and phenotypes among the progeny is : 50% blood type = AB I AI B 50% blood type = A I Ai
EXAMPLE/ Jill is with blood type O. She has two older brothers with blood types A and B. What are the genotypes of her parents with respect to this trait? Jill blood type O, 2 brothers blood type A and B, then The genotypes of her parents are I Ai (Male) I Bi (Female)
Example/ A test was done to determine the biological father of a child. The child’s blood type is A and the mother’s is B. Dude # 1 has a blood type of O and Dude # 2 has blood type AB. Which Dude is the biological father? Dude # 1 blood type ‘O’ Dude # 2 blood type ‘AB’ Dude # 2 is the biological father of AB.
EXAMPLE/ One parent is A blood type and the other parent is B blood type. Give their respectivegenotypes if they produce a large number of children whose blood types are : (1) All AB (2) Half AB and other half B (3) Half AB and other half A (4) 1/4 AB, 1/4 A, 1/4 B, 1/4 O (1) If both the parents are homozygous then all the children will be AB. I AI A^ X IBI B AB All will be AB (2) If A homozygous and B is heterozygous. I AI A^ X IBi IAI B^ , I Ai Half AB and other half A (3) If B is homozygous and A is heterozygous. IAi X IBI B I AI B^ , I Ai Half AB and other half B (4) If both the parents are heterozygous, then I Ai X IBi I AI B^ , I Ai, I Bi, ii 1/4 AB, 1/4 A, 1/4 B, 1/4 O
