If the mother is Rh negative and foetus is Rh positive, anti D antibodies should be administered to the mother at 28th and 34th week of gestation as a prophylactic measure. If the Rh negative mother delivers Rh positive child then anti D antibodies should be administered to the mother soon after delivery. This develops passive immunity and prevents the formation of anti D antibodies in the mother's blood by destroying the Rh foetal RBC before the mother's immune system is sensitized. This has to be done whenever the woman attains pregnancy.

I^A allele produces N-acetyl galactose transferase and can add N-acetyl galactosamine (NAG) and IB allele encodes for the enzyme galactose transferase that adds galactose to the precursor (i.e. H substances). In the case of I^O/I^O allele no terminal transferase enzyme is produced and therefore called "null" allele and hence cannot add NAG or galactose to the precursor.

(i) They are cytoplasmic symbionts occurring in some strains of the ciliated paramecium which have their own DNA.
(ii) It liberates a toxin paramecium and strains which possess these particles are called 'killer paramecia'. Inheritance of killer trait, is by extra chromosomal inheritance.

Certain characters are controlled by non - nucleas genomes found in chloroplast, Mitochondria, infective agents and plasmids, and do not reveal Mendelian pattern of Inheritance. This is called as extra chromosomal inheritance. They exhibit maternal influence in their pattern of inheritance. Eg. Inheritance of the shell coiling pattern in fresh water snail Limnaea peregra.

i) Chromosomal disorders are caused by errors in the number or structure of chromosomes.
ii) Chromosomal anomalies usually occur when there is an error in cell division . Failure of chromatids to segregate during cell division resulting in the gain or loss of one or more chromosomes is called aneuploidy. It is caused by non -disjunction of chromosomes. E.g Down's syndrome.

Intersexes: 
1. Intersexes refers to the individuals having the characteristics of both female and male sexes and their sexual anatomy does not seem to fit the typical definition of male or female.
Supersexes: 
1. Supersexes ar formed as a result of abnormal combination of sex chromosomes. 
2. Example : Super males in humans human beings have 44+XYY

(i) Fisher and Race hypothesis: 
Rh factor involves three different pairs of alleles located on three different closely linked loci on the chromosome pair. This system is more commonly in use today, and uses the 'Cde' nomenclature.

2. In the above Figure, three pairs of Rh alleles (Cc, Dd and Ee) occur at 3 different loci on homologous chromosome pair- 1.
3. The possible genotypes will be one C or c, one D or d, one E or e from each chromosome
For e.g. CDE/cde; CdE/cDe; cde/cde; CDe/CdE etc.
4. All genotypes carrying a dominant 'D' allele will produce Rh positive phenotype and double recessive genotype 'dd' will give rise to Rh negative phenotype.
(ii) Wiener Hypothesis 
1. Wiener proposed the existence of eight alleles (R¹, R², R^O, R^Z, r, r¹, r¹¹, r^y) at a single Rh locus.
2. All genotypes carrying a dominant 'R allele' (R¹, R^2, R^O, R^Z) will produce 'Rh- positive' phenotype and double recessive genotypes (rr, rr¹, rr¹¹, rr^y) will give rise to Rh^- negative phenotype.

Heterogametic Males:
In this method of sex determination the males are heterogametic producing dissimilar gametes while females are homogametic producing similar gametes.
It is of kinds XX-XO type and XX-XY type.
(i) XX-XO Type
(a) This method of sex determination is seen in bugs and some insects such as cockroaches and grasshoppers.
(b) The female with two X chromosomes are homogametic (XX) while the males with only one X chromosome are heterogametic (XO).
(c) The presence of an unpaired X chromosomes determines the male sex. The males with unpaired 'X' chromosome produce two types of sperms, one half with X chromosome and other half without X chromosome.
(d) The sex of the offspring depends upon the sperm that fertilizes the egg.
 
(ii) XX-XV type (Lygaeu Type):
This method of sex determination is seen in human beings and in Drosophila.
(a) The females are homogametic with XX chromosome, while the males are heterogametic with X and Y chromosome.
(b) Homogametic females produce only one kind of egg, each with one X chromosome, while the heterogametic males produce two kinds of sperms some with X chromosome and some with Y chromosome.
(c) The sex of the embryo depends on the fertilizing sperm. An egg fertilized by an 'X' bearing sperm produces a female, if fertilized by a 'Y' bearing sperm, a male is produced.

1. The sex determining mechanism of humans is XX-XY type.
2. In humans, out of 23 pairs of chromosomes present, 22 pairs are exactly same in both males and females known as autosomes (body).
3. The 23rd chromosome is the sex chromosome. (i.e) Pair of X-chromosome (XX) is present in females and males having one X and one Y chromosome (XY).
4. During, spermatogenesis, in case of males two types of gametes are produced (x and y).
5. The 50% total sperms produced carry X-chromosomes and the rest 50% carry Y - chromosomes besides autosomes. This condition is called male diagamety.
6. The Y containing sperms and X containing sperms are called androsperms and gynosperms respectively.
7. Female produces only one type of ovum with an X-chromosome. If an ovum fertilizes with a sperm carrying X chromosome the zygote develops into a female (XX) and if an ovum is fertilized with sperm carrying Y-chromosome, zygote thus, formed will be male (YY).

8. Hence, the genetic makeup of sperm, which fertilizes the ovum determines the sex of a child there are 50% chances of having either a male or female in each progeny.
9. Thus, it is by chance phenomenon, so women should not be blamed for giving birth to a girl child

Genetic basis of blood grouping in human population
1. ABO blood grouping in human shows the phenomenon of codominance.
2. Alleles are able to express themselves independently when present together.
3. More than two alleles govern the same character.
4. Karl Landsteiner discovered two kinds of antigens called antigen 'A' and antigen 'B' on the surface of RBC's of human blood.
5. In 1902 two of Landsteiner's students Von De Castelle and Sturli discovered fourth rarest blood group 'AB' (universal recipient).
6. Bernstein in 1925 discovered that the inheritance of different blood groups in human beings is determined by a number of multiple allelle series.
7. The three autosomal alleles located on chromosome are concerned with the determination of blood group in any Person.
8. The gene controlling blood types has been labeled as 'L' (after the name of the discoverer, Landsteiner) or I (from iso -agglutination).
9. The I gene exists in three allelic forms, I^A, I^B and I^o specifies A antigen.
10. I^B allele determines B antigen and I^o allele specifies no antigen.
11. Individuals who possess these antigens in their fluids such as the saliva are called secretors
Genetic basis of the human ABO blood groups
Genotype ABO blood group phenotype Antigens present on red blood cell Antibodies present in blood plasma I^AI^A Type A A Anti -B I^AI^O Type A A Anti -B I^BI^B Type B B  Anti -A I^BI^O Type B B Anti -B I^AI^B Type AB A and B Neither Anti - A nor Anti -B I^OI^O Type O Neither A nor B Anti - A and anti -B