CO-DOMINANCE ||Class 12 Biology

By -
     In heterozygous condition both the alleles are expressed. Both alleles are expressed in dominant forms. The alleles which shows this property are called codominant alleles and the phenomenon is known as co-dominance.
      In this condition, the offsprings shows resemblance to both the parents, eg- ABO blood groups in humans. ABO blood groups are controlled by the gene I. The plasma membrane of the red blood cells (RBCs) has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene (I) has three alleles: IA, IB and i. The alleles IA and IB produce a slightly different form of the sugar while allele i does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three I gene alleles. IA and IB are completely dominant over i, in other words when IA and i are present only IA expresses (because i does not produce any sugar) and when IB and i are present IB expresses. But when IA and IB are present together they both express their own types of sugars: this is because of Co-dominance.




Location: India

Comments

Post a Comment

If you have any doubts,please let me know

Popular posts from this blog

Spermatogenesis : Definition & Process ||Class 12 Biology

By -
Image
    Spermatogenesis is the process of formation of spermatozoa (sperms) in the testes which originate from the primordial germ cells (PCGs).     The process of Spermatogenesis initiates at puberty and continues even in the old age.       The process of Spermatogenesis comprised the following two main stages- 1. Formation of spermatids 2. Spermiogenesis 1. Formation of spermatids : It include the following three phases- i) Multiplication Phase ii) Growth Phase iii) Maturation Phase   i) Multiplication Phase : During this phase, the immature germ cells present in the Seminiferous tubules of the testes known as spermatogonia increases in number by mitotic divisions and so that the newly formed spermatogonium possesses the same number at chromosomes.  ii) Growth Phase : Each spermatogonium is diploid (2n) and contains 46 chromosomes. Some of the spermatogonia called primary spermatocytes.  iii)  Maturation Phase : Primary spermatocytes periodically undergo meiosis  division. A primary sper
Read more

Sperm: Structure ||Class 12 Biology

By -
Image
     A mature spermatozoa or a sperm cell is a microscopic, tadpole-shaped structure of about 2-5 micrometer in diameter and 50 micrometer long. A plasma membrane encloses the whole body of sperm.      Sperm consists of head, neck, middle piece and tail.       1. Head: It is flat, oval and composed of a large haploid nucleus and a small cap-like structure called acrosome. It lies at the tip of the nucleus and is formed from the Golgi complex. It contains hydrolytic enzymes and is used to contact and penetrate the egg (ova) during fertilization.       2. Neck: Neck is the smallest part, it is short structure that contains two centrioles- one parallel to the base of the nucleus and called proximal centriole and other distal centriole perpendicular to the previous one. The proximal centriole enters into the egg during fertilization and starts the first cleavage division of the egg which has no centriole. The distal centriole gives rise to the axial filament which forms the tail.       3.
Read more

Placenta: Structure & function ||Class 12 Biology

By -
Image
     The placenta is an organ attached to the lining of womb during pregnancy. Structure:       After implantation, finger-link projections appears on the trophoblast called chorionic villi which surrounded by the uterine tissues and maternal blood. The chorionic villi and the uterine tissue become interdigitated with each other and jointly form a structural and and functional unit between foetus and maternal body called placenta. Placenta is forms from the chorian and allantois. In human, the placenta averages 22cm (9 inch) in length and 2-2.5cm (0.8-1inch) in thickness. it has dark reddish-blue or crimson colour. It connects to the foetus by an umbilical cord. Function:      1. It facilitates the supply of oxygen and nutrients to the embryo.     2. Responsible for the removal of carbon dioxide and waste materials produced by the foetus.    3. The placenta is connected to the embryo through the umbilical cord which helps in the transport of substances to and from the embryo.    4. It
Read more