Genetics of haemophilia | X Linked recessive inheritence | class 12 скачать в хорошем качестве

Genetics of haemophilia | X Linked recessive inheritence | class 12

Aslam o alikum I am Hassam ur Rahman and I am teaching Fsc biology since 2014 .I am always trying to improve myself and provide best lecture to students.i am taking content for the lecture from authentic and relevant sources but human errors are possible . you are requested to please highlight the mistakes.My lectures are equally reliable for Fsc and mdcat students #visiblescience #mdcatbiology #alevelbiology #neetbiology #fscbiology My personal channel, I am sure it will change your life and very beneficial for you https://youtube.com/@hassamurRahman?f... My Facebook page link https://www.facebook.com/hassam.urahm... This lecture is about Sex - Linkage in Humans Humans have many X - linked traits of which some like haemophilia and colour blindness are recessive while others like hypophosphatemic or vitamin D resistant rickets are dominant. X - linked dominant is a trait which is determined by an X linked dominant gene, while X - linked recessive is a trait that is determined by an X - linked recessive gene. Their patterns of inheritance are very diferent from each other. X - linked recessive inheritance: Experimental matings are not practically possible in humans. Mode of inheritance of human traits can be traced through pedigrees. Genetics of Haemophilia: Haemophilia is a rare X — linked recessive trait. Haemophiliac’s blood fails to clot properly after an injury, because it has either a reduction or malfunction or complete absence of blood clotting factors. It is a serious hereditary disease because a haemophiliac may bleed to death even from minor cuts. Haemophilia is of three types: A, B and C. Haemophilia A and B are non - allelic recessive sex - linked, but haemophilia C is an autosomal recessive trait. 80% haemophiliacs, sufer from haemophilia A due to abnormality of factor VIII, about 20% sufer from haemophilia B due to disturbance in factor IX, but less than 1% sufer from haemophilia C due to reduction in factor XI. Being X - linked recessives, haemophilia A and B afect men more than women, but haemophilia C afects both the sexes equally because it is autosomal. Chances for a man to be afected by haemophilia A and B are greater than a woman. A woman can sufer from haemophilia A or B only when she is homozygous for the recessive allele, but a man with just one recessive allele will display the trait. Haemophilia A and B zigzag from maternal grandfather through a carrier daughter to a grandson. It never passes direct from father to son. Gene for normal is H. Gene for haemophilia A is h. In generation I of this pedigree (Fig. 22.27) a man (I - 2) sufering from haemophilia A marries a normal woman (I - 1). He passes haemophilia gene to his daughter (II - 2) through his X chromosome. He cannot pass this gene to his son (II - 3) because the son receives only Y chromosome from him. His daughter (II - 2) also receives another X but with normal dominant allele from her mother (I - 1). The daughter looks phenotypically normal, but she is heterozygous and a carrier for the recessive gene. When she marries a normal man (II - 1) she passes her father’s trait to one of her two sons (HI - 4) who inherits grandfather’s X from her. The single recessive allele for haemophilia expresses successfully in the hemizygous son because his Y chromosome does not carry its counterpart. The other son (III - 3) is normal as he inherits grand mother’s X with normal gene, One daughter (III - 1) with both normal X is normal, but the other daughter (III - 2) is carrier like her mother.