DECODE The Script of LIFE

Sex Determination in Humans The mechanisms for sex determination are genotypic sex determination systems, in which sex is governed by the genotype of the zygote and environmental sex determination systems in which sex is governed by internal and external environmental conditions. In genotypic sex determination the sex chromosomes play a decisive role in the inheritance and determination of sex. Chromosomal sex is determined at fertilization. Sexual differences begin in the 7th week. Sex is influenced by genetic and environmental factors. Females (generally XX) do not have a Y chromosome. Males (generally XY) have a Y chromosome. Sex determination mechanism is humans is XY type. 22 pairs are similar in male & females whereas presence of X/Y chromosomes determine human sex. In spermatogenesis male produce 50% of sperms with X-Chromosomes and the other 50% with Y-Chromosomes. Female have only X-Chromosomes. It is hence a matter of chance, since there is equal probability of getting fe

  Types of Genetic disorders Genetic disorders can be grouped into two types: Mendelian Disorders Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. Most common and prevalent Mendelian disorders are Hemophilia, Cystic fibrosis, Sickle-cell anemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is evident that this X-linked recessive trait shows transmission from carrier female to male progeny. Examples: Name Genetic Trait Cause Effects Inheritance pattern Sickle cell anaemia Autosome-linked recessive A single point mutation in the beta-globin chain of haemoglobin Anaemia Offsprings may get the disease when both the parents are a carrier (heterozygote) Thalassemia Autosome-linked recessive Mutation in the genes HBA1 and HBA2 present on the chromosome 16 Formation of abnormal haemoglobin molecule resulting in anaemia Offsprin