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Sex Determination in Humans

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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 fertilized with sperm carrying X or Y chromosomes.

    • If X chromosome gets fertilized ā€“ XX (Female)

    • If Y chromosome gets fertilized ā€“ XY (Male)

 

Sex Determination in Honeybees

  • An offspring formed from the union of a sperm and an egg develops into queen/worker.

  • The unfertilized egg develops as a male (drone) by parthenogenesis.

  • Males thus have half the number of chromosomes than female.

  • Females have 32 chromosomes and male have 16 chromosomes.

  • It is called as haplodiploid sex determination system and has its own importance such as male produce sperm by mitosis.

Mutation

Mutation is the phenomenon which results in alteration of DNA sequence and consequently results in changes in the genotype and phenotype of an organism. There are two types of genetic mutation:

  • Point mutation: There is a substitution in the single base pair of DNA, e.g. in the sickle cell anaemia. The 6th codon of the gene coding for the š›ƒ-globin chain of haemoglobin changes from GAG to GUG, resulting in the substitution of glutamic acid by Valine.

  • Frameshift mutation: It results from the insertion or deletion of one or more pairs of bases in DNA. it changes the reading frame of triplet codons, that code for certain amino acids of the protein.

Genetic Disorders

There are many disorders in the human being that are inherited and caused due to mutation in the gene or alteration in chromosomes.

Pedigree Analysis

It helps in determining the risk of getting a genetic disorder in the offspring by studying the inheritance pattern of a particular trait present in various generations of an individual.

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