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Which one of the following conditions correctly describes the manner of determining the sex?

Correct answer: B. XO type of sex chromosomes determine male sex in grasshopper.

  • A. Homozygous sex chromosomes (ZZ) determine female sex in birds.
  • B. XO type of sex chromosomes determine male sex in grasshopper.
  • C. XO condition in humans as found in Turner's syndrome, determines female sex.
  • D. Homozygous sex chromosomes (XX) produce male in Drosophila.

Explanation

XO type of sex chromosomes determines the male sex in grasshoppers. This type of sex­-determination comes under the XX­-XO type. Its common examples are cockroaches, grasshoppers, and bugs. The female has two homomorphic sex chromosomes XX and is homogametic. It produces similar eggs, each with an X­-chromosome. The male has one chromosome only and is heterogametic. It produces 2 types of sperms and gymnosperms with X and angiosperms without X. Fertilization of an egg by X­-bearing sperm yields female offspring and by no X sperm yields male offspring.

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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.

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