BIO270H1 Lecture Notes - Lecture 6: Seminiferous Tubule, Yolk Sac, Sertoli Cell
Document Summary
Sexual reproduction creates a population that is a collection of distinct genotypes. Sexual reproduction generates genomic variation at 3 levels: an animal produces haploid gametes with genomes consisting of chromosomes originally provided by the animal"s own diploid parents. Asexual reproduction is advantageous for animals that live in a constant and stable environment it has much lower energetic costs than sexual reproduction. Asexual reproduction results in identical offspring with the same genetic material as their parent. In mammals, the y chromosome is called the sex- determining chromosome: a male results when the zygote is heterogametic (xy) and a female when it is homogametic (xx). However, in birds and butterflies, the female is the heterogametic individual (zw) and the male is the homogametic individual (zz). In haplo-diploidy (seen in honeybees) if an egg is fertilised, the diploid offspring is female; if the egg is unfertilised, a haploid male results.
