Sexual Reproduction

• Sexual reproduction results in a greater amount of genetic variability in gametes (sperm & egg) due to random assortment and crossing over in meiosis
• Two parents of the opposite sex are required for sexual reproduction, where 2 gametes come together to produce a unique offspring
• Offspring in sexual reproduction is a mixture of the DNA of both parents and requires a lot of energy to produce
• Low amounts of offspring are produced in sexual reproduction, but there is high variation in DNA
• Advantages of sexual reproduction include better survival chances in changing environments due to the large amount of variation
• Meiosis involves sex cells (sperm and egg) which have half the chromosomes of somatic cells
• Fertilization results in the formation of a zygote from the union of egg and sperm, with the zygote undergoing mitosis to develop into a human baby
• In humans, during fertilization, sperm (n=23) unites with an egg (n=23) to produce a diploid (2n=46) zygote
• Homologous chromosomes carry information for the same hereditary traits and form pairs in the cell
• Genes are located at specific positions (loci) on chromosomes, with two copies of a specific trait at each locus, one from each parent
• Alleles are different forms of the same gene found at the same locus on homologous chromosomes
• Meiosis occurs only in the reproductive tissues of sexually reproducing organisms, while mitosis consists of a single division of the nucleus
• Meiosis has two main divisions, Meiosis I and Meiosis II, each subdivided into prophase, metaphase, anaphase, and telophase
• Key terms in meiosis include tetrad (pair of homologous chromosomes), synapsis (pairing of homologous chromosomes), and crossing over (exchange of chromosome segments)
• Gametogenesis is the formation of sex cells in meiosis, with spermatogenesis producing sperm cells and oogenesis forming egg cells
• Spermatogenesis results in the formation of 4 equal-sized sperm cells, while oogenesis produces one ovum and 3 polar bodies that die
• A karyotype chart sorts and arranges chromosomes to identify disorders or in forensic investigations
• Sex chromosomes determine the sex of an individual, with XX chromosomes indicating female and XY chromosomes indicating male
• All other chromosomes besides sex chromosomes are referred to as autosomes