Gametogenesis Flashcards
Gametogenesis
the production of gametes through the process of meiosis
Two types:
* Spermatogenesis (males)
* Oogenesis (females)
Spermatogenesis
Meiosis in males, which occurs in testes
* Starts w diploid cell (2n) = spermatogonium
Spermatogenesis produces four non-identical haploid sperm cells
* Begins at puberty → occurs continuously from puberty until death
* Takes approximately 68-74 hours for sperm to be created
* Meiosis produces ~250 000 000 sperm eery day in males
Oogenesis
Meiosis in females occurs in ovaries
* Starts with diploid cell (2n) = oogonium
Oogonia reproduce via mitosis
* Meiosis starts before a female is born, but pauses in Prophase I
* Meiotic process resumes at puberty with ovulation for 1 cell every month
Meiosis II is completed when fertilization w sperm occurs to create a viable egg
* After telophase I and II, only one of the cells receives the majority of the cytoplasm
* Results in one egg cell and 3 polar bodies → Do not have the ability to be fertilized
Why does unequal division of cytoplasm occur in females
Unequal division allows the egg cell to have sufficient nutrients to support a zygote immediately after fertilization
Independent Assortment
During metaphase 1, chromosomes arranged in homologous pairs along equator
* Chromosome of maternal origin oriented toward one pole, and vice versa for the paternal chromosome
* This orientation of chromosomes is independent of orientation of the other chromosomes
* Depending on how chromosomes line up determines variety of combinations that can be produced in gametes
Importance of Crossing Over
- When homologous chromosomes line up for prophase I, non-sister chromatids of homologous chromosomes may exchange pieces of chromosome
- One section of chromosome that is crossed over may contain hundreds to thousands of genes
- As a result, some chromosomes contain some genes from maternal origin and some of paternal origin - dramatically increases genetic diversity
