Sexual Reproduction in Mammals Flashcards
What are gametes?
Cells with half the usual chromosome number
Haploid cells
What is fertilisation?
The fusion of two gamete nuclei to make a zygote nuclei
What is a zygote?
The cell formed from the fusion of two gamete nuclei
What is sex?
Has a genetic basis which depends on the activation of the SRY chromosome - activated means male, inactive means female
What is gametogenesis?
The production of gametes
What are the gonads?
An animal organ where gametes are produced
What are the female gonads?
Ovaries
What are the male gonads?
Testes
What are the female gametes?
Ova
What are the male gametes?
Spermatazoa
What is the germinal epithelium?
The layer of cells that undergoes regular mitosis
Where is the germinal epithelium in females?
Outer layer of the ovaries
Where is the germinal epithelium in males?
Seminiferous tube
Explain spermatogenesis
Germinal epithelium in seminiferous tube divide by mitosis to form spermatagonium
Grow into primary spermatocytes
Divide by meiosis I to form secondary spermatocyte
Divide by meiosis II to form spermatids
Spermatids mature into spermatazoa
Are primary spermatocytes 2n or n?
2n
Are secondary spermatocytes 2n or n?
n
Are spermatids 2n or n?
n
When does spermatagonium occur?
After puberty, producing millions of sperm cells every day throughout adult life
What is a Graafian follicle?
A fluid filled sac formed from follicle of cells around the nucleus
How often does ovulation occur?
Every 28 days
What is a corpus luteum?
When the secondary oocyte leaves the Graafian follicle during ovulation and fills with hormone secreting cells to produce a yellow body
When does the corpus luteum degenerate?
When fertilisation does not occur
Explain the process of oogenesis
Germinal epithelium of the ovaries divides by mitosis to form oogonium
Oogonium grow into primary oocytes
Primary oocytes divide by meiosis I to form secondary oocyte and a polar body
Meiosis II happens after fertilisation
Primary oocyte divides into secondary oocyte and polar body. OG polar body divides into two polar bodies
What is the stimulus needed for secondary oocytes to complete meiosis 2?
Fertilisation
Name some differences between oogenesis and spermatogenesis?
Ovum is non-motile, sperm is
Oogonium made in the fetus pre-birth, sperm made every day post puberty
Four sperm cells made from spermatagonium, one ovum made from an oogonium
Ejected by ejaculation vs ovulation
Sperm cells reach completion during sperm production, ovum halt at prophase 2
What are cortical granules?
Vesicles around the outside of the cytoplasm of the oocyte
What is the zona pellucida?
Layer of glycoprotein between cytoplasm and the follicle cells
Where is sperm produced?
Seminiferous tubules in the testis
What do the Sertoli cells do?
Nourish the sperm cells as they mature
What does the head of the sperm contain?
Haploid nucleus and an acrosome
What does the middle piece of the sperm contain?
Mitochondria for energy to move
What does the tail of the sperm contain?
Microtubules
What is the head of the sperm covered in?
Glycoprotein from the epididymus
How is the secondary oocyte moved along the oviduct?
Beating action of the cilia on the cells lining the oviduct
What is capacitation?
Changes to the head of the sperm which make it fully capable of fertilisation
What are the two events which occur during capacitation?
Head stripped of glycoprotein
Acrosome reaction
What is the acrosome reaction?
Acrosome swells
Fuses to membrane of egg cell
Hydrolytic enzymes released by exocytosis
Moves through zona pellucida
How do sperm get through the zona pellucida?
Enzymes from acrosome reaction hydrolyse the glycoprotein from which the zona pellucida is made
What are the three main stages of gametogenesis?
Multiplication
Growth
Maturation
What is spermatogenesis?
Formation of spermatazoa in the testes
Are oogonium haploid or diploid?
Diploid
Are primary oocytes haploid or diploid?
Diploid
Are secondary oocytes haploid or diploid?
Haploid
What are the products of oogenesis?
A haploid ovum and three polar bodies
What are the adaptations of a sperm cell?
Acrosome - hydrolytic enzymes to break down zona pellucida
Mitochondria - ATP for energy for movement
Flagellum - movement
Haploid nucleus - restore diploid cell number
Streamlined - move quickly and efficiently
Where does the sperm fertilise the secondary oocyte?
In the upper oviduct
What is released from the Graafian follicle during ovulation?
Secondary oocyte
When does the acrosome reaction occur?
When the head of the sperm touches the zona pellucida of the egg
Name the stages of fertilisation
Acrosome reaction
Membrane fusion
Cortical reaction
Meiosis II
Explain what happens during membrane fusion in fertilisation
Membrane of egg and sperm fuse so haploid nuclei can fuse
What is the purpose of the cortical reaction?
To stop polyspermy