Unit 11: Reproduction Flashcards
What are the differences between sexual and asexual reproduction
asexual: 1 parent, mitosis is used, offspring are genetically identical, existing gene combos are maintained (no genetic variation), organisms adapted to an unchanging environment produce offspring that are also adapted
sexual: 2 parents, meiosis is used once per generation, offspring are genetically different to parents, new gene combos are made (genetic variation generated), organisms better adapted to a changing environment
What is the role of meiosis and fusion of gametes in the sexual life cycle?
MEIOSIS: During meiosis, the number of chromosomes HALVES. Parental combos of genes are broken up, allowing new combos to form when gametes fuse.
FERTILIZATION (fusion of gametes (haploid cells)): DOUBLES the number of chromosomes each time it occurs.
What are the differences between male and female sexes in sexual reproduction?
MALE: male gametes travel to female, smaller gametes, less food reserves, more numbers
FEMALE: female gametes are sessile, larger, have more food reserves (enough for embryo development), and only a few produced/released
What is the function of a testis?
produces sperm and testosterone
What is the function of a scrotum?
maintains lower temperature than core body temperature
What is the function of a epididymis?
coiled section at the back of the testis, stores sperm until ejaculation
What is the function of a sperm duct?
transports sperm during ejaculation
What is the function of a seminal vesicle and a prostate gland?
secrete fluid containing alkali, proteins and fructose, which is added to sperm to make semen
What is the function of a urethra?
transfers semen during ejaculation and urine during urination
What is the function of a penis?
penetrates the vagina for ejaculation of semen near the cervix
What is the function of an ovary?
produces eggs, oestradiol and progesterone
What is the function of a oviduct?
collects eggs at ovulation, provides a site for fertilisation then moves the embryo to uterus
What is the function of a uterus?
provides the needs of the embryo and then foetus during pregnancy
What is the function of a cervix?
protects foetus during pregnancy and then dilates to provide a birth canal
What is the function of a vagina?
provides stimulation to the penis to cause ejaculation, provides a birth canal
What is the function of a vulva?
protects internal parts of the female reproductive system
Describe changes during the ovarian and uterine cycles
Ovarian + Uterine cycle = Menstrual cycle
(see diagram)
OVARIAN:
1. Follicular phase - when a group of follicles develop in the ovary, then most developed follicle breaks open (ovulation) and releases egg into oviduct
2. Luteal phase - wall of the follicle that released the egg develops into the corpus luteum. if no fertilization, the corpus luteum breaks down to the corpus albicans and the ovary returns to follicular phase
UTERINE: (changes that occur to the endometrium)
1. endometrium becomes thick + more richly supplied w/ blood during the LUTEAL phase
2. if no embryo, thickening starts to break down at the END of the LUTEAL phase
3. this material is shed during menstruation
What is FSH?
Follicle Stimulating Hormone (gonadotropin = cause changes to gonads)
- RISES to a peak towards end of follicular phase
- stimulates development of follicles
- stimulates OESTRADIOL secretion by the follicle wall
What is oestradiol?
- RISES to a peak towards the end of the follicular phase
- stimulates repair and thickening of the endometrium after menstruation
- stimulates increase in FSH receptors –> make follicles more receptive to FSH, boosting oestradiol production
- if high level, oestradiol inhibits FSH secretion and stimulates LH secretion
What is LH?
Luteinising Hormone (gonadotropin = cause changes to gonads)
- RISES to a sharp peak towards the end of follicular phase
- stimulates completion of meiosis in the oocyte and partial digestion of the follicle wall, allowing it to burst open at ovulation
- promotes post-ovulation development of the corpus luteum follicle wall
- corpus luteum secretes oestradiol (positive feedback) and progesterone
What is progesterone?
- RISES at the start of the luteal phase, reaches a peak and then drops back to a low level by the end of this phase
- promotes thickening and maintenence of the endometrium
- inhibits FSH and LH secretion by the pituitary gland (negative feedback)
Describe what occurs during human fertilisation
- Plasma membranes of sperm have receptors that detect chemicals released by the egg
- enables directional swimming of sperm
towards the egg
- enables directional swimming of sperm
- Egg is surrounded by a cloud of follicle cells and a layer of glycoproteins
- Sperm pushes between cells and digests its way through the glycoproteins to reach plasma membrane of the egg cell
- Sperm’s plasma membrane has proteins that bind to the egg cell’s plasma membrane
- First sperm to penetrate the zona pellucida binds and the membranes of sperm and egg fuse together
- Sperm nucleus enters the egg cell = moment of FERTILIZATION
Describe what happens post human fertilization
- layer of glycoprotein around egg hardens to prevent any other sperm from entering, ensuring a diploid zygote is produced, rather than an unviable cell with more than 2 sets of chromosomes
- sperm tail either does not penetrate the egg or is broken down inside the zygote
sperm mitochondria are usually all destroyed - nuclei from both sperm + egg separate until zygote’s first mitosis
nuclear membranes break down, releasing 23 chromosomes from each nucleus - these chromosomes participate jointly in mitosis using the same spindle of microtubules
- 2 genetically identical nuclei are produced, each with 46 chromosomes.
Describe the process of IVF treatment
IVF = in vitro fertilisation (outside of the body)
STAGE 1: DOWN-REGULATION
1. every day, woman has injection or nasal spray containing a drug that suppresses the production of FSH or LH in the pituitary gland, therefore also stopping production of oestradiol and progesterone
2. Intramuscular injections of FSH are then given daily for 7-12 days, stimulating follicles to develop
- aims to generate a much higher FSH concentration than during a normal menstrual cycle, therefore more follicles will develop (8-15)
3. When follicles are 18mm in diameter, they are stimulated to mature by an injection of hCG (human chorionic gonadotropin) = SUPEROVULATION
- normally secreted by a human embryo when it is about a week old, signalling to its mother that it is alive and in need of sustenance from the endometrium
STAGE 2: EGG COLLECTION & FERTILISATION
4. egg collection is performed 34-35 hours after hCG injection (takes about 20 mins)
5. each egg is mixed w/ 50k-100k sperm cells in sterile conditions in a shallow dish, then incubated at 37ºC.
6. if fertilization is successful, one or more embryos are placed in the uterus when they are about 48 hours old.
7. extra progesterone is given as a table placed in the vagina to ensure the endometrium is maintained.
8. if embryo implants = basically a regular pregnancy