1 - Reproduction I Flashcards
Asexual reproduction
A single parent produces genetically identical offspring (clones) / no gamete formation or fertilization is involved.
Asexual reproduction advantages
- Fast reproduction – no need for mating.
- Rapid population growth – efficient colonization.
- Independent reproduction – no mate required.
- Genetic stability – offspring inherit identical traits.
- Energy-efficient – no resources spent on attracting mates.
Asexual reproduction disadvantages
- Lack of genetic diversity – makes species vulnerable to diseases.
- Limited adaptability – cannot respond well to environmental changes.
- Harmful mutations accumulate – no recombination to remove bad genes.
- Inbreeding depression – reduced fitness over generations.
- Success depends on environmental stability – poor resilience to sudden changes.
Sexual reproduction
Involves gamete production (sperm and egg) / requires fertilisation between male and female gametes / leads to genetic variation, which improves adaptability and evolution.
Mixing of genetic material from two individuals - Involves Gamete production (spermatogenesis & oogenesis) / hormonal regulation / fertilisation and pregnancy
Female Reproductive Organs
Ovaries - produce oocytes (eggs) and hormones
Fallopian tubes - transport eggs and are the site of fertilization
Uterus - site of embryo implantation and fetal development
Cervix - narrow opening between the uterus and vagina
Vagina - birth canal and site of sperm deposition
Oogenesis (Egg Formation)
Oogonia (germ cells) form before birth
Meiosis begins but halts at Prophase I until puberty
At ovulation, meiosis resumes; fertilisation completes it (meiosis II only happens if fertilisation occurs)
Menstrual Cycle and Hormonal Regulation
- Hypothalamus releases GnRH —> stimulates the pituitary gland.
- Pituitary gland secretes FSH and LH
- Ovarian hormones (Oestrogen & Progesterone) regulate the menstrual cycle
Menstrual cycle phases
Follicular phase
Luteal phase
Mensturation
Follicular Phase (Days 1-14)
FSH stimulates follicle growth in the ovary
Follicles produce oestrogen, which thickens the uterine lining
Surge in LH triggers ovulation (egg release around Day 14)
Luteal Phase (Days 15-28)
Corpus luteum (remains of the follicle) secretes progesterone to maintain the uterine lining
f no fertilisation occurs, the corpus luteum degenerates → leading to menstruation
Menstruation (Day 1)
Uterine lining sheds if no pregnancy occurs
Male Reproductive System
Testes - produce sperm and testosterone
Seminiferous tubules - site of sperm production
Sertoli cells - support and nourish developing sperm
Leydig cells - produce testosterone, which promotes spermatogenesis
Spermatogenesis (Sperm Formation)
Starts at puberty and continues throughout life
- Spermatogonia (stem cells) —> divide by mitosis
- Primary spermatocytes undergo Meiosis I —> producing two haploid secondary spermatocytes
- Secondary spermatocytes undergo Meiosis II —> forming four spermatids
- Spermatids mature into spermatozoa
Spermatogenesis vs Oogenesis
Spermatogenesis - Continuous production from puberty onwards.
4 functional gametes per spermatocyte (vs. 1 egg per oogonium).
Hormonal Control of Male Reproduction
GnRH (Hypothalamus) → FSH & LH (Pituitary)
LH stimulates Leydig cells → testosterone production.
FSH stimulates Sertoli cells → supports sperm development.
Fertilisation and Pregnancy
- Ejaculation —> sperm travels through the vagina, uterus, and Fallopian tube
- Fertilisation occurs in the Fallopian tube —> forming a zygote
- Zygote undergoes mitotic divisions —> becomes a blastocyst
- Blastocyst implants in the uterus (around day 6)
Hormonal Control of Pregnancy
Corpus luteum secretes progesterone (maintains the uterine lining).
Placenta develops → starts producing oestrogen and progesterone.
HPO axis is suppressed → prevents further ovulation.
Genetic Diversity in Meiosis
Meiosis ensures genetic variation through - independent assortment and
Errors in Meiosis can cause chromosomal disorders:
Non-disjunction (failure of chromosomes to separate properly) / Trisomy 21 (Down syndrome) – extra chromosome 21 / Klinefelter syndrome (XXY) – male with an extra X chromosome / Turner syndrome (XO) – female missing one X chromosome.
Pregnancy Complications - Ectopic Pregnancy
Implantation occurs outside the uterus (e.g., Fallopian tubes) / cause rupture and life-threatening bleeding.
Pregnancy complications - Preeclampsia
High blood pressure in pregnancy / cause organ damage in the mother and restrict fetal growth.
Pregnancy complications - Miscarriages and Chromosomal Abnormalities
Trisomy conditions often result in pregnancy loss / hormonal imbalances can prevent implantation.
The placenta
Forms after implantation
Provides nutrients and oxygen to the fetus
Removes waste and CO2 from fetal blood
Produces hormones (hCG, progesterone, oestrogen)
Chorionic villi increase surface area for exchange
