D3.1 reproduction

Define reproduction

• the way organisms pass on their genes to future generations and ensure the continuity of their species

Compare and contrast asexual vs. sexual reproduction, giving pros and cons and examples

Asexual

• 1 parent only

• Ex. bacteria, fungi —> fission, budding, fragmentation, parthenogenesis

• Involves mitosis, cell division

• offspring are clones of parents and each other

• Pros:

  • ensures a large amount of offspring is produced in a short time (advantage for living in a stable area —> organisms can be better adapted to colonise a habitat faster)

  • less energy and time

  • less complex

• cons:

  • low chances of genetic variation

  • have disasterous consequences when environment changes

  • harmful mutations can be catastrophic

Sexual

• 2 parents

• offspring are similar but not genetically identical

• pros:

  • results in genetic variation

  • is better adapted to changing environment

What are 2 ways that genetic variation can occur in sexual reproduction?

• When the gametes fuse

• 1. Formation of gametes

  • In meiosis I, where DNA is exchanged in crossing over, between nonsister chromatids of homologous chromosomes

  • leads to new combination of genes in each chromosomes

  • Or, in independent assortment (meiosis I) where maternal/paternal chromosome of homologous pairs separate, making gametes with different variations

  • Ex. a diploid cell with these 3 pairs of homologous chromosomes (Aa Bb Cc) can give 8 combinations using independent assortment

• 2. fertilisation

  • Its a random event, so gametes that fuse create variation

Do changes in uterus and ovary happen at the same time?

yes

List the 2 cycles and how long the menstrual cycle lasts

• 28 days

• 1. Ovarian cycle

• 2. Uterine cycle

What are the 3 phases in ovarian cycle

1. follicular

• 14 days

• begins with first day of bleeding

• levels of ovarian and pituitary hormones are low

• anterior pituitary secrets FSH and LH

  • FSH stimulates follicle growth, allowing it to secrete oestradiol

2. Ovulation

• middle of cycle

• sharp rise in oestradiol stimulates anterior pituitary to secrete more LH (causing follicle to rupture to release mature egg) and less FSH

• egg starts going to uterus

3. Luteal

• 14 days

• LH and FSH levels drop

• under influence of LH, ruptured follicle is converted into corpus luteum

  • It secretes progesterone and oestradiol, which inhibits FSH and LH with a negative feedback loop

What is corpus luteum

A temporary organ formed in each menstrual cycle from the ruptured follicle which secretes hormones.

Describe the 3 phases in uterine cycle

1. menstruation

• at end of luteal phase, the decrease in FSH and LH causes corpus luteum to break down

• Decrease in progesterone and oestradiol causes uterus lining to break down

• due to low levels of ovarian hormones, anterior pituitary secretes FSH and LH → causes a new follicle to develop for a new cycle

2. proliferative

• coincides with follicular, until ovulation

• oestradiol secreted by growing follicle thickens endometrial uterus lining

3. secretory

• corresponds to luteal phase

• due to progesterone, uterine lining thickens more and changes into a secretory layer to prepare for implantation