D3.1 Reproduction

sexual reproduction

involves the fusion of haploid gametes from two parents.

sexual reproduction advantage

produces offspring with new combinations of alleles, and the wide genetic variation of offspring allows the species to adapt to a changing environment.

Asexual Reproduction

reproduction involving one parent that produces offspring that are genetically identical to the parent.

Advantage of asexual reproduction

production of genetically identical offspring by individuals that are already adapted to the existing environment.

Meiosis in sexual reproduction

maintains the number of chromosomes, produces haploid eggs and sperm, creates genetic diversity by crossing over and independent assortment

Sperm

small cells that swim to egg. Do not have many nutrients. Males produce alot of sperm.  streamlined shape, adapted to swimming.

Sperm are composed of three sections, a head, a midpiece and a flagellum (tail)

Eggs

large cells with rich supply of nutrients for development of embryo. females produce fewer eggs than sperm. (Ova) are large cells that contain a haploid nucleus with the maternal genetic information, which is combined with the male genetic information at fertilization.

male vs female mating techniques

males in many species want to mate with as many females as possible. females are choosier as they invest more time in taking care of offspring.

Scrotum

holds testes

testis

produces testosterone and sperm

Edipididymis

stores maturing sperm before ejaculation

vas deferens

A duct that carries sperm away from epididymis

Cowper’s gland

provides a lubricating mucus

Seminal Vesicle

Produces a fluid containing fructose

Prostate Gland

Produces fluids which neutralize vaginal fluids

urethra

Sperm leaves the penis via the urethra

penis

Delivers sperm to the vagina

Ovary

Produces eggs, oestradiol and progesterone

Oviduct

Moves the egg/zygote from the ovary to the uterus

Uterus

Foetus develops within the uterus

Cervix

Muscular opening to the vagina

Vagina

Sperm are deposited in the vagina. The vagina is the birth canal

Labia

Protects vaginal opening

Clitoris

sexual pleasure

Menstrual cycle

Ovulation and menstruation. regulated by hormones. Made up of Ovarian and uterine cycles.

hormones produced by pituitary gland

Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)

hormones prduced by ovaries

Oestradiol and progesterone

Follicle stimulating hormone (FSH)

stimulates the development of follicles containing eggs.

Luteinizing hormone (LH)

stimulates follicles to mature and release egg also known as ovulation

Oestradiol

Stimulates repair of endometrium

endometrium

uterine lining

progesterone

maintains the endometrium in preparation for pregnancy.

Ovarian cycle

is the series of changes that occur in the ovary during the menstrual cycle.

uterine cycle

 the series of changes that occur in the uterus during the menstrual cycle.

Steps in menstrual Cycle

1.falling oestradiol and progesterone levels stimulate pituitary gland to produce FSH and the endometrium breaks down'

2. FSH causes follicles to develop

3. developing follicles secrete oestradiol

4. rise in oestradiol leads to repair of endometrium

5. oestradiol reaches peak and stimulates pituitary gland to secrete LH

6. LH rises to peak and egg is released from dominant follicle (ovulation)

7. rise in LH causes less oestradiol to be secreted(negative feedback)

8. corpus luteum

9. secretes large quantities of progestrone which causes endometrium to prepare for pregnancy

10. high porgesterone inhibits the production of fsh and lh

11. corpus luteum breaks down if the egg is not fertilized, resulting in falling levels of progesterone

12. cycle begins agains as fsh increases in relation to. falling progesterone

corpus luteum

 remains of the follicle

pos feedback in menstrual cycle

Increasing levels of oestradiol stimulates the pituitary gland to secrete more luteinizing hormone (LH).

negative feedback in menstrual cycle

Decreasing levels of progesterone (and oestradiol) stimulates the pituitary gland to secrete follicle stimulating hormone (FSH).

fertilization

is the fusion of an egg with a sperm. Fertilization occurs in the oviduct of the female reproductive system.

where does fertilization occur

Fertilization occurs in the oviduct of the female reproductive system.

sperm at fertilization

 the sperm’s tail detaches, and the sperm’s mitochondria are destroyed, sperm nucleus enter egg and membrane breaks down.

In Vitro Fertilization

fertilization occurs outside of the female body.

In vitro fertilization steps

1. mentrual cycle halted using oestradiol

2. high doeses of fsh are injected into female and stimulate follicle developement(superovulation)

3. The hormone human chorionic gonadotropin (hCG) is injected into the female, which stimulates the eggs to mature.

4. The eggs are harvested.

5. Sperm are collected from the male. They may be screened to ensure that they are healthy.

6. The eggs are mixed with up to 100,000 sperm to allow fertilization, and incubated (at 37°C). OR a single sperm is micro-injected directly into the egg.

7. The fertilized egg is now a zygote which divides by mitosis to produce an embryo.

8. One or more embryos are placed in the woman’s uterus after 48 hours (again, screening is possible)

9. Extra progesterone is provided (a tablet inserted in the vagina), to maintain the endometrium.

The pregnancy continues as a normal pregnancy.

superovulation

high doses of FSH are injected into the female, to stimulate follicle development. This is known as superovulation as up to 20 eggs can develop.

FSH and LH in childhood

 inhibited by low levels of gonadotropin-releasing hormone.

FSH and LH after childhood

the hypothalamus increases the secretion of gonadotropin-releasing hormone (GnRH), which leads to an increase in the secretion of FSH and LH.

LH and FSH in males

LH stimulates the production of testosterone, and FSH supports sperm production.

LH and FSH in females

FSH and LH regulate the menstrual cycle and the production of oestradiol and progesterone.

puberty

increase in secretion of the sex hormones leads to the development of secondary sexual characteristics during puberty.

male secondary sexual charecteristics

body hair growth, enlargement of penis, development of muscles, enlargement of larynx leading to deeper voice, increases secretions of oil and sweat(acne and body odour)

Female Secondary Sexual Characteristics

Growth of body hair, including pubic hair,Enlargement of breasts, Widening of the hips, Fat deposits, especially around buttocks, thighs and hips, Onset of the menstrual cycle

sperm adaptions

haploid nucleus

acrosome

midpiece

flagellum

head of sperm

haploid nucleus and an acrosome.

haploid nucleus

ontains the paternal genetic information which combines with the maternal genetic information at fertilization.

acrosome

contains hydrolytic enzymes, which help the sperm to fertilize the egg.

midpiece and flagellum

the midpiece contains many mitochondria that provide the sperm with ATP energy to swim.

The flagellum allows the sperm to swim through the female reproductive system to reach the egg.

egg cell adaptions

zona pellucida, many vesicles/corticle granules, cytoplasm

zona pellucida

glycoprotein matrix, which prevents polyspermy after fertilization.

cortical granules

known as vesicles which make the zona pellucida impenetrable to sperm after fertilization.

cytoplasm of egg

contains many lipid droplets which provide the developing embryo with energy after fertilization.

Gametogenesis

is the production of haploid gametes. spermatogensiss and oogenesis

spermatogenesis

watch video animation

oogenesis

watch video animatio

spermatogenesis and oogensisism similarities

• Growth and mitosis

• Two divisions of meiosis

• A reduction in chromosome number to produce haploid gametes

• Differentiation (to produce eggs and sperm)

• Regulation by hormones

oogenesis pauses

prophase I and metaphase II

fertilization steps

1. Sperm are attracted by chemicals released by the ovum.

2. The first sperm to break through the follicle cells binds to proteins in the zona pellucida of the ovum.

3. Binding triggers the acrosome reaction, releasing the acrosome enzymes.

4. The enzymes digest a route to the plasma membrane of the ovum.The plasma membrane of the ovum and sperm fuse, and the nucleus of the sperm enters the ovum. The tail and mitochondria of the sperm are broken down.

6. Meiosis II is completed within the ovum.

7. The cortical reaction is triggered. The cortical granules move towards the plasma membrane of the ovum, releasing enzymes into the zona pellucida.

8. Enzymes from the cortical granules cause the cross linking of glycoproteins in the zona pellucida.

9. The cross linking of the zona pellucida prevents polyspermy (prevents a second sperm from fertilizing the egg).

zygote

results from fertilization, and carries out mitosis and cytokinesis to create 2 cell embryo

Morula

The embryo continues to divide to produce a morula. A morula is a hollow ball of identical cells.

blastocyst

The cells in the morula begin to differentiate to form a blastocyst.

The blastocyst is a hollow ball of cells containing an inner mass of cells which will continue to develop into an embryo. 

The outer cells develop into the placenta.

implantation of blastocyst

The energy supplies of the ovum are used up as it develops into a blastocyst. The blastocyst requires a new energy source. The outer layer of the blastocyst develops “finger-like” projections which penetrate the uterus lining.  This is implantation, which is essential for the continuation of pregnancy as it allows the exchange of materials between the mother and embryo. This will develop into the placenta. 

Human chorionic gonadotropin (hCG)

 is a hormone that is released by the embryo and developing placenta. maintains the corpus luteum, so that the uterine lining does not break down.

Pregnancy Tests

Pregnancy test kits use monoclonal antibodies, which bind to human chorionic gonadotropin.

Monoclonal antibodies

are antibodies produced by a single cell line, and are all identical.

The human chorionic gonadotropin is the antigen for the monoclonal antibodies.

Tge placenta

disc-shaped structure with many projections called placental villi. It is embedded in the endometrium.  

 foetus.

The embryo develops bone tissue after 8 weeks of development, The foetus connects to the placenta by an umbilical cord.

placenta co2 and o2 exchange

Oxygen and carbon dioxide diffuse according to concentration gradients. Oxygen diffuses from the maternal blood into foetal blood, and carbon dioxide diffuses from foetal blood to maternal blood.

placenta nutrient exchange

Nutrients such as glucose, amino acids and vitamins are transferred from maternal blood to foetal blood through facilitated diffusion and active transport

Waste removal: placenta

Metabolic wastes such as urea produced by the foetus diffuse into maternal blood.

The Placenta and Maintaining Pregnancy

The placenta secretes hormones, including oestradiol, progesterone and human chorionic gonadotropin (hCG), which are involved in maintaining pregnancy. The placenta allows the human foetus to be retained in the uterus until a later stage of development than in mammals that do not develop a placenta.

hormones maintaining preganancy

Progesterone and oestradiol secreted by the corpus luteum in early pregnancy maintain the uterine lining.

The corpus luteum is maintained by the secretion of human chorionic gonadotropin (hCG).

Later in pregnancy, the placenta secretes oestradiol and progesterone to maintain pregnancy.

Hormones and Childbirth

Late in pregnancy, the foetus pushes on the walls of the uterus, which stimulates a rise in oestradiol levels.

Oestradiol increases the number of oxytocin receptors in the uterine wall, and decreases the concentration of progesterone.

The decrease in progesterone stimulates uterine contractions.

Uterine contractions stimulate the posterior pituitary gland to release oxytocin.

The hormone oxytocin binds to oxytocin receptors in the uterine wall, and stimulates stronger contractions.

Stronger contractions stimulate the posterior pituitary gland to release more oxytocin.

Childbirth and feedback loops

A positive feedback loop develops as stronger contractions stimulate the secretion of more oxytocin which stimulates stronger contractions.

As the contractions become stronger, the cervix relaxes and dilates in preparation for childbirth.

hormone replacement theraphy

 treats women with additional hormones to relieve symptoms of menopause.
Early epidemiological studies suggested that women undergoing hormone replacement therapy (HRT) had reduced incidence of coronary heart disease (CHD) and this was deemed to be a cause-and-effect relationship. 

Later randomized controlled trials showed that use of HRT led to a small increase in the risk of CHD. 

The correlation between HRT and decreased incidence of CHD is not actually a cause-and-effect relationship. HRT patients have a higher socioeconomic status, and this status has a causal relationship with lower risk of CHD.