Copulation and Fertilisation

Question 1

External factors control reproductive cycles

Answer 1

• Photoperiod
• Lactation
• Nutrition
• Animal interaction

Question 2

Sexual behaviour regulated by hormones

Answer 2

• Oestrogen and gonadotrophin releasing hormone in females

* Testosterone in males

Question 3

Sexual arousal

Answer 3

Psychogenic stimuli include; • Visual cues
Mating in others
Lordosis
• Olfactory cues
Sniffing of vulva Female urination Pheromones
Physiological factors for erection;
• Stimulation of pelvic nerve
Causes arterial dilation and increased blood flow into corpus cavernosa
• Relaxation of the retractor penis muscle Straightening of the sigmoid flexure

Question 4

Copulation and ejaculation

Answer 4

• Movement of sperm into epididymis and vas deferens
• Muscles of vas deferens and accessory glands contract
• Spermatozoa and seminal plasma expelled via penile urethra
• Sympathetic control from autonomic nervous system

Question 5

Hyperactivation

Answer 5

• Increased head movement and less linearity
• Variation in ejaculate
• Ejaculate can be assessed, a key part of fertility assessment and following semen collection in the process of artificial insemination

Question 6

Epididymis

Answer 6

Surface molecules added to head of sperm

Question 7

Ejaculation

Answer 7

Surface molecules coated with seminal plasma proteins

Question 8

Capacitatiom

Answer 8

Female tract strips some proteins leaving exposed areas for sperm egg binding

Question 9

Fertilisation

Answer 9

• Acrosomal enzymes digest small hole in zona pellucida
• Sperm move into perivitelline space between zona pelucida and oocyte plasma membrane
• Oocyte plasma membrane fuses with sperm
• Sperm is engulfed

Question 10

Acrosome reaction

Answer 10

• Capacitation exposes zona pellucida binding proteins on sperm plasma membrane (ZP3)
• Sperm binds to oocyte zona pellucida via ZP3 initiating the acrosome reaction
• Release of enzymes to digest the zona pellucida

Question 11

Overview of fertilisation

Answer 11

Sperm capacitation
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Hyperactivation
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Binding to zona pellucida
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Acrosome reaction
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Penetration of zona pellucida
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Sperm – Oocyte binding Fertilisation

Question 12

Early embryo – zygote cleavage

Answer 12

• Following fertilisation the zygote undergoes a series of mitotic divisions known as cleavage
• The first cleavage division creates a two-cell embryo
• Each of the two cells in the embryo is called a blastomere
• Blastomeres cleave to form 4, 8, 16 cells
• Each blastomere is genetically identical
• After the 8-cell stage the ball of cells if called a morula

Question 13

Formation of a blastocyst

Answer 13

• At the morula stage the cells separate into 2 distinct layers
–Inner ball of cells (inner cell mass)
–Cells at the periphery (trophoblast)
• Known as the blastocyst
• Cells in the outer cell mass pump sodium into the blastocyst creating accumulation of fluid, blastocoele
• Inner cell mass develops into the embryo
• Trophoblast cells become the placenta

Question 14

Blastocyst hatching

Answer 14

• The blastocyst continues to move down the oviduct towards the uterus
• Implantation is prevented by the zona pellucida
• At the uterus the blastocyst hatches by digesting a hole in the zona
pelucida
• Blastocyst becomes a free-floating embryo
• Dependant on the uterus for survival

Question 15

Implantation

Answer 15

• Attachment of the embryo to the uterine mucosa followed by placentation
• Requires oestrogen and progesterone to prepare the endometrium
• May be invasive or non-invasive

Question 16

In vitro fertilisation (IVF)

Answer 16

Harvesting of an ovum and sperm so that the fertilisation process can be achieved ‘in vitro’ prior to the embryo being placed inside the female for
implantation.

Question 17

Artificial Insemination Process

Answer 17

• Ejaculate collected
• Ejaculate assessed
• Ejaculate diluted in ‘extender fluid’
• Ejaculate stored
• Room temperature (routinely used in pigs)
• Frozen (routinely used in cows, sheep and humans but unsuccessful in pigs and can be transported by post)
• Female inseminated with semen

Question 18

Why use artificial insemination?

Answer 18

–Transport of animals
stressful and expensive
–Global genetic selection
–Direction of selective breeding programmes -promote beneficial traits
–Transgenic mouse strains
Preservation of endangered species –Bio-security –HIV, Foot and Mouth