Reproduction in Animals:
Asexual reproduction-only one parent (one-celled organisms/some plants)
Sexual reproduction-two parents (male and female-one each)
In mammals genetic material is shared in the offspring from both parents (half/half)
Gametes are produced by both the male (sperm) and the female (egg), when these unite a
new animal is formed and is called a zygote. The sperm and egg have material
(DNA) that dictates what the young animal will look like
The zygote divides by a process called mitosis
Genes are specific groups of DNA, each gene has unique structure that controls a trait of
an animal (example: gene determines whether Angus has horns or not)
Chromosomes are groups of genes (threadlike structures) means “colored body”, each
cell in an animal contains a number of chromosomes
Animal
Chromosome Count (2n)
Donkey
62
Horse
64
Mule
63
Swine
38
Sheep
54
Cattle
60
Human
46
Dog
78
Domestic cat 38
Chicken
78
In body cells chromosomes always come in pairs, different species have varying #s of
pairs
Each gamete has one of each of the pairs of the chromosomes (or half) (example: each
horse cell contains 32 pairs or 64 chromosomes-sperm would contain 32, egg would
have 32)
When the egg/sperm unite at conception, each contribute 32 chromosomes that go
together to form full set of 64 (in horse example). Chromosomes from father/mother
are matched
*note the difference between donkey and horse…mule is result of that cross, but mules
cannot breed successfully because the chromosomes cannot pair up so mules are
almost always sterile (incapable of reproducing), remember 63 doesn’t divide
evenly
Production of Gametes:
The formation of the sperm cell occurs in testicles of the male, called spermatogenesis.
The formation of the egg cell occurs in the ovaries of the female, called oogenesis.
Meiosis is the process by which these gametes are formed. This is what allows
contribution from both parents.
Male Reproductive System:
Roosters testicles are housed within the body, while other livestock animals are outside
the body in a sac called the scrotum. This helps to keep the temperature cooler
which is important to viability of the sperm. During the winter the sac is drawn
closer to the body by small muscles to keep the testicles warm. The scrotum is
relatively hairless and contains no subcutaneous fat, which aids in temperature
regulation.
If one or both testicles does not descend this condition is called cryptorchidism-which
usually affects fertility of the male animal and is undesirable.
The testicles produce sperm but also produce testosterone, the hormone that controls the
animal’s libido (sexual drive) and stimulates sex characteristic development. An
example would be large forequarters in a bull and large tusks and bad odor in boars.
The sperm mature and are stored in the epididymis (a tuberous structure along outside of
testicles). During ejaculation the sperm travel through the vas deferens.
The seminal vesicles is one of three accessory glands in the male system. It secretes a
fluid that is mixed with the sperm to protect them and provide a way for the sperm to
be transported. The other two glands also secrete fluids and this mixture of fluids is
called semen. The Cowper’s gland secretes a fluid that cleans the urethra before
sperm is passed along the tube. The fluid also thickens the semen. The prostate
gland secretes fluid added to the semen to provide nutrients for the sperm and expel
sperm during mating process.
The penis is the male organ that deposits sperm in the female reproductive tract. This
organ also expels urine from the body. The boar, bull, and ram penis has a lot of
connective tissue that flexes and extends the penis while the stallion penis has more
vascular tissue which engorges the organ with blood until erect. The covering of the
penis is called the sheath or prepuce and its purpose is protection of the penis.