livestock breeding and genetics
Post on 24-Feb-2016
89 Views
Preview:
DESCRIPTION
TRANSCRIPT
Livestock Breeding and Genetics
Sperm and Egg Production
• We are beyond the mid-point of the semester.
• What’s ahead: - Livestock Breeding and Genetics- Animal Health- Livestock Pests- Waste Management
In this lesson…
• Describe the difference between oogenesis and spermatogenesis.
• Describe the genetic factors that influence the sex of an offspring.
Some Main Points to Ponder:
• What are gonocytes and oocytes?• Focus in on stage 2 of oogenesis
and the divisions that occur.• Focus in on the divisions and
products thereof during spermatogenesis.
• How do males and females play a role in sex determination of the offspring?
Big Picture of Today:• Oogenesis: Creation of Eggs in
female livestock• Spermatogenesis: Creation of
Sperm in male livestock
Oogenesis• The process of the formation of
eggs with (GONOCYTES) OOCYTES
What are Gonocytes?
• The precursors of both male and female gametes (sex cells).
• Originate in the embryonic animal during its formation in the womb.
What are Oocytes?
• They are gonocytes that have differentiated in the fetal ovaries.
• They are the sole reservoir of all future ova.
Microscopic Image of Oocytes
Growth of the oocyte (aka Oogenesis)
Stage 1 - the OOCYTE grows in size (lasts from birth to puberty)
Stage 2 - the OOCYTE and follicle matures (during puberty)
Cell divisionOccurs during Stage 2 of oogenesis (previous slide)1) The OOCYTE undergoes 2 meiotic
divisions during which 2 daughter cells arise, each having half the chromosome complement.
So what about these daughter cells….
• One of these 2 daughter cells acquires nearly all of the cytoplasm, and this large cell is called the SECONDARY OOCYTE.
• The much smaller cell with only a little cytoplasm is called the POLAR BODY.
2) At the second maturation division, the SECONDARY OOCYTE divides into the OOTID and a second POLAR BODY.
3) The POLAR BODIES degenerate, leaving the OOTID ready for fertilization.
Oogenesis: Big Picture
FYI• The OOTIDS or OVUM actually
undergo oogenesis at different times, depending on the species.
Moving forward to: Spermatogenesis
• The process of sperm formation which commences at puberty.
• At birth, SPERMATOGONIA are present
• These SPERMATOGONIA also are called SPERM MOTHER CELLS.
Phases of Spermatogenesis
• SPERMATOGONIA undergo mitotic division and become dormant, thus ensuring a continuous supply of SPERMATOGONIA.
• One SPERMATOGONIUM becomes active and divides 4 more times so that there are now 16 PRIMARY SPERMATOCYTES.
These primary spermatocytes go through meiotic division.
• At this time, the number of chromosomes is HALVED
• These new cells are now called SECONDARY SPERMATOCYTES
• The secondary spermatocytes undergo one more division to become SPERMATIDS.
• SPERMATIDS undergo a metamorphosis which involves a radical alteration in cellular form during which most of the cytoplasm is lost.
Spermatogenesis: Big Picture
Sex Determination• Every cell in the mammalian body,
except the gametes (sperm and ova), contains a pair of sex chromosomes
• In females, the 2 members of the sex chromosome pair resemble one another and are known as the X chromosomes (XX).
• In males, the sex chromosomes differ from one another, one is the X chromosome, the other is smaller and is called the Y chromosome (XY).
• The gametes contain only a single sex chromosome:
In the female, each ovum contains an X chromosome.
In the male, the sperm contains either an X or a Y chromosome.
Determination: • In normal fertilization, the embryo
develops as a male or female according to whether the ovum is fertilized by a sperm carrying an X or a Y chromosome. In effect, the father determines the sex of the offspring.
What influences the sex of the offspring?
• If the 2 types of sperm are present in equal numbers, the ratio of male to female sperm at the time of conception should be 1:1.
• The sex of the offspring is important to many livestock producers since one sex may be more valuable than the other.
For example:1) beef cattle - steers bring a higher
market price than heifers;2) dairy cattle - heifers are the milk
producers so they are more valuable than bull calves; and
3) poultry - egg production operations keep all the laying hen chicks, but often dispose of the male chicks.
Let’s Review• What are gonocytes and oocytes?• What divisions occur in stage 2 of
oogenesis?• What were the divisions and
products thereof during spermatogenesis?
• How do males and females play a role in sex determination of the offspring?
Sources• California Ag Ed Tech Prep• Scientific Farm Animal Production:
An Introduction to Animal Science
top related