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Livestock Breeding and Genetics

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.

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Livestock Breeding and Genetics

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  1. Livestock Breeding and Genetics Sperm and Egg Production

  2. We are beyond the mid-point of the semester. • What’s ahead: • Livestock Breeding and Genetics • Animal Health • Livestock Pests • Waste Management

  3. In this lesson… • Describe the difference between oogenesis and spermatogenesis. • Describe the genetic factors that influence the sex of an offspring.

  4. 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?

  5. Big Picture of Today: • Oogenesis: Creation of Eggs in female livestock • Spermatogenesis: Creation of Sperm in male livestock

  6. Oogenesis • The process of the formation of eggs with (GONOCYTES)OOCYTES

  7. What are Gonocytes? • The precursors of both male and female gametes (sex cells). • Originate in the embryonic animal during its formation in the womb.

  8. What are Oocytes? Microscopic Image of Oocytes • They are gonocytes that have differentiated in the fetal ovaries. • They are the sole reservoir of all future ova.

  9. 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)

  10. Cell division Occurs 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….

  11. 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.

  12. 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.

  13. Oogenesis: Big Picture

  14. FYI • The OOTIDS or OVUM actually undergo oogenesis at different times, depending on the species.

  15. Moving forward to: Spermatogenesis • The process of sperm formation which commences at puberty.

  16. At birth, SPERMATOGONIA are present • These SPERMATOGONIA also are called SPERM MOTHER CELLS.

  17. 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 16PRIMARY SPERMATOCYTES.

  18. These primary spermatocytes go through meiotic division. • At this time, the number of chromosomes is HALVED •  These new cells are now called SECONDARY SPERMATOCYTES

  19. 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.

  20. Spermatogenesis: Big Picture

  21. Sex Determination • Every cell in the mammalian body, except the gametes (sperm and ova), contains a pair of sex chromosomes

  22. 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).

  23. 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.

  24. 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.

  25. 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.

  26. The sex of the offspring is important to many livestock producers since one sex may be more valuable than the other.

  27. 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.

  28. 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?

  29. Sources • California Ag Ed Tech Prep • Scientific Farm Animal Production: An Introduction to Animal Science

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