Sex Determination Flashcards
Describe the chromosomes in a zygote?
23 chromosomes from its mother and 23 from its father
- 23 pairs of homologous chromosomes
Note:
The first 22 pairs are called autosomal chromosomes
The 23rd pair are the sex chromosomes
Describe the sex pair in women?
consist of two X chromosomes
Describe the sex pair in men?
consist of one X and one Y chromosome
Why are gametes haploid?
they only contain half the number of chromosomes of the diploid parent
- Half of the sperm contain X and half contain Y
- All ova contain X chromosomes
Describe how sperm can determine the gender of the zygote?
- If a Y-bearing sperm fertilizes the ovum the zygote will be XY and male
- If an X-bearing sperm fertilizes the ovum the zygote will be XX and female
What is the state of the 2 X chromosomes in a woman?
- only one of each pair of X chromosomes remains active
- The other X chromosome forms a clump of inactive “heterochromatin” seen as a dark spot called a Barr body
When are the gonads of males and females similar in appearance?
first 40 days of development
- At this stage the embryonic structures have the potential to become either testes or ovaries
What is testis-determining factor (TDF)?
The substance that promotes the conversion of gonads into testes
What is the gene for testis-determining factor and where is it located?
sex-determining region of the Y (SRY)
- is located on the short arm of the Y chromosome
When do seminiferous tubules appear in embryonic development?
43-50 days following conception
When do sertoli and leydig cells appear in embryonic development?
Sertoli cells appear at about day 42 while
Leydig cells appear at about day 65
When do ovarian follicles appear in embryonic development?
second trimester of pregnancy (about 105 days)
Function of embryonic Leydig cells in sex determination in embryonic development?
secrete large amounts of androgens (testosterone).
- Testosterone serves the very important function of masculinizing the embryonic structure
Note: The developing testes move within the abdominal cavity and gradually descend into the scrotum
Male accessory glands are derived from?
Wolffian (mesonephric) ducts
Female accessory organs are derived from?
Mullerian (paramesonephric) ducts
Describe the development of accessory sex organs and external genitalia?
The Wolffian and Mullerian duct systems are present in both male and female embryos between day 25 to day 50, so the embryos of both sexes have the potential to form the accessory organs characteristic of either sex
Testes castration from male embryonic animal results?
regression of the Wolffian ducts and development of the Mullerian ducts into female accessory organs
- Female accessory organs therefore develop as a result of the absence of testes rather than as a result of the presence of ovaries
Testes castration from male embryonic animal results?
regression of the Wolffian ducts and development of the Mullerian ducts into female accessory organs
- Female accessory organs therefore develop as a result of the absence of testes rather than as a result of the presence of ovaries
What do Sertoli cells in embryonic development secrete?
Mullerian inhibition factor (MIF)
- a peptide that causes regression of the Mullerian ducts beginning at about day 60
Describe how the secretion of testosterone by Leydig cells aids in the development of accessory sex organs and external genitalia?
causes growth and development of the Wolffian ducts into male accessory sex organs