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14 Cards in this Set

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What are the advantages and disadvantages of sexual reproduction?
Advantages: increased genetic variability due to crossing over and information from mother and father, mutations, deletions and addition can also occur
Disadvantages: less % of success, can be dangerous and cost resources (dimorphism)
Describe the different dimorphisms seen in the anatomy and physiology of the different sexes.
• Ovary: produce a few gametes; synthesis and secretion of several hormones necessary for the female phenotype and female behavior (adapted to nurture and carry the embryo; to feed and care for the newborn)
• Testis: produce tons of gametes; synthesis and secretion of hormones necessary for phenotype and behavior; the male tract can NOT sustain the growth of an embryo
List the different levels that can be use to define sex.
• Genetic: XX, XY
• Gametic: by the types of gametes produced
• Gonadal: by the type of gonads present
• Phenotypic: internal and external structures
• Behavioral and metabolic: differential behaviors
How is genetic sex determined? When is it determined?
• Homogametic: can only produce X
• Heterogametic: can produce X and Y gametes
Determined by the chromosomes carried by the father at fusion.
What are the two generalizations that can be made regarding the nature and location of sex determination gene?
• The absence of the Y chromosome will lead to a female individual, regardless of the number of X chromosomes (XO, XX, XXX will all be female). Also, if you have the Y chromosome, regardless of number of X chromosomes present, it will develop into a male (xy, xxy). Two exceptions:
o XX male: SRY gene sequence was present in the X chromosome
o Xy female: SRY gene was deleted
How does the Y chromosome determine gonadal sex?
• The presence of the SRY gene deactivates feminizing genes and activates genes used for development of male characteristics
Discuss how the SRY gene was discovered.
Researchers studying an XY female found that she had a deletion in the y chromosome that prevented testis development.
How is gonadal sex determined?
Development of internal genitalia.
Describe the migration and settlement of PGC’s.
Around the 5th week of gestation, the primordial germ cells colonize the gonadal ridge, possibly in response to chemical signals from the GRCs. This area will become the testes or ovaries.
What do we mean by hormonal sex?
Production of androgens or MIH.
Describe how the male and female internal genitalia develop. Make sure to include hormones involved and their function.
Regulated by androgens and MIH.
In the male: Ridge is invaded by the selomic epithelium. PGCs form the seminiferous tubules. Mesenchymal cells give rise to Sertoli and Leydig cells. The mesonephric duct forms the duct system, and the paramesonephirc duct disintegrates.
In the female: No invasion of selomic epithelium. The mesonephric duct disintegrates, and the paramesonephric duct forms the fallopian tubes. The mesenchymal cells surround the PGCs to form Granulosa and Theca cells.
• How is phenotypic sex determined?
Development of external genitalia.
• Describe the developmental process that results in the male and female external genitalia. Don’t forget hormones.
Androgens direct differentiation of external structures. There are 3 bipotential parts: the genital tubercle (glans penis or clitoris), urethral folds (urethral opening or labia minora), and the labioscrotal swelling (scrotum or labia majora).
• List and describe the three stages of testicular descent.
Nephric displacement: The testes are anchored to the abdominal cavity by the cranial ligament, and the gubernaculum connects the testes to the scrotum.
Transabdominal passage: the kidneys are pulled up and the gubernaculums swell and shorten, pulling the testes down. The CSL degenerates and lets go of the testes.
Inguinal passage: thought that the gubernaculums pull the testes down to the scrotum.