Reproduction 1 (sexual development) Flashcards
What is homeostasis?
The maintenance by highly coordinated, regulated actions of the body system of a relatively stable chemical & physical condition in the internal fluid environemnt that bathes the body’s cells
Reproduction plays no role in homeostasis
What do gonads produce?
Eggs & sperm
What are autosomes?
Are chromosomes that are not involved in determining the sex of an organism
Where are X chromosomes found?
- Found in males & females
- Has essential genes
Where are Y chromosomes found & what are they for?
- Only in males
- Has essential genes for developing into a male
Why is there a 50% chance of offspring being male of female?
XX chromosome splits into 2 cells & so does XY, 50% chance of male or female
What are the male & female gonads?
- Male = testes
- Female = ovaries
What are the 2 functions of the gonads?
- Produce gametes
- Secrete sex hormone
What are the male & female gametes?
- Male = spermatozoa
- Female = ova
Are gametes haploid or diploid?
Haploid
23 chromosomes = 22 autosomes & 1 sex chromosome
Is a zygote haploid or diploid?
Diploid
46 chromosome = 44 autosomes & 2 sex chromosomes
What are the ways gametogenesis can happen (production of gametes)?
Mitosis = normal cell division
- DNA replicated once
- Cells undergo division once
Meiosis = cell division to produce gametes
- DNA replicated once
- Cells undergo division twice
What are gametes produced from?
From undifferentiated germ cells
What are all 10 stages of meiosis?
(Meiosis I to V)
1- Diploid germ cell (2n)
2- DNA replicated - (2x2n) sister chromatids
3- Homologous chromosomes group in pairs
4- Maternal opposite paternal
5- Exchange of DNA segments = crossing over
6- New chromosomes w mixed source of genes
7- Random alignment of sister chromatids at midline = independent assortment
8- First meiotic division 2 cells with 2n chromosomes
9- 2nd meiotic division occurs
10- 4 cells with n chromosomes
What happens in meiosis I?
1 - Diploid germ cell (2n)
2 - DNA replicated (2 x 2n)
What happens in meiosis II?
3 - Homologous chromosomes group in pairs
4 - Maternal opposite paternal
What happens in meiosis III?
5 - Exchange of DNA segments occurs = crossing over
6 - New chromosomes w mixed source of genes
What happens in meiosis IV?
7 - Random alignments of sister chromatids at midline - independent assortment
8 - First meiotic division 2 cells with 2n chromosomes
What happens in meiosis V?
9 - 2nd meiotic division occurs
10 - 4 cells w n chromosomes
How does the production of gametes differ in males & females?
Females = born w all the eggs she will ever produce
Males = will be able to produce sperm all thru their lives
Refer to the male vs female gametogenesis diagram
:)
What is sex determination?
Chromosomes determine whether fetus develops ovaries or testes
What is the srY gene?
Found on Y chromosome - the sex determining region on Y
What happens if the srY gene is present/not present?
- If srY gene present = testes develop
- If srY gene absent = ovaries develop
What does the srY gene code for?
For testis-determining factor
Until what age is the embryo sexually indifferent
2 weeks
What is the precursor male tract?
Wolffian ducts
What is the precursor femal tracts?
Mullerian ducts
When testes are present (due to srY gene), what do they secrete & what does this do?
- Testosterone (and dihydrotestosterone DHT)
- Mullerian-inhibiting substance (MIS)
These hormones stimulate development of Wolffian ducts & degeneration of Mullerian ducts
When testes aren’t present (no srY gene), what happens?
Hormones absent –> Wolffian ducts regress, Mullerian ducts develop
What does the genital tubercule form for men/women?
Men = glans penis
Female = clitoris
What does the urethral folds & groove form for men/women?
Men = shaft of penis
Women = labia minora, opening of vagina & urethra
What does the Wolffian duct form in men?
Becomes epididymis, vas deferents & seminal vesicle
(Testosterone present)
What does the Mullerian duct form in women?
Becomes fallopian tube, uterus, cervix & upper 1/3 of vagina
(Anti-Mullerian hormone absent)
What does the gonad (cortex) do in men/women?
Men = regresses
Women = forms ovaries
What does the gonad (medulla) do in men/women?
Men = forms testes
Women = regresses
What are the stages of female internal organs development?
1 - Gonadal cortex becomes ovary in the absence of srY protein
2 - Absence of testosterone causes Wolffian duct to degenerate
3 - Absence of anti-Mullerian hormone allows Mullerian duct to become the fallopian tube, uterus & upper part of vagina
What are the stages of male interns organ development?
1 - srY proteins in male embryo directs the medulla of the biopotential gonad to develop into testis
2 - Anti-Mullerian hormone from testis causes the Mullerian ducts to degenerate
3 - Testosterone from testis converts Wolffian duct into seminal vesicle, vas deferent & epididymis. DHT controls prostatee development
What is the bipotential stage?
6 weeks of fetal development
The internal reproductive organs have the potential to develop into male or female structures
How does female external genitalia develop?
In the absence of androgens, the external genetalia are feminized
How does the male external genetalia develop?
1 - DHT causes development of male external genetalia
2 - The testes descend from the abdominal cavity into the scrotum
What are the 3 main stages in developing reproductive activity & what age do these happen?
- Adolescence (up to 10-14 years)
- Puberty (starts at 10-14 years, later in boys)
- During sexual maturation (from late teens onward)
What is reproductivity like during adolescence (up to 10-14 years)?
Inability to reproduce
What is reproductivity like during puberty (starts at 10-14 years, later in boys)?
- Sexual maturation
- Reproductive organs mature (can produce gametes)
- Secondary sexual characteristics develop
What is reproductivity like during sexual maturation (from late teens onward)?
- Female reproductive system cycles
- Female lose ability to reproduce around 45-50
- Menopause: loss of female reproductive capacity
- Male retains ability to produce sperm
Give some examples of secondary sexual characteristics importance in some species:
- Rooster’s comb attracts female attention
- Stag’s antlers ward off other males
- Peakcock’s feathers
What are human secondary sexual characteristics like?
- Do attract opposite sex
- But strongly influenced by society & cultural behaviour
What are genotypic vs gonadic vs phenotypic sex?
- Genetic sex = determined by XY or XX
- Gonadic sex = determined by presence of testes/ovaries
- Phenotypic sex = the apparent anatomic sex of an individual
Genetic sex usually = ?
Phenotypic sex
Genetic male - anatomical male - functional male
What happens if testes development fails?
Anatomical female in genetic male = will be infertile
What happens in testicular feminisation syndrome?
Will be infertile
Anatomical female in a genetic male - will be infertile
What does genetic deficiency in the conversion of testosterone to DHT cause?
Genetic male w testes, male reproductive tract, female external genetalia
DHT important in developing secondary characteristics
Andrenal glands secrete weak androgen - dehydroepiandrosterone (DHEA), what happens when there is excess of this in a female?
Excess levels in a genetic female at key stages of development will give genetic female w male reproductive tract & external genetalia
