Reproductive 1 Flashcards
is reproductive system necessary for survival
no, but needed for survival of species
provides biological variation by the merging of parental chromosomes
how many pairs in humans
23 pairs chromosomes
- 22 pairs - autosomes
- 1 pair- sex chromosomes
cell divison -somatic
replace dead/injured cells and add new ones during tissue growth
cell division -reproductive
produces gametes (spermatozoa in males and ova in females )
primary reproductive organs males and females
gonads :
males - testes
females - ovaries
dual function of primary reproductive organs
- gametogenesis to produce gametes
- secrete sex hormones
what happens when gametes unite
fertilization -> resulting zygote (ovum and sperm combined) which contains one sex chromosome from each parent
maternal
(from mother)
paternal
from father
in humans how many chromosomes do we have
46 total = diploid (46n)
-> diploid = two copies of each chromosome
23 chromosomes = haploid (23n)
-> haploid = one copy of each chromosome
chromatid
each of the strands (sister chromatids)
centromere
linking point for sister chromatids (at the centre)
Gametogenesis - Spermatogenesis
- primarily begins at puberty
- some spermatogonia remain as precursor
- Mitosis : sister chromatids formed in cell
- Meiosis I : only 1 member of homologous pair per cell
- Meiosis II : homologous seperate; 1 sister chromatid per cell
- Spermatids differentiate to spermatozoa
- 1 spermatogonium poduces 4 spermatozoa
spermatogonia -> (mitosis) -> primary spermatocytes -> (1st meiotic divison) -> secondary spermatocytes -> (2nd meiotic division) -> spermatids -> (differentiation) -> spermatozoa
- after 1st meiotic division there is 23 chromosomes per cell (46 before)
- after 2nd meiotic division there is 1 chromatid per chromosome (2 before)
gametogenesis - oogenesis
- begins before birth
- each ovary has a number of primary oocytes
- > at birth 200000 - 2000000
- > at puberty 40000
- > mature to ovulate 400
- most primary oocytes : atresia (cell death)
- meiosis I - not completed till just prior to ovulation; also forms 1st polar body
- meiosis II : completed after fertilization; also forms 2nd polar body
- 1 oogonium produces 1 ovum
oogonium -> (growth/maturation) -> primary oocyte -> (meiosis I) -> secondary oocyte and first polar body ->(meiosis II) -> ootid and secondary polar body -> (differentiation) -> ovum
- 23 chromosomes per cell after 1st meiotic division
- 1 chromatid per chromosome after 2nd meiotic division
gameotogenesis - crossing over
- homologous (pair during meiosis; one maternal one paternal) chromosomes align closely
- non-sister chromatids can undergo an exchange of sections (breakage and recombination)
- sister chromatids are no longer identical
- recombinant vs. non-recombinant chromosomes (foreign DNA vs no foreign DNA)
- this allows sexual reproduction to greatly increase genetic diversity
- occurs prior to the completion of meiosis I
sex determination
-determined by genetic inheritance of sex chromosomes : X (larger), Y (smaller)
Males : One X and one Y chromosome ->X from maternal and Y from paternal
Females : two X chromosomes -> X from maternal and X from paternal
-presence or absence : SRY gene (sex-determining region of the Y chromosome)
-SRY gene will lead to presence of AMH (anti-mullerian hormone) and testosterone which will give male sexual characteristics.
-They are triggered through sertoli cells and leydig cells in the gonads
Graph*
sex differentiation
- multiple processes in reproductive development along male or female lines
- phenotype : sexual appearance and function
- presence or absence : anti-Mullerian hormone, testosterone
sertoli cells
produce anti-mullerian hormone (AMH) in primordial gonads
-leads to regression of mullerian ducts in men
leydig cells
produce testosterone in primordial gonads
-leads to transformation of wolfian ducts to epididimis, vas deferens, seminal vesicles, ejaculatory duct
primary and secondary sexual characteristics
specific physical traits that set apart males and females
-
primary sexual characteristics
there from birth (inner and outer genital structures)
secondary sexual characteristics
emerge at puberty
-eg. low voices and beards in males/ high voices and no facial hair in females
