Gametogenesis Flashcards
What is the three fold importance of meiosis?
1) Crossing over shuffles genes to provide recombination of gene material
2) Haploid gametes are produced, retaining a constancy of chromosomenumber
3) Random assortment of maternal and paternal chromosomes
When does the first meiotic division occur in oogenesis?
Not until puberty is reached and OVULATION occurs
At what age is there a peak number of 7 million primary oocytes?
5-month fetal age (ie before birth)
In Oogenesis, when does the oocye become halted in meiosis II?
What cell type is halted and at what phase in meiosis II is it halted at?
The SECONDARY OOCYTE becomes halted in METAPHASE II at OVULATION (after puberty obviously)
When is the PRIMARY oocyte halted in meiosis I and at what stage?
Before birth it is halted in Prophase I at which point it is in the dictyotene stage
What is the result cell type for oogenesis?
One oocyte and 3 polar bodies
What are the 5/6 cell types for speratogenesis?
What are the processes in b/w each?
Spermatogonia (A ->B) (via multiple mitotic divisions)
Primary spermatocytes formed when B divides
Secondary spermatocytes formed via meiosis I
Spermatids formed via meiosis II
Spermatozoa (ie sperm) formed via SPERMIOGENESIS
How long does it take to go from spermatogonia form to spermatozoa form?
64 days
When does the ooccye complete Meiosis II?
At fertilization
What are the layers of the oocyte?
Surrounded by zona pellucida and follicular cells (AKA corona radiata)
What are the 4 morphological changes that take place for the maturation of a sperm cell?
1) Most of cytoplasm is shed
2) Formation of neck, middle piece, and tail
3) condensation of nucleus
4) Fomation of acrosome, containing enzymes needed to penetrate egg
Where do sperm go following spermiogenesis?
They enter the lumen of the seminiferous tubules in the testis, and will be stored in the EPIDIDYMUS.
What are the 2 main types of chromosomal abnormalitites?
Numerical and Structural
What is the main cause of numerical chromosomal abnormalities?
Nondisjunction
What is aneuploidy and what is polyploidy?
What are the principle causes?
Aneuploidy: Deviation from the chromosome # that is NOT multiple of the haploid # of 23 (eg trisomy or monosomy). Principle cause: nondisjunction
Polyploidy: deviation from chromosome # that is a multiple of the haploid # (eg triploidy which is 69 chromosomes). Principle cause: dispermy (when an oocyte is fertilized by 2 sperm)
Trisomy of the autosomes is associated w/ what 3 major syndromes?
What are the main characteristics of each?
Trisomy 21: Down’s syndrome: flat nasal bridge, simian crease in palm of hands, eyes
Trisomy 18: Edward’s syndrome: short sternum, rocker-bottom feet, characteristic finger positioning
Trisomy 13 Patau’s syndrome: sloping forehead, malformed ears, bilater cleft lip/palate, polydactyly
Describe 3 trisomies/monosomies of sex chromosomes and their main characteristics.
1) Klinefelter syndrome (XXY males): tall, small testes, sterile
2) Triple X (XXX female/XXY): usually tall, and agressive for males, 15-25% mildly retarded
3) Turner syndrome (45, XO): monosomy where female infants usually show webbed neck w/ extra skin, short stature and lack of sexual maturity
How do structural chromosmal abnormalities usually occur?
Usually result from chromosome breakage (induced by environmental factors like drugs, radiation, viruses, etc)
What is cri-du-chat and what is characteristic of it?
It is a structural chromosomal abnormality when a chromosome breaks and a piece of chromosome 5 is deleted.
Affected humans have a weak, cat-like cry, and severe mental retardation
What % of malformations are caused by gene defects?
7-8%
What is genomic imprinting?
It is when expression of characteristics of the syndrome can be dependent upon paternal or maternal genetic material
An example of GENOMIC IMPRINTING is when a deltion of band q12 on chromosome 15 happens.
What is it called if the deletion occurs on chromosome 15 of the 1.Mother, 2.Father?
- Mother: Angelman syndrome (AKA Happy Puppet syndrome)
- Father: Prader-Willi syndrome (child becomes obese)
