Gametogenesis -Conversion of germ cells into gametes Flashcards
Where are gametes derived?
Primordial germ cells that are formed in the epiblast during the second week and that move to the wall of the yolk sac
What are teratomas?
Tumors of disputed origin that often contain a variety of tissues such as bone ,hair , tissues
How many pairs of matching chromosomes(autosomes)are there?
How am any pairs of sex chromosomes?
22 pairs of autosomes
1pair of sex chromosomes
If the sex pair is XX the individual is genetically a ______
Female
If the sex pair is XY the individual is genetically a_____
Male
What is Synapsis?
Process by which homologous chromosomes align themselves in pairs
What happens as a result of meiotic division
- Genetic variability enhanced through crossover which redistributes genetic material and random distribution of genetic material
- Each germ cel contains a haploid number of chromosomes so that the diploid number is restored at fertilization
What happens to the primary oocyte during meiosis?
Gives rise to 4 daughter cells each with 22+ 1X chromosome. Only one develops into mature gamete the other three polar bodies receive little cytoplasm and degenerate during subsequent development
What happens to primary spermatocyte during meiosis
Gives rise to 4 daughter cells . Two with 22+ 1X chromosomes and two with 22+1Y chromosomes. All develop into mature gametes unlike oocytes
Most common chromosomal abnormalities in abortuses
Turner syndrome, triploidy and trisomy 16
Chromosomal abnormalities can be classified as either _____ or ____
Numerical or Structural
What is Euploid?
Any exact multiple of n ( eg. diploid, Triploid)
What is aneuploid?
Any number that is not euploid.
What is trisomy
A trisomy is a chromosomal condition characterised by an additional chromosome. A person with a trisomy has 47 chromosomes instead of 46. Down syndrome, Edward syndrome and Patau syndrome are the most common forms of trisomy.
What is Monosomy?
Monosomy is the state of having a single copy of a chromosome pair instead of the usual two copies found in diploid cells. ( One chromosome of the pie is missing)
What is non disjunction?
Failure of paired chromosomes to separate (to disjoin) during cell division, so that both chromosomes go to one daughter cell and none go to the other. Nondisjunction causes errors in chromosome number, such as trisomy 21 (Down syndrome) and monosomy X (Turner syndrome).
Usually occurs during the first or second meiotic division of germ cells
Can be autosomes or sex chromosomes
What is mosaicism
Mitotic nondisjunction in embryonic cells during early cell divisions , producing cells with a normal chromosome number and and some abnormal.
Affected individuals may exhibit few or many symptoms of a particular syndrome depending on the number of cells in the distribution
What is translocation
A genetic change in which a piece of one chromosome breaks off and attaches to another chromosome. Sometimes pieces from two different chromosomes will trade places with each other.
Common between chromosomes 13,14,15,21 and 22 because they cluster during meiosis
Trisomy 21
Down syndrome or Down’s syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual disability, and characteristic facial features. Increased frequency of developing early onset Alzheimer’s
Trisomy 18
A baby with Edwards’ syndrome has 3 copies of chromosome number 18 instead of 2. This affects the way the baby grows and develops. Having 3 copies of chromosome 18 usually happens by chance, because of a change in the sperm or egg before a baby is conceived.
Cleft palate
Clenched fists with overlapping fingers that are hard to straighten
Defects of the lungs, kidneys, and stomach/intestines
Deformed feet (called “rocker-bottom feet” because they’re shaped like the bottom of a rocking chair)
Feeding problems
Heart defects, including a hole between the heart’s upper (atrial septal defect) or lower (ventricular septal defect) chambers
Low-set ears
Severe developmental delays
Chest deformity
Slowed growth
Small head (microcephaly)
Small jaw (micrognathia)
Weak cry
Klinefelter syndrome
Klinefelter syndrome is a genetic condition that results when a boy is born with an extra copy of the X chromosome. Klinefelter syndrome is a genetic condition affecting males, and it often isn’t diagnosed until adulthood.
They normally have 48 (XXXY) pairs of chromosomes: 44 autosomes and 4 sex chromosomes
Klinefelter syndrome may adversely affect testicular growth, resulting in smaller than normal testicles, which can lead to lower production of testosterone. The syndrome may also cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue. The effects of Klinefelter syndrome vary, and not everyone has the same signs and symptoms.
Men produce little or no sperm
Turners Syndrome
Turner syndrome is a genetic disorder affecting girls and women. The cause of Turner syndrome is a completely or partially missing X chromosome. Turner syndrome symptoms include short stature and lack of breast development and periods , webbed neck, gonodal dysgenesis ( lack of ovaries)
Triple x syndrome
Found in girl’s only.Girls with triple X syndrome — also known as XXX syndrome, trisomy X, and 47,XXX, — might be taller than other girls. Other symptoms can include problems with spoken language and processing spoken words, coordination problems, and weaker muscles.
Angelmans Syndrome
Angelman syndrome is due to a lack of function of part of chromosome 15 inherited from a person’s mother. Most of the time, it is due to a deletion or mutation
