Gametogenesis -Conversion of germ cells into gametes

Question 1

Where are gametes derived?

Answer 1

Primordial germ cells that are formed in the epiblast during the second week and that move to the wall of the yolk sac

Question 2

What are teratomas?

Answer 2

Tumors of disputed origin that often contain a variety of tissues such as bone ,hair , tissues

Question 3

How many pairs of matching chromosomes(autosomes)are there?

How am any pairs of sex chromosomes?

Answer 3

22 pairs of autosomes

1pair of sex chromosomes

Question 4

If the sex pair is XX the individual is genetically a ______

Answer 4

Female

Question 5

If the sex pair is XY the individual is genetically a_____

Answer 5

Male

Question 6

What is Synapsis?

Answer 6

Process by which homologous chromosomes align themselves in pairs

Question 7

What happens as a result of meiotic division

Answer 7

1. Genetic variability enhanced through crossover which redistributes genetic material and random distribution of genetic material
2. Each germ cel contains a haploid number of chromosomes so that the diploid number is restored at fertilization

Question 8

What happens to the primary oocyte during meiosis?

Answer 8

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

Question 9

What happens to primary spermatocyte during meiosis

Answer 9

Gives rise to 4 daughter cells . Two with 22+ 1X chromosomes and two with 22+1Y chromosomes. All develop into mature gametes unlike oocytes

Question 10

Most common chromosomal abnormalities in abortuses

Answer 10

Turner syndrome, triploidy and trisomy 16

Question 11

Chromosomal abnormalities can be classified as either _____ or ____

Answer 11

Numerical or Structural

Question 12

What is Euploid?

Answer 12

Any exact multiple of n ( eg. diploid, Triploid)

Question 13

What is aneuploid?

Answer 13

Any number that is not euploid.

Question 14

What is trisomy

Answer 14

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.

Question 15

What is Monosomy?

Answer 15

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)

Question 16

What is non disjunction?

Answer 16

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

Question 17

What is mosaicism

Answer 17

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

Question 18

What is translocation

Answer 18

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

Question 19

Trisomy 21

Answer 19

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

Question 20

Trisomy 18

Answer 20

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

Question 21

Klinefelter syndrome

Answer 21

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

Question 22

Turners Syndrome

Answer 22

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)

Question 23

Triple x syndrome

Answer 23

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.

Question 24

Angelmans Syndrome

Answer 24

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

Question 25

Prader-Willi Syndrome

Answer 25

rare genetic, neurodevelopmental syndrome characterized by hypothalamic-pituitary dysfunction with severe hypotonia and feeding deficits during the neonatal period followed by an excessive weight gain period with hyperphagia with a risk of severe obesity during childhood and adulthood, learning difficulties, deficits of social skills and behavioral problems or severe psychiatric problems.

Caused by micro deletion of paternal chromosome 15

Question 26

What happens to oogonia by the end of the 3rd month

Answer 26

They are arranged in cluttered surrounded by a layer of epithelial cells

Question 27

What are the flat epithelial cells known as? (Oogenesis)

Where do they originate?

Answer 27

They are known as Follicular Cells which originate from surface epithelium converting the ovary

Question 28

At which stage of meiosis do oocytes stop their division forming primary oocytes?

Answer 28

Prophase 1

Question 29

What happens at the 5th month of prenatal development ( Oogennsis)

Answer 29

Total number of germ cells in ovary reaches its maximum estimate of 7 million and then they get atretic (degenerate before reaching maturity)

Several oogonia and primary oocytes die

Question 30

What is a primordial follicle

Answer 30

Primary oocyte together with its surrounding flat epithelial cells

Question 31

Diplotene stage of oogenesis

Answer 31

Near time of birth , primary oocytesrain arrested in Prophase 1 of meiosis and do not finish their meiotic division before puberty is reached

This arrested state is produced by OOCYTE MATURATION INHIBITOR (OMI) a small peptide secreted by follicular cells

Question 32

Number of primary oocytes at birth

Answer 32

600,000 to 800k

Question 33

Number of oocytes at puberty

Answer 33

40,000

Fewer than 500 ovulate