2-Gametogenesis Flashcards
first phase of gametogenesis is identical in males and females,
whereas distinct differences exist between the male and female patterns in the last three phases.
Chromosomes
Carriers of genetic material
35000
On 46 chromosomes
Linked genes
Genes on the same chromosomes
Autosomes
22 pairs of matching chromosomes
One chromosome of each pair is derived from ___1___ and one from the ___2____
1- maternal gamete ( oocyte )
2- paternal gamete ( sperm )
Each gamete contain a haploid number of
23 chromosomes
Before entering mitosis each chromosome replicates its
DNA
Crossover
critical events in meiosis I- interchange of chromatid segments between paired homologous chromosomes
Genetic variability is enhanced through
Crossover and through random distribution
Numerous ooginia undergo
programmed degeneration
called atresia until menopause
Meiosis in Males
Begins after puberty
not all spermatogonia enter
meiosis at the same time unlike oogonia
When the spermatogonium enter the meiotic phase as primary spermatocyte
they spend several weeks dividing
DNA replication in Spermatogonium (type b)
Primary spermatocyte
First meiotic division ➡️
2 secondary spermatocytes
Second meiotic division ➡️
4 spermatids
Spermiogenesis ➡️
4 spermatozoa
haploid gametes
meiotic divisions and result in four haploid spermatids takes
64 days
acrosome
which covers half of the nuclear surface and contains enzymes to assist in fertilization
Maturation of sperms
1- Formation of the acrosome 2- Condensation of the nucleus 3- Formation of the neck, middle piece, and tail 4- Shedding of most of the cytoplasm as residual bodies
Chromosomes fail to separate during meiosis, known as
nondisjunction
General term for abnormal number of chromosomes in an embryo is termed
aneuploidy
Down Syndrome
Trisomy 21
Down syndrome
Symptoms and characteristics
- delayed growth
- distinct facial characteristics
- intellectual disability
- Premature aging
- thyroid dysfunction
- infections
The risk of having a child with Down syndrome increases with
maternal age
Trisomy 18
- mental retardation
- congenital heart defects
- low set ears
- flex ion of fingers and hands
Trisomy 18 Incidence rate
1:5000
usually all die by 2 months of age
Trisomy 13
- cleft lip and palate
- eye defects
- deafness
- mental retardation
Incidence is 1/20,000
More than 90% die in their first month after birth
Chromosome 13 in fluorescence
Green
Chromosome 21 Fluorescence
Red
