Transcript Chapter 13. - Waterford Public Schools

Meiosis 1
Meiosis 2
Random fertilization
• Any 2 parents will produce a zygote with over
70 trillion (223 x 223) diploid combinations
Sexual reproduction creates variability
Sexual reproduction allows us to maintain both genetic
similarity & differences.
Michael & Kirk
Douglas
Baldwin brothers
Martin & Charlie Sheen, Emilio Estevez
Mitosis vs. Meiosis
Changes in Chromosomes Number
 Euploidy = correct # of chromosomes
 Aneuploidy = a change in chromosomes
number due to non-disjunction during meiosis
 Monosomy- only 1 copy of an individual chromosome
 Trisomy- 3 copies of an individual chromosome
Non-disjuction
Primary nondisjuction = Meiosis I
Secondary nondisjuction = Meiosis II
Trisomy 21 : Down Syndrome
• Delayed mental and social skills
• Decreased muscle tone at birth
• Asymmetrical or odd-shaped skull
• Small skull
• Small mouth with protruding tongue
• Broad short hands
• Increased risk of developing
Leukemia and Alzheimer’s later in life
Trisomy 18 : Edward’s Syndrome
•
•
•
•
•
•
•
•
•
•
Most children die in the first year of life, some have lived 10 years
Growth deficiency
Feeding difficulties
Breathing difficulties
Developmental delays
Mental Retardation
Overlapped, flexed fingers
Webbing of the second and third toes
Clubfeet
Structural heart defects at birth
Trisomy 13 : Patau Syndrome
•
•
•
•
•
•
•
•
•
•
Mental retardation, severe
Seizures
Small head
Scalp defects
Cleft lip and/or palate
Eyes close set (hypotelorism) –may fuse
Extra digits (polydactyl)
Hernias
Undescended testicle
Children die in the first year of life
Procedure: Amniocentesis and
Karyotyping
Karyotyping
• https://youtu.be/BD6h-wDj7bw
Changes in Sex Chromosome #
SRY gene (located on short arm of Y chromosome)
-hormone= testis-determining factor
 Turners Syndrome (XO) – missing Barr Body
 Kleinfelter’s Syndrome (XXY)
 Swyer Syndrome (XY female) Y chromosome is
missing the SRY gene - The uterus and
fallopian tubes are normally-formed, but the
gonads (ovaries or testes) are not functional;
affected individuals have undeveloped clumps
of tissue called streak gonads. Because of the
lack of development of the gonads, Swyer
syndrome is also called 46,XY
complete gonadal dysgenesis.
 La Chapelle Syndrome (XX male)
 XX male syndrome Caused by unequal crossing over between the X
and Y chromosomes during meiosis in the father, which results in
the X chromosome containing the SRY gene. When this X combines
with a normal X from the mother during fertilization, the result is an
XX male.
 Poly-X Females (XXX, XXXX)
• Triple X syndrome, also called trisomy X or 47,XXX, is characterized by the
presence of an additional X chromosome in each of a female's cells.
Although females with this condition may be taller than average, this
chromosomal change typically causes no unusual physical features. Most
females with triple X syndrome have normal sexual development and are
able to conceive children.
• Triple X syndrome is associated with an increased risk of learning
disabilities and delayed development of speech and language skills.
Seizures or kidney abnormalities occur in about 10 percent of affected
females.
• This condition occurs in about 1 in 1,000 newborn girls. Five to 10 girls
with triple X syndrome are born in the United States each day.
 Jacob’s Syndrome (XYY males)
• What is 47,XYY syndrome?
• 47,XYY syndrome is characterized by an extra copy of the Y
chromosome in each of a male's cells. Although males with
this condition may be taller than average, this
chromosomal change typically causes no unusual physical
features. Most males with 47,XYY syndrome have normal
sexual development and are able to father children.
• 47,XYY syndrome is associated with an increased risk of
learning disabilities and delayed development of speech
and language skills.
• A small percentage of males with 47,XYY syndrome are
diagnosed with autistic spectrum disorders
• This condition occurs in about 1 in 1,000 newborn boys.
Chromosomal Mutations
Deletion Syndromes
• Williams Syndrome (deletion of a piece of
chromosome 7)
• Cri du chat (cat’s cry) (deletion of a piece of
chromosome 5)
Spermatogenesis
• Production of sperm
– Continuous and prolific
– Each ejaculation contains ~100-650 million sperm
• Occurs in the testes
– Seminiferous tubules
• Spermatogonia (stem cells that give rise to sperm)
are located at the periphery of each seminiferous
tubule
– Spermatogonia are diploid
• Developing sperm move toward the central opening
(lumen) of the tubule as they undergo meiosis and
differentiation
• 4 cells result
– Develop into mature sperm
– Haploid
The structure of sperm
Campbell
Oogenesis
• The development of ova
– Mature, unfertilized eggs cells
– Happens in the ovary
• Oogonia (stem cells that give rise to ova)
–
–
–
–
Multiply and begin meiosis
STOPS at prophase 1
At this phase, the cells are called primary oocytes
Remain in this phase until the onset of puberty, when they
are activated by hormones
• Activated by LH and FSH
• Beginning at puberty, FSH periodically stimulates a
follicle to grow and induces its primary oocyte to
complete meiosis 1 and start meiosis 2
• Meiosis then STOPS again
– The secondary oocyte, released during ovulation, does not
continue meiosis right away
– Penetration of the egg cell by sperm triggers the
completion of meiosis
– Then meiosis is complete
– LH stimulates the completion of meiosis
Campbell
Growing follicle
Major difference #1
• 1. unevenness in the mitotic
division/cytokinesis of oogenesis
– Almost all the cytoplasm  1 daughter cell
(secondary oocyte)
– 3 polar bodies which degenerate
– Spermatogenesis = four mature sperm
Major difference #2
The cells that produce sperm continue to divide
by mitosis throughout life (males)
Not the case for women
*born with all the primary oocytes
Major difference #3
• Oogenesis has long resting periods
• Sperm is produced in an uninterrupted
sequence