Ch. 28 (Development + Inheritance) pt.1 + pt.2

How long is an oocyte viable? Sperm?

Oocyte:

• 12-24 hours

Sperm:

• 24-48 hours

How many sperm are released upon ejaculation vs. how many make it to the ovulated oocyte?

Released:

• Millions

Survive:

• Couple Hundred

What is fertilization?

• Sperm chromosomes COMBINE with those of SECONDARY oocyte to form fertilized egg (Zygote)

What mechanism guides sperm towards the oocyte. Be specific.

Chemotaxis guides the sperm towards the oocyte

→ oocyte + Cumulus cells secrete chemoattractants (e.g., progesterone) that guide sperm

• Sperm have olfactory receptors

Describe the events the occur during each step required for a sperm to fertilize an egg:

a. Sperm arrive at oocyte

• Enzyme on cell surface of sperm acts to digest corona radiata

• Sperm heads then bind to sperm-binding receptors in zona pellucida,

  causing sperm membrane calcium channels to open

• Ca2+ flows into each sperm

(Triggering the following step)

b. Acrosomal reaction

• When triggered by calcium influx, enzymes from many sperm are

  released that digest holes in zona pellucida

• Spermall release enzymes at same time to digest zona pellucida

• Many are required to clear a path to oocyte membrane

c. Sperm binds to oocyte membrane receptor

• After path has been cleared in zona pellucida, a single sperm forcibly swims towards oocyte membrane

  • Acrosomal collar (tip of sperm) on rear portion of acrosomal membrane binds to oocyte plasma membrane sperm-binding receptor

d. Binding causes

• Oocyte to form microvilli that wrap around sperm head

• Trigger fusing of oocyte and sperm membrane

e. Membrane fusion

• Cytoplasmic contents of sperm enter oocyte

• Tail and other parts, such as sperm cell membrane/ mitochondria, are left behind

  on oocyte cell membrane surface

____________________________ refers to the transfer of genetically determined characteristics from generation to generation, and _____________________________ is the study of the mechanisms responsible for this transfer of information.

Heredity refers to the transfer of genetically determined characteristics from generation to generation, and Genetics is the study of the mechanisms responsible for this transfer of information.

How many sperm are required to break down the corona radiata prior to fertilization? How many sperm are required to fertilize the oocyte?

Break down corona radiate:

• HUNDREDS

Fertilize the oocyte:

• 1

Describe the mechanisms prevents polyspermy?

1) Fast-block (1-3 seconds)

• When sperm binds to sperm-binding receptors on oocyte, sodium channels shift RMP to positive (sperm can’t bind to positively charges oocyte plasma membrane)

2) Slow-block (60 seconds after sperm binds)

• Ca + surge from oocyte ER that causes

• The release of enzymes that destroy the zone pellucid sperm-binding receptors + harden zone pellucida

Has an oocyte completed the process of meiosis by the time it is ovulated? Explain.

NO

• Has not completed meiosis by the time it is ovulated

• it is arrested in metaphase II of meiosis II and will only complete meiosis upon fertilization by a sperm cell

How many chromosomes are contained with a human zygote? Where do they come from?

# of chromosomes:

• 46 chromosomes

Come from:

• 23 from mom

• 23 from dad

What is cleavage? Where/when does this happen?

Cleavage:

→ series of rapid mitotic cell divisions that occur in the zygote shortly after fertilization.

• Embryo travels through uterine tube to uterus + floats freely until it implants

• Zygote moves towards uterus

1st cleavage:

• after 36 hours + produces 2 daughter cells = BLASTOMERES

• after 72 hours, cluster of cells contains 16 or more cells = MORULA

What phase of cleavage is the embryo in upon implantation in the uterus? How many days after ovulation does implantation take place?

→ blastocyst stage of cleavage

• 6-10 days after ovulation

What is the difference between a morula and blastocyst?

• Morula: Solid ball of 16–32 cells, no cavity, forms ~day 3–4.

• Blastocyst: Hollow with fluid-filled cavity, inner cell mass + trophoblast, forms ~day 5

What are the 2 primary structures that make up the blastocyst? Which of these structures will give rise to the embryo?

• Trophoblast: Outer layer; forms the placenta.

• Inner cell mass: Cluster of cells inside; gives rise to the embryo.

The trophoblast proliferates into 2 layers of cells, the inner cytotrophoblast and the outer syncytiotrophoblast.

• What is the fate of each (what do the become/do)?

→ IMPLANTATION: (6-7 days after ovulation)

• Trophoblast invades uterine wall

Cytotrophoblast:

• Inner layer of cells

• gives rise to new trophoblast cells and helps form chorionic villi

Syncytiotrophoblast:

• Cells in outer layer

• invades the uterine lining, secretes hCG, and helps establish maternal-fetal circulation

What is the significance of hCG? How long is hCG necessary to secrete before it is no longer consequential to the fate of the fetus?

hCG:

• crucial for maintaining the corpus luteum, which continues to produce progesterone during early pregnancy, preventing menstruation and supporting the uterine lining for implantation and embryo development

Takeover:

• first 8–10 weeks (2 months) of pregnancy, after which the placenta takes over progesterone production, and hCG levels decrease.

What is the placenta? What is the function of the placenta? What types of things can cross the placental barrier?

Placenta:

• Organ providing interface btw maternal and fetal circulation

Site of:

• Gas exchange

• Transfer nutrients to fetus

• Transfer of waste from fetus to mother

• Fetotoxic substances (ALCOHOL)

• Nicotine

• Antibiotics

• Certain pathogens

The placenta is a contribution of both embryonic and maternal tissues. What structures of the placenta are embryonic/fetal? Maternal?

Embryonic:

• Chorion: Derived from the trophoblast (outer layer of the blastocyst), forms the fetal part of the placenta.

• Chorionic villi: Finger-like projections from the chorion that invade the uterine wall and facilitate nutrient and gas exchange.

Maternal:

• Decidua basalis: endometrium located between chorionic villi and stratum basalis of endometrium

  • Decidua capsularis: part of endometrium at uterine cavity face of implanted embryo

  • Portion of placenta that expands to accommodate growing fetus

  • Villi in decidua capsularis degenerate as fetus grows, while villi in decidua basalis increase in number and branches

  • Together chorionic villi and decidua basalis make up placenta

What is the difference between the decidua basalis and decidua capsularis?

• Decidua basalis: The part of the decidua located beneath the implanted embryo, where the placenta develops and attaches to the uterine wall.

• Decidua capsularis: The part of the decidua that surrounds the fetal side of the embryo, forming a capsule around the growing blastocyst.

What are the 2 layers of the embryonic disc?

In which layer is the primitive streak formed?

1) Ectoderm

2) Mesoderm

3) Endoderm

Primitive streak:

What is gastrulation?

Embryonic disk transforms into 3 layered embryo (3 primary germ layers are present)

What are the 3 primary germ layers?

a. During gastrulation, The first epiblast cells to migrate through the streak displace the hypoblast to form the __________.

b. The __________ is formed next, as more cells migrate in and begin to move laterally.

c. The remaining epiblast cells that do not migrate are now considered the ___________.

23. Name the germ layer which contributes the following:

a. the epithelial lining of the digestive, respiratory and urogenital systems  _________

b. the majority of the mass of the human body  _____________

c. the nervous system and epidermis  ______________

What is neurulation?

What is the notochord and what role does it play in neurulation?

• a. The notochord will eventually be replaced by what structure? The only remnant of the notochord in the adult body is the _____________ ________________.

 During neurulation, the ______________ folds inward to form ____________ and ____________. The ______________ fuse to form the ___________________.

What is spina bifida? Rank the 3 major forms of spina bifida from least to most severe 

What are somites? What three parts do they subdivide into and what are the fates of each?

Between which weeks does the embryonic period end and the fetal stage begin?

How many weeks does it take for the fetus to fully form (full term)? Why is the gestational period 40.5 weeks?

How is the gestational period divided?

What type of maternal adaptations occur in the second and third trimesters?

What is the technical term for stretch marks and why do they form?

 In addition to its role in the nutrition of the fetus, the placenta acts as an endocrine organ. Identify the placental hormones from the descriptions below (hormones may be used more than once):

a. Increases the flexibility of the pubic symphysis and dilates the cervix ___________

b. Used in pregnancy testing ________

c. Secreted by trophoblast cells and later chorion ________________

d. Suppresses FSH and LH, preventing ovulation (2 hormones) _________

e. Promotes fetal growth and viability, as well as uterine enlargement _________

f. Helps prepare the mammary glands for milk production __________

g. During the first trimester, these two hormones are secreted by the corpus luteum to maintain the pregnancy. ____________

h. Prompts corpus luteum to persist, continuing secretion of progesterone and estrogen _______

i. Increases maternal metabolic rate ________

j. During the last two trimesters, these two hormones are secreted by the placenta to help maintain the endometrium and continue the pregnancy  ________

What is parturition?

What stimulates contractions in later pregnancy?

What are Braxton-Hicks contractions?

What is the bloody show? Is this normal?

What event is happening when a pregnant woman’s water breaks? Why does delivery need to follow within 24-48 hours of this event?

Describe the positive feedback mechanism that helps childbirth progress quickly.

What is Pitocin and when is it administered?

For the following events, indicate which stage of labor they occur in (Dilation, Expulsion, Afterbirth)

a. This stage lasts from onset of labor until the cervix is fully dilated. __________

b. Strong contractions every 2–3 minutes. __________

c. Longest stage of labor. ____________

d. Baby’s neck extends as head exits perineum followed by delivery of the rest of the body ______

e. Strong contractions continue, causing detachment of placenta. _________

f. Crowning occurs during this stage. __________

g. This stage lasts from full dilation to delivery. __________

What is vertex position? Breech?

a. Which is the natural delivery position?

b. Which position might require a Caesarian section?

c. What is a Caesarian section?

What is involution of the uterus?

What is lochia?

What is preeclampsia?

What is gestational diabetes?

What is the APGAR score? Describe what is being tested?

What is colostrum and how does it differ from True milk?

Which hormone is involved in the positive feedback mechanism of labor as well as the milk let-down reflex of lactation?

What is a gene?

What is genetics and who is considered the father of genetics? In what year did scientists successfully map the first complete human genome?

What is the genome?

If every nucleated cell has the same genome, why do some cells look and function differently than others?

Compare and contrast genotype and phenotype.

If you examine a karyotype, the first 22 pair of chromosomes are known as _______

__________. The 23rd pair of chromosomes is known as your __________.

Define the following terms:

a. homologous chromosomes

b. autosomes

c. sex chromosomes

d. allele

e. homozygous

f. heterozygous

g. dominant

h. recessive

How are dominant and recessive alleles designated?

What differentiates monogenic (Mendelian) inheritance from polygenic (non-Mendelian) inheritance? What are some examples of traits determined by each type of inheritance?

What is segregation? Independent assortment?

What is a Punnett square? Be able to use one on the exam. Be able to calculate genotypic and phenotypic ratios based on the type of inheritance.

Do the probabilities of offspring inheriting a particular trait change if a mating results in one phenotype rather than another?

Compare and contrast the three types of simple inheritance:

a. strict dominance

b. codominance

c. incomplete dominance

What conditions must exist for a recessive trait to be expressed?

What is a carrier?

Complete a Punnett square and list the expected genotypic and phenotypic ratios for the following example of strict dominance:

Free earlobes (F) are dominant to attached earlobes (f). A heterozygous male is mated with a heterozygous female.

Complete a Punnett square and list the expected genotypic and phenotypic ratios for the following example of strict dominance:

A carrier of Tay-Sachs disease (Tt) decides to have a child with a person that is homozygous normal (TT) for this allele. (Hint: Tay-Sachs follows a autosomal recessive pattern of inheritance.)

Sickle cell anemia is an example of incomplete dominance. Assume “S” is a normal shaped blood cell, and “s” is a sickle shaped blood cell. (“SS” = normal, “Ss” = has the sickling trait, and “ss” = has sickle cell disease)

Complete a Punnett square and list the expected phenotypic ratios for the following example of incomplete

Dominance: A man with sickling trait has children with a woman who has the sickling trait.

Blood types are determined by three genes...............”A” is a dominant gene, “B” is a dominant gene, and “O” is a recessive gene. There are 4 blood types created by combinations of these genes. AA and AO yield type A blood, BB and BO yield type B blood, AB creates AB blood, and OO creates type O blood.

Complete a Punnett square and list all possible phenotypes for the following example of codominance: A person with type AB blood has a child with a person that has type B blood.

Complete a Punnett square and list all possible phenotypes for the following example of codominance:

A person with type A blood has a baby with a person with type B blood.

Why are X-linked traits expressed differently in males

Sex-linked inheritance is unique, because the traits are passed on with the X-chromosome only. For the disorders listed, the Y-chromosome does not carry a corresponding gene. When performing a Punnett square for sex-linked traits, be sure to keep track of the % of male offspring and % of female offspring expressing the disorders. For our purposes, a superscript indicates that the chromosome carries the disorder. The lack of a superscript is interpreted as the presence of a normal gene.

• Complete a Punnett square and list the % of male and female children which will be normal and the % of male and female children which will express the disorder for the following example of sex-linked inheritance: A female carrier for color blindness (XcX) mates with a man that has normal color vision (XY).

A man with hemophilia (XhY) decides to have children with a woman who is a carrier for hemophilia (XhX). What % of the male and what % of the female offspring would express hemophilia? Are there any carriers produced? If so, what is the sex of the carrier?

What is a pedigree?

What is an amniocentesis? Chorionic villus sampling? Why are these tests only administered if there is a known risk of a genetic disorder?