Chapter 27 Review Sheet

Attachment to and penetration of the endometrium by the blastocyst is referred to as ________.

Implantation

What does happen during amphimixis?

When the male and female nuclei fuse together, the cell is now a zygote and contains the normal complement of 46 chromosomes

The infancy stage of life is considered to be over when the baby reaches ________ of age.

one year

The period of gestation that is characterized by the largest fetal weight gain and fat deposition is the ________trimester.

third

Stretching of the cervix causes an increase in the blood levels of ______.

oxytocin

During gestation, contraction of the myometrium is inhibited by ________, produced by the placenta.

progesterone

A ________ is used to show all possible combinations of genes that can result from a given parental cross.

punnett squares

The embryonic heart starts beating as blood begins to flow through chorionic vessels at approximately ________ of development.

the third week

Deoxygenated blood is carried to the placenta by the _________.

umbilical arteries

Oxygenated blood is carried away from the placenta by the ________.

umbilical veins

Name the four extra-embryonic membranes.

yolk sac, amnion, allantois, and chorion

The extra-embryonic membrane that forms the fetal portion of the placenta is the ________.

Chorion

The process of cell division that divides the cytoplasm of the zygote among blastomeres is called ________.

Cleavage

After fertilization, the first cell division is completed ______.

More than a day later

After 3 days, a pre-embryo becomes a solid ball of cells known as a _________.

Morula

Why are numerous sperm required tofertilize a secondary oocyte?

One sperm does not contain acrosomal enzymes to erode the corona radiata surrounding the secondary oocyte.

Which hormone causes the milk ejection (milk let-down) reflex?

Oxytocin

Which hormone stimulates the milk let-down reflex?

Oxytocin

The hormone that increases the flexibility of the pubic symphysis during pregnancy is

Relaxin

List and describe the factors involved in initiating labor contractions.

Relaxin produced by the placenta, softens the pubic symphysis, and dilates the cervix. The weight of the fetus distorts the myometrium of the uterus. Distortion of the cervix and rising estrogen levels promote the release of oxytocin, and the already stretched smooth muscles of the myometrium become more excitable

How can you tell that the karyotype shown here is male?

The XY for the 23rd pair of chromosomes

Describe the trophoblast.

The cell layer surrounding the blastocyst, these cells nourish the embryo and later form part of the placenta

Define fertilization.

The fusion of the oocyte and a sperm to form a zygote

When does the placenta become sufficiently functional to continue the pregnancy?

after the first trimester

The trophoblast has many of the characteristics of ________ cells.

cancer

The first stage of labor is the ________ stage.

dilation

A zygote whose genotype is XX will develop as a ______.

female

How many chromosomes are contained within a human zygote?

46

How many chromosomes do human somatic cells contain?

46

The gradual modification of anatomical structures during the period from conception to maturity is ________.

Development

Distinguish among embryonic, fetal, and prenatal development.

Embryonic - the events that occur during the first two months after fertilization Fetal - development begins at the start of the ninth week and continues until birth Prenatal - consists of both embryonic and fetal development

The oval, three-layered sheet produced by gastrulation is called the _________.

Embryonic disc

Which of the following hormones is the cause of most puberty-related changes in a female?

Estrogen

Which chemicals are primarily responsible for initiating contractions of true labor?

Estrogens and oxytocins stimulate to production of prostaglandins, which are then primarily responsible for initiating true labor

The placenta is expelled from the uterus during the ________ stage of labor.

Expulsion

Describe the placenta.

Forms the interface between the embryonic/fetal system and maternal system. Becomes the primary structure for the developing embryo and fetus. The site for nutrient, gas, and waste exchange between the maternal and the embryonic/fetal bloodstreams

A person's original chromosomes and their component genes constitute that person's __________.

Genotype

Describe the chorionic villi.

Structures that extend outward into maternal tissues, forming an intricate, branching network through which maternal blood flows. Embryonic blood vessels extend into each.

Define organogenesis.

The process of organ formation

Why sex-linked traits are expressed more frequently in males than in females?

The small y chromosome of males contains few genes that correspond to those on larger X chromosomes

Define gestation.

The time the developing embryo and fetus spend within the uterus, or womb. Period of three integrated trimesters, each three months long

Which trimester does a fetus undergoes its largest absolute weight gain?

Third trimester

Why does a mother's blood volume increase during pregnancy?

To compensate for the reduction in maternal blood volume resulting from blood flow through the placenta

A portion of the allantois, blood vessels, and remnants of the yolk sac forms the _______.

Umbilical Cord

Define single nucleotide polymorphism.

Variation in a single base pair in a DNA sequence

The extra-embryonic membrane that forms blood cells is _________.

Yolk sac

If a color-blind (X-linked recessive trait) man marries a woman who is heterozygous for the trait, what proportion of their male offspring can be expected to be colorblind?

50%

The extra-embryonic membrane that forms a fluid-filled sac is _________.

Amnion

How do autosomes and sex chromosomes differ?

Autosomes (non-sex chromosomes) are the 22 homogolous pairs that affect somatic characteristics. The chromosomes of the 23rd pair are the sex chromosomes determine whether the individual is male (XY) or female (XX)

The individual cells produced by cleavage are called _____.

Blastomeres

_______ is the time spent in growing within the uterus.

Gestation

The presence of which hormone in the urine provides a reliable indicator of pregnancy, as detected by home pregnancy tests?

HCG (human chorionic gonadotropin)

Define homozygous and heterozygous.

Homozygous means that homogolous chromosomes carry the same allele of a given gene Heterozygous means that the homogolous chromosomes carry different alleles of a given gene

The region known as the primitive streak is the site of ________.

Migration of the ectodermal cells to form the mesoderm (migration process is called gastrulation)