Chapter 28:Development and Inheritance

recessive

recessive

it was masked in the offspring if one of the purebred parents possessed the dominant characteristic.

dominant

it was expressed in offspring when it was present in a purebred parent.

heterozygous state

it is also possible for a person to have two different alleles

homozygous state

Although a person can have two identical alleles for a single gene

phenotype

The characteristics that the genes express, whether they are physical, behavioral, or biochemical, are a person’s

karyotype

Each human body cell has a full complement of DNA stored in 23 pairs of chromosomes. the pairs in a systematic arrangement called a

colostrum

a thick, yellowish substance that is high in protein but contains less fat and glucose than mature breast milk

prolactin

The pituitary hormone _ is instrumental in the establishment and maintenance of breast milk supply.

Gastrointestinal and Urinary Adjustments

In adults, the gastrointestinal tract harbors bacterial flora—trillions of bacteria that aid in digestion, produce vitamins, and protect from the invasion or replication of pathogens. In stark contrast, the fetal intestine is sterile. The first consumption of breast milk or formula floods the neonatal gastrointestinal tract with beneficial bacteria that begin to establish the bacterial flora.

Thermoregulatory Adjustments

The fetus floats in warm amniotic fluid that is maintained at a temperature of approximately 98.6°F with very little fluctuation. Birth exposes newborns to a cooler environment in which they have to regulate their own body temperature. Newborns have a higher ratio of surface area to volume than adults.

Circulatory Adjustments

The process of clamping and cutting the umbilical cord collapses the umbilical blood vessels. In the absence of medical assistance, this occlusion would occur naturally within 20 minutes of birth because the Wharton’s jelly within the umbilical cord would swell in response to the lower temperature outside of the mother’s body, and the blood vessels would constrict.

Respiratory Adjustments

Although the fetus “practices” breathing by inhaling amniotic fluid in utero, there is no air in the uterus and thus no true opportunity to breathe. (There is also no need to breathe because the placenta supplies the fetus with all the oxygenated blood it needs.)

Afterbirth

The delivery of the placenta and associated membranes

episiotomy

an incision in the posterior vaginal wall and perineum.

Cervical Dilation

For vaginal birth to occur, the cervix must dilate fully to 10 cm in diameter wide enough to deliver the newborn’s head

morula

(morula = “little mulberry”).

foramen ovale

The fetal circulation therefore bypasses the lungs by shifting some of the blood through the

involution

which also allows the mother’s abdominal organs to return to their pre-pregnancy locations.

recessive lethal

inheritance patterns, a child who is born to two heterozygous (carrier) parents and who inherited the faulty allele from both would not survive.

lochia

Although postpartum uterine contractions limit blood loss from the detachment of the placenta, the mother does experience a postpartum vaginal discharge called

sex chromosomes

that determines the sex of the individual (XX in females, XY in males).

Mutations

is a change in the sequence of DNA nucleotides that may or may not affect a person’s phenotype.

autosomal chromosomes

The remaining 22 chromosome pairs are called

Dominant lethal

inheritance patterns are much more rare because neither heterozygotes nor homozygotes survive.

recessive lethal

inheritance patterns, a child who is born to two heterozygous (carrier) parents and who inherited the faulty allele from both would not survive.

incomplete dominance

the offspring express a heterozygous phenotype that is intermediate between one parent’s homozygous dominant trait and the other parent’s homozygous recessive trait.

Codominance

is characterized by the equal, distinct, and simultaneous expression of both parents’ different alleles.

X-linked recessive

inheritance is much more common because females can be carriers of the disease yet still have a normal phenotype.

X-linked dominant

When an abnormal allele for a gene that occurs on the X chromosome is dominant over the normal allele, the pattern is described as

X-linked

An _ transmission pattern involves genes located on the X chromosome of the 23rd pair.

Carriers

for an autosomal recessive disorder may never know their genotype unless they have a child with the disorder.

allele

is inherited from each parent, the alleles in these complementary pairs may vary.

genotype

An individual’s complete genetic makeup is referred to as his or her

foremilk

is watery, translucent, and rich in lactose and protein. Its purpose is to quench the infant’s thirst.

Hindmilk

is delivered toward the end of a feeding.

dilation

stage is the longest stage of labor and typically takes 6–12 hours.

Braxton Hicks contractions

also called false labor.

ductus arteriosus

diverts a portion of this blood into the aorta.

vernix caseosa

Sebaceous glands coat the skin with a waxy, protective substance called

lanugo

A silky hair called

lightening

During the last several weeks of pregnancy, the pelvis becomes more elastic, and the fetus descends lower in a process called

parturition

typically occurs within a week of a woman’s due date, unless the woman is pregnant with more than one fetus, which usually causes her to go into labor early.

Integumentary System Changes

The dermis stretches extensively to accommodate the growing uterus, breast tissue, and fat deposits on the thighs and hips. Torn connective tissue beneath the dermis can cause striae (stretch marks) on the abdomen, which appear as red or purple marks during pregnancy that fade to a silvery white color in the months after childbirth.

Respiratory System Changes

During the last several weeks of pregnancy, the pelvis becomes more elastic, and the fetus descends lower in a process called lightening.

Circulatory System Changes

The greater blood volume helps to manage the demands of fetal nourishment and fetal waste removal.

Weight Gain

The second and third trimesters of pregnancy are associated with dramatic changes in maternal anatomy and physiology.

trimesters

The 40 weeks of an average pregnancy are usually discussed in terms of three _, each approximately 13 weeks.

meconium

or fetal feces, begins to accumulate in the intestines.

ductus arteriosus

diverts a portion of this blood into the aorta.

ductus venosus

From the umbilical vein, the oxygenated blood flows toward the inferior vena cava, all but bypassing the immature liver, via the __ shunt

shunt

is an anatomical (or sometimes surgical) diversion that allows blood flow to bypass immature organs such as the lungs and liver until childbirth.

organogenesis

Within the first 8 weeks of gestation, a developing embryo establishes the rudimentary structures of all of its organs and tissues from the ectoderm, mesoderm, and endoderm.

embryonic folding

The embryo, which begins as a flat sheet of cells, begins to acquire a cylindrical shape through the process of

notochord

which eventually becomes the nucleus pulposus of intervertebral discs.

somites

Block-like structures called

neural tube

The two folds converge to form the

neural fold

During the fourth week, tissues on either side of the plate fold upward into a

neural plate

Specialized neuroectodermal tissues along the length of the embryo thicken into the

neurulation

Following gastrulation, rudiments of the central nervous system develop from the ectoderm in the process of

placentation

is complete by weeks 14–16.

chorionic villi

The chorionic membrane forms finger-like structures called

chorionic membrane

which envelops the entire conceptus as the chorion.

placenta previa

If the embryo implants in the inferior portion of the uterus, the placenta can potentially grow over the opening of the cervix, a condition called

ectoderm

The cells of the epiblast that remain (not having migrated through the primitive streak) become the

umbilical cord

The placenta connects to the conceptus via the

mesoderm

The second layer of cells fills in as the middle layer, or

gastrulation

As the third week of development begins, the two-layered disc of cells becomes a three-layered disc through the process of _

endoderm

a sheet of cells that displaces the hypoblast and lies adjacent to the yolk sac.

chorion

The last of the extra-embryonic membranes is the_, which is the one membrane that surrounds all others.

allantois

a primitive excretory duct of the embryo that will become part of the urinary bladder.

yolk sac

extend into the blastocyst cavity and form a

hypoblast

On the ventral side of the embryonic disc, opposite the amnion, cells in the lower layer of the embryonic disk

amnion

creating a membranous sac that forms into the _ by the end of the second week.

amniotic cavity

At the beginning of the second week, the cells of the inner cell mass form into a two-layered disc of embryonic cells

epiblast

Cells from the upper layer of the disc

ectopic pregnancy

the embryo implants either outside the uterus

placenta previa

If the embryo implants in the inferior portion of the uterus, the placenta can potentially grow over the opening of the cervix

human chorionic gonadotropin (hCG)

a hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses.

syncytiotrophoblast

a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall.

Implantation

At the end of the first week, the blastocyst comes in contact with the uterine wall and adheres to it, embedding itself in the uterine lining via the trophoblast cells.

trophoblasts

The cells that form the outer shell are called _ (trophe = “to feed” or “to nourish”).

blastocoel

The ball of now tightly bound cells starts to secrete fluid and organize themselves around a fluid-filled cavity

blastocyst

the conceptus is referred to as a

blastomere

Each daughter cell produced by cleavage is called a _ (blastos = “germ,” in the sense of a seed or sprout).

cleavage

Although each _ results in more cells, it does not increase the total volume of the Conceptus.

conceptus

Following fertilization, the zygote and its associated membranes

fetus

a _ from the ninth week of gestation until birth.

embryo

A developing human is referred to as an _ during weeks 3–8

gestation

(gestare = “to carry” or “to bear”).

fertilization membrane

The mucopolysaccharides then coat the nascent zygote in an impenetrable barrier that, together with hardened zona pellucida, is called a

acrosome

releases its stored digestive enzymes.

acrosomal reaction

in which the enzyme-filled “cap” of the sperm,

zygote

contains all of the genetic material needed to form a human half from the mother and half from the father.

capacitation

During the journey, fluids in the female reproductive tract prepare the sperm for fertilization through a process called

corona radiata

is an outer layer of follicular (granulosa) cells that form around a developing oocyte in the ovary and remain with it upon ovulation.

zona pellucida

The underlying __(pellucid = “transparent”) is a transparent, but thick, glycoprotein membrane that surrounds the cell’s plasma membrane.