Chapter 28:Development and Inheritance

 **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.