Chapter 29: Development and Inheritance

Define (cellular) differentiation.

The formation of different types of cells and specialization; occurs through selective changes in genetic activity, developing specific characteristics and functions

Define inheritance.

heredity; transfer of genetically determined characteristics (alleles) from generation to generation and how they present (phenotypes)

Define fertilization.

Process which a haploid sperm and haploid oocyte fuse to form a diploid zygote; fusion of gametes (n, 23 chromosomes) to form a zygote (2n, 46 chromosomes)

What enzyme is released from the acrosome that is used to penetrate the corona radiata?

hyaluronidase

After sperm binds to sperm receptors in the zona pellucida, two enzymes are released. State their names and their collective function.

hyaluronidase and acrosin; their function is to digest and degrade the zona pellucida toward the surface of the oocyte.

In general, what is oocyte activation?

Series of metabolic and ionic changes in the oocyte, triggered when the sperm fuses with the oocyte (egg)

What is polyspermy?

Fertilization by more than one sperm; creates a zygote incapable of normal development

What is amphimixis?

Combination of male and female chromosomes during fertilization

Define gestation.

Period of prenatal development; consists of 3 trimesters, 3 months each

What are two general processes that occur in the pre-embryonic period of the first trimester?

Cleavage and implantation

What are two general processes that occur in the embryonic period of the first trimester?

Placentation and embryogenesis

Define placenta.

An organ in the uterine wall that permits exchange (diffusion) between maternal and embryonic blood

Define cleavage.

Sequence of rapid cell divisions that begins immediately after fertilization and marks the start of the pre-embryonic period (first 14 days after frtzn)

What is a morula?

the pre-embryo becomes a solid ball of cells that resembles a rounded mulberry after 3 days of cleavage -> reaches the uterus on day 4 or 5

What is a blastocyst and blastocoele?

Blastocyst: a hollow ball within an inner cavity consists of outer trophoblast and inner cell mass

Blastocoele: inner cavity of blastocyst

What is the trophoblast?

Outer layer of cells; primary role is to provide nutrients to the embryo

What does the inner cell mass of a blastocyte become?

The embryo

Define ectopic pregnancy.

Implantation occurs somewhere other than within the uterus, such as one of the uterine tubes; embryo is not viable and can be life-threatening to mother

What hormone does trophoblast and chorion produce?

Human chorionic gonadotropin (hCG)

What hormones do the corpus luteum and placenta produce?

Progesterone and estrogen

What occurs during gastrulation?

Cell migration process that transforms the early embryo from a simple two-layered disc into a three-layered structure

Name the three germ layers.

1. Ectoderm- superficial

2. Mesoderm- middle layer

3. Endoderm- inner layer

What are the two main functions of the yolk sac?

1. primary nutrient source for early embryonic development

2. important site for blood cell formation

What does the amnion produce?

Amniotic fluid

What organ does the chorion develop into?

placenta

What is the function of the umbilical cord?

Supplies the fetus with life-sustaining substances and removes wastes

What vessels carry blood from the fetus to the placenta?

umbilical arteries

What is the function of the chorionic villi?

to maximize the surface area for physiological exchange between the mother and the developing embryo, including the transfer of nutrients, oxygen, and metabolic wastes, while keeping fetal and maternal blood separated

Which trimester is the most critical for fetal development?

Third

During which trimester is the most weight gained by the fetus?

Third

Which pregnancy hormone is detected in the urine when performing a home pregnancy test?

Human chorionic gonadotropin (hCG)

What is the function of human chorionic gonadotropin?

Maintains the integrity of the corpus luteum and promotes the continued secretion of progesterone

What is the function of human placental lactogen?

(hPL) helps prepare the mammy glands for milk production and has a stimulatory effect on other maternal tissues comparable to GH, ensuring glucose and protein are available for the fetus.

Which hormone produced by the placenta and corpus luteum suppresses the release of oxytocin by the hypothalamus and delays the onset of labor contractions?

Relaxin

Define parturition and labor.

Parturition: childbirth- the forcible expulsion of the fetus from the uterus through the cervix and vagina

Labor: serious of strong, rhythmic uterine contractions

What are Braxton Hicks contractions?

False contractions that are irregular; spasms in uterine musculature late in pregnancy

List the three stages of labor in the order they occur.

1. dilation: begins with onset of true labor, as cervix dilates and fetus begins to shift towards cervical canal by gravity and contractions 

2. expulsion: begins as the cervix pushed open by the fetus dilates to 10cm; contractions reach max intensity at 2–3-minute intervals, lasting usually less than 2 hours and resulting in delivery (birth) 

3. placental: muscle tension builds in the walls of the partially empty uterus which gradually decrease in size; ends with the ejection of the placenta (afterbirth)

What membrane ruptures when a birthing person's water breaks?

Amniochorionic

What does the Apgar score indicate?

An assessment of the newborn's health within five areas—heart rate, breathing, skin color, muscle tone, and reflex response. Scored from 0-2, with 8-10 indicating a healthy baby

What is a breech birth?

Legs or buttocks of fetus enter the vaginal canal first

What is the difference between dizygotic and monozygotic twins?

Dizygotic: fraternal twins- develop when two separate oocytes are ovulated and fertilized 

Monozygotic: identical twins- result either from separation of blastomeres early in cleavage or from the splitting of the inner cell mass before gastrulation; same pair of gametes 

When does the neonatal period occur?

4 week period immediately after birth (birth-1 month)

List two proteins contained in colostrum. What are their functions?

Antibodies and mucin;

help the infant ward off infections until its own immune system becomes functional and inhibits replication of viruses (rota) that can form dangerous gastroenteritis and diarrhea

What enzyme is found in breast milk? What properties does it have?

Lysozyme; antibiotic properties

Which hormone stimulates the milk ejection reflex?

oxytocin

When does adolescence begin?

Puberty (period of sexual maturation and end of growth)

In general, why are boys usually taller than girls?

Estrogen causes more rapid epiphyseal cartilage closure than does testosterone and the period of skeletal growth ends earlier in females than males

Why do premenopausal women have a lower incidence of arterial plaque formation?

Estrogens decrease plasma cholesterol levels and slow the formation of plaque, leading to a lower risk of atherosclerosis (hard arteries) than males

Define senescence.

Aging— leads to reduced functional capabilities of an individual

Define gene, genotype, and phenotype.

Gene- functional segments of DNA 

Genotype- genetic makeup of an organism ex. XY chromosomes

Phenotype- anatomical and physiological characteristics of an organism ex. Male 

What is the difference between homologous chromosomes and sex chromosomes?

Homologus- 22 chromosome pairs are known as autosomes that affect somatic, or body, characteristics, such as hair color and skin pigmentation. 

Sex chromosomes- the 23rd pair are not truly homologous and function to determine whether the individual is genetically male or female.  

What is a karyotype?

entire set of chromosomes that is prepared from dividing cells that have been stopped in the metaphase stage of the cell cycle, when they are most condensed.

Define locus and alleles.

Locus- A gene’s position on a chromosome 

Alleles- The various forms of a given gene. These alternative forms determine the precise effect of the gene on phenotype. 

When referring to gene traits, what is the difference between homozygous and heterozygous?

Homozygous- If the two chromosomes of a homologous pair carry the same allele of a particular gene

Heterozygous-  If a person has two different alleles for the same gene

What is the difference between simple inheritance and polygenic inheritance?

Inheritance- the phenotype is determined by interactions between a single pair of alleles. 

Polygenic inheritance- phenotypic traits are determined by interactions among several genes.

What are the differences between strict dominance, co-dominance, and incomplete dominance?

Strict dominance- one allele dominates the other allele and determinants phenotype ex. Dominant = normal skin pigmentation vs recessive = albino 

Co-dominance- both alleles are expressed in the phenotype ex. Type AB blood

Incomplete dominance- two different alleles produce intermittent traits in the phenotype ex. Hemoglobin A production

What are Punnett squares used for?

helps to predict the probabilities that children will have particular phenotypic traits by showing the various combinations of biological parental alleles they can inherit.

What sex chromosome alleles do males have?

A and a.

What sex chromosome alleles do females have?

a and a

What are X-linked genes?

Genes found on the X chromosome but not on the Y chromosome. The X chromosome also carries genes that affect somatic structures.

Why are men more likely to be affected by recessive X-linked traits?

Men carry only one X chromosome, so whichever allele is present will be dominant over the Y

List three conditions that occur with recessive X-linked traits

Red-Green Color Blindness: A common condition that affects a person's ability to distinguish between shades of red and green.

Hemophilia: A bleeding disorder in which the blood lacks enough clotting factors, causing excessive, prolonged bleeding even after minor injuries.

Duchenne Muscular Dystrophy: A severe, progressive genetic disease characterized by the weakening and wasting away of muscle tissue.

others include diabetes

What is the result of genetic recombination?

increased the genetic variation among gametes, and thus among the genotypes formed when those gametes combine in fertilization.

Why do you think that only 0.5% of newborns have chromosomal abnormalities when ~10 percent of zygotes have chromosomal abnormalities?

natural biological selection

What of clinical significance can the analysis of amniotic fluid detect?

Amniocentesis (amniotic fluid analysis) permits the identification of many congenital conditions, including Down syndrome, sickle cell disease, and neural tube defects.

What is a translocation defect?

an exchange occurs between different (nonhomologous) chromosome pairs. ex. a piece of chromosome 8 may become attached to chromosome 14. The genes moved to their new position may function abnormally, becoming inactive or overactive.

What genetic abnormality is the cause of Down's syndrome?

Trisomy 21; one of the gametes involved in fertilization carries an extra copy of one chromosome, so the zygote then has three copies on the 21st chromosome rather than two.

What direct correlation has been observed that increases the risk of having a baby with Down's syndrome?

advancing maternal age and the risk of having a child with trisomy 21

Define epigenetics.

the study of inherited traits that are not due to changes in a person’s genotype or DNA sequences.

What are spontaneous mutations?

random errors in DNA replication. Such errors are relatively common, but in most cases the error is detected and repaired by DNA repair enzymes in the nucleus.

errors that go undetected and unrepaired have the potential to change the phenotype in some way.

What are teratogens?

Factors that result in abnormal development. Drugs, including certain antibiotics, alcohol, and nicotine in cigarette smoke, can disrupt fetal development.

What is gene therapy?

a medical approach aimed at treating disorders or diseases caused by genetic defects. Ex. inserting corrective genes made in a laboratory into a patient’s cells to genome editing in which molecular tools are used on a cell’s existing DNA to repair a gene, turn genes on or off, or remove a gene.