Chapter 3
I. Define DNA, chromosome, genome, and gene.
a. DNA: stands for deoxyribonucleic acid, the famed double helix.
b. Chromosome: a molecule of DNA and it contains the instructions to make
all the proteins a living being needs.
c. Genome: is the code for making life. It is an enormous and complex
packet of instructions.
II. Describe the beginnings of human life at conception.
a. It all begins when a male’s reproductive cell or sperm penetrates the
membrane of a female reproductive cell, or ovum. Each reproductive cell,
or gamete, contains 23 chromosomes which then once the cell fuse
together the zygote forms.
III. Define: gamete, zygote, gene, and genotype.
a. Gamete: a reproductive cell that carries 23 chromosomes.
b. Zygote: when the reproductive cells fuse now containing 23 pairs.
c. Gene: is a unit of the chromosome that carries specific instructions to
specific proteins.
d. Genotype: is the genetic inheritance of a human being.
IV. Explain how the 23rd pair determines sex.
a. The 23rd pair determines sex because each male and female has different
shape chromosomes. The male have an X chromosome and a Y
chromosome, while the female has two X shaped chromosomes. The Y
chromosome contains a gene called SRY that directs a developing fetus to
make male organs. The X chromosome doesn’t have this thus female
organs will be made.
V. Define spontaneous abortion.
a. Also called miscarriage. Is when the naturally occurring termination of a
pregnancy before the fetus is fully developed.
VI. Differentiate between monozygotic twins and dyzygotic twins.
a. Monozygotic twins are identical twins due to the zygote splitting into two
identical organisms early in development.
b. Dyzygotic twins are fraternal twins and it happens when two ova are
fertilized by separate sperms at the same time and thus give two zygotes.
VII. Describe the role of following gene-gene interactions.
a. On-off switching mechanism: is a process in which certain genes codes for
proteins that switch other genes on and off, making sure that the other
genes produce proteins at the appropriate times. This mechanism
continues lifelong, instructing cells to repair damage, to take in
nourishment, to multiply, to atrophy, and even die.
b. Additive Genes: A gene that through interactions with other genes affects
specific traits such as skin color or height. So a tall father and a short
mother won’t have kids either taller than the dad or shorter than the mom.
c. Dominant and recessive genes: Is the interaction of a pair of alleles in
such a way that the phenotype reveals the influence of one allele
(dominant gene) more than that of the other (recessive gene).
VIII. Define phenotype.
a. A person’s actual appearance and behavior, which are the result of both
genetic and environmental influences.
IX. Define behavior genetics.
a. The study of the genetic origins of psychological characteristics, such as
personality pattern, psychological disorder, and intellectual abilities.
X. Identify factors that contribute to the following disorders:
a. Alzheimer’s disease: not having normal blood pressure, accumulation of
protein amyloid B, loss of intellectual activity, genetics and less emotional
expression (also old age).
b. Schizophrenia: one is genetics, slow acting virus, head injury, inadequate
oxygen at birth, and birth during late winter.
c. Alcoholism: biochemistry inherited by the person, selective adaptation,
addiction, and culture.
XI. Define mosaic.
a. Referring to a condition in which a person has a mixture of cells, some
normal and some with the incorrect number of chromosomes.
XII. Describe the characteristics of individuals with Down syndrome (trisomy-21).
a. People with this syndrome have extra-chromosome condition. They have
specific facial characteristics such as thick tongue, round face, slanted
eyes as well as distinctive hands and feet. They also have mental slowness.
They age faster than other adults. They develop Alzheimer’s by their 30s
invariably. Prone to cancer and cataracts. Life expectancy is very low for
them.
XIII. Define fragile x syndrome.
a. A genetic disorder in which part of the X chromosome is attached to the
rest of it by a very thin string of molecules; often produces mental
deficiency in males who inherit it. This is caused by a mutation of the X
chromosome having too many repetition of CGG.
XIV. Define genetic counseling.
a. A process of consultation and testing that enables individuals to learn
about their genetic heritage, including conditions that might harm any
children they have.
XV. Identify persons for whom genetic counseling is recommended.
a. Individuals who have parents, siblings, or child with serious genetic
conditions that is known to be either dominant or recessive.
b. Couples who have a history of early spontaneous abortion, stillbirths, or
infertility.
c. Couples who are from the same ethnic group or subgroup-particularly if
the couples are close relatives.
d. Women age 35 or older and men age 40 or older.
XVI. Describe following prenatal tests and risks.
a. Alfa-fetoprotein assay: A sample of the mother’s blood is tested for the
level of alpha-fetoprotein. The test itself is not risky, but non-normal AFP
levels indicate that additional testing is needed.
b. Ultrasound (sonogram): High-frequency sound waves are used to produce
a picture of the fetus. No known risks for this test.
c. Amniocentesis: About half an ounce of the fluid inside the placenta is
taken out. The cells are cultured and analyzed. This test cannot be safely
performed until mid-pregnancy (at least 14 weeks). About once in 200
pregnancies, amniocentesis causes spontaneous abortion.
d. Chorionic villi sampling: A sample of the placental tissue that surrounds
the fetus is obtained and analyzed. This test, compared to amniocentesis, is
more likely to cause spontaneous abortion.