Chapter 2
Beginnings
Module 2.1: Genetic Influences on Development
LEARNING OBJECTIVES
LO1: Define chromosomes and genes
LO2: Describe mitosis and meiosis
LO3: Differentiate between identical and fraternal twins
LO4: Define dominant and recessive traits, and provide examples of each
LO5: Discuss chromosomal disorders
LO6: Discuss genetic disorders
LO7: Describe prenatal testing methods for chromosomal and genetic abnormalities
LO8: Differentiate between genotypes and phenotypes
LO9: Explain how twin studies and adoption studies are used to sort out the effects of nature and
nurture
KEY TERMS
allele A member of a pair of genes
alpha-fetoprotein assay A blood test that assesses the mother’s blood level of alpha-fetoprotein, a
substance linked with fetal neural tube defects
amniocentesis A procedure for drawing and examining fetal cells sloughed off into amniotic fluid to
determine the presence of various disorders
autism A developmental disorder characterized by failure to relate to others, communication problems,
intolerance of change, and ritualistic behavior
autosome A member of a pair of chromosomes (with the exception of sex chromosomes)
carrier A person who carries and transmits characteristics but does not exhibit them
chorionic villus sampling (CVS) A method for the prenatal detection of genetic abnormalities that
samples the membrane enveloping the amniotic sac and fetus
chromosome A rod-shaped structure, composed of genes, found within the nuclei of cells
cystic fibrosis A fatal genetic disorder in which mucus obstructs the lungs and pancreas
deoxyribonucleic acid (DNA) Genetic material that takes the form of a double helix composed of
phosphates, sugars, and bases
dizygotic (DZ) twins Twins that derive from two zygotes; fraternal twins
dominant trait A trait that is expressed
Down syndrome A chromosomal abnormality characterized by mental retardation and caused by an
extra chromosome in the 21st pair
estrogen A female sex hormone produced mainly by the ovaries
gene The basic unit of heredity. Genes are composed of deoxyribonucleic acid (DNA)
genetic counselor A health worker who compiles information about a couple’s genetic heritage to
advise them as to whether their children might develop genetic abnormalities
genetics The branch of biology that studies heredity
genotype The genetic form or constitution of a person as deter- mined by heredity
hemophilia A genetic disorder in which blood does not clot properly
heterozygous Having two different alleles
homozygous Having two identical alleles
Huntington’s disease A fatal genetic neurologic disorder with onset in middle age
Klinefelter syndrome A chromosomal disorder found among males that is caused by an extra X sex
chromosome and characterized by infertility and mild mental retardation
meiosis The form of cell division in which each pair of chromosomes splits so that one member of each
pair moves to the new cell. As a result, each new cell has 23 chromosomes
miscarriage The expulsion of an embryo or fetus before it can sustain life on its own, most often due to
defective development
mitosis The form of cell division in which each chromosome splits lengthwise to double in number.
Half of each chromosome combines CG with chemicals to retake its original form and then moves to the
new cell
monozygotic (MZ) twins Twins that derive from a single zygote that has split into two; identical twins.
Each MZ twin carries the same genetic code
multifactorial problems that stem from the interaction of heredity and environmental factors
mutation A sudden variation in a heritable characteristic, as by an accident that affects the composition
of genes
muscular dystrophy A chronic disease characterized by a progressive wasting away of the muscles
ovulation The releasing of an ovum from an ovary
phenylketonuria (PKU) A genetic abnormality in which phenylalanine builds up and causes mental
retardation
phenotype The actual form or constitution of a person as deter- mined by heredity and environmental
factors
polygenic Resulting from many genes
prenatal Before birth
recessive trait A trait that is not expressed when the gene or genes involved have been paired with
dominant genes
sex chromosome A chromosome in the shape of a Y (male) or X (female) that determines the gender of
DNA “unzip.” (c) The double helix is rebuilt in the cell as each incomplete “rung” combines with
appropriate of a child
sex-linked chromosomal abnormality An abnormality that is transmitted from generation to generation
and carried by a sex chromosome
sex-linked genetic abnormality An abnormality resulting from genes that are found on the X sex
chromosome; more likely to be shown by male offspring (who do not have an opposing gene from a
second X chromosome) than by female offspring
sickle-cell anemia A genetic disorder that decreases the blood’s capacity to carry oxygen
Tay-Sachs disease A fatal genetic neurological disorder
testosterone A male sex hormone produced mainly by the testes
Turner syndrome A chromosomal disorder found among females that is caused by having a single X sex
chromosome and characterized by infertility
uterus The hollow organ within females in which the embryo fetus develop
DISCUSSION TOPICS
The Human Genome Project was sponsored by the U.S. Department of Energy and the National
Institutes of Health and ran from October 1990 to April 2003. It was an international effort to identify
all of the approximately 25,000 genes in human DNA and determine the species-specific sequence base
pairs that make up human DNA. Volunteers around the world submitted genetic material to collection
centers around the world.
Explore an online resource defining and describing the Human Genome Project. What are some of the
benefits of such a large-scale project? What will the mapping of the human (and other species) genome
help scientists understand?
LO1: Define chromosomes and genes
When in vitro fertilization is successful, and a woman becomes pregnant with twins, are those siblings
identical or fraternal twins? Explain your answer.
In twin adoption studies, which type of twin (monozygotic or dyzygotic) are most often enlisted and
why? What factors contribute to major differences in siblings studied and how does this help inform the
controversy over nature versus nurture? Ask the class for examples of scenarios in which a twin
adoption study might inform the relationship between genetics and adolescent drug abuse.
LO3: Differentiate between identical and fraternal twins
LO9: Explain how twin studies and adoption studies are used to sort out the effects of nature and
nurture
A woman with bright red hair marries a man with brown hair. They have three sons together, all who are
born with brown hair. As adults, those brothers each mate and have two of their own children (so, six
cousins total). The oldest son has no redheaded children, the middle son has two redheaded children,
and the youngest son has a one redheaded child and one brunette.
Map out this family on a classroom board with student volunteers, indicating how the gene
traveled and how it is possible that some of the grandchildren were redheads. Identify which family
members are carriers of a recessive gene for red hair, which have a dominant gene, and which members
likely have no redhead gene at all.
LO4: Define dominant and recessive traits, and provide examples of each
In a study of ADD, researcher A evaluates each member of a single family on measures of cognitive
function and personality factors, and conducts a structured clinical interview of their psychological and
emotional history. Researcher B takes each family member’s blood and examines the DNA in
comparison to other members of the family and to human genome project data. In this example, which
researcher is conducting phenotyping and which researcher is conducting genotyping?
LO8: Differentiate between genotypes and phenotypes
Matching Characteristics of Meiosis and Mitosis
LO2: Describe mitosis and meiosis
Draw lines to correlate mitosis and meiosis with their characteristics.
PRODUCES A GENETIC REPLICA
ASEXUAL REPRODUCTION OF CELLS
NUMBER OF CHROMOSOMES REDUCED BY HALF
MEIOSIS
CHROMOSOMES REPRODUCE IDENTICALLY
MIXES CHROMOSOMES
CREATES BODY CELLS OTHER THAN SPERM OR EGG
FUNCTION FOR GENERAL GROWTH AND REPAIR
CREATES FEMALE EGG CELL
MITOSIS
FUNCTION IN SEXUAL REPRODUCTION
PRODUCES GENTICALLY DIFFERENT CELLS
OCCURS IN ALL ORGANISMS
CREATES MALE SPERM CELL
Chromosomal and Genetic Disorders
LO5: Discuss chromosomal disorders
LO6: Discuss genetic disorders
Categorize the disorders in the following chart by supplying the missing information.
(NOTE: some may fall into more than one column)
DISORDERS
Muscular
dystrophy
Down
Syndrome
Turner
syndrome
Diabetes
Mellitus
Tay-Sachs
disease
Cystic
fibrosis
hemophilia
Klienfelter
Syndrome
color blindness
sickle cell
anemia
Epilepsy
Ulcers
Phenylketonuria
(PKU)
Huntington’s
Disease
SEX LINKED
FATAL/
POTENTIALLY FATAL
MULTIFACTORIAL
RESOURCES
INTERACTIVE:
NOVA. (2003). Journey Into DNA by Rick Groleau. [Presentation slides].
Available at the PBS NOVA website.
This visual tool presents DNA from the outside to deeper and deeper levels of detail.
PODCAST:
Palca, J. (host). (2007, October 18). Neanderthals, humans share language gene [Audio file]. Available at
the National Public Radio website.
Scientists speculate that the changes in the human version of a gene found to occur across species might
partly explain why humans can talk and chimps can't. The piece also discusses that Neanderthals had the
same version of the gene that modern humans do.
LO1: Define chromosomes and genes
WEBSITE:
The National Human Genome Research Institute
This site was established in 1989 to carry out the role of the National Institutes of Health (NIH) in the
International Human Genome Project (HGP). The HGP was developed as the US Department of Energy
began to map the human genome in 1990. The Division of Intramural Research was instituted to apply
genome technologies to the study of specific diseases.
ONLINE READING:
Fausto-Sterling, A. (2001, October 30). Two sexes are not enough [Posting]. Available at the PBS NOVA
website.
This is an excerpt from the book Sexing the Body: Gender Politics and the Construction of Sexuality,
which argues for a redefinition of our two-sex-only world and offers new guidelines on how doctors
should handle intersex babies.
LO5: Discuss chromosomal disorders
LO6: Discuss genetic disorders
JOURNAL ARTICLE:
de Jong A, Dondorp WJ, Frints SGM, de Die-Smulders CEM, de Wert GMWR. Advances in prenatal
screening: the ethical dimension. Nature Reviews Genetics 2011; 12, 657-663 (September 2011) |
doi:10.1038/nrg3036
This article describes new testing techniques and non-invasive prenatal diagnoses that raise ethical
questions about reproductive choice (among other issues at the intersection of genetics and childbirth
practice.)
LO7: Describe prenatal testing methods for chromosomal and genetic abnormalities
MAGAZINE ARTICLE:
Winerman, L. (2004, April) A second look at twin studies. Monitor, 35(4), p. 46.
This review covers the methods, theory, relevance and controversy of genetic twin studies.
LO9: Explain how twin studies and adoption studies are used to sort out the effects of nature and
nurture.