HDF 351 Exam 2

What is a cross-sectional study?

Compares different age groups at one time; it does not follow the same people as they age.

What are two advantages of cross-sectional studies?

They are relatively quick and inexpensive.

What are two disadvantages of cross-sectional studies?

They do not directly track individual development and confound age with cohort.

What is a longitudinal study?

Follows the same participants across multiple ages or testing occasions.

What are advantages of longitudinal studies?

They directly observe within-person development and track changes in the same children.

What are disadvantages of longitudinal studies?

They are costly, slow, and vulnerable to attrition, practice effects, and cohort limitations.

What is selective attrition?

Nonrandom dropout: certain types of participants leave more often, biasing the remaining sample.

Why does selective attrition threaten validity?

Those remaining may differ systematically from those who left, distorting developmental conclusions.

What are practice effects?

Improved performance due to repeated exposure to the same or similar tests, not necessarily development.

What is a cohort?

People born around the same period who share historical and cultural experiences.

What is a cohort effect?

Differences caused by historical or generational experiences rather than age alone.

What is the main confound in a cross-sectional study?

Age is confounded with cohort: age groups also come from different birth periods.

What is the main confound in a longitudinal study?

Age is confounded with time of testing: participants age as historical time advances.

Why may longitudinal findings not generalize?

Results from one birth cohort may not apply to cohorts raised in other historical conditions.

What is the Groundhog Day problem in developmental research?

Findings tied to one historical period may need replication with new cohorts.

What three factors are shown in a Schaie diagram?

Age, birth cohort, and time of testing.

What equation connects age, cohort, and test year?

Approximate birth year (cohort) = testing year − age.

How is a Schaie diagram organized?

Rows represent birth cohorts, columns ages, and cells show calendar years of testing.

How do you identify a longitudinal study on a Schaie diagram?

Follow one cohort across ages: move horizontally along a row as test years increase.

How do you identify a cross-sectional study on a Schaie diagram?

Select people of different ages tested in the same year: cells form a diagonal.

In 2020, compare 20-, 40-, and 60-year-olds: what design?

Cross-sectional; same testing year, different ages and cohorts.

Follow people born in 2000 at ages 20, 40, and 60: what design?

Longitudinal; same cohort measured in 2020, 2040, and 2060.

Why is a Schaie diagram useful?

It reveals which of age, cohort, and time of testing are confounded by a design.

What is internal validity in developmental research?

How confidently observed differences can be attributed to age or development rather than confounds.

What is genotype?

An individual's genetic makeup.

What is phenotype?

Observed developmental outcome, including appearance and behavior, shaped by genes and experience.

How do mechanistic theories explain phenotype?

They emphasize environmental influences; genotype is treated as relatively unimportant.

How do maturation theories explain phenotype?

They emphasize genetically programmed maturation; genotype largely determines phenotype.

How do interaction theories explain phenotype?

Genotype × prior phenotype × environment interact to shape development.

Which theory most closely resembles genetic determinism?

Maturation theory: genetic makeup is treated as strongly determining outcomes.

What is an autosome?

Any chromosome other than a sex chromosome.

How many chromosome pairs do humans typically have?

23 pairs: 22 autosomal pairs and one sex-chromosome pair.

What are sex chromosomes?

The X and Y chromosomes, involved in sex development and sex-linked inheritance.

What is a gene?

A DNA sequence that contributes to a functional product and can influence traits.

What are alleles?

Alternative versions of a gene at the same chromosome location.

What does homozygous mean?

Having two identical alleles for a gene, such as AA or aa.

What does heterozygous mean?

Having two different alleles for a gene, such as Aa.

What is a dominant allele?

An allele expressed in the phenotype when one copy is present in a simple dominant pattern.

What is a recessive allele?

An allele usually expressed only when two copies are present in a simple autosomal pattern.

Can a dominant phenotype be homozygous or heterozygous?

Yes: AA and Aa can both express a dominant trait.

In simple autosomal recessive inheritance, who expresses the condition?

A person with two recessive alleles, aa.

What offspring genotypes result from Aa × Aa?

25% AA, 50% Aa, and 25% aa.

What is sex-linked inheritance?

Inheritance of a gene on a sex chromosome, often the X chromosome.

Why are X-linked recessive conditions more common in XY individuals?

They generally have only one X chromosome, so there is no second X allele to mask the variant.

Can a father transmit an X-linked allele to his son?

Typically no: fathers pass a Y chromosome to sons and an X chromosome to daughters.

What is a twin study?

A comparison of twins, often identical and fraternal, to investigate genetic and environmental contributions.

How do monozygotic twins differ from dizygotic twins?

Identical twins originate from one zygote; fraternal twins originate from two separate eggs.

Why compare identical and fraternal twin similarity?

Greater similarity among identical twins can suggest genetic contributions, with environmental caveats.

What is a limitation of twin studies?

Identical twins may share more similar environments, complicating purely genetic interpretations.

What is reaction range (norm of reaction)?

The range of possible phenotypes that can develop from a given genotype across environments.

Does reaction range mean genes completely determine outcomes?

No. Genes constrain possible outcomes, but environments influence the realized phenotype.

How does reaction range illustrate gene–environment interaction?

The same genotype can produce different outcomes under different environmental conditions.

What type of genetic condition is PKU?

An autosomal recessive single-gene metabolic condition associated with chromosome 12.

Which enzyme is deficient in PKU?

Phenylalanine hydroxylase, needed to convert phenylalanine into tyrosine.

What builds up in untreated PKU?

Phenylalanine and harmful metabolites, including phenylpyruvic acid.

Why can untreated PKU harm intelligence?

Toxic metabolite buildup damages the developing nervous system and can cause severe intellectual impairment.

Is PKU sex-linked?

No. It is autosomal recessive and can affect people of any sex.

What is the main intervention for PKU?

Early detection and a carefully managed low-phenylalanine diet.

What does the Guthrie test illustrate?

Newborn metabolic screening that helped make early PKU dietary treatment possible.

How does PKU illustrate a broad reaction range for intelligence?

Early dietary treatment can preserve cognitive development; untreated PKU may cause severe impairment.

What does the PKU IQ-versus-diet-start graph show?

Earlier dietary intervention is associated with substantially better IQ outcomes.

What foods tend to be high in phenylalanine?

Protein-rich foods such as meat, fish, eggs, dairy, nuts, and legumes.

Why is aspartame relevant to PKU?

It contains phenylalanine and requires attention in PKU dietary management.

What type of condition is Down syndrome?

An autosomal chromosome-number or chromosome-structure variation involving chromosome 21.

Is Down syndrome sex-linked?

No. It affects males and females.

What is trisomy 21?

Three copies of chromosome 21 material rather than the usual two.

What is nondisjunction?

Failure of chromosomes to separate normally during cell division.

What is the most common form of Down syndrome?

Trisomy 21 caused by nondisjunction during gamete formation.

What is translocation Down syndrome?

Extra chromosome 21 material attached to another chromosome.

What is mosaic Down syndrome?

Some cells have trisomy 21 while others have the usual chromosome pattern.

How does mosaic Down syndrome differ developmentally?

It can have a broader range of outcomes; phenotype depends partly on affected cells.

What physical characteristics are associated with Down syndrome?

physical: Possible hypotonia, characteristic facial features, and a single palmar crease.

What medical risks are associated with Down syndrome?

Higher rates of congenital heart defects and hearing, vision, thyroid, and other problems.

What cognitive and language patterns may occur in Down syndrome?

Variable intellectual disability and delayed language development; outcomes differ among individuals.

What IQ range does PowerPoint 3 list as typical for Down syndrome?

About 40–70, a lecture estimate rather than a fixed limit for individuals.

What is the reaction range for intelligence in Down syndrome?

The lecture describes moderate environmental influence; mosaic cases may show a broader range.

How can environment influence Down syndrome outcomes?

Supportive rearing and early interventions can improve developmental outcomes.

How does maternal age relate to trisomy 21?

The chance of trisomy 21 increases with maternal age.

What is Lesch-Nyhan syndrome?

A rare X-linked recessive single-gene metabolic disorder.

Which enzyme is deficient in Lesch-Nyhan syndrome?

HGPRT (hypoxanthine-guanine phosphoribosyltransferase).

What metabolic product accumulates in Lesch-Nyhan syndrome?

Uric acid.

What are characteristic Lesch-Nyhan symptoms?

Severe motor-control problems, limited spoken language, and self-injurious behavior.

Is Lesch-Nyhan syndrome sex-linked?

Yes. It is X-linked recessive and predominantly affects males.

What is the reaction range in Lesch-Nyhan syndrome?

Narrow according to the lecture; care focuses on managing symptoms and preventing injury.

Why is intellectual ability difficult to assess in Lesch-Nyhan syndrome?

Severe movement and communication limitations interfere with standard testing.

What genetic makeup is associated with Turner syndrome?

Typically 45,X (one X chromosome), with possible mosaic forms such as 45,X/46,XX.

Is Turner syndrome a sex-linked single-gene disorder?

No. It is a sex-chromosome variation, not a single-gene X-linked condition.

What physical features may occur in Turner syndrome?

Short stature, ovarian insufficiency, and sometimes neck, heart, or kidney differences.

What is the typical intelligence profile in Turner syndrome?

Overall intelligence is often in the typical range; some have visuospatial or math difficulties.

What is the reaction range for intelligence in Turner syndrome?

Broad/near typical overall, with individual differences; no numeric IQ range.

What genetic makeup is associated with Klinefelter syndrome?

Usually 47,XXY; mosaic forms such as 46,XY/47,XXY can occur.

Is Klinefelter syndrome an X-linked recessive single-gene condition?

No. It is a sex-chromosome-number variation.

What physical or reproductive features may occur with Klinefelter syndrome?

Often tall stature, small testes, lower testosterone, and reduced fertility.

What learning profile may occur with Klinefelter syndrome?

Intelligence is often in the typical range, with possible language or learning difficulties.

What is the reaction range for intelligence in Klinefelter syndrome?

Generally broad and often typical; the lecture provides no precise numerical range.

Which studied conditions are single-gene versus chromosomal?

Single-gene: PKU, Lesch-Nyhan. Chromosomal: Down, Turner, Klinefelter.

Which studied conditions involve autosomes versus sex chromosomes?

Autosomal: PKU, Down. Sex-linked or sex-chromosome: Lesch-Nyhan, Turner, Klinefelter.

Which conditions show strong benefit from early environmental intervention?

PKU is a particularly clear example; supportive care also helps Down syndrome outcomes.

What are the three main prenatal developmental stages?

Zygote (germinal), embryo, and fetus.

When is the zygote/germinal stage?

Approximately conception through 2 weeks, ending around implantation.