Beyond Mendel's Laws

Flashcards reviewing concepts beyond Mendel's Laws, covering topics such as color blindness, sex chromosomes, mutations, chromosomal changes, triplet repeats, genomic imprinting, and quantitative genetics.

Color Blindness Inheritance

Color blindness inheritance does not conform to Mendel's laws; it involves difficulty in distinguishing red and green, and occurs more frequently in males.

Sex Chromosomes

Females have two X chromosomes, males have one X and one Y chromosome. Color blindness is caused by a recessive allele on the X chromosome.

X-linked Recessive Gene

A greater incidence in males is the hallmark; the expected frequency of disorder in males would be 10% if the allele frequency is 10%, but only 1% in females.

Inheritance of X and Y Chromosomes

Both sons and daughters inherit one X chromosome from their mother; daughters inherit their father's X, and sons inherit their father's Y chromosome.

Color-blind Mothers and Unaffected Fathers

Sons always inherit the c allele and are color blind; daughters carry one c allele but are carriers.

Color-blind Fathers and Non-carrier Mothers

None of the children are color blind, but daughters are carriers because they inherit their father's X chromosome with the recessive c allele.

Skip-a-generation Phenomenon

Color-blind fathers have no color-blind sons or daughters (assuming normal mothers), but their daughters are carriers. The daughters' sons have a 50% chance of being color blind.

New Mutations

DNA mutations that occur during the formation of the parent's eggs or sperm and are passed on according to Mendel's laws.

Changes in Chromosomes

An important source of mental retardation. For example, Down syndrome is caused by the presence of an entire extra chromosome.

Nondisjunction

Failure to apportion chromosomes equally during gamete formation, potentially leading to conditions like Down syndrome.

Expanded Triplet Repeats

Short segments of DNA repeat sequences that expand and cause problems, such as in Huntington's disease and Fragile X mental retardation.

Genetic Anticipation

Symptoms appear at earlier ages and with greater severity in successive generations due to expanded triplet repeats.

Fragile X Mental Retardation

Caused by an expanded triplet repeat that makes the X chromosome fragile. A premutation can expand in the next generation, causing retardation.

Genomic Imprinting

The expression of a gene depends on whether it is inherited from the mother or the father, often involving inactivation of a part of the gene by methylation.

Angelman Syndrome

Results from a deletion of a small part of chromosome 15 inherited from the mother, involving severe mental retardation.

Prader-Willi Syndrome

Results from a deletion of a small part of chromosome 15 inherited from the father, causing overeating, temper outbursts, and obesity.

Morbidity Risk Estimate

The chance of being affected by a disorder during an entire lifetime, age-corrected. This is a special incidence figure used in genetic studies.

Correlation Coefficient

An index of resemblance that ranges from .00, indicating no resemblance, to 1.0, indicating perfect resemblance, used to describe family resemblance for quantitative traits.

Quantitative Inheritance

Nearly all complex psychological as well as physical traits are inherited through quantitative inheritance.

Polygenic Trait

A complex trait influenced by several genes, each inherited according to Mendel's laws.

Quantitative Genetics

The branch of genetics that studies quantitative traits, based on the notion that multiple-gene effects lead to quantitative traits.

Twin Study

A study that compares the resemblance within pairs of identical twins to the resemblance within pairs of fraternal twins to disentangle genetic and environmental factors.

Adoption Study

A study that separates genetic and environmental influences by examining resemblance between biological parents and adopted-away offspring and between adoptive parents and adopted children.

Liability-Threshold Model

A model that assumes risk is distributed normally, but the disorder occurs only when a certain threshold of liability is exceeded.