Sex Linkage, Genetic Mapping, and Human Geneticsm (Slide 5)

A set of 32 comprehensive vocabulary flashcards covering the chromosomal theory of inheritance, sex linkage, dosage compensation, non-Mendelian inheritance, genetic mapping, pedigrees, and human genetic disorders.

Chromosomal Theory of Inheritance

A foundational biological theory stating that chromosomes carry the units of heredity, proposed based on observations that similar chromosomes pair with one another during meiosis.

Carl Correns

The German geneticist who in 1900 first suggested a central role for chromosomes in heredity and co-authored one of the papers announcing the rediscovery of Gregor Mendel's work.

Walter Sutton

The American biologist who formulated the chromosomal theory of inheritance in 1902 after observing that homologous chromosomes pair with each other during meiosis.

SRY Gene

A master regulatory gene located on the $Y$ chromosome that is required for the development of maleness in humans; without it, the developmental default is female.

Dosage Compensation

A genetic mechanism ensuring equal expression of genes on sex chromosomes between males and females, compensating for differences in the number of $X$ chromosomes.

Barr Body

A highly condensed, transcriptionally inactive $X$ chromosome found in the somatic cell nuclei of mammalian females.

Genetic Mosaic

An individual female consisting of cells with different active $X$ chromosomes due to random embryonic $X$-chromosome inactivation, as seen in the coat coloration of calico cats.

Rett Syndrome

An $X$-linked dominant disorder that is lethal to male embryos prior to birth and produces symptoms of variable severity in females depending on the pattern of $X$-inactivation.

Maternal Inheritance

A non-Mendelian pattern of extranuclear inheritance where traits governed by genes in mitochondria or chloroplasts are passed to progeny exclusively from the mother.

Genomic Imprinting

An epigenetic phenomenon in which the expression and phenotypic effect of an allele depend strictly on which parent transmitted the allele to the offspring.

igf2 (Insulin-Like Growth Factor 2)

A mouse gene encoding a growth factor critical for prenatal growth and development in which only the paternally inherited allele is expressed.

Angelman Syndrome

A human neurodevelopmental disorder resulting from a specific partial deletion of chromosome 15 when the affected chromosome is inherited from the mother.

Prader-Willi Syndrome

A human genetic condition resulting from a specific partial deletion of chromosome 15 when the affected chromosome is inherited from the father.

Epigenetic Inheritance

A mitotically and/or meiotically stable alteration in gene function that occurs without any modification to the primary DNA nucleotide sequence.

Alfred Sturtevant

An undergraduate researcher in T.H. Morgan's laboratory who first quantified the relationship between crossover frequency and chromosomal distance to build genetic linkage maps.

Centimorgan (cM)

A standard unit for measuring genetic linkage distance, equivalent to one map unit (m.u.), where $1\,\text{cM}$ corresponds to a $1\%$ recombination frequency.

Recombination Frequency

The proportion of recombinant gametes or offspring produced in a cross, calculated as: $\text{Recombination frequency} = \frac{\text{recombinant progeny}}{\text{total progeny}}$

Three-Point Testcross

A mapping technique that evaluates three linked gene loci simultaneously; analyzing the middle gene enables tracking of double crossovers, which represent the least frequent progeny class.

Pedigree Analysis

A family tree diagram used to track and analyze the inheritance mode—dominant, recessive, or sex-linked—of specific human phenotypes across successive generations.

Hereditary Juvenile Glaucoma

An autosomal dominant disorder causing progressive optic nerve degeneration and blindness, characteristically appearing in every generation of an affected lineage.

Albinism

An autosomal recessive condition resulting from a nonfunctional allele for the enzyme tyrosinase, preventing the synthesis of the pigment melanin.

Hemophilia

An $X$-linked recessive bleeding disorder caused by a deficiency in blood-clotting factor VIII, with an incidence of approximately $\frac{1}{10{,}000}$ in Caucasian males.

Sickle Cell Anemia

An autosomal recessive condition caused by a single amino acid substitution in hemoglobin; heterozygotes show mild symptoms while gaining resistance against the malaria parasite.

Cystic Fibrosis

An autosomal recessive disease with a frequency of $\frac{1}{2500}$ in Caucasians, caused by a defective chloride ion transport mechanism that leads to thick mucus obstructing the lungs, liver, and pancreas.

Tay-Sachs Disease

An autosomal recessive disorder occurring in $\frac{1}{3500}$ Ashkenazi Jewish births, caused by a defective hexosaminidase A enzyme that causes rapid central nervous system deterioration in infancy.

Phenylketonuria (PKU)

An autosomal recessive inborn error of metabolism affecting $\frac{1}{12{,}000}$ births, characterized by deficient phenylalanine hydroxylase that causes infant brain damage unless managed by diet.

Huntington Disease

An autosomal dominant disorder affecting $\frac{1}{24{,}000}$ individuals, caused by the production of an inhibitor of brain cell metabolism that causes progressive neurological deterioration in middle age.

Duchenne Muscular Dystrophy

An $X$-linked recessive condition occurring in $\frac{1}{3700}$ males, caused by degradation of the myelin coating of nerves stimulating muscles, resulting in severe muscle wasting.

Hypercholesterolemia

An autosomal dominant disorder with an incidence of $\frac{1}{500}$, caused by an abnormal form of the cholesterol cell surface receptor, resulting in excessive blood cholesterol and cardiovascular disease.

Aneuploidy

An abnormal chromosomal condition involving the gain or loss of individual chromosomes as a consequence of nondisjunction during meiotic cell division.

Trisomy 21 (Down Syndrome)

An autosomal aneuploid condition involving an extra chromosome 21 (or translocation); it is one of the few human autosomal trisomies permitting survival into adulthood.

Klinefelter Syndrome

A sex-chromosome aneuploidy in human males caused by nondisjunction resulting in an $XXY$ karyotype, characterized by somewhat abnormal physical features and survival to maturity.