Chromosomal Basis of Inheritance – Lecture 15

Vocabulary flashcards summarizing essential terms and definitions from Lecture 15 on the chromosomal basis of inheritance.

Chromosome Theory of Inheritance

Idea that genes are located on chromosomes and that their behavior during meiosis accounts for inheritance patterns.

Cytology

The study of cell structure and function using microscopy; provided early evidence correlating chromosomes with inheritance.

Thomas Hunt Morgan

Geneticist whose work with fruit flies provided the first solid evidence linking a specific gene to a specific chromosome.

Drosophila melanogaster

The fruit fly species extensively used as a model organism in genetics because it breeds quickly and has only four chromosome pairs.

Wild Type

The phenotype most commonly found in natural populations of an organism.

Mutant Phenotype

A trait that differs from the wild type due to a genetic mutation.

Linked Genes

Genes located near each other on the same chromosome that tend to be inherited together.

Genetic Recombination

Production of offspring with trait combinations differing from either parent, often via crossing over.

Parental Type

Offspring phenotype that matches one of the parents.

Recombinant Type (Recombinant)

Offspring displaying a new combination of traits not seen in the parents.

Crossing Over

Exchange of corresponding segments between homologous chromosomes during meiosis, breaking linkage.

Linkage Map

Genetic map of a chromosome based on recombination frequencies.

Map Unit (Centimorgan)

Unit of distance in linkage maps representing a 1 % recombination frequency.

Alfred Sturtevant

Student of Morgan who developed linkage maps using recombination data.

Law of Segregation

Mendelian principle stating that two alleles for a gene separate during gamete formation.

Law of Independent Assortment

Mendelian principle stating that alleles of genes on non-homologous chromosomes assort independently.

Sex-Linked Gene

A gene located on a sex chromosome (X or Y).

X-Linked Gene

Gene located on the X chromosome; many encode traits unrelated to sex.

Y-Linked Gene

Gene located on the Y chromosome; most are involved in male sex determination.

SRY Gene

Sex-determining region of the Y chromosome responsible for initiating testes development.

Hemizygous

Having only one copy of a gene instead of two; describes X-linked genes in males.

X-Inactivation

Random inactivation of one X chromosome in female mammals, forming a Barr body.

Barr Body

Condensed, inactive X chromosome found in female cell nuclei.

Mosaic (Genetics)

Individual with cells expressing different alleles due to X-inactivation.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Aneuploidy

Condition of having an abnormal number of a particular chromosome.

Monosomic

Zygote possessing only one copy of a specific chromosome (2n − 1).

Trisomic

Zygote possessing three copies of a specific chromosome (2n + 1).

Polyploidy

Having more than two complete sets of chromosomes (e.g., triploidy, tetraploidy).

Deletion (Chromosomal)

Loss of a chromosome segment.

Duplication (Chromosomal)

Repetition of a chromosome segment.

Inversion (Chromosomal)

Reversal of a segment within a chromosome.

Translocation (Chromosomal)

Movement of a chromosome segment to a non-homologous chromosome.

Down Syndrome (Trisomy 21)

Aneuploid condition caused by an extra copy of chromosome 21.

Klinefelter Syndrome

Aneuploid condition in males with an extra X chromosome (XXY).

Turner Syndrome

Monosomy X (X0) in females, the only viable human monosomy.

Cri du Chat Syndrome

Disorder caused by deletion on chromosome 5, characterized by intellectual disability and catlike cry.

Philadelphia Chromosome

Reciprocal translocation between chromosomes 9 and 22 associated with chronic myelogenous leukemia.

Genomic Imprinting

Phenomenon in which gene expression depends on whether the allele is inherited from the mother or father.

Methylation (DNA)

Addition of –CH₃ groups to DNA; mechanism involved in genomic imprinting.

Extranuclear Gene

Gene located outside the nucleus, such as in mitochondria or chloroplasts.

Mitochondrial Inheritance

Maternal transmission of genes found in mitochondrial DNA.

Mitochondrial Myopathy

Disease caused by defective mitochondrial genes leading to muscle weakness.

Leber’s Hereditary Optic Neuropathy

Mitochondrial disorder causing sudden blindness due to optic nerve degeneration.

Haplo-Diploid System

Sex–determination system in which females are diploid and males develop from unfertilized haploid eggs.

Testcross

Cross between an individual of unknown genotype and a homozygous recessive to determine linkage or genotype.

Recombination Frequency

Percentage of recombinant offspring; used to estimate distance between genes.