Ch 15 Chromosomal Basis of Inheritance

Chromosomal Theory of Inheritance

Mendelian genes have specific loci on chromosomes that segregate during meiosis.

Law of Segregation

The two alleles for each gene separate during gamete formation.

Law of Independent Assortment

Alleles of genes on non-homologous chromosomes assort independently during gamete formation.

Thomas Hunt Morgan

Used Drosophila melanogaster to provide solid evidence for the chromosome theory.

Wild type

The phenotype most commonly observed in natural populations.

X-Y system

Sex determination system found in humans and other mammals.

Hemizygous

Having only one copy of a gene, as with X-linked genes in males.

X Inactivation

Process in female mammals where one X chromosome condenses into a Barr body.

Barr body

The inactive, condensed X chromosome in female mammalian cells.

Linked genes

Genes located close together on the same chromosome that tend to be inherited together.

Recombination frequency

Increases with the distance between genes on a chromosome.

Karyotype

An ordered display of an individual's chromosomes arranged in pairs.

Nondisjunction

Failure of homologous chromosomes to separate properly during meiosis.

Aneuploidy

A condition of having an abnormal chromosome number, such as monosomy or trisomy.

Polyploidy

Having more than two complete sets of chromosomes.

Structural chromosomal alterations

Deletion, duplication, inversion, and translocation.

Down Syndrome

A human disorder caused by Trisomy 21.

Turner Syndrome

A human condition resulting from XO aneuploidy, the only viable monosomy.

Genomic imprinting

Phenotypic variation dependent on whether an allele is inherited from mother or father.

Organelle genes inheritance

Mitochondrial and chloroplast DNA are passed on exclusively from the mother.