Bio 161 Chapter 15 Chromosomal Basis of Inheritance

Chromosome theory of inheritance

• Genes have specific loci (positions) on chromosomes

• Chromosomes undergo segregation and independent assortment

Wild type phenotype

A trait that is most commonly found in natural populations

Mutant phenotypes (alternative traits)

Traits that are a result of alleles that are assumed to arise through mutation

w or w+

Popular notation for alleles

Sex-linked chromosomes

Genes that are located on sex chromosomes (X or Y)

Hemizygous

Men’s X-Linked genes (because they only carry one X)

Genetic recombination

The production of offspring with combinations of traits differing from either parent

Unlinked genes

• On different chromosomes

• 2 genes assort into gametes independently of each other

• Expected phenotype ratios 9:3 3:1

Linked genes

• On the same chromosomes

• Do not assort into gametes independently of each other

• Unexpected phenotypic ratios

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies OR are deficient in number; results from the fertilization of gametes in which nondisjunction occurs

Monosomic

Refers to a diploid cell that has only one copy of a particular chromosome instead of the normal two

Trisomic

Refers to a diploid cell that has three copies of a particular chromosome instead of the normal two

Polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets; result from an accident of cell division

Diandry

The extra haploid set is from the father

Digyny

The extra haploid set is from the mother

Deletion

• Occurs when a chromosomal fragment is lost

• The chromosome is then missing certain genes\

Duplication

• The deletes fragment becomes attached as an extra segment to a sister chromatid

• It can also attach to a nonsister chromatid of a homologous chromosome

Inversion

The chromosomal fragment from a deletion event can reattach to the original chromosome, but in reverse orientation

Translocation

The chromosomal fragment from a deletion event can join a nonhomologous chromosome