AP Bio - Ch.12: The Chromosomal Basis of Inheritance

chromosome theory of inheritance

Basic principle stating that genes are located at specific locations (loci) and that these locations account for these genes’ inheritance patterns

Sex-linked genes

Genes related to and inherited with the sex gene. Virtually all are located on the X-chromosome, as both male and female possess them and X-chromosomes are larger than Y-chromosomes

Linked Genes

Genes that are “linked” from their high tendency to be inherited together

• within a shorter distance together → has lower tendency to make recombinants

• exception to Mendel’s law of Independent Assortment

Genetic recombination

Production of offspring with combinations of traits that differ from those found in either P generation parent

• from crossing over

• occurs in “linked genes” as well → partial linkage → recombines from genes being far enough

Linkage map

Genetic map based on recombination frequencies

(Max recombination frequency possible: 50% ; this frequency is already achieved by genes on different chromosomes)

Recombinant Frequency

Percent of recombinant offspring

• ( recombinants/total ) * 100

Barr body

What an inactivated X-chromosome is called

(as both female and males only need one X chromosome to function → females inactivate one)

Parental types

Same combination of traits as those in P-generation.

Recombinant types

New combination of traits, created from crossing over in prophase I in Meiosis

Chi-Square

X² = (observed - expected)²/expected

Referring to a given table, where the degrees of freedom = # of phenotypes - 1, if the X² value is less than 0.05 (5%), a genetic exception is present and there is some unknown genetic relationship that leads to the expected ratio not matching the actual ratio.

Aneuploidy

Abnormal chromosome number from nondisjunction

• trisomy — 2n+1 — one extra chromosome

• monosomy — 2n - 1 — missing a chromosome

Polyploidy

Extra sets of chromosomes in somatic cells

Nondisjunction

Error in mitosis or meiosis

Deletion

Alternation of chromosomal structure that leads to a chromosomal fragment being lost

Duplication

Alternation of chromosomal structure via reattachment of a broken fragment to a nonsister fragment

Inversions

Alternation of chromosomal structure via reattachment of a chromosome to the original , in the reverse orientation

Translocation

Alternation of chromosomal structure through a fragment joining a non-homologous chromosome