Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory III. Allelic, Genic, and Environmental Interactions IV. Sex Determination and Sex Linkage V. Linkage A. Overview Independent Assortment A a b B AB ab Ab aB

V. Linkage Independent Assortment A a b B AB ab Ab aB Linkage A a AB A. Overview A a b B AB ab Ab aB Linkage A a AB ab B b

V. Linkage Linkage A a B b AB ab A. Overview Linkage A a B b AB ab In Prophase I of Meiosis – Crossing-over A a B b AB ab A a b B Ab aB

V. Linkage AABB aabb AB ab X ab AB Overview Complete Linkage Test Cross AABB aabb AB ab X ab AB

V. Linkage Overview Complete Linkage - if genes are immediate neighbors, they are almost never separated by crossing over and are ‘always’ inherited together. The pattern mimics that of a single gene. X AABB aabb AB ab Gametes F1

V. Linkage Overview Complete Linkage - if genes are immediate neighbors, they are almost never separated by crossing over and are ‘always’ inherited together. The pattern mimics that of a single gene. AB ab ab F1 x F1 X ab Gametes ab AB ab

V. Linkage Overview Complete Linkage - if genes are immediate neighbors, they are almost never separated by crossing over and are ‘always’ inherited together. The pattern mimics that of a single gene. X AB ab Gametes AaBb aabb 1:1 ratio A:a 1:1 ratio B:b 1:1 ratio AB:ab NOT 1:1:1:1 F1 x F1 Phenotypes AB ab aB ? Ab ?

C. Incomplete Linkage B a b b a b A a

C. Incomplete Linkage - So, since crossing-over is rare (in a particular region), most of the time it WON’T occur and the homologous chromosomes will be passed to gametes with these genes in their original combination…these gametes are the ‘parental types’ and they should be the most common types of gametes produced. B a b b a b A a a b A B

C. Incomplete Linkage - But during Prophase I, homologous chromosomes can exchange pieces of DNA. B a b b a b A a a b A B - This “Crossing over” creates new combinations of genes… These are the ‘recombinant types’ a B The frequency with which they occur correlates with the distance between the loci!!! A b

C. Incomplete Linkage As the other parent only contributed recessive alleles, the phenotype of the offspring is determined by the gamete received from the heterozygote… B a b b a b A a gamete genotype phenotype ab aabb AaBb AB aaBb aB Aabb Ab a b LOTS of these A B a B FEW of these A b

V. Linkage Overview Complete Linkage Incomplete Linkage 1. Determining if the genes are linked, or are assorting independently:

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross - determine expectations under the hypothesis of independent assortment AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 The frequency of ‘AB’ should = f(A) x f(B) x N = 55/100 x 51/100 x 100 = 28 The frequency of ‘Ab’ should = f(A) x f(B) x N = 55/100 x 49/100 x 100 = 27 The frequency of ‘aB’ should = f(a) x f(B) x N = 45/100 x 51/100 x 100 = 23 The frequency of ‘ab’ should = f(a) x f(b) x N = 45/100 x 49/100 x 100 = 22

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross - determine expectations under the hypothesis of independent assortment AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Easy with a 2 x 2 contingency table B b Row Total A 43 12 a 8 37 Col. Total

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross - determine expectations under the hypothesis of independent assortment AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Easy with a 2 x 2 contingency table Compute Row, Columns, and Grand Totals B b Row Total A 43 12 55 a 8 37 45 Col. Total 51 49 100

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross - determine expectations under the hypothesis of independent assortment AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Easy with a 2 x 2 contingency table Compute Row, Column, and Grand Totals E = (RT x CT)/GT B Exp. b Row Total A 43 28 12 55 a 8 37 45 Col. Total 51 49 100

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - test cross - determine expectations under the hypothesis of independent assortment AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Easy with a 2 x 2 contingency table Compute Row, Column, and Grand Totals E = (RT x CT)/GT B Exp. b Row Total A 43 28 12 27 55 a 8 23 37 22 45 Col. Total 51 49 100

V. Linkage B Exp. b Row Total A 43 28 12 27 55 a 8 23 37 22 45 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: - Chi-Square Test of Independence B Exp. b Row Total A 43 28 12 27 55 a 8 23 37 22 45 Col. Total 51 49 100 Phenotype Obs Exp (o-e) (o-e)2/e AB 43 28 15 8.04 Ab 12 27 -15 8.33 aB 8 23 9.78 ab 37 22 10.23 X2 = 36.38

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: 2. Detemining the arrangement of alleles in the F1 individual; which alleles are paired on each homolog? AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 A B a b Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: 2. Detemining the arrangement of alleles in the F1 individual; which alleles are paired on each homolog? - most abundant types are ‘parental types’ AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 A B a b

V. Linkage A B a b Overview Complete Linkage Incomplete Linkage 1. Determining if the genes are linked, or are assorting independently: 2. Detemining the arrangement of alleles in the F1 individual; which alleles are paired on each homolog? - most abundant types are ‘parental types’ - least abundant are products of crossing-over: ‘recombinant types’ A B a b

V. Linkage AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 A B a b Overview Complete Linkage Incomplete Linkage  1. Determining if the genes are linked, or are assorting independently: 2. Detemining the arrangement of alleles in the F1 individual; which alleles are paired on each homolog? 3. Determining the distance between loci: Add the recombinant types and divide by total offspring; this is the percentage of recombinant types. Multiply by 100 (to clear the decimal) and this is the index of distance, in ‘map units’ or centiMorgans. 20/100 = 0.20 x100 = 20.0 centiMorgans AaBb x aabb Offspring Number AB 43 Ab 12 aB 8 ab 37 A B a b 20 map units

V. Linkage Overview Complete Linkage Incomplete Linkage Summary - by studying the combined patterns of heredity among linked genes, linkage maps can be created that show the relative positions of genes on chromosomes.