linkage

<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> linkage

Genetic 342 A&B

Kenneth G Wilson

Professory of Botany

Mendel's Second Law is Blemished

The chromosome theory of inheritance is born in two decades following the discovery of Mendel's work.

Bateson and Punnett encounter a strange dihybrid ratio in using purple vs white flower color and round vs long pollen grains in Sweet Pea (Lathrus).

P1 - Purple Long x Red Round

F1- all Purple Long

F2 progeny			Number of Progeny
Phenotype	Genotype	Expected Ratio	Observed	Expect
Purple, Long	P_,L_	9/16	284	215
Purple, Round	P_,ll	3/16	21	71
Red, Long	pp,L_	3/16	21	71
Red, Round	pp,ll	1/16	55	24
			381	381

Why are there any recombinants (purple-round and red-long)?

Thomas Hunt Morgan investigates Fruit Flies ! Wins Nobel Prize in 1933

In Drosophila the following wild type alleles are used for analysis cv (cross-veinless) and ct (cut or snipped wing edges). Flies doubly recessive and homozygous (cvcv,ctct) are crossed with flies homozygous (cv+cv+, ct+ct+). Female progeny that are cvcv+, ctct+ are then test crossed with the doubley recessive males ( cvcv, ctct)

Phenotype	Genotype
wild type	cv+ct+	674
crossveinless, cut	cv ct	681
crossveinless	cv ct+	50
cut	cv+ct	43
Total		1448

Description	Geneotype	Observed	expected independant assortment	Expected complete linkage	Actual percentage
Parental	cv+ct+	674	25%	50%	46.55%
Parental	cv ct	681	25%	50%	47.03%
Recombinant	cv ct+	50	25%	0	3.45%
Recombinant	cv+ct	43	25%	0	2.97%
% recombination = map distance	centimorgans		50 cm	0 cm	6.42 cm

If male progeny that are cvcv+, ctct+ are then test crossed with the doubley recessive females ( cvcv, ctct)

Phenotype	Genotype	results
wild type	cv+ct+	715
crossveinless, cut	cv ct	733
crossveinless	cv ct+	0
cut	cv+ct	0
		1448

How can you interpret these results?

This is our friend Oliver the parrotlet,

Oliver is a true parrot,

the smallest in the world.