CHROMOSOME THEORY OF INHERITANCE. Proposed in 1902 by Walter Sutton and Theodor Boveri Noticed that transmission of chromosomes closely parallels Mendelian.
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CHROMOSOME THEORY OF
INHERITANCE
Proposed in 1902 by Walter Sutton and Theodor Boveri
Noticed that transmission of chromosomes closely parallels
Mendelian pattern
Theory states: chromosomes are the carriers of the genes
Theory strongly supported after discovery of sex chromosomes
Female: homogameticMale: heterogametic
Cruzamientos realizados por Morgan
F1: Toda de ojos rojos
Conclusion: Ojo Blanco es recesivo
Generación Parental
Parental femenino Parental masculino
OJOSROJOS
OJOSBLANCOS
Morgan’s eye-color crosses
F1: All red-eyed
Conclusion? White eye is recessive
Resultados de la F2
1/2 Hembras ojo rojo : 1/4 machos ojo rojo : 1/4 machos ojo blanco
Todas las hembras son de ojo rojo
En base a este resultado Morgan propone que el carácter ojo blanco debe estar asociado al cromosoma X
Cruzamientos realizados por Morgan
Generación F1
Fenotipos F1 OjosRojos
OjosRojos
Morgan’s eye-color crosses
What was going on?
All the white-eyed flies were males!
White-eyed flies have lower viability than wild-type
Morgan’s eye-color crosses
So, the ratio was probably really 3 : 1
On the basis of these results from crosses, Morgan proposed that w is on the X
Hypothesized the following model as an explanation:
El macho tiene ojos blancos porque es hemicigoto.
Muestra el fenotipo de un alelo recesivo en simple dosis
Cruzamientos realizados por Morgan
Generación Parental
Genotipo Parentaldiploide
Gametoshaploides
Cruzamientos realizados por Morgan
Gametos masculinos
Gametos femeninos
Generación F1
Genotipos F1
½ w+/w (o X+/Xw) ½ w+/Y (o X+/Y)
Fenotipos F1½ hembras ½ machosTodos de ojos rojos
Morgan’s eye-color crosses
Morgan’s eye-color crosses
Morgan’s eye-color crosses
Morgan’s crosses showed a transmission pattern of:
Male P to Female F1 to Male F2
This pattern is called crisscross inheritance
It is indicative of X-linked recessives
Morgan’s eye-color crossesReciprocal crosses:
Morgan’s eye-color crosses
Morgan’s eye-color crosses
Morgan’s eye-color crosses
Morgan’s eye-color crosses
The difference in the phenotypic ratios in the 2 sets of crosses is because of the sex
linkage
Morgan’s eye-color crosses
When the results of reciprocal crosses are not the same,
Different ratios are seen for the sexes of the offspring
Sex-linkage is strongly suspected
Morgan’s results strongly supported the chromosome theory of inheritance
The transmission pattern of the phenotypes neatly fit the pattern of the X
chromosome
The theory is further supported by the parallel behavior between Mendelian traits and chromosomes in meiosis:
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