F1 crosses - First Filial Crosses

The F1 or first filial cross was first described by Mendel (1865).  The F1 cross is generally given very little attention in most genetics textbooks.   These books seldom discuss its analytical power, especially in relationship to sex-linked traits and the different dominance relationships.  All too often the F1 cross is treated as  a "trivial" cross that one does on the way to "more interesting crosses" such as the  F2 (second filial cross)  or the various backcrosses.  (inactive link)

Classic Paper

Mendel's Original Paper (in translation) http://www.esp.org/foundations/genetics/classical/gm-65.pdf


Information Available from the F1 and F1 reciprocal progeny. 

The F1 cross is very important in its own right.  First, heterozygous F1 progeny illustrate Mendel's principle of uniformity. Second, when they make gametes, the heterozygous F1 progeny illustrate Mendel's principle of segregation .  Finally,  by looking at the phenotypes of the F1 and F1 reciprocal progeny you can determine:

(a) whether the traits are dominant, incompletely dominant, overdominant, codominant,  or recessive and 
(b) whether the traits are autosomal or sex-linked

    How to Do an F1 and F1 reciprocal  cross

To do an F1 cross you need two pure-breeding or homozygous lines. Such homozygous lines are also called  parental lines .   Parental Lines differ in a pair of contrasting traits (e.g, red eyes or white eyes in Drosophila, tall or short pea plants).

Females from one of the parental lines (Parental Line 1 or P1)  are mated to males from the other parental line (Parental Line 2 or P2).  The mating  is called the F1 cross and the progeny resulting from this mating are the F1 progeny or F1 generation.   

Alternatively, P2 females can be mated with P1 males.  from Parental Line 1.  This is called the reciprocal F1 cross (or the F1 reciprocal or F1R cross) and the progeny from this mating are the reciprocal F1 progeny or the reciprocal F1 generation.

These crosses are illustrated below


Alternative Wording The F1 cross is called the Parental cross in some introductory genetic text books. The important distinction is to separate the experimental mating (cross) from the resultant progeny or generation.  Whether you use the term F1 cross or the term Parental cross the resulting progeny of that mating are the F1 progeny or the  F1 generation. 

Genetic analyses are done on the phenotypes of the F1 progeny.


F1 crosses

1 F1 cross -definition
2 Information Available from the F1 and F1 reciprocal progeny. 
4 F1  Autosomal Inheritance
4 FX - Linkage
5 FZ-Linkage
6 Summary Dominance Patterns for Autosomal & Sex-Linkage.
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