Genes come in different versions called ____; for example, there is a ____ that controls the color of petals in many flowering plants. One ____ or allele may result in red flowers. A different allele might produce white flowers. The ____ color of an individual flower is strongly ____ by the alleles that it ____. Alleles are either ____ or ____. ____ alleles have an effect even if the individual only has ____ copy. In humans, for instance, the main gene that causes freckles comes in different ____. If a person ____ one or ____ copies of the dominant freckle-causing allele, that individual ____ have freckles. Dominant alleles are represented with ____ letters. ____ alleles only have an effect if the individual carries ____ copies. In humans, there is a recessive allele that leads to the ____ of freckles. If someone carries two copies of this ____, that individual will ____ develop freckles. Recessive alleles are represented with ____ letters. If an organism carries two ____ alleles of a particular gene, it is said to be ____ for that ____. If an organism carries two different ____ of a particular gene, it is said to be ____ for that gene. Gregor ____ was a nineteenth-century monk who lived in the Czech Republic, then part of Austria. He experimented with ____ in order to explore the laws that determine ____ inheritance. The results of his research were published in 1866. Today, it forms the basis of ____ genetics.Mendel discovered that "hereditary units" determine plant ____. We now know these units are ____. He realized that offspring inherit ____ unit from each parent, and that the units can be ____ or recessive. This information can be used to ____ the outcome of genetic ____ between plant varieties. Today, we use ____ to explain this.

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