Chapter 14: Mendel and the gene Idea

a heritable feature that varies among individuals such as flower color

variant for a character

Referring to organisms that produce offspring of the same variety over many generations of self-pollination.

the mating of 2 true-breeding varieties

the true-breeding parent

hybrid offspring of P generation

Determined by Mendel.First Law of Inheritance.States that the two alleles for a heritable character separate during gamete formation and end up in different gametes.


1. Alternative Versions of Genes Account for Variations in inherited characters.

2. For each character, an organism inherits two alleles, one from each parent. 

3. If the two alleles at a locus differ, then one, the dominate allele determines the organism's appearance. The other, the recessive allele has not noticeable effect on the organism's appearance. 

4. Two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes.

alternative versions of a gene

determines the organism's appearance

no noticiable effect on the organism's appearance

A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.

a pair of identical alleles.

an organism that has a pair of identical alleles for a character. Homozygous plants "breed true" because of all of their gametes contain the same allele.

two different alleles.

an organism that has two different alleles for a gene. Not true-breeding because they produce gametes with different alleles.

the way we refer to an organism's appearance or observable traits. Refers to physiological traits as well as traits that relate directly to appearance.

The genetic makeup, or set of alleles, of an organism.

Breeding an organism of unknown genotype with a recessive homozygote. It can reveal the genotype of that organism

when offspring are heterozygous for one character.

A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.

A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).

• * Chromosomes align independently
•    . During Mitosis I
•    . Not all mom on one side
•    . Not all dad on other
•    . Independent of other pairs

The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

• * Most genes exist in population in more that two allelic forms.
• * For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme(I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i.
•  * The enzyme encoded by the IA allele adds the A carbohydrates, whereas the enzyme encoded by IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither.

most genes have multiple phenotypic effects.

a gene at one locus alters the phenotypic expression of a gene at a second locus