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The study of heredity.


Biological inheritance.

Gregor Mendel

"Father of Modern Genetics;" studied garden peas in a monastery garden (1860s).


Homozygous, such as AA or aa.


Heterozygous, such as Aa.


Individual factors that control each trait in living organisms.


Different forms of the same gene (such as a dominant form and a recessive form).


A "stronger" allele that can mask or hide a "weaker" (recessive) allele.


A "weaker" allele that can be masked or hidden by a "stronger" (dominant) allele.

P Generation

The original, parental generation.

F1 Generation

The first generation produced by a cross (the offspring of the P generation).

F2 Generation

The second generation produced by a cross (the offspring of the F1 generation).

Punnett Square

Shows the possible gene combinations among the offspring that result from a cross.


Reproductive cell.


Physical characteristics of an organism. ("What you see.")


Genetic makeup of an organism. ("Alleles they are carrying.")


Organisms that have two identical alleles; also known as purebred.


Organisms that have two different alleles; also known as hybrid.


A genetic cross in which the parents differ in only ONE characteristic; solved using a Punnett square with four boxes.


A genetic cross in which the parents differ in TWO characteristics; solved using a Punnett square with sixteen boxes.


An unknown dominant organism (such as AA or Aa) is crossed with a recessive organism (aa). The offspring are examined to determine if the unknown parent is homozygous dominant or heterozygous.

Incomplete Dominance

Situation in which the dominant allele is unable to completely hide the recessive allele. The heterozygous organism has an intermediate phenotype (such as pink flowers).


Situation in which two alleles are equally dominant and both are expressed (such as Type AB blood).

Multiple Alleles

Situation in which a gene contains three or more alleles (instead of the usual two). For example, the blood type gene has three alleles (A, B, O).

Polygenic Inheritance

Complicated traits with lots of variety are controlled by two or more genes. This is common in humans.

Universal Donor

Special term for Type O- blood which can be given to individuals of any blood type.

Universal Recipient

Special term for Type AB+ blood which can receive blood from individuals of any blood type.

Sex Chromosomes

XY in human males and XX in human females.


All the chromosomes other than the sex chromosomes.

Sex-Linked Gene

Any gene located on a sex chromosome (usually the X chromosome).


Most common form of a trait in nature.


Family tree used to trace the inheritance of a trait through several generations.

Chromosome Theory of Heredity

Each chromosome contains many genes that control inheritance of traits from parents to offspring.

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