GENETICS AND HEREDITY GENETICS The branch of biology

GENETICS AND HEREDITY

GENETICS The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms.

HEREDITY The passing of traits to offspring.

GREGOR MENDEL (1822 -1884) An Austrian monk. Studied math and science. Often referred to as “The Father of Genetics. ” Curious about the color of the pea plant flower. He began to study and experiment with the pea plants in 1856.

GENES The material that controls which traits are expressed in an organism. Come in pairs. Offspring inherit one copy of each gene from each parent. Think a genetic code…tells the body what trait is to be expressed.

ALLELE One member of a pair or series of different forms of a gene. An individual’s genotype (genetic makeup) is the set of alleles it happens to possess. The genotype can be heterozygous or homozygous. The genotype determines what the phenotype, or outward physical appearance and behavior of an organism is.

HETEROZYGOUS VS. HOMOZYGOUS Heterozygous Homozygous Having one of each type of gene present. In this case, you will have one dominant trait gene and recessive trait gene. Therefore, the phenotype will be dominant. Having two of the same types of genes present. Can either be homozygous recessive or homozygous dominant depending on the type of genes present.

TRAIT A characteristic, or property, of something. May be recessive or dominant.

RECESSIVE TRAIT A trait that is covered over, or dominated, by another form of that trait and seems to disappear. This is represented by a lower case letter.

DOMINANT TRAIT A trait that covers over, or dominates, another form of the trait. This is the trait that always shows up, even when only one of the two alleles is in the dominant form. Heterozygous Shown by a capital letter.

CO-DOMINANCE In co-dominance neither phenotype is dominant over the other. Therefore, heterozygous individuals will display both phenotypes. Example: Blood Type Proteins A and B are codominant so both proteins are expressed.

INCOMPLETE DOMINANCE The heterozygous genotype produces an intermediate phenotype. Example: Carnation colors red and white display incomplete dominance. When a red carnation is crossed with a white carnation the result is a pink carnation.

PUNNETT SQUARE The genetic combinations possible with simple dominance can be expressed by a diagram called a Punnett Square. One parent’s alleles are listed across the top and the other parent’s alleles are listed down the left side. The interior squares represent possible offspring, in the ratio of their statistical probability.

SETTING UP A PUNNETT SQUARE Draw a large square, and then divide it into four equal sections. Place one of the parents genotypes on top, and one along the left. Finally take each letter in each column and combine it with each letter from each row in the corresponding square.