How Characteristics Are Inherited
Have you ever walked through a flower garden and noticed the many
different sizes, shapes, colors, and textures of flowers? These flowers contain the
parts necessary for reproduction among their species. Flowers trade sweet nectar
and protein-rich pollen in return for pollination service provided by insects and
other creatures. For many plants, the production of seeds, which are their
offspring, depends on the transfer of pollen from one flower to another flower of
the same kind. One pollinator, the honey bee, has many little hairs on its body
which collects pollen as the bee visits flowers. Some of this pollen brushes off as
the bee visits other flowers. This process of pollination enables one parent plant to
transfer information about its traits to the other parent plant, and thus to their
offspring.
Gregor Mendel, a monk and a scientist, also known as the “father of
genetics” spent much of his time working with plants in a garden. He observed
that some pea plants were tall while others were short. He also observed that some
plants produced green peas and others produced yellow peas. He knew traits were
inherited, but he didn’t understand how.
In 1857 Mendel began experimenting by crossbreeding different pea plants.
He kept detailed records of his results, which were published in 1865.
Mendel first bred a tall pea plant with a short pea plant. All the offspring,
the first generation, were tall plants. He then bred two of these tall plants. In the
second generation, three-fourths of the offspring were tall and one-fourth were
short.
Mendel hypothesized that every trait is controlled by a pair of factors. For
each trait, an offspring inherits one factor from each parent. The way the factors
combine determines which trait appears in the offspring.
In peas, tallness is a strong trait, or dominant trait. Shortness is a weak
trait, or recessive trait. Factors for both dominant and recessive traits may
occur in an organism’s chromosomes. However, recessive traits can be seen only
if both parents pass the factor for it to the offspring. If only one parent pea plant,
for example, passes a factor for shortness, the factor remains hidden. Then none of
the offspring are short.
Punnett Square
Chromosomes are tiny, threadlike structures inside most cells of every
organism, or living thing. Chromosomes carry information about the
organism in units called genes. When living things reproduce, they pass
their genes along to their offspring. Each parent has 23 chromosomes.
Maternal
Grandma
Maternal
Grandpa
Paternal
Grandma
MOM
Paternal
Grandpa
DAD
Offspring
Maternal
Grandma
Maternal
Grandpa
Paternal
Grandma
MOM
Paternal
Grandpa
DAD
Offspring