Living Environment Translated Arabic 2014 | Page 56

3. General Notes:
 Heredity is the passing of traits from parent to offspring.
 Genetics is the study of how traits are inherited through the
interactions of alleles
 Gregor Mendel is known as the “ Father of Genetics”- he worked
with pea plants and showed patterns of inheritance
 Mendel used the word “ trait” to describe characteristics that can be
inherited ( ex: eye color, leaf shape)
 Mendel’s first law is called the Law of Segregation.
o Organisms inherit two copies of each gene , one from each
parent
o Organisms donate only one copy of each gene in their gametes
( sex cells). The two copies of each gene segregate ( separate)
during gamete formation ( meiosis)
 Mendel’s second law is called the Law of Dominance.
o A dominant allele always shows up in the phenotype if it is
present .
o A recessive allele only shows up in the phenotype if there are
no dominant alleles present.
 Mendel’s third law is the Law of Independent Assortment. It says
that during meiosis alleles are randomly separated into the sex cells.
 A gene is a piece of DNA that provides a set of instructions to the cell
to make a certain protein. Each protein is controlled by a different
gene.
 Each gene has a specific location on a given chromosome.
 Each gene is generally made up of two alleles. They may be :
o Homozygous- the same ( 2 dominant alleles{ TT} or two
recessive alleles {tt} )
o Heterozygous – two different alleles ( one dominant allele and
one recessive allele {Tt}