Download Genetics - Science 7

Chapter 4: Genetics: The Science of Heredity
Section 1: Mendel’s Work
Gregor Mendel’s work was the foundation for understanding
why offspring have traits similar to those of their parents.
Mendel’s Experiments
Mendel used purebred plants, which always produce
characteristics similar to their parents.
Homozygous- same letter designation representing
traits.(TT, tt, DD,dd)
(Filial-son in Latin)
Mendel, an Austrian monk in the 1850’s, worked with pea
plants and identified characteristics. By controlling pollination and
through careful data collecting Mendel is often referred to as the
Father of Genetics.
Dominant and Recessive Alleles
Genes are the factors that control traits. Different forms of a
gene are called alleles.
Individual alleles control the inheritance of traits. Some alleles are
dominant, while other alleles are recessive.
Dominant- a trait that always shows up when the allele is present.
Recessive- is masked, or covered up whenever the dominant allele
is present.
Hybrid- two different alleles resulting in dominant appearance.
Also called heterozygous.(Tt, Dd)
Traits are controlled by alleles of genes. Organisms inherit one
allele from each parent.
Opener:Take a Class Survey Lab Pg.76-77
Section 2: Probability and Genetics
 Probability is the likelihood that a particular event will
occur. (Coin flip)
 Mendel was the first scientist to interpret his data using the
principles of probability.
 Geneticists use Punnett squares to show all the possible outcomes of
a genetic cross. Punnett squares allow a person to determine the
probability of a particular outcome.
Phenotype- physical appearance
Genotype- genetic makeup ( ie: allele assortment)
w w
b b
Codominance- occurs when neither allele is dominant or
recessive. F F (white feathers) F F (black)
Skills Check: Construct a Punnett square for a cross between two heterozugous Erminette chickens
that show all the possible genotypes and phenotypes of the offspring. Calculate the probabilities of
each genotype and phenotype.
b w
Erminette Chicken- F F