Download Genetics Notes - davis.k12.ut.us

Objective 1. Students will define the following terms: recessive, dominant, genetics, gene,
allele, genotype, phenotype, heredity, heterozygous, homozygous.
2. Students will state the Laws of Inheritance.
3. Students will explain punnett squares, monohybrid cross, di-hybrid cross,
incomplete dominance and co-dominance.
4. Students will explain how punnett squares and pedigrees are used by geneticists.
II. Genetics
a. Genetics is the study of heredity or how traits are passed from parent to offspring. A trait is a
genetically determined characteristic and may be passed as a dominant (an allele which is
expressed) trait or a recessive (an allele which is present but not expressed) trait. Alleles may
be homozygous (both alleles for a trait are the same) or heterozygous (the alleles for a trait are
different). An allele, (an alternative form of a gene), may occur due to mutations which create
genetic variation. A gene is a distinct sequence of nucleotides forming a part of a chromosome.
A genotype is the combination of genes present in an organism, whereas the phenotype is the
physical characteristics that appear within/on an organism.
b. Hereditary factors do not combine, but are passed intact is known as the Law of Segregation.
Each member of the parental generation transmits only half of its hereditary factors to each
offspring with certain factors "dominant" over others is the Law of Dominance. Different
offspring of the same parents receive different sets of hereditary factors is the Law of
Independent Assortment.
c. Punnett squares and Pedigree charts are used by geneticists for genetic counseling with
couples that may have a possibility for a genetic disorder that may be passed to their offspring.
A punnett square is a grid diagram/table that shows the possible outcomes of a genetic cross.
Punnett squares can be used to illustrate monohybrid (shows only 1 trait) cross, di-hybrid cross
(show 2 independent traits), incomplete dominance (when traits are not completely dominant
and result in an intermediate phenotype of the trait), and co-dominance (when dominance does
not occur and two traits are both expressed).