Genetics
The branch of Biology that
studies hereditary information
and how it is passed from
parents to offspring
Heredity
Biological Inheritance
Crossing Over
Occurs during Anaphase of
Meiosis I when genes are
switched on chromosomes.
Results in genetic variation
Gregor Mendel
Father of Genetics
Traits
Characteristics of an organism
Self-Pollination
Cross- Pollination
When the pollen of a plant
fertilizes the egg of the same
plant.
When the pollen of a plant
fertilizes the egg of a different
plant
Gene
A unit of hereditary material
found on chromosomes which
control traits
Law of Segregation
The alleles of a gene occur in
pairs which separate during
Meiosis and recombine upon
fertilization
Alleles
Different forms of the gene for a
trait
Dominant
Determines the trait of an
individual when the dominant
allele is present
Recessive
Determines the trait of an
individual when the dominant
allele is not present
Law of Independent
Assortment
Genes for two traits are
separated and distributed into
cells independently of one
another
Law of Dominance
An organism will only have the
recessive trait when the
dominant allele for a trait is not
present
Homozygous
When an organism has two of
the same alleles for a certain trait
(ex: tt, or TT)
Heterozygous
When an organism has two
different alleles for a certain trait
(ex: Tt)
Genotype
Combinations of gene alleles for
an individual
Phenotype
Physical expression of genes that
determine an individual’s
appearance
Punnett Square
A diagram that is used to predict
the outcome of a cross between
two organisms
Polygenic Inheritance
When more than one gene
affects the phenotype of an
individual
Incomplete Dominance
When the two alleles in a
heterozygous genotype
contribute to a phenotype that is
a blend of both parents
Co-Dominance
When two dominant alleles are
expressed at the same time
Multiple Alleles
When there are more than two
alleles for a trait
Mutation
A sudden change in the structure
or amount of genetic material
Chromosomal Mutation
An abnormal change in the
structure or amount of
chromosomes an individual has
Deletion
When a piece of chromosome is
missing
Addition (Duplication)
When a piece of chromosome is
added to a homologous
chromosome
Translocation
When a piece of chromosome is
added to a nonhomologous
chromosome
Inversion
When the order of genes on a
chromosome is switched
Nondisjunction
When disjunction doesn’t occur
correctly during Meiosis, resulting
in a gamete with too many or too
few chromosomes
Karyotype
A picture which shows all 46
chromosomes of an individual in
a diploid cell
Autosomes
Chromosome pairs #1-22
Sex Chromosomes
Chromosome pair #23 which
determines the sex of an
individual
Sex Linked Disorders
Genetic Disorders on the Sex
Chromosomes (ex: Color
Blindness)
Autosomal Disorders
Genetic Disorders on the
Autosomes (ex: Sickle Cell
Anemia, Huntington’s Disease)
Chromosomal
Disorders
Disorders caused by
nondisjunction
Nondisjunction
The failure of homologous
chromosomes to separate during
Meiosis, resulting in missing or
extra chromosomes in gametes
Trisomy 21
The presence of an extra copy of
chromosome #21 (aka Down’s
Syndrome)
Kleinfelter’s Syndrome
The presence of an extra X
chromosome in males
Turner’s Syndrome
The presence of only one X
chromosome in females
Sex-Linked Trait
A trait that is controlled by a
gene found on the sex
chromosome
Pedigree
A diagram that shows the
presence or absence of a
particular trait in each generation