ENDURING UNDERSTANDING 3.A: Heritable information provides continuity of life.
Essential Knowledge 3.A.3: The chromosomal basis of inheritance provides an understanding of the pattern of
passage (transmission) of genes from parent to offspring.
ENDURING UNDERSTANDING 3.C: The processing of genetic information is imperfect and is a source of genetic
variation.
Essential Knowledge 3.C.1: Changes in genotype can result in changes in phenotype
OUTLINE
A.
B.
C.
D.
E.
Mutation- beneficial, harmful, neutral
Mutations are the primary source of genetic variation
Environmental causes of mutations- x-rays, UV rays, chemicals
DNA has repair mechanisms to minimize mutations
Mutated genes and their products
a. Base-pair substitution
b. Base-pair insertion or deletion, causing frameshiftF. Changes in chromosomes structure
a. Main categories of structural change
i. Duplication occurs when DNA sequences are repeated 2 or more times; unequal crossovers at
prophase I can cause duplications resulting in neural problems and physical abnormalities
ii. A deletion is the loss of a portion of a chromosome by unequal crossovers, inversions, or
chemical attack, usually causing serious disorders or death in mammals
iii. An inversion alters the position and sequence of the genes so that gene order is reversed
iv. A translocation occurs when a part of one chromosome becomes attached to another
chromosome
G. Human genetic disorders due to inheritance of a single chromosome or a specific chromosome change
Possible examples include:
a. Albinism
b. Sickle Cell
c. Tay-Sachs disease
d. Huntington’s disease
e. Trisomy 21
H. Changes in chromosome number
a. Aneuploidy- a condition in which the gametes or cells of an affected individual end up with one extra or
one less chromosome than is normal
b. Nondisjunction
i. If a gamete with an extra chromosome (n+1) joins a normal gamete at fertilization, the diploid
cell will be 2n+1; this condition is called TRISOMY
ii. If an abnormal gamete is missing a chromosome, the zygote will be 2n-1; this is MONOSOMY
c. Polyploidy- is the presence of three or more of each type of chromosome in gametes or cells. It is
common in plants but fatal in humans
d. Autosomal Change and Down Syndrome
i. Trisomy 21; most frequent type of altered chromosome number in humans
I. Change in the Sex Chromosome Number
a. Female Sex Chromosome Abnormalities
i. Turner Syndrome-XO (missing the second sex chromosome)
ii. XXX condition
b. Male Sex Chromosome Abnormalities
i. XXY- Klinefelter Syndrome
ii. XYY
J. Changes in genotype may affect phenotypes that are subject to natural selection
Possible examples include:
a. Sickle cell and the advantage of being a heterozygote (no malaria/no sickle cell- increases survival rate)
b. Streptococcus bacteria that has become resistant to penicillin
K. Human Chromosomes
a. Humans are difficult to study genetically
b. Pedigrees are used to determine the pattern of inheritance for traits in human families.
i. Autosomal-dominant traits typically appear in every generation of a family
ii. Autosomal-recessive traits typically skip generations; unaffected parents may have affected
parents
iii. X-linked recessive traits are caused by genes located on the X chromosome; these traits are
typically more common in males than females
iv. X-linked dominant traits are also caused by genes located on the X-chromosome; these traits are
typically more common in females than males
L. Examples of Autosomal Inheritance Patterns
a. Autosomal Dominant Inheritance
b. Autosomal Recessive Inheritance
M. Genetic Screening
a. Genetic screening is early detection of genetic disorders; newborns are routinely screened for many
genetic disorders
b. Many disorders, if detected early, can be controlled by diet, surgery, drugs, and hormone replacement
therapy
c. Newborn screening
d. Pre-Pregnancy Screening
e. Prenatal Screening
f. Pre-implantation Diagnosis