Download Chapter 3: Genetics: From Genotype to Phenotype

Structural genes: genes that contain the information
to make a protein.
 Regulatory genes: guide the expression of structural
genes, without coding for a protein themselves.
 Genotype: the genetic makeup of an individual.
Genotype can refer to the entire genetic complement
or more narrowly to the alleles present at a specific
locus on two homologous chromosomes.
 Phenotype: an observable or measurable feature of
an organism. Phenotypes can be anatomical,
biochemical, or behavioral.

ABO blood system type: refers to the genetic system
for one of the proteins found on the surface of red
blood cells. Consists of one gene with three alleles: A,
B, and O.
 Recessive: in a diploid organism, refers to an allele
that must be present in two copies (homozygous) in
order to be expressed.
 Dominant: in a diploid organism, an allele that is
expressed when present on only one of a pair of
homologous chromosomes.
 Co-dominant: in a diploid organism, two different
alleles of a gene that are both expressed in a
heterozygous individual.

Homozygous
Heterozygous
Genotype
Phenotype
AA
Type A
BB
Type B
OO
Type O
AO
Type A
BO
Type B
AB
Type AB
A complex interaction between genes, environments, and phenotypes.


Blending inheritance: discredited 19th
century idea that genetic factors from the
parents averaged-out or blended together
when they were passed on to offspring.
Particulate inheritance: the concept of
heredity based on the transmission of genes
(alleles ) according to Mendelian principles.


Heredity characteristics are controlled by
particulate unit factors that exist in pairs in
individuals.
When an individual has two different unit
factors responsible for a characteristic, only
one is expressed and is said to be dominant
to the other, which is said to be recessive.
During the formation of gametes, the paired unit
factors separate, or segregate, randomly so that each
sex cell receives one or the other with equal
likelihood.  Mendel’s law of segregation: the two
alleles of a gene found on each of a pair of
chromosomes segregate independently of one
another into sex cells.
 During gamete formation, segregating pairs of unit
factors assort independently of each other. 
Mendel’s law of independent assortment: genes
found on different chromosomes are sorted into sex
cells independently of one another.



Point mutation: a change in the base
sequence of a gene that results from the
change on a single base to a different base.
Autosomal recessive disease: a disease
caused by a recessive allele; one copy of the
allele must be inherited from each parent for
the disease to develop.

Sickle cell disease: an
autosomal recessive
disease caused by a
point mutation in an
allele that codes for
one of the polypeptide
chains of the
hemoglobin protein.
Insertion mutation: a change in the base sequence of
a gene that results from the addition of one or more
base pairs in the DNA.
 Deletion mutation: a change in the base sequence of
a gene that results from the loss of one or more base
pairs in the DNA.
 Trinucleotide repeat diseases: a family of autosomal
dominant diseases that is caused by the insertion of
multiple copies of a three-base pair sequence (CAG)
that, which codes for the amino acid glutamine.
Typically, the more copies inserted into the gene, the
more serious the disease.  Ex. Huntington disease


X-linked disorders: genetic conditions that
result from mutations to genes on the X
chromosome. They are almost always
expressed in males, who have only one copy
of the X chromosome; in females, the second
X chromosome containing the normally
functioning allele protects them from
developing X-linked disorders.
Polygenic traits: phenotypic traits that result
from the combined action of more than one
gene, most complex traits are polygenic.
 Heritability: the proportion of total
phenotypic variability observed for a given
trait that can be ascribed to genetic factors.
Variability caused by genetics
---------------------------------------------------------Variability caused by genetics + Variability
caused by the environment
