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Genetics and Heredity
Lab Exercise 40
BI 233
Definitions
 Heredity = the inheritance of traits
 Genetics = the study of mechanisms of heredity.
 Genes: A portion of a DNA strand that functions as a
hereditary unit, is located at a particular site on a specific
chromosome, and codes for a specific protein or polypeptide
Chromosomes
 We inherit 23 DNA
molecules from our
mothers and 23 DNA
molecules from our fathers
for a total of 46.
 22 pairs of these
chromosomes are called
autosomes
 The remaining pair are
called sex
chromosomes.
Gene Expression
 A person has two genes for
every inherited
characteristic.
 If one gene is always
expressed, geneticists call
that gene dominant.
 A gene that is not
expressed when its mate is
different is termed a
recessive gene
Genome
 All of the genes in all of the
chromosomes together are
called the genome
 The study of all the genes
in the human species is
called genomics
Inherited characteristics
 The characteristic actually
expressed in an individual is
called a phenotype.
 The genetic constitution of an
individual, along with
environmental influences is
called the genotype.
 If both genes for a trait are
the same the individual is
homozygous.
 If genes are not the same they
are heterozygous.
Taste differences
 Sodium benzoate test –
The ability to taste
something sweet, salty, or
bitter in the paper is
dominant.
 PTC
(phenylthiocarbamide) test
The ability to sense a bitter
taste is dominant.
 Thiourea test – the
ability to taste something
bitter is dominant
Anatomical characteristics of hand
 Bent little finger – If distal
phalanx of the little finger
bends toward the fourth
finger, you have dominant
trait.
 Middigital hair – hair on
middle phalanges is
dominant.
 Hitchhiker’s thumb- If
you can hyperextend the
distal joint of the thumb
noticeable, you have the
recessive trait.
Facial Features
 Pigmented anterior of the
iris – If you have pigment
on the anterior and
posterior of the iris, your
eyes are green, brown,
black and hazel.
 If you lack pigment on the
anterior aspect of the iris,
yours eyes are blue or grey.
 Pigmentation is dominant
Phenotypes of facial features
 Attached earlobes – Lobe
of the ear is attached rather
than free, you have the
recessive trait.
 Widow’s peak – hairline
straight across forehead is
recessive trait
 Tongue roll – curling
tongue is dominant
 Freckles – if your face is
free of freckles you have the
recessive form of this
characteristic
ABO blood types
 There are two dominant





genes for ABO blood types
Type A (IA):signifies the A
antigen
Type B (IB): signifies the B
antigen.
Type O (i): is recessive to
both Type A and Type B
A person with Type A blood
can have IAIA or IAi
Type B blood can have IBIB or
IB i
Rh Blood Type
 The presence of the Rh
antigen is dominant
Probability
 Is the likelihood of a the
offspring of a particular set
of parents will have a
certain inherited condition.
 Genetic counselors
work with prospective
parents to determine their
possible genotypes for a
variety of traits and then
predict the probability of
their children having those
traits.
Activities
 Follow the instructions in your lab manual to determine your
phenotype for the listed traits.
 After you have determined your phenotype then determine
your possible genotypes.
 Answer the questions in your lab manual using the Punnett
square