GENETICS
Pedigrees, Mutations and
Karyotypes
Pedigree
Chart that shows how a trait and the
genes that control it are inherited within a
family
Female
Male
Affected Person
Carrier
Marriage
Connects Children &
Parents
Twins
Homozygous Recessive Disorders
Must have two recessive genes to
have the disorder
Examples:
Tay-Sachs: the body can’t break down a
certain lipid so it builds up in the brain; it
is a fatal disorder
Cystic Fibrosis: excess mucus
accumulates in the digestive tract and
lungs
Dominant Allele Disorders
Rare because the offspring usually dies
before sexual maturity is reached
If you have at least one dominant gene,
you have the disorder
Huntington’s disease: disorder in which
the brain deteriorates; doesn’t show
symptoms until an individual is in his late
30’s or early 40’s
Genetic Counseling
If a disorder is present in past family
members, genetic counselors can
give parents the probability of passing
the genetic disorder to their children
Genetic counselors construct
pedigrees and use tests (i.e. alphafetoprotein, PKU) to determine
probabilities
Mutations
Changes in the DNA that can involve one
or more genes; Mutations can be:
Harmful: cause diseases or deformities
Helpful: organism is better able to
survive
Neutral: organism is unaffected
If a mutation occurs in a sperm or egg cell,
that mutation is passed onto offspring
If a mutation occurs in a body cell, that
mutation affects only the organism and is
not passed onto offspring
Gene Mutations
Random changes in the sequence of
nucleotides in DNA
It’s a mistake that’s made during
replication or transcription
There are 4 types:
Base Substitution
Base Deletion
Base Insertion
Jumping Gene
Base Substitution
One base is replaced by another base; this is also
called a point mutation
ACGUCAGUA  Threonine—Serine—Valine
ACGUUAGUA  Threonine—Leucine—Valine
Depending on where the mutation occurs, it may
have no affect on the protein
ACGUCAGUA  Threonine—Serine—Valine
ACGUCGGUA  Threonine—Serine—Valine
Wobble: Base pairing between codon and
anticodon in which there is nonstandard pairing at
the third position of the codon; allows more than
one codon to pair with the same anticodon
Base Deletion
Deletion of a base that disrupts the codons;
also called a frameshift mutation
ACGUCAGUA  Threonine—Serine—Valine
ACGUAGUAC  Threonine--STOP
Base Insertion
Insertion of a base that disrupts the
codons; also called a frameshift mutation
ACGUCAGUAC Threonine—Serine—
Valine
ACGUCGAGUAC  Threonine—Serine–
Serine
Jumping Genes
Occur when large stretches of DNA are
inserted into the gene; this can disrupt the
DNA sequence
ACGTCAGTAC
ACGTCTACTGACGTAAGTAC
Chromosomal Mutations
Involve the entire chromosome
Deletion: a chromosome breaks and a
piece of the chromosome is lost
Chromosomal Mutations (cont.)
Duplication: part of a chromosome
breaks off and is incorporated into its
homologous chromosome; the
homologous chromosome now has an
extra copy of one of its parts
Chromosomal Mutations (cont.)
Translocation:
a part of a
chromosome
breaks off and
attaches to a
different, nonhomologous
chromosome
Chromosomal Mutations (cont.)
Inversion:
a part of a
chromosome
breaks off, turns
around, and
reattaches in the
reverse order
Genome & Karyotype
Genome: base
sequence of all of
the DNA in an
organism
Karyotype:
photograph of all
of an organism’s
chromosomes
Nondisjunction
Failure of the
chromosomes to
separate during cell
division
If it occurs during mitosis,
the individual cell is
affected, but the organism
is not usually harmed
If it occurs during meiosis,
the entire organism is
affected
Monosomy & Trisomy
Monosomy: the zygote has only
one copy of a particular
chromosome
Trisomy: the zygote has three
copies of a particular chromosome
In humans, monosomy and trisomy
are so disruptive in most
chromosomes that it kills the embryo
In some chromosomes, however,
the embryo survives, but it has
developmental difficulties
Diseases Caused by
Nondisjunction
Down’s Syndrome
Caused by trisomy of chromosome 21
Symptoms include mental retardation
and a “moon” face
Trisomy 18
Caused by trisomy of chromosome 18
Symptoms include a webbed neck,
severe mental retardation, and hernia
(inguinal, umbilical, and diaphramatic)
90% mortality by 1 year
Diseases Caused by Nondisjunction
(cont.)
Klinefelter’s Syndrome
Caused by trisomy of the sex chromosomes,
XXY
Symptoms include lack of facial and body hair,
rounded body type, and infertility
Turner’s Syndrome
Caused by monosomy of the sex
chromosomes, XO
Symptoms include no sexual development,
learning disabilities, infertility, heart & kidney
abnormalities
Diseases Caused by Nondisjunction
(cont.)
Trisomy 13
Caused by trisomy of chromosome 13
Symptoms include severe mental
retardation and hernias (inguinal and
umbilical)
72% mortality by 1 year
Polyploidy
Nondisjunction occurs in all chromosome pairs
Almost always lethal in animals
Usually has a positive effect in plants
Constructing a Pedigree
Construct a pedigree using the
following information. Make sure to
shade in the affected individuals and
carriers. Number each generation with
Roman numerals (I, II, III, etc.) and
each individual in a generation with
Arabic numerals (1, 2, 3, etc.) Write
each individual’s genotype under their
symbol.