Chromosomes and Human Inheritance
 Diploid
= 46, Haploid = 23
 Sex chromosomes different than others

Not homologous pairs
 Female
= two X chromosomes (XX)
 Male = one X & one Y chromosome (XY)
 Autosomes—non-sex chromosomes, same in
both genders
 Culture
cells, stimulate
mitosis, stop division at
metaphase
 Hypotonic solution
swells cells, separates
them & chromosomes
 Take picture, cut &
paste
 Autosomal


Dominant
Allele expressed in
heterozygotes
AA or Aa show
dominant phenotype
 Achondroplasia


Embryonic cartilage in skeleton
doesn’t develop properly
“Dwarf”, average 4’ tall
 Huntington’s



Disease
Nervous system deteriorates
Symptoms often not seen until
after 30
Die in 40s or 50s
 Autosomal


Recessive
Recessive phenotype
only shown with
homozygous
recessive
Heterozygous is
“carrier”
 Albinism

Lack of normal amounts
of melanin (pigment) in
body
 Cystic



fibrosis
Thick mucus in lungs &
digestive tract
Breathing & digestion
difficult
Most common lethal
genetic disorder among
caucasians
Humans



XX = Female
XY = Male
 Fetal



development
7 weeks, “uncommitted”
Y chromosome present  male sex organs
Y chromosome absent  female sex organs
 Different
species have
different systems
 X-Y

XX = Female, XY = Male
 X-O

XX = Female, X = Male
 Z-W

ZW = Female, ZZ = Male
 Haplo-Diploid

2n = Female, n = Male
 Non-sexual
gene “linked” to a sex
chromosome (X)
 NOT present on Y chromosome
 Recessive & dominant alleles
 XR, Xr, Y
 XRXR, XRXr, XRY = dominant phenotype
 XrXr, XrY = recessive phenotype
XB = Bald, recessive trait
XB
X XXB
Y
XY
XXB
XY
X
XB
X
X
Y
XXB XBY
XX
XY
X, Y = Non-bald, dominant trait
XB
X
XB
Y
X BXB XBY
XXB
XY
XBXB = bald woman
XXB = carrier woman
XX = normal woman
XBY = bald man
XY = normal man
 Baldness
 Red-Green
Color
Blindness
 Hemophilia A


Lack of certain
clotting factors
Blood cannot clot,
bleed
uncontrollably
 Changes
in physical structure of chromosome
 Cause genetic disorders or abnormalities
 Rare
 Duplication
 Deletion
 Inversion
 Translocation
DNA sequences are
repeated 2 or more
times
 Unequal crossing-over
 Broken piece of
chromosome attaches
to homologous
chromosome
 Huntington’s Disease

Affects coordination &
movement
 Affects mental abilities,
personality

 DNA
sequence deleted
 Unequal crossing-over
 Chemical damage
 Most cause serious disorders
or death
 Cri du chat syndrome



Severe developmental &
neurological problems
Unusual cry of infant (“cry of
the cat”)
Unusual physical appearance
 DNA
sequence reverses
 No loss of DNA or
chromosome part
 No problem for carrier if
non-crucial gene
 Some may not know until
children have problem
 Chromosome 9


No health problems for
parent
May increase risk of
miscarriage
 Broken
part of one
chromosome attaches
to another
 Usually reciprocal
(both exchange
broken parts)
 Often cause reduced
fertility
 Severe problems rare

Can include several
cancers
 Aneuploidy—one
more one less chromosome
than normal
 Usually fatal for humans

Most miscarriages
 Nondisjunction—one
or more pairs do not
separate during meiosis
 Polyploidy—cells with 3 or more copies of
one or more chromosomes
 Trisomic—cells with 2n+1 of one
chromosome, 2n of all others
 Only
trisomy that reaches adulthood
 Extra copy of chromosome 21
 Mostly through nondisjunction at meiosis
 Abonormal mental, heart, and skeletal
development
 Turner





syndrome
Nondisjunction of sex chromosomes
Only one X, noted as “XO”
98% of embryos miscarry
Adults very short, but well proportioned
Sterile, limited sex hormones
 Klinefelter





syndrome
2/3 Nondisjunction of sex chromosomes
XXY
Mostly normal, some learning disabilities
Lower testosterone, higher estrogen
“Feminized” male characteristics
 Phenotype


Phenylketonuria (PKU)—lack of enzyme, can’t
convert certain amino acid, brain function
problems
Restrict intake, can lead normal life
 Genetic


screening
Detect alleles that can cause disorders
 Prenatal

treatments
diagnosis
Amniocentesis—collect fluid from around fetus
Cells in fluid from fetus, can analyze for
disorders