HUMAN CHROMOSOMES 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
KARYOTYPING Culture cells,
stimulate mitosis, stop division at metaphase
Hypotonic solution swells cells, separates them & chromosomes
Take picture, cut & paste
AUTOSOMAL INHERITANCE
Autosomal DominantAllele expressed in
heterozygotesAA or Aa show
dominant phenotype
AUTOSOMAL DOMINANT Achondroplasia
Embryonic cartilage in skeleton doesn’t develop properly
“Dwarf”, average 4’ tall
Huntington’s DiseaseNervous system deterioratesSymptoms often not seen until
after 30Die in 40s or 50s
AUTOSOMAL INHERITANCE Autosomal
RecessiveRecessive
phenotype only shown with homozygous recessive
Heterozygous is “carrier”
AUTOSOMAL RECESSIVE 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
SEX DETERMINATION Fetal development
7 weeks, “uncommitted”Y chromosome present male sex organsY chromosome absent female sex organs
SEX DETERMINATION Different species have
different systems X-Y
XX = Female, XY = Male
X-OXX = Female, X = Male
Z-WZW = Female, ZZ =
Male Haplo-Diploid
2n = Female, n = Male
X-LINKED INHERITANCE 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
X-LINKED INHERITANCE
XXB XY
XXB XY
XB YX
X
XB = Bald, recessive trait X, Y = Non-bald, dominant trait
XBXB
XBY
XXB XY
XB YXB
X
XXB XBY
XX XY
X YXB
X
XBXB = bald womanXXB = carrier womanXX = normal womanXBY = bald manXY = normal man
X-LINKED INHERITANCE Baldness Red-Green Color
Blindness Hemophilia A
Lack of certain clotting factors
Blood cannot clot, bleed uncontrollably
CHROMOSOME STRUCTURE Changes in physical structure of
chromosome Cause genetic disorders or
abnormalities Rare
Duplication Deletion Inversion Translocation
DUPLICATION 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
DELETION 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
INVERSION 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
TRANSLOCATION 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
CHROMOSOME NUMBER 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
DOWN SYNDROME Only trisomy that reaches adulthood Extra copy of chromosome 21 Mostly through nondisjunction at
meiosis Abonormal mental, heart, and skeletal
development
SEX CHROMOSOME ABNORMALITIES 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
HUMAN GENETIC DEVELOPMENTS Phenotype treatments
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 diagnosis
Amniocentesis—collect fluid from around fetus
Cells in fluid from fetus, can analyze for disorders