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  X R, X r, Y  X R X R, X R X r, X R Y = dominant phenotype  X r X r, X r Y = recessive phenotype

XX B XY XX B XY X B Y XXXX X B = Bald, recessive traitX, Y = Non-bald, dominant trait XBXBXBXB XBYXBY XX B XY X B Y XBXXBX XX B XBYXBY XXXY XBXXBX X B X B = bald woman XX B = carrier woman XX = normal woman X B Y = 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 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