AP Biology AP Question of the Day Which is true about a testcross? A. It is a mating between 2 hybrid individuals B. It is a mating between a hybrid and homozygous recessive individual C. It is a mating between an individual with an unknown genotype and a homozygous recessive individual D. It is a mating to determine which individual is homozygous recessive

AP Biology Today…  Human chromosomal disorders  Case Study

AP Biology Human Genetics and Disorders

AP Biology Chromosomal Abnormalities  Nondisjunction  chromosomes don’t separate properly during meiosis  Chromosomal Mutations  deletion  duplication  inversion  translocation

AP Biology Changes in chromosome structure  deletion  loss of a chromosomal segment  duplication  repeat a segment  inversion  reverses a segment  translocation  move segment from one chromosome to another error of replication error of crossing over

AP Biology Autosomal Disorders  Dominant  Acondroplasia  Dwarfism  Lethal in homozygous cond.  Acromegaly  Gigantism  Overactive pituitary  Huntington’s  Degeneration of nervous system  Manifests around 40 years of age  Recessive  Albinism  Melanin pathway mutated  photosensitivity  Phenylketoneuria  Cannot break down phenylalanine  Lead to mental retardation  Cystic fibrosis  Cl - channel problem  Mucus buildup  Death around 40

AP Biology Nondisjunction  Problems with meiotic spindle cause errors in daughter cells  homologous chromosomes do not separate properly during Meiosis 1  sister chromatids fail to separate during Meiosis 2  too many or too few chromosomes - aneuploidy 2n n n n-1 n+1

AP Biology Alteration of chromosome number all with incorrect number1/2 with incorrect number error in Meiosis 1 error in Meiosis 2

AP Biology trisomy 2n+1 Nondisjunction  Cause of aneuploidy (wrong chromosome #)  trisomy  cells have 3 copies of a chromosome  monosomy  cells have only 1 copy of a chromosome n+1 n monosomy 2n-1 n-1 n

AP Biology Down syndrome  Trisomy 21  3 copies of chromosome 21  1 in 700 children born in U.S.  Chromosome 21 is the smallest human chromosome  but still severe effects  Frequency of Down syndrome correlates with the age of the mother

AP Biology Down syndrome & age of mother Mother’s age Incidence of Down Syndrome Under 30<1 in in in in in in in in in in in in in 12 Rate of miscarriage due to amniocentesis:  1970s data 0.5%, or 1 in 200 pregnancies  2006 data <0.1%, or 1 in 1600 pregnancies

AP Biology Sex Chromosomes Abnormalities  Human development more tolerant of wrong numbers in sex chromosome  Cause is nondisjunction  But produces a variety of distinct syndromes in humans  XXY = Klinefelter’s syndrome male  XXX = Trisomy X female  XYY = Jacob’s syndrome male  XO = Turner syndrome female

AP Biology Genetic testing  Amniocentesis in 2nd trimester  sample of embryo cells from fluid  stain & photograph chromosomes  Analysis of karyotype

AP Biology Case Study  Put your genetics knowledge into practice!  Work with a partner on the case study.  Due next time.