AP Biology March 22, 2012  BellRinger  If two genes are located close together on the same chromosome, how might this affect expected inheritance predictions?  Objective  Calculate recombination frequencies  Differentiate between various chromosomal disorders  Homework  Chp 14 & 15 quiz

AP Biology © 2011 Pearson Education, Inc. Animation: Crossing Over Right-click slide / select”Play”

AP Biology Recombination of Genes:  Mendel observed that combinations of traits in some offspring differ from either parent  Parental types  Offspring with a phenotype matching one of the parental phenotypes are called  Recombinant types/Recombinants  Offspring with nonparental phenotypes (new combinations of traits)  A 50% frequency of recombination is observed for any two genes on different chromosomes © 2011 Pearson Education, Inc.

AP Biology Figure 15.UN02 Gametes from green- wrinkled homozygous recessive parent ( yyrr ) Gametes from yellow-round dihybrid parent ( YyRr ) Recombinant offspring Parental- type offspring YR yr Yr yR yr YyRr yyrr Yyrr yyRr

AP Biology Figure 15.10a Testcross parents Replication of chromosomes Gray body, normal wings (F 1 dihybrid) Black body, vestigial wings (double mutant) Replication of chromosomes Meiosis I Meiosis II Meiosis I and II Recombinant chromosomes Eggs b  vg  b vg b  vg  b  vg b vg  b vg b  vg  b  vg b vg b vg  Sperm b vg

AP Biology Figure 15.10b Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal Sperm Parental-type offspringRecombinant offspring Recombination frequency 391 recombinants 2,300 total offspring  100  17%  b  vg  b vg  b  vg b vg Eggs Recombinant chromosomes b  vg  b vg b  vg b vg 

AP Biology  As genes are located closer to one another, what happens to their recombination frequency? Learning Check

AP Biology  If gene A recombines 12% of the time with gene B, but 16% of the time with gene C, which gene is closer to gene A?  If gene B and C recombine with one another 28% of the time, what is the order of genes A, B, and C along the chromosome? Recombination frequencies BAC

AP Biology  The following is a map of four genes on a chromosome:  Between which two genes would you expect the highest frequency of recombination?  A) A and W  B) W and E  C) E and G  D) A and E  E) A and G  Learning Check

AP Biology Errors of Meiosis Chromosomal Abnormalities

AP Biology Karyotyping Activty  Read through the first page of the Karyotyping activity 1. What is a karyotype? 2. How are they made?

AP Biology Chromosomal abnormalities  Incorrect number of chromosomes  nondisjunction  chromosomes don’t separate properly during meiosis  breakage of chromosomes  deletion  duplication  inversion  translocation

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 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  Baby has wrong chromosome number  trisomy  cells have 3 copies of a chromosome  monosomy  cells have only 1 copy of a chromosome n+1n monosomy 2n-1 n-1n

AP Biology Human chromosome disorders  High frequency in humans  most embryos are spontaneously aborted  alterations are too disastrous  developmental problems result from biochemical imbalance  imbalance in regulatory molecules?  hormones?  transcription factors?  Certain conditions are tolerated  upset the balance less = survivable  but characteristic set of symptoms = syndrome

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

AP Biology Genetic testing  Amniocentesis in 2nd trimester  sample of embryo cells  stain & photograph chromosomes  Analysis of karyotype 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  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  XXY male  one in every 2000 live births  have male sex organs, but are sterile  feminine characteristics  some breast development  lack of facial hair  tall  normal intelligence Klinefelter’s syndrome

AP Biology Klinefelter’s syndrome

AP Biology Jacob’s syndrome male  XYY Males  1 in 1000 live male births  extra Y chromosome  slightly taller than average  more active  normal intelligence, slight learning disabilities  delayed emotional maturity  normal sexual development

AP Biology Trisomy X  XXX  1 in every 2000 live births  produces healthy females  Why?  Barr bodies  all but one X chromosome is inactivated

AP Biology Turner syndrome  Monosomy X or X0  1 in every 5000 births  varied degree of effects  webbed neck  short stature  sterile

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 Don’t hide… Ask Questions!!