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Genetics

Genetics. Terry Kotrla, MS, MT(ASCP)BB. Terminology. Genes Chromosomes Locus Alleles Homozygous Heterozygous Syntenic Cis and Trans Linked Crossing over. Gene. Basic unit of inheritance.

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Genetics

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  1. Genetics Terry Kotrla, MS, MT(ASCP)BB

  2. Terminology • Genes • Chromosomes • Locus • Alleles • Homozygous • Heterozygous • Syntenic • Cis and Trans • Linked • Crossing over

  3. Gene • Basic unit of inheritance. • hold the information to build and maintain an organism's cells and pass genetic traits to offspring.

  4. Chromosomes • organized structure of DNA and protein that is found in cells • 46 total • 23 homologous • 22 autosomes • 1 sex chromosome – X or Y • XX female • XY male

  5. Chromosomes

  6. Locus • Location of a gene on a chromosome

  7. Homozygous or Heterozygous • Homozygous – both alleles the same • Heterozygous – alleles are different

  8. Syntenic • two genetic loci have been assigned to the same chromosome but still may be separated by a large enough distance in map units that genetic linkage has not been demonstrated.

  9. Linked or Genetic Linkage • Genetic linkage occurs when particular genetic loci or alleles for genes are inherited jointly. • Genetic loci on the same chromosome are physically close to one another and tend to stay together during meiosis, and are thus genetically linked

  10. Crossing Over • Alleles at loci linked but sited at some distance from each other will often be separated by crossing over. • Crossing over happens at the first meiotic division of gametogenesis. • offspring that have different genetic make up from each other as well as different from either parent

  11. Segregation • Alleles at loci which are carried on different chromosomes or at loci far apart on the same chromosome, and whose entry together into a sex cell is a matter of chance, are said to segregate independently.

  12. Phenotype and Genotype • A phenotype is the assortment of antigens actually detectable on an individual's red cell. • Genotypes cannot be determined with certainty and can only be accomplished through family studies.

  13. Genotype versus Phenotype • In example on left unless you knew parents type you would not know children’s genotype. • In example on right knowing children’s phenotype you can determine parents genotype.

  14. Genotype • The mother in the first generation has the AB genes since her phenotype is AB.   • In the mating for the second generation, the genotype for the father could either be BB or BO since his father's phenotype is unknown.  It would appear the mother is AA since both her parents are A, but..... • Look at their children's blood types.  What is the mother's genotype now since both children are B?

  15. Traits • Traits are the observed expressions of genes.

  16. Dominant and Recessive • Dominant – gene present trait will be expressed • Recessive – trait will not be expressed unless present in a double dose

  17. Traits

  18. Blood Group Antigens • Codominant • If the allele is inherited it will be expressed. • Zygosity does not matter.

  19. Blood Groups

  20. Blood Groups

  21. Parentage Testing • Codominant traits are useful. • Two types of exclusions • Direct • Indirect

  22. Direct Exclusion • Genetic marker present in child absent from mother and alleged father • Child A • Mother O • Father O • The A gene MUST have come from the “real” father as both parents are O.

  23. Indirect Exclusion • Genetic markers are absent from the child that should be transmitted by the alleged father • Child Fy(a+b=) = Fya/Fya • Mother Fy(a+b=) = Fya/Fya • Father Fy(a=b+) = Fyb/Fyb • Child should have inherited Fyb from dad but it is not there. • Indirect because absence could be due to some rare Fy genes that cause suppression of expression. Dad may really be heterozygous Fy/fy and child inherited the fy gene making it appear homozygous.

  24. Parentage Testing • Direct exclusions much better. • DNA testing now the “gold standard”, very cheap and relatively fast.

  25. Population Genetics • Important when attempting to find compatible blood. • Phenotype frequencies performed by testing a population and determining frequency of presence and absence of certain alleles. • Phenotype frequencies should be 100% • Jka+ = 77% • Jka- = 23% • 23% of the population would be compatible for a patient with Jka antibodies.

  26. Population Genetics • Some patients have MULTIPLE antibodies. • Knowing the frequency of each allele allows one to calculate the number of units which would need to be screened to find compatible blood. • Performed by multiplying the percentages of each antigen negative allele.

  27. Population Genetics • The following frequencies are found:

  28. Exam 2 Online

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