Unit 5 Genetics Terry Kotrla, MS, MT(ASCP)BB

Terminology  Genes  Chromosomes  Autosome  Sex chromosome  Locus  Alleles  Homozygous  Heterozygous  Antithetical

Terminology  Polymorphic  Syntenic  Cis and Trans  Linked  Crossing over  Phenotype  Genoytpe  Independent segragation

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

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

Chromosomes

Locus  Location of a gene on a chromosome

Homozygous or Heterozygous  Homozygous – both alleles the same  Heterozygous – alleles are different

Antithetical  Term used to describe allelic antigens and means opposite.  Kp a and Kp b are alleles.  If an individual is heterozygous there will be one copy of each on “opposite” chromosomes.  Kp a is then said to be antithetical to antigen Kp b

Polymorphic  Term used to describe having 2 or more alleles at a given locus.  ABO system is an example  Rh blood group system is highly polymorphic because of the greater number of alleles.

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.

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

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

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.

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.

Genotype versus Phenotype  Example on left unless you knew parents type you would not know children’s genotype.  Example on right knowing children’s phenotype you can determine parents genotype.

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?

Traits  Traits are the observed expressions of genes.

Traits

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

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

Blood Groups GenotypesAO OAO O

Blood Groups GenotypesAO BABBO OAOOO

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

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.

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

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

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% Jk a+ = 77% Jk a- = 23% 23% of the population would be compatible for a patient with Jk a antibodies.

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

Population Genetics  Must be able to perform calculation on next Exam.  The following frequencies are found: Antigen Frequency of individuals negative for antigen c20% (0.20) K91% (0.91) Jk a 23% (0.23) 0.20 s 0.91 x 0.23 = 0.04 x100 = 4 out of 100 units

Exam 2 Online