Part II

1. Maximal equational or random chromatid segregation increases the probability of homozygotes and decreases the probability of heterozygote gametes. Maximal equational occurs when alpha is a maximum. Random chromosome segregation occurs when bivalents always form or there is no crossover between the centromere and the locus. A locus very close to the centromere will be unlikely to crossover between the centromere and the locus.
   
   
2. Alpha can be equal or greater than zero and equal or less than 1/6. When alpha equals zero, random chromosome segregation ratios occur. When alpha equals 1/6, maximal equational segregation ratios occur. When alpha is between zero and 1/6, then the segregation ratio is random chromatid.
3. Autotetraploid zygote ratios can be determined using a Punnett square whe the gametic ratios have been determined.
   
   
4. Aneuploid pollen produced by a trisomic male is largely inviable. The euploid pollen produced by a trisomic male is viable. This results in abnormal segregation ratios when the trisomic male is crossed to a diploid female. The abnormal ratio will occur for genetic stock that is trisomic for the chromosome which contains the genetic marker.
   
   
5. 'A' chromosomes are the normal chromosomes of maize. 'B' chromosomes are referred to as supernumery and are abnormal. The centromere of B type chromosomes does not always divide during the second mitosis of microsporogenesis. The second mitosis occurs when the haploid generative nucleus divides into two haploid sperm nuclei.
   
   
6. An A-B translocation occurs when a portion of the A chromosome is exchanged with a portion of the B chromosome. The translocated portion of the A chromosome is attached to the abnormal B chromosome centromere. Non-disjunction of the B centromere occurs when the generative nucleus divides to form two sperm nuclei and results in a hyperploid and hypoloid sperm nuclei. The hyperploid sperm nuclei has a duplication and the hypoploid sperm nuclei has a deficiency. When a dominant form of an allele is on the translocated segment of the A chromosome, the deficiency in one sperm nuclei can result in a recessive genotype for the endosperm tissue that was fertilized by the hypoploid sperm nucleus. The homozygous recessive phenotype will be expressed in endosperm tissue fertilized by a hypoploid sperm nucleus when the female parent is homozygous recessive. The genetic stock that is used as the male parent and has the reciprocal A-B translocation for the chromosome which carries the marker locus will result in progeny that have the homozygous recessive phenotype, even though the male parent carries a dominant marker.