BIO 325 Lecture 4: Tetrad
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Tetrad
• All 4 haploid products of meiosis are contained in ascus
• Ascospores within ascus germinate into haploid individuals
• Ascus = tetrad
• Saccharaomyces Cerevisiae Life Cycle
o Single cell eukaryote
o Monoploid or diploid
o Two mating types: aa
o Diploid may sporulate, undergo meiosis
o Can observe phenotypes in haploids
• Tetrads – can be characterized by the number of parental and recombinant spores they
contain
• Tetratype – mixture of parental and nonparental
Lecture 6
• Parental Ditype (PD) – AB, ab (homozygous, dominant or recessive only)
• Nonparental Ditype (NPD) – Ab, aB (heterozygous, dominant and recessive)
• Tetratype (T) – Ab, aB, AB (mixture of homozygous and heterozygous)
• RF = ½(T)+NPD
o PD = NPD two genes are independent, not linked
o PD > NPD two genes are linked
o PD = no cross over
o T = single cross over
o PD, T, NPD = double cross over
Recombination Frequency
• Recombination frequency works when 2 genes are closely linked, PD > NPD
• Gametes = haploid result from recombination
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