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Unformatted text preview: 75-1890 Microscopic understanding of mitosis/meiosis If you really understand this figure, you know all the main points!
Starting with two true-breeding pea plants, we follow two genes through the F1 and F2 generations. The two genes specify seed color (allele Y for yellow and allele y for Y green) and seed shape (allele R for round and allele r for wrinkled). These two genes are on different chromosomes. (Peas have seven chromosome pairs, but only two pairs are illustrated here.) Gametes P Generation Yellow-round seeds (YYRR) Y R R y Meiosis Fertilization RY r y r Green-wrinkled seeds (yyrr) Figure 15.2 y r All F1 plants produce yellow-round seeds (YyRr) R Law of Segregation = F1 Generation r Y y R r Y y Meiosis LAW OF SEGREGATION R r Two equally probable arrangements of chromosomes at metaphase I r R LAW OF INDEPENDENT ASSORTMENT 1902 Sutton & Boveri Chromosomal Theory of Inheritance separation of alleles at anaphase I Y y Y y 1 The R and r alleles segregate R at anaphase I, yielding two types of daughter cells for this locus. Y r Anaphase I y r r Metaphase II r R Y 1 Alleles at both loci segregate in anaphase I, yielding four types of daughter cells depending on the chromosome arrangement at metaphase I. Compare the arrangement of y the R and r alleles in the cells on the left and right R Law of Independent Assortment = combinations of alleles for different genes depend on arrangement at metaphase I 2 Each gamete gets one long chromosome with either the R or r allele. Y Gametes R R Y y y y Y R 1 YR 4 r Y Y r 1 yr 4 r Y Y r 1 yr 4 R y R 1 yR 4 2 Each gamete gets a long and a short chromosome in one of four allele combinations. y F2 Generation 3 Fertilization recombines the R and r alleles at random. Fertilization among the F1 plants 3 Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. 9 :3 :3 :1 Chromosome Theory of Inheritance Thomas Hunt Morgan
Provided first evidence that Mendel’s heritable factors were on chromosomes Nobel Prize-winning experiments using Drosophila genetics (1933) Mendelian genes reside at specific locations on chromosomes. Chromosomes undergo segregation and independent assortment....
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This note was uploaded on 04/03/2010 for the course BIOLOGY BILD 1 taught by Professor Traver during the Winter '10 term at UCSD.
- Winter '10