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3 The Ancient World

Elof Axel Carlson Indiana University Press ePub

Cellular life, sex determination, reproduction, and the processes associated with gestation are largely unseen and unknowable without the tools of science. A major reason for this is the scale at which life takes place. Most of the fundamental processes occur at the level of cells, chromosomes, genes, and molecules, none of which are visible to the unaided eye. Even the concepts of cells, chromosomes, genes, and molecules were not known to the ancient world except in the vaguest theoretical or speculative ways (e.g., atoms as ultimate units that are indivisible, or atoms as vortices of energy or motion). In Greek philosophic writings, Democritus of Abdera (460–370 BCE) believed females arose from the left testis and males from the right testis. Pythagoras (580–500 BCE) believed the male semen gave rise to the “noble parts” of the body and the female semen gave rise to the “gross parts.” Hippocrates (460–377 BCE) referred to the “liquor” or “sperma” produced by a copulating couple, and he believed strong sperma from either sex would produce males, while weak sperma from either sex would produce females. The “liquors” were believed to represent the entire body of the individual at the time of copulation, a view not too far from Charles Darwin’s (1809–1882) idea of pangenesis in 1868.1

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2: Breeding Sweetpotato for Yield and Beta-carotene Content in Burkina Faso

Low, J. CABI PDF

2 

Breeding Sweetpotato for Yield and

Beta-carotene Content in Burkina Faso

K. Somé,1,2* T.J. Ouedraogo,1 J. Belem,1 K.I. Asante,2

G. Vernon2,3 and Y.E. Danquah2

1

Institut de l’Environnement et de Recherches Agricoles (INERA), Ouagadougou,

Burkina Faso; 2West Africa Centre for Crop Improvement (WACCI), University of

Ghana, Accra, Ghana; 3Cornell University, New York, USA

Abstract

The potential of sweetpotato to address food security, malnutrition and poverty is acknowledged in sub-Saharan Africa. The present study was undertaken to develop varieties combining yield and quality in order to address food security and malnutrition in Burkina Faso. Eight parents (five farmers’ preferred varieties with various flesh colours and three introduced orange-fleshed sweetpotato varieties) were selected to develop populations and, subsequently, to estimate heritability and genetic gain from breeding. One hundred and thirty F1 hybrids and their eight parental clones were evaluated in three locations in an Alpha Lattice design to identify high yielding and beta-carotene rich clones with specific to wide adaptation to the local environments. Parent–offspring regression analyses and estimated genetic gain suggested that rapid progress could be attained in increasing dry matter content which was highly heritable (0.76 ± 0.03) and exhibited high genetic gain (22.60%). The same was true for beta-carotene content which was also highly heritable (0.90 ± 0.04). Low heritability (0.21 ± 0.16) associated with low genetic gain indicated that increased storage root yield improvement would be slow.

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13 Biotic Stress Signalling: Ca2+-mediated Pathogen Defence Programmes

Shabala, S. CABI PDF

13 

Biotic Stress Signalling:

Ca2+-mediated Pathogen Defence

Programmes

Yi Ma and Gerald A. Berkowitz*

Department of Plant Science and Landscape Architecture,

University of Connecticut, Storrs, Connecticut, USA

Abstract

Plant cells sensing pathogenic microorganisms evoke defence systems that can confer resistance to infection. This immune reaction can include triggering of basal defence responses as well as programmed cell death, or hypersensitive response (HR). In both cases (basal defence and HR), pathogen perception is translated into elevated cytosolic Ca2+ (mediated by plasma membrane and intracellular channels) as an early step in a signalling cascade. Cyclic nucleotide-gated channels contribute to this influx of Ca2+ into the cell. The identification of specific steps in the signalling pathway leading from pathogen perception to generation of defence molecules in the cytosol, transcriptional reprogramming and other aspects of the plant immune response is not completely delineated at present and is an active area of current research. This chapter will present current information about this

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ch-13

Rehana Khan Laxmi Publications PDF

INTERFERENCE

AND

COINCIDENCE IN PRO

AND E UKARYOTES

13

In most higher organisms it has been found that one chiasma formation reduces the probability of mother chiasma formation in an immediately adjacent region of the chromosome, probably because of physical inability of the chromatids to bend back upon themselves within certain minimum distances. The tendency of one cross-over to interfere with the other cross-over is called interference. Thus, the proximity of one cross-over to another decreases the probability of another very close by. The centromere has a similar interference effect; frequency of crossing over is also reduced near the ends of the chromosome arms. The net result of this interference is the observation of fewer double cross-over types than would be expected according to map distances. The strength of interference varies in different segments of the chromosome and is usually expressed in terms of a coefficient of coincidence, or the ratio between the observed and the expected double cross-overs.

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16 The Seven Sexes of Humans

Elof Axel Carlson Indiana University Press ePub

In 1958, when I was a freshly minted PhD from Muller’s laboratory at Indiana University, I took my first academic job at Queen’s University in Kingston, Ontario. There, I was asked to teach a course in human genetics for medical students, which was a challenge because I had never had a human genetics course. As an offshoot from my dissertation study on the structure of the dumpy locus in fruit flies, I had published an article on the parallel of that gene complex to the Rh blood groups. That was my only contact with human genetics. I spent a lot of time in the library at Indiana University, and at Queen’s University when I arrived there, reading what I could about human genetics, including Curt Stern’s pioneering text in this field.1 I hit the medical books and journals, looking for human parallels to genetic processes in fruit flies and other organisms. When I came to the topic of sex determination, I knew that fruit flies and humans both had XX female and XY male sex chromosomes. I read Jones and Scott’s fine text on hermaphroditic and pseudohermaphroditic disorders, and dipped into some human embryology texts to follow what was then known about sex differentiation in humans, both in normal and in clinically abnormal sexual development.2 I organized the information in my mind and presented it in a series of lectures that I called, at the time, “the seven sexes of man.”

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