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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

ON THE MECHANISM OF TOXICITY OF LEAD IN THE MALE REPRODUCTIVE SYSTEM

BATARSEH, LAYLA ISSA. January 1986 (has links)
Thesis (Ph. D.)--University OF MICHIGAN.
42

ON THE MECHANISM OF TOXICITY OF LEAD IN THE MALE REPRODUCTIVE SYSTEM

BATARSEH, LAYLA ISSA. January 1986 (has links)
Thesis (Ph. D.)--University OF MICHIGAN.
43

Estrogen regulation of testicular function in the adult ram

Melnyk, Peter M. (Peter Michael) January 1989 (has links)
During the nonbreeding season (July), three groups of five Dorset x Leicester x Suffolk rams were assessed over a period of 5 days. One group of rams (control) was implanted (sc) with five 5cm empty Silastic capsules (i.d. 3.4mm, o.d. 4.6mm); two other groups, designated as Low-E$ sb2$ and High-E$ sb2$, received five estradiol filled capsules of either 5cm or 10cm, respectively for 4 days. Estradiol treatment elevated serum estradiol concentration about 150% in the Low-E$ sb2$ groups (15.7 $ pm$ 1.3 pg/ml) and 300% in the High-E$ sb2$ groups (26.6 $ pm$ 2.4 pg/ml) compared with controls (6.3 $ pm$ 0.8 pg/ml). In the absence of LH pulsing, mean LH, FSH and testosterone concentrations were all decreased significantly (P $<$.05) with increasing estradiol concentration, while PRL concentration was increased (P $<$.05) by as much as 105%. In the LH-pulsed groups, LH-peak height on day 4 was comparable for all three groups of rams and peak frequency was, as expected, consistently increased to 4 peaks per 6 hours. The increase in mean testosterone concentration (P $<$.05) in all three groups was due to an increase in testosterone baseline concentration and testosterone peak frequency.
44

MATERNAL REPRODUCTIVE INVESTMENT IN THE DESERT ANNUAL LESQUERELLA GORDONII: REGULATION AND PATTERNS.

Delph, Lynda Ferrell. January 1983 (has links)
No description available.
45

Studies of the environmental and endocrine control of reproduction in the four striped field mouse, Rhabdomys pumilio

Jackson, Claire January 2003 (has links)
Previous studies of the control of reproduction in Rhabdomys pumilio have shown that day length alone does not inhibit spermatogenesis, that a reduction in food availability and ambient temperature results in an inhibition of gametogenesis, that females are more susceptible to inhibition than are males, and that mice that are able to maintain a body fat store in the face of an energetic challenge, are less likely to show reproductive inhibition than those that lose their fat store. In the present study, field and laboratory experiments were conducted to examine the effects of winter food supplementation on reproduction and population dynamics, and the effects of exogenous GnRH, leptin and mercaptoacetate (MA) on reproductive activity of Rhabdomys pumilio exposed to an energetic challenge. In the field food supplementation experiments in Thomas Baines Nature Reserve (2000, 2001), there was no winter inhibition of reproduction and provision of supplementary food had little effect. While at Mountain Zebra National Park (2002) winter was harsher, females became reproductively inactive, spermatogenesis continued and the provision of extra food resulted in higher rates of individual growth and larger reproductive organs. Treatment of mice that had been exposed to a prolonged energetic challenge, with exogenous GnRH (1µg/mouse/treatment) resulted in an increase in the masses of the testes and epididymides, and in the activity of the reproductive organs. Treatment with exogenous leptin (40µg/mouse/treatment), concurrently with an energetic challenge, countered the negative effects of the energetic challenge, and treated males had larger reproductive organs. MA (600µmol/kg body mass), given concurrently with an energetic challenge, did not inhibit fat metabolism, although the high-fat diet countered the effects of the energetic challenge. Results suggest that the first response of male Rhabdomys pumilio to an energetic challenge is a reduction in the size of the reproductive organs, without an inhibition of spermatogenesis. It is likely that this effect is mediated via white fat and leptin, and leptin’s influence on the hypothalamic-pituitary-gonad axis. Results of the study support the suggestion that females are more sensitive to reproductive inhibition than males and that reproduction in Rhabdomys pumilio is truly opportunistic.
46

A study of spontaneous rosette formation in the bovine female during the immediate postestral period

Fahmi, Hisham Ahmad January 2011 (has links)
Typescript (photocopy). / Digitized by Kansas Correctional Industries
47

Heterosis and heterosis retention for reproductive and maternal traits in Brahman - British crossbred cows

Key, Kelli Loren 17 February 2005 (has links)
Reproductive, maternal, and weight traits were analyzed for Angus (A), Brahman (B), and Hereford (H) straightbred cows; F1 and F2 BA and BH cows; and 3/8 B 5/8 A first (Bn) and second (Bn2) generation cows in Central Texas. Heterosis was estimated for calf crop born (CCB), calf crop weaned (CCW), and cow weight at palpation (PW) by linear contrasts within cow breed groups. F1 BA cows expressed heterosis (P<0.01) for CCB (0.10) and CCW (0.11), while F2 BA cows expressed negative heterosis (P<0.10) for CCB (-0.06) and CCW (-0.07). F1 BH cows expressed heterosis (P<0.001) for CCB (0.15) and CCW (0.16), and F2 BH cows retained F1 heterosis (P<0.001) for CCB (0.13) and CCW (0.15). Bn2 cows expressed heterosis (P<0.01) for CCB (0.14), but Bn cows did not express heterosis (P>0.10) for CCB or CCW. Only the F1 BA (22.9 kg) and F2 BH (42.1 kg) groups expressed heterosis (P<0.10) for PW. Bn2 cows (-65.7 kg) expressed negative heterosis (P<0.01) for PW. Heterosis for calf survival (CS), birth weight (BW), and weaning weight (WW) was estimated by linear contrasts within calf breed groups for B- and H-influenced calves. F1 BH (0.11) and F2 BH (0.14) calves expressed heterosis (P<0.01) for CS. None of the groups expressed heterosis (P>0.10) for BW, but B-sired F1 BH calves were 5.5 kg heavier (P<0.01) than H-sired F1 calves at birth. F1 BH (22.4 kg) and F2 BH (26.2 kg) calves expressed heterosis (P<0.001) for WW, and H-sired F1 BH calves were 20.7 kg heavier (P<0.10) than B-sired F1 calves at weaning.
48

An analysis of alternative forms of plant reproduction using Gossypium barbadense and Arabidopsis thaliana

Biddle, Kelly Denise 15 May 2009 (has links)
Apomixis holds vast potential for improving agriculture worldwide. It would make plant breeding faster, allow for fixation of hybrid genotypes, and help genetically isolate transgenic crops. However, efforts to introduce apomixis into agriculturally important crops, through either plant breeding or molecular genetics, have failed to produce any new apomictic varieties. This could possibly be remedied if researchers better understood the genetics of apomixis, including the underlying genes, their regulation, and the cellular pathways they control. My work increased our knowledge of these processes by using a mixture of novel methods and underutilized resources. In this study I pursued a two-pronged approach that involved both traditional and reverse molecular genetic techniques. I analyzed the Semigamy mutation from Pima Cotton (Gossypium barbadense), which produces large numbers of haploid and chimeric offspring. Although interesting and potentially useful, little is known about this gene, its expression, regulation, and localization, or the cellular processes in which it is involved. This knowledge advanced our understanding of both this part of apomixis and plant reproduction in general. I was able to determine that the Semigamy mutation is recessive to the wild-type and is incompletely expressed even in the homozygous state. Second, I attempted to recreate the various steps of apomixis in the model species Arabidopsis thaliana using the host of tools made available by its fully sequenced genome. Mutants in various organisms, including microbes, plants, and animals, have phenotypes resembling various components of apomixis, and the sequences of most of the genes involved are available in public databases. I identified homologous Arabidopsis genes by comparing these sequences against the entire Arabidopsis genome. Mutants carrying altered versions of these genes were then studied and characterized using various techniques to see if they had any effect on plant reproduction. This method had not been used to study apomixis before this study and revealed several new reproductive Arabidopsis mutations, specifically those in genes homologous to the S. cerevisiae ste12 and rec8 genes. These results will advance the study of apomixis and potentially enable researchers to one day apply it to agriculturally important crop species.
49

Sexual reproduction of four gorgonian corals in southern Taiwan

Chang, Tsung-chin 22 August 2008 (has links)
The sexual reproduction of four gorgonian corals, Ellisella robusta, Subergorgia suberosa, Subergorgia mollis and Bebryce indica at Wanlitong, a non-upwelling area, and Talauko, an upwelling area, in south Taiwan were compared in order to understand their reproductive strategies. Four species were gonochoric. E. robusta, S. suberosa and S. mollis were broadcasting spawners with annual reproductive cycle. The reproductive mode of B. indica was not certain and it may reproduce several times within one year. The mean diameter of mature oocytes of E. robusta, S. suberosa, S. mollis and B. indica was 360, 322, 461, and 312 £gm, respectively. Their fecundity was 3.2, 1.4, 1.1, and 2.0 oocytes/polyp, respectively. Corals with longer oogenesis duration produce larger mature oocytes. The three broadcasting species spawned in September, October and November after the seasonal disturbances. It may be advantageous for the survival of their offspring. The reproductive traits of E. robusta, S. suberosa, and B. indica were similar between Wanlitong and Talauko populations. It suggests that reproductive traits of theses species may be not influenced by upwelling.
50

Embryo sac development in Cleome spinosa Jacq. ; together with taxonomic considerations.

Francis, Jean Burrows. January 1955 (has links)
This thesis is a morphological study of the megagametophyte of Cleome spinosa Jacq. from the archesporium to the mature embryo sac. The characteristic structures of the ovule of various genera of the tribe Cleomoideae, of which C. spinosa is typical, are compared with those of genera of the tribe Capparidoideae found in the literature. [...]

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