46.5). Ans: There was peculiarity result of F, of cross of TI-1 Morgan on drosophila.All the w bite-eyed fl ies were only males. 2012). 46.8) is a definite proof of Autosome carrying factors of sex determination. 1983. As females are heterogametic it is designated as ZW. male moths (see figure 12.2 and Table 12.1), there can be little doubt that male courtship pheromones have arisen through sexual selection (Birch et al. Males are homogametic (ZZ), undergoing typical interchromosomal exchange accompanied by chiasmata. So it seems that the unguarded X hypothesis contains some truth. The female produces only one type of gametes while male produces two types of gametes ‘X’ and ‘Y’. X-A ratio for sex determination in Drosophila: Bridges experimentally produced various combinations of X chromosomes and autosomes (A) in Drosophila and deduced from comparisons that one ‘X’ chromosome and two sets of autosomes (A) produce a normal male. Allen (1919) found that the sporophyte of Spaerocarpos contains two sex chromosomes (XY) and it produces two kinds of meiospores (X and Y type) ‘X’ meiospores germinate into female gametophyte and ‘Y’ meiospores germinate into male gametophyte. In some insects like grasshopper, bugs, etc., females are homogametic XX type but the male has only one sex chromosome, i.e., ‘X’ only, there is no ‘Y’ chromosome; hence the chromosome number of the male and female will be different. In both Drosophila and man, normal females have XX chromosomes and male has XY chromosomes. Female determining genes are carried on ‘X’ and male determiner genes were located on the three autosomes of Drosophila. 2009; Walters and Hardcastle 2011; Meisel et al. If the female gamete is fertilized by ‘X’ sperm the embryo will be carrying female sex while if it is fertilized by ‘Y’ sperm the embryo will be male (Fig. B. mori females are heterogametic (WZ) and undergo no genetic recombination; their chromosomes form specialized elimination chromatin which ensures regular disjunction of homologs in meiosis. By contrast, some organisms (birds and some reptiles, butterflies and moths) the male … Heterogametic males produce 2 types of gametes, while homogametic females form only one type and, hence, homogametic. In this plant, which is Dioecious ‘XY’ individuals are staminate and ‘XX’ plants are pistillate. 46.4). In birds, moths, and some fish, the females are heterogametic while males are homogametic. The body surface is covered with scales. The presence of triploid intersexes in the experiment conducted by Bridges (Fig. [2], Heterogamesis can lead to reduced or absent meiotic recombination between the sex chromosomes, and in some species this extends to the autosomes, a phenomenon called achiasmy. In man, other mammals, plants and many insects like Drosophila, etc., the female has homogametic XX type while male has X and Y chromosomes. The sex of the embryo depends on the type of sperm or male gamete (X or Y type). 46.2). TOS 7. Brief notes on Heterogametic males and Heterogametic Females – Cell Biology! The males are heterogametic with half the male gametes (gynosperms) carrying X-chromo- some (A+X) while the other half (androsperms) being devoid of it (A + 0). [1], However, in birds, and some reptiles, males have two Z sex chromosomes and so are the homogametic sex, while females, with one Z and one W chromosome, are the heterogametic sex. This is referred as ZZ-ZW type instead of XX-XY system. A mosaic body pattern is established one nucleus in the two nuclei stage would be XX (female) and the other would be XO (male). ‘Y’ chromosome is must for maleness, e.g., XXXXY. What were the hypothesis of T.H. Immediately after emerging from the pupa the moths mate, lay eggs and die. The sex is determined on the basis of egg type being fertilized by the sperm if it contains Z the embryo will be male if not the embryo will be female. In birds, butterflies, and moths, it is the male of the species that has the homogametic sex chromosomes (denoted by ZZ) while the female has the heterogametic chromosomes (ZW). In birds, butterflies and moths, it is the male of the species that has the homogametic sex chromosomes (denoted by ZZ) while the female has the heterogametic chromosomes (ZW). Because of 2 types of gametes produced by males it is called heterogametic sex (male). 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