how does evolution explain different number of chromosomes
(2008) found a statistically significant difference in the frequency of blood type A between homosexuals and heterosexuals. [111][112], Equal protection analysis in U.S. law determines when government requirements create a “suspect classification" of groups and therefore eligible for heightened scrutiny based on several factors, one of which is immutability. As both blood type and Rh factor are genetically inherited traits controlled by alleles located on chromosome 9 and chromosome 1 respectively, the study indicates a potential link between genes on autosomes and homosexuality. the humans usually has 46 chromosomes. Explain the terms analogous and homologous organs with examples. In 1993, Dean Hamer and colleagues published findings from a linkage analysis of a sample of 76 gay brothers and their families. p. 8. Female relatives of the homosexual men on their mother's side tended to have more offspring than those on the father's side. (1993) and Hu et al. A 2008 study of all adult twins in Sweden (more than 7,600 twins)[22] found that same-sex behaviour was explained by both heritable genetic factors and unique environmental factors (which can include the prenatal environment during gestation, exposure to illness in early life, peer groups not shared with a twin, etc. There have also been reports of variations in brain structure corresponding to sexual orientation. 1. [37] Graves' disease is associated with TSHR abnormalities, with previous research indicating that Graves' disease is more common in gay men than in straight men. [64], A 2010 study by Garcia-Falgueras and Swaab stated that "the fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. The records of the remaining heterosexual subjects contained no information about their sexual orientation; they were assumed to have been primarily or exclusively heterosexual "on the basis of the numerical preponderance of heterosexual men in the population". A review authored by J. Michael Bailey states: "childhood gender nonconformity comprises the following phenomena among boys: cross-dressing, desiring to have long hair, playing with dolls, disliking competitive sports and rough play, preferring girls as playmates, exhibiting elevated separation anxiety, and desiring to be—or believing that one is—a girl. They found that women had significantly higher anti-NLGN4Y levels than men. [citation needed], A number of sections of the brain have been reported to be sexually dimorphic; that is, they vary between men and women. [37] The research supports another study which had been done by the neuroscientist Simon LeVay. [48] Male fetuses produce H-Y antigens which are "almost certainly involved in the sexual differentiation of vertebrates". A review of retrospective studies that measured gender nonconforming traits estimated that 89% of homosexual men exceeded heterosexual males level of gender nonconformity, whereas just 2% of heterosexual men exceeded the homosexual median. The process of becoming a scientific theory. For Example: The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar. These chromosomes help in ⦠There is no indication that social environment after birth has an effect on gender identity or sexual orientation."[65]. 1. Why or why not? Some of these variants had sex-specific effects, and two of these variants suggested links to biological pathways that involve sex hormone regulation and olfaction. In people with no brain injury it's caused by a genetic predisposition - genes not normal chromosomes. 14b. There is no 'cure' for homosexuality because it is not a disease. Explain the terms analogous and homologous organs with examples. [29], In addition to sex chromosomal contribution, a potential autosomal genetic contribution to the development of homosexual orientation has also been suggested. [5][6] In simple terms, the developing fetal brain begins in a "female" typical state. This suggests that the genetic make-up of the tall parent can be depicted as, 3. 1. 2. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. Evolutionary oddities about chromosomes. 2. What am I missing? (2005) performed a full-genome scan (instead of just an X chromosome scan) on individuals and families previously reported on in Hamer et al. The researchers identified four variants more common in people who reported at least one same-sex experience on chromosomes 7, 11, 12, and 15. A chromosome mutation is an unpredictable change that occurs in a chromosome.These changes are most often brought on by problems that occur during meiosis (division process of gametes) or by mutagens (chemicals, radiation, etc. Gene Duplications and Divergence Gene duplications create genetic redudancy and can have various effects, including detrimental mutations or divergent evolution. [4]:76, A number of twin studies have attempted to compare the relative importance of genetics and environment in the determination of sexual orientation. [54] The conclusion is that sexual attraction, whether same-sex or opposite-sex oriented, operates similarly on a biological level. [68] Additional research in Western cultures and non-Western cultures including Latin America, Asia, Polynesia, and the Middle East supports the validity of childhood gender nonconformity as a predictor of adult non-heterosexuality. This is consistent with the common finding that parenting and culture appears to play no role in male sexual orientation, but may play some small role in women. ), although a twin study cannot identify which factor is at play. Bem cited cross-cultural studies which also "appear to contradict the EBE theory assertion", such as the Sambia tribe in Papua New Guinea, which ritually enforced homosexual acts among teenagers; yet once these boys reached adulthood, only a small proportion of men continued to engage in homosexual behaviour - similar to levels observed in the United States. [117] The journalist Chandler Burr has stated that "[s]ome, recalling earlier psychiatric "treatments" for homosexuality, discern in the biological quest the seeds of genocide. Dogs have 78! A variety of other assessments such as childhood home videos, photos and reports of parents also confirm this finding. Why or why not? [43], A study suggests linkage between a mother's genetic make-up and homosexuality of her sons. A child's temperament predisposes the child to prefer certain activities over others. [10], The fraternal birth order effect, however, does not apply to instances where a firstborn is homosexual. It has been hypothesized that gay men may have been exposed to little testosterone in key regions of the brain, or had different levels of receptivity to its masculinizing effects, or experienced fluctuations at critical times. But species have different numbers of chromosomes. Average volumes of the equivalent cell group in sheep (oSDN) for heterosexual and homosexual rams and for ewes. ... Meiosis is important because it ensures that all organisms produced via sexual reproduction contain the correct number of chromosomes. Without the gene, the mice exhibited masculine sexual behavior and attraction toward urine of other female mice. "[119] LeVay has said in response to letters from gays and lesbians making such criticisms that the research "has contributed to the status of gay people in society". They conjure up the specter of the surgical or chemical "rewiring" of gay people, or of abortions of fetal homosexuals who have been hunted down in the womb. The inactivation of the X chromosome occurs randomly throughout the embryo, resulting in cells that are mosaic with respect to which chromosome is active. Evolution and, in particular, natural selection, does not shape âperfectâ adaptations as it was generically understood before (Nesse, 2005). Hershberger, Scott L. 2001. 13% of mothers with one gay son, and 23% of mothers with two gay sons, showed extreme skewing, compared to 4% of mothers without gay sons. Explain why different gametes produced by the same person can have different combinations of alleles for genes that are located on two different chromosomes. What are fossils? [8][5], Other studies in humans have relied on brain imaging technology, such as research lead by Ivanka Savic which compared hemispheres of the brain. Bisexuality is romantic attraction, sexual attraction , or sexual behavior toward both males and females, or to more than one sex or gender . However, none of the four variants could reliably predict sexual orientation. This led to medical experiments in which newborn and infant boys were surgically reassigned into girls after accidents such as botched circumcisions. Chromosome 2 is one of the twenty-three pairs of chromosomes in humans.People normally have two copies of this chromosome. found that the gay men had more gay male uncles and cousins on the maternal side of the family than on the paternal side. All published cases providing sexual orientation grew up to be strongly attracted to women. Because of their temperament, which is influenced by biological variables such as genetic factors, some children will be attracted to activities that are commonly enjoyed by other children of the same gender. [15] Rice et al. Some studies have found correlations between physiology of people and their sexuality; these studies provide evidence which suggests that: J. Michael Bailey has argued that the early childhood gender nonconforming behavior of homosexuals, as opposed to biological markers, are better evidence of homosexuality being an inborn trait. Why or why not? 6. During pregnancy, male cells enter a mother's bloodstream, which are foreign to her immune system. Please explain.? This proposal is known as the "exotic becomes erotic" theory. Although the exact function of the oSDN is not fully known, its volume, length, and cell number seem to correlate with sexual orientation, and a dimorphism in its volume and of cells could bias the processing cues involved in partner selection. Fruit flies have four chromosomes. [5], Long-term studies of domesticated sheep lead by Charles Roselli have found that 6-8% of rams have a homosexual preference through their life. Lesbians on average, have significantly more masculine digit ratios, a finding which has been replicated numerous times in studies cross-culturally. "[118], Some advocates for the rights of sexual minorities resist what they perceive as attempts to pathologise or medicalise 'deviant' sexuality, and choose to fight for acceptance in a moral or social realm. The failure of these experiments demonstrate that socialization effects does not induce feminine type behavior in males, nor make them attracted to men, and that the organizational effects of hormones on the fetal brain prior to birth have permanent effects. It had been suggested that the overactive TSHR hormone lowered body weight in gay people, though this remains unproven. Extra Questions from Heredity and Evolution, CBSE Previous Year Question Paper for Class 10, CBSE Previous Year Question Paper for Class 12. [62]:110, J. Michael Bailey has criticized LeVay's critics – describing the claim that the INAH-3 difference could be attributable to AIDS as "aggravating", since the "INAH-3 did not differ between the brains of straight men who died of AIDS and those who did not have the disease". [67] Medical experiments in which infant boys were sex reassigned and reared as girls did not make them feminine nor attracted to males.[5]. A mutated chromosome is not the same as a normal one, and it's not based on the NUMBER of chromosomes you have. By way of analogy, the allele (a particular version of a gene) which causes sickle-cell anemia when two copies are present, also confers resistance to malaria with a lesser form of anemia when one copy is present (this is called heterozygous advantage). Gay and non-gay people's brains respond differently to two putative sex pheromones (AND, found in male armpit secretions, and EST, found in female urine). In heterosexual women, the two hemispheres were the same size. In some cases though, it appears that this switching off can occur in a non-random fashion. Since anaphase I only separates the homologous chromosomes, neither the chromosome number nor the chromatid number changes during anaphase. LeVay's research suggested that the hypothalamus of gay men is different from straight men. In Drosophila melanogaster, there are only 4 pairs of chromosomes (n = 4, 2n = 8). Evolution is the process by which populations of organisms change over generations. In a 1991 study, Bailey and Pillard conducted a study of male twins recruited from "homophile publications", and found that 52% of monozygotic (MZ) brothers (of whom 59 were questioned) and 22% of the dizygotic (DZ) twins were concordant for homosexuality. How does the theory of evolution explain the descent of a species with a different chromosome number than its ancestors? Describe how the chromosome banding pattern may explain why there are different haploid chromosome numbers for humans (n = 23) and chimpanzees (n = 24) The banding pattern in stained chromosomes suggested that the ancestral version of current chimp-chromosomes 12 and 13 fused end-to-end, forming chromosome 2 in an ancestor of the human lineage. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. In addition, mothers of gay sons, particularly those with older brothers, had significantly higher anti-NLGN4Y levels than did the control samples of women, including mothers of heterosexual sons. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb. Lesbian women and straight men have, on average, slightly larger right brain hemispheres. [5][7][6][8], Maternal immune responses during fetal development are strongly demonstrated as causing male homosexuality and bisexuality. [48] It is this antigen which maternal H-Y antibodies are proposed to both react to and 'remember'. [4], Daryl Bem, a social psychologist at Cornell University, has theorized that the influence of biological factors on sexual orientation may be mediated by experiences in childhood. Significant linkage was also detected in the pericentromeric region of chromosome 8, overlapping with one of the regions detected in the Hamer lab's previous genomewide study. [66], Childhood gender nonconformity, or behaving like the other sex, is a strong predictor of adult sexual orientation that has been consistently replicated in research, and is thought to be strong evidence of a biological difference between heterosexual and non-heterosexuals. [5] Supporting this are studies of the finger digit ratio of the right hand, which is a robust marker of prenatal testosterone exposure. Several theories have been advanced to explain this contradiction, and new experimental evidence has demonstrated their feasibility. Outline a project which aims to find the dominant coat colour in dogs. Figure 7.10 Embryonic inactivation of one of two different X chromosomes encoding different coat colors gives rise to the tortoiseshell phenotype in cats. [11] This effect is estimated to account for between 15 and 29% of gay men, while other gay and bisexual men are thought to owe sexual orientation to genetic and hormonal interactions.