To explain the frequency and distribution of heteromorphic sex chromosomes in the lizard genus Anolis, we compared the relative roles of sex chromosome conservation versus turnover of sex‐determining mechanisms. We used model‐based comparative methods to reconstruct karyotype evolution and the presence of heteromorphic sex chromosomes onto a newly generated Anolis phylogeny. We found that heteromorphic sex chromosomes evolved multiple times in the genus. Fluorescent in situ hybridization (FISH) of repetitive DNA showed variable rates of Y chromosome degeneration among Anolis species and identified previously undetected, homomorphic sex chromosomes in two species. We confirmed homology of sex chromosomes in the genus by performing FISH of an X‐linked bacterial artificial chromosome (BAC) and quantitative PCR of X‐linked genes in multiple Anolis species sampled across the phylogeny. Taken together, these results are consistent with long‐term conservation of sex chromosomes in the group. Our
Genetic sex determination in some groups of animals appears to make frequent shifts between male heterogamety (XY) and female heterogamety (ZW) systems (Ezaz et al. 2006). Several mechanisms can cause these transitions, including selection on pleiotropic effects of the sex-determination genes, selection on sex ratio, and meiotic drive. Our results add to this list of possibilities. We find that sexually antagonistic selection on loci linked to the sex-determination genes can trigger a heterogamety transition. Sex-antagonistic selection is thought to be key to the evolution of other aspects of sex chromosomes (Charlesworth 1991), and so it seems plausible that it may commonly be involved in these transitions as well.. The way that sex-antagonistic selection drives a transition can be understood in simple terms. Selection naturally and automatically builds up positive associations (linkage disequilibria) between sex-determination genes that make individuals become male and genes that increase male ...
This dataset contains the digitized treatments in Plazi based on the original journal article Souza, Lucas Henrique Bonfim, Brescovit, Antonio Domingos, Araujo, Douglas (2017): A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea). Zootaxa 4303 (1): 140-150, DOI: https://doi.org/10.11646/zootaxa.4303.1.9 ...
The contrasting dose of sex chromosomes in males and females potentially introduces a large-scale imbalance in levels of gene expression between sexes, and between sex chromosomes and autosomes. In many organisms, dosage compensation has thus evolved to equalize sex-linked gene expression in males and females. In mammals this is achieved by X chromosome inactivation and in flies and worms by up- or down-regulation of X-linked expression, respectively. While otherwise widespread in systems with heteromorphic sex chromosomes, the case of dosage compensation in birds (males ZZ, females ZW) remains an unsolved enigma. Here, we use a microarray approach to show that male chicken embryos generally express higher levels of Z-linked genes than female birds, both in soma and in gonads. The distribution of male-to-female fold-change values for Z chromosome genes is wide and has a mean of 1.4-1.6, which is consistent with absence of dosage compensation and sex-specific feedback regulation of gene expression at
The evolution of sex chromosome dimorphism (SCD) is generally thought to follow a repeatable pattern. If one of the sex chromosomes carries a sex-determining region with at least two loci that should be linked together, selection favours the process of preventing sex chromosomes from recombination [1,2]. In turn, the lack of recombination leads to degeneration of the chromosome that is present only in one sex. The genetic degeneration of the hemizygous chromosome can occur because of Hill-Robertson effects, such as Mullers ratchet, background selection and the hitchhiking of deleterious alleles to advantageous mutations (reviewed in Charlesworth & Charlesworth [3]). Genetic degeneration, accompanied by morphological shrinking of hemizygous chromosomes, is observed in both XY and ZW chromosome systems [2,4]. Yet, most of the research focus has been on the mammalian Y chromosome [5], in which rapid degeneration can, to some extent, be attributed to a higher mutation rate in males (owing to more ...
Darren has published a review of sex chromosomes evolution and speciation in birds and other ZW systems. This is an invited submission for a special issue of Molecular Ecology, on "Sex Chromosomes and Speciation.". Heres the citation and link:. Irwin, D.E. 2018. Sex chromosomes and speciation in birds and other ZW systems. Molecular Ecology, online Early View: https://doi.org/10.1111/mec.14537. ...
The human pseudoautosomal region 1 (PAR1) is essential for meiotic pairing and recombination, and its deletion causes male sterility. Comparative studies of human and mouse pseudoautosomal genes are valuable in charting the evolution of this interesting region, but have been limited by the paucity of genes conserved between the two species. We have cloned a novel human PAR1 gene, DHRSXY, encoding an oxidoreductase of the short-chain dehydrogenase/reductase family, and isolated a mouse ortholog Dhrsxy. We also searched for mouse homologs of recently reported PGPL and TRAMP genes that flank it within PAR1. We recovered a highly conserved mouse ortholog of PGPL by cross-hybridization, but found no mouse homolog of TRAMP. Like Csf2ra and Il3ra, both mouse homologs are autosomal; Pgpl on chromosome 5, and Dhrsxy subtelomeric on chromosome 4. TRAMP, like the human genes within or near PAR1, is probably very divergent or absent in the mouse genome. We interpret the rapid divergence and loss of ...
The human sex chromosomes have stopped recombining gradually, which has left five evolutionary strata on the X chromosome. Y inversions are thought to have suppressed X-Y recombination but clear evidence is missing. Here, we looked for such evidence by focusing on a region-the X-added region (XAR)-that includes the pseudoautosomal region and the most recent strata 3 to 5. We estimated and analyzed the whole set of parsimonious scenarios of Y inversions given the gene order in XAR and its Y homolog. Comparing these to scenarios for simulated sequences suggests that the strata 4 and 5 were formed by Y inversions. By comparing the X and Y DNA sequences, we found clear evidence of two Y inversions associated with duplications that coincide with the boundaries of strata 4 and 5. Divergence between duplicates is in agreement with the timing of strata 4 and 5 formation. These duplicates show a complex pattern of gene conversion that resembles the pattern previously found for AMELXY, a stratum 3 locus. ...
The cognitive deficits present in individuals with sex chromosome aneuploidies suggest that hemispheric differentiation of function is determined by an X-Y homologous gene [Crow (1993); Lancet 342:594-598]. In particular, females with Turners syndrome (TS) who have only one X-chromosome exhibit deficits of spatial ability whereas males with Klinefelters syndrome (KS) who possess a supernumerary X-chromosome are delayed in acquiring words. Since spatial and verbal abilities are generally associated with right and left hemispheric function, such deficits may relate to anomalies of cerebral asymmetry. We therefore applied a novel image analysis technique to investigate the relationship between sex chromosome dosage and structural brain asymmetry. Specifically, we tested Crows prediction that the magnitude of the brain torque (i.e., a combination of rightward frontal and leftward occipital asymmetry) would, as a function of sex chromosome dosage, be respectively decreased in TS women and increased in KS
Sex chromosomes have evolved from non-sex-determining chromosomes (autosomes) many times throughout the tree of life. Ever since their discovery, these chromosomes have captivated researchers because of their obvious involvement in fundamental aspects of an organisms life, such as sex determination, sexual reproduction and sexual conflicts. Despite this long-lasting fascination, their biology remains unclear in several central aspects, in particular regarding their almost ubiquitous evolution of recombination cessation and impoverished gene content, and the multifaceted consequences thereof. This lack of detailed knowledge about sex chromosome evolution compromises our understanding of fundamental biological questions (e.g. the evolution of sexual conflicts) as well as more practical ones (e.g. about sex-linked genetic diseases).. Our research focuses mainly on Sylvioidea passerine birds where we have recently detected a new sex chromosome, a neo-sex chromosome, which has been formed by a ...
In species with genetic sex-determination, the chromosomes carrying the sex-determining genes have often evolved non-recombining regions and subsequently evolved the full set of characteristics denoted by the term sex chromosomes. These include size differences, creating chromosomal heteromorphism, and loss of gene functions from one member of the chromosome pair. Such characteristics and changes have been widely reviewed, and underlie molecular genetic approaches that can detect sex chromosome regions. This review deals mainly with the evolution of new non-recombining regions, focusing on how certain evolutionary situations select for suppressed recombination (rather than the proximate mechanisms causing suppressed recombination between sex chromosomes). Particularly important is the likely involvement of sexually antagonistic polymorphisms in genome regions closely linked to sex-determining loci. These may be responsible for the evolutionary strata of sex chromosomes that have repeatedly ...
A common characteristic of sex chromosomes is the accumulation of repetitive DNA, which accounts for their diversification and degeneration. In grasshoppers, the X0 sex-determining system in males is considered ancestral. However, in some species, derived variants like neo-XY in males evolved several times independently by Robertsonian translocation. This is the case of Ronderosia bergii, in which further large pericentromeric inversion in the neo-Y also took place, making this species particularly interesting for investigating sex chromosome evolution. Here, we characterized the satellite DNAs (satDNAs) and transposable elements (TEs) of the species to investigate the quantitative differences in repeat composition between male and female genomes putatively associated with sex chromosomes. We found a total of 53 satDNA families and 56 families of TEs. The satDNAs were 13.5% more abundant in males than in females, while TEs were just 1.02% more abundant in females. These results imply differential
Male Human Sex Chromosomes X and Y (Pair 23), scanning electron micrograph (SEM). There are 23 pairs of chromosomes in most normal human cells.
Research published in this weeks Science reveals that the Y chromosome developed from an X-like ancestor around 300 million years ago.. Of our 46 human chromosomes, 44 form matched pairs. But two - the X and the Y chromosomes - stand apart because they have no perfect match. But it wasnt always like this. Researchers at the Howard Hughes Medical Institute have found that the X and Y chromosomes evolved from a standard identical pair around 300 million years ago - shortly after the divergence of the evolutionary lines leading to mammals and birds.. "The first events that created the sex chromosomes had been thought to have occurred at least 170 million years ago," says researcher Dr David Page. "Were pushing that back another 100 million years or so.". Page and colleague Dr Bruce Lahn reconstructed the stages of sex chromosome evolution, and the time course over which these chromosomes were built. "By fossil digging on the sex chromosomes, we were able to reconstruct the four events that drove ...
Approach and Results-We used transgenic male mice expressing Sry (sex-determining region Y) on an autosome to create Ldlr (low-density lipoprotein receptor)-deficient male mice with an XY or XX sex chromosome complement. Transcriptional profiling was performed on abdominal aortas from XY or XX males, demonstrating 1746 genes influenced by sex chromosomes or sex hormones. Males (XY or XX) were either sham-operated or orchiectomized before AngII infusions. Diffuse aortic aneurysm pathology developed in XY AngII-infused males, whereas XX males developed focal AAAs. Castration reduced all AngII-induced aortic pathologies in XY and XX males. Thoracic aortas from AngII-infused XY males exhibited adventitial thickening that was not present in XX males. We infused male XY and XX mice with either saline or AngII and quantified mRNA abundance of key genes in both thoracic and abdominal aortas. Regional differences in mRNA abundance existed before AngII infusions, which were differentially influenced by ...
Mammalian sex chromosomes appear, behave and function differently than the autosomes, passing on their genes in a unique sex-linked manner. The publishing of Ohnos hypothesis provided a framework for discussion of sex chromosome evolution, allowing it to be developed and challenged numerous times. In this report we discuss the pressures that drove the evolution of sex and the mechanisms by which it occurred. We concentrate on how the sex chromosomes evolved in mammals, discussing the various hypotheses proposed and the evidence supporting them. ...
Heteromorphic sex chromosomes, such as the X/Y pair in mammals, differ in size and DNA sequence yet function as homologs during meiosis; this bivalent asymmetry presents special challenges for meiotic completion. In Caenorhabditis elegans males carrying mnT12, an X;IV fusion chromosome, mnT12 and IV form an asymmetric bivalent: chromosome IV sequences are capable of pairing and synapsis, while the contiguous X portion of mnT12 lacks a homologous pairing partner. Here, we investigate the meiotic behavior of this asymmetric neo-X/Y chromosome pair in C. elegans. Through immunolocalization of axis component HIM-3, we demonstrate that the unpaired X axis has a distinct, coiled morphology while synapsed axes are linear and extended. By showing that loci at the fusion-proximal end of IV become unpaired while remaining synapsed as pachytene progresses, we directly demonstrate the occurrence of synaptic adjustment in this organism. We further demonstrate that meiotic crossover distribution is markedly ...
Sex chromosomes determine the sex of an organism. A human somatic cell has two sex chromosomes: XY in male and XX in female. A human germ cell has one sex chromosome: X or Y in a sperm and X in an egg. When an X-sperm is combined with an egg, the resulting zygote (fertilized egg) will contain two X chromosomes. A person developed from the XX-zygote will have the characteristics of a female. Combination of a Y-sperm and an egg will produce a male.Usually, a woman has two X chromosomes (XX) and a man one X and one Y (XY). However, both male and female characteristics can sometimes be found in one individual, and it is possible to have XY women and XX men. Analysis of such individuals has revealed some of the molecules involved in sex determination, including one called SRY, which is important for testis formation. SRY (which stands for sex-determining region Y gene) is found on the Y chromosome. In the cell, it binds to other DNA and in doing so distorts it dramatically out of shape. This alters ...
Genetics: Sex-linked inheritance calculation helpBrown-eyed girl with normal sight get married to the brown-eyed man with normal sight. The father of...
Just published in Nature is a study revealing the origins of maleness in mammals. The team of Prof. Henrik Kaessmann at the Center for Integrative Genomics and the Swiss Institute of Bioinformatics concludes that the key male-differentiating features in the Y chromosome appeared 180 million years ago in placentals and marsupials with the arrival of…
Scientists have long suspected that the sex chromosome that only males carry is deteriorating and could disappear entirely within a few million years, but until now, no one has understood the evolutionary processes that control this chromosomes demise. Now, a pair of Penn State scientists has discovered that this sex chromosome, the Y chromosome, has evolved at a much more rapid pace than its partner chromosome, the X chromosome, which both males and females carry ...
Synonyms for sex-chromosome at Thesaurus.com with free online thesaurus, antonyms, and definitions. Dictionary and Word of the Day.
Sex chromosome: Sex chromosome, either of a pair of chromosomes that determine whether an individual is male or female. The sex chromosomes of human beings and other mammals are designated by scientists as X and Y. In humans the sex chromosomes comprise one pair of the total of 23 pairs of chromosomes. The other
Sex chromosomes determine the sex of an individual. Humans have two sex chromosomes: XX for females and XY for males (as shown in this karyotype).
BACKGROUND: Long-term evolution of sex chromosomes is a dynamic process shaped by gene gain and gene loss. Sex chromosome gene traffic has been studied in XY and ZW systems but no detailed analyses have been carried out for haploid phase UV sex chromosomes. Here, we explore sex-specific sequences of seven brown algal species to understand the dynamics of the sex-determining region (SDR) gene content across 100 million years of evolution. RESULTS: A core set of sex-linked genes is conserved across all the species investigated, but we also identify modifications of both the U and the V SDRs that occurred in a lineage-specific fashion ...
Each chromosome is a pair of distinct, separate DNA molecules. A chromosome of an eukaryotic cell nucleus is a (long) helix of two linear molecules and so has two ends, which are called telomeres. DNA naturally forms a double helix with its complementary DNA molecule, and the double helix can further curl in what are called supercoils.. In humans, the chromosomes occur in 23 pairs (totaling 46). Except for the sex chromosome pair, each member of the pair is identical in appearance in a karyotype (picture) and each such pair has a number assigned from 1 to 22; the numbering generally follows the size of the chromosome, with chromosome 1 being the longest. In mammals, the sex chromosomes in a male are quite different in size and are labelled X and Y; a female has two identical X chromosomes.. ...
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Researchers find that boas and pythons use an XY sex chromosome system, rather than the previously assumed ZW system found in some other snakes.
Chromosomes are cell structures made up of genetic material (DNA). They are a part of most types of cells in the body. Humans have 46 chromosomes (23 pairs). Half of a persons chromosomes come from the mother and half from the father. One of the 23 pairs determines a persons gender. The sex chromosomes are called X and Y. For a child to be female, she must inherit an X chromosome from each parent (XX). For a child to be male, he must inherit an X chromosome from his mother and a Y chromosome from his father (XY). The DNA of the chromosomes is divided up into genes. The genes determine the features a person inherits from his or her parents, such as blood type and other characteristics, including risks for developing certain diseases. Changes in chromosomes or genes may cause changes in certain body processes or functions. These changes may be undetectable or may cause genetic diseases, such as hemophilia or Down syndrome. Gene changes can be passed from parents to children or can occur through ...
An allosome (also referred to as a sex chromosome, heterotypical chromosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. In humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are called autosomes. Autosomes are homologous chromosomes i.e. chromosomes which contain the same genes (regions of DNA) in the same order along their chromosomal arms. The chromosomes of the 23rd pair are called allosomes consisting of two X chromosomes in women, and an X chromosome and a Y chromosome in men. Women therefore have 23 ...
Biologically speaking, nearly every species on Earth has two opposite sexes, male and female. But with some fungi and other microbes, sex can be a lot more complicated. Some...
The male sex chromosome has long been called our genetic junkyard, a clutter of meaningless DNA surrounding a handful of genes--and those only good for making more men. But after rummaging through the scrap heap, two biologists say they have discovered five genes that are used throughout the body to help keep cells working properly. The researchers also describe in todays issue of Science another seven genes that are unique to the Y chromosome and lie in regions known to be involved in infertility.. Massachusetts Institute of Technology biologists Bruce Lahn and David Page knew that the Y chromosomes barren reputation rested on limited evidence. Panning for gold, the researchers examined cells from human testes, where they guessed genes on the Y chromosome should be particularly active. They collected messenger RNA (mRNA), which is made from active genes and eventually codes for proteins; because each gene has a unique corresponding mRNA strand, mRNA levels reveal which genes are actively ...
Juvenile CLN3 disease occurs because of disruptions or changes (mutations) of the CLN3 gene located on the short arm (p) of chromosome 16 (16p12.1). The function of the protein encoded by this gene is not yet understood.. Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 16p12.1" refers to band 12.1 on the short arm of chromosome 16. The numbered bands specify the location of the thousands of genes that are present on each chromosome.. Researchers suspect that juvenile CLN3 disease is caused by alterations within the cell so that the body ...
Gottron syndrome is a rare disorder that appears to be inherited as an autosomal recessive genetic trait. Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 11p13" refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.. Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother. Recessive genetic disorders occur when an individual inherits the same ...
Newsroom America) -- There are significant gaps in our knowledge on the evolution of sex, according to a research review on sex chromosomes from Lund University in Sweden. Even after more than a century of study, researchers do not know enough about the evolution of sex chromosomes to understand how males and females emerge.. Greater focus on ecological aspects would increase this knowledge, according to evolutionary biologists at Lund University, who have reviewed a lot of the research conducted in this field in the last 100 years.. Female and male bodies work differently, even though they have the same genome. One example is reproduction.. "There is a form of genetic conflict between the sexes - a conflict in the genome itself - which we know little about", says professor Bengt Hansson at Lund University.. Together with senior lecturer Jessica Abbott and doctoral student Anna Nordén, he has read more than 100 scientific articles and papers describing the evolution of sex chromosomes and the ...
... are cell structures that carry genetic material (DNA), or genes. They are a part of every cell in the body. Humans have 46 chromosomes (23 pairs). Half of a persons chromosomes come from the mother and half from the father. One of the 23 pairs determines a persons sex. The sex chromosomes are called X and Y. For a child to be female, she must inherit an X chromosome from each parent
This study is the first to examine the involvement of sex chromosomes in the diseases development in the absence of sex hormones. In humans, females typically have two copies of the X chromosome, while males typically have one X and one Y chromosome.METHODIn the lab, the researchers engineered mice with different chromosomal makeups and measured their development of pulmonary hypertension in an environment with 10 percent oxygen, which is a well-established setting for inducing the disease.One group of mice was engineered with sex chromosomes that were independent of their gonadal sex, or sex based on their genitalia, so that the researchers could isolate the impact of sex chromosomes. The other group of mice in the experiment had different variants of sex chromosomes in order for the res.... MedWorm Message: Have you tried our new medical search engine? More powerful than before. Log on with your social media account. 100% free.. ...
View Notes - Lec6_illustrations from BICD 100 at UCSD. LECTURE 6 Thursday, January 26 Sex determination and sex chromosomes Announcements/reminders/comments Review from lecture #5 Sex-limited and
Male fruit fly (Drosophila sp.) karyotype. A karyotype is the complete set of chromosomes of an organism. Fruit flies have 8 chromosomes in total: 4 inherited from the mother and 4 from the father. The sex chromosomes, which determine the individuals gender, are at bottom right. Males have an X sex chromosome and a Y sex chromosome, females have two X sex chromosomes. - Stock Image C001/8373
List of words make out of Heterogametic. All anagrams of Heterogametic. Words made after unscrambling Heterogametic. Scrabble Points. Puzzle Solver. Word Creation.
The sex chromosomes of mammalian germ cells must match those of the surrounding soma in order for the germ cells to successfully complete development as sperm o...
In a new research, biologists have genetically mapped the sex chromosomes of several species of cichlid fish from Lake Malawi, East Africa, and identified a mechanism by
Breaking things down to the building blocks of life this week is Mark Ross, who discusses the evolution of sex chromosomes, genetics and genomes, Michael Traugott describes a novel way of using genetics to find out who is eating whom in underground food webs, and Derek Thorne gets fruity with Lucy Wheatley extracting DNA from a kiwi...
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Description of disease Chromosome complement. Treatment Chromosome complement. Symptoms and causes Chromosome complement Prophylaxis Chromosome complement
The male sex refers to that division of a species which produces sperm. In most mammals, sperm develops inside the testes. Sperm allows the propagation of the species to continue through the creation of offspring. In humans, an XY sex chromosome structure is a male and a XX sex chromosome structure is a female. The process of going from a child to developing the secondary sex characteristics that cause full maturation takes place mostly in puberty. ...
Eukaryotic genomes contain a large proportion of repetitive DNA sequences, mostly transposable elements (TEs) and tandem repeats. These repetitive sequences often colonize specific chromosomal (Y or W chromosomes, B chromosomes) or subchromosomal (te
A short but nice article by Doris Bachtrog, looking at whether there is a faster mutation rate in males compared to females in Drosophila. Studies of a number of vertebrates have shown a faster rate of substitution on the Y compared to the X at putatively neutral sites, thus suggesting a faster male mutation rate (as under neutrality the substitution rate is the mutation rate). This high rate of mutation in males is thought to be due to the larger number of cell divisions in the germ line of males compared females. Previous work has not seen this effect in Drosophila. Bachtrog used a set of orthologous genes on the recently formed neo-sex chromosomes of D. miranda (I discussed some of her work on this system in a previous post). The recent sex linkage of these chromosomes means that the genes on them have altered the proportion of generations they spend in the male and female germ line, making them an excellent system for looking at male and female mutation rates. To look at putatively neutral ...
Results. Segregation ratio. After mating a blind male from each family to a wild-type White leghorn female, male progeny were found to be sighted while females were blind, indicating sex-linked inheritance. This contradicted previous publications in which the rdd trait was described as autosomal recessive in inheritance [2,3,23]. However on careful examination, the crosses described by Randall and co-workers [2], while consistent with autosomal recessive inheritance, are in fact equally consistent with Z-linked inheritance. These authors crossed blind hens (rdd/-) with sighted (carrier) cocks (rdd/+) and obtained a 1:1:1:1 ratio of sex and affectation status, but the reverse cross described above (rdd/rdd males against +/- females) revealed the linkage between sex and the trait.. For subsequent mapping studies, the heterozygous males from this cross were backcrossed to the blind dams and a total of 77 progeny were classified, of which 39 were blind (18 males and 21 females) and 38 sighted (21 ...
But we dont always need to go alien species. There are interesting variations among extant earthly taxa. You are almost certainly aware that some organisms have haploid genomes, while others are diploid. Some organisms are sexual, and others are asexual. And so forth. These structural issues are relevant to both mechanism, and the population and evolutionary phenomena. Consider for example sex determination. In many species there is a heterogametic sex (e.g., XY). This sex has a marginally functional sex-determining chromosome (e.g., Y), and is dependent on the other pair for most of the remaining functionality. Therefore, humans males are subject to "sex-linked traits." Diseases with recessive expression in females (i.e., both copies need to be mutant) are not recessive in males, who have only one copy. One of the possible evolutionary implications of this is that the X chromosome is subject to more selection than the autosome. The literature in this area is murky for possible implications, so ...