The Sex Determination System in Grasshoppers, Animals

The Sex Determination System in Grasshoppers

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Although grasshopper species differ somewhat in appearance, they all sport three distinct body segments. These consist of the head, thorax and abdomen. If you’re examining a grasshopper specimen, it’s the abdomen that allows you to identify the insect’s sex. If you can’t obtain a specimen, you can figure out the sex by watching grasshoppers during mating season.

Male Grasshoppers

Male grasshoppers are smaller than females. That’s the easiest way to tell the difference if you don’t have a specimen in hand. If you do have a grasshopper to examine, check the end of the abdomen. Grown males have a hard and smooth plate on the abdomen’s end, which ranges in size from small to quite prominent. There are no protrusions from the blunt end of the male’s abdomen. Inside the abdomen, the male has two testes, each of which joins a vas deferens, or sperm duct. These ducts join another, single duct for ejaculatory purposes.

Female Grasshoppers

At the end of their abdomens, females have four pointed protrusions, darker than the rest of their bodies. These are the ovipositors, which help her dig holes in which to deposit her fertilized eggs. These protrusions generally are closed, but could be open if the female recently laid eggs. Inside the body, her ovaries consist of ova-producing egg tubes. Each ovary adjoins an oviduct, which leads to the vagina. Female grasshopper anatomy includes a spermatheca, which stores sperm after mating.

Grasshopper Reproduction

Male grasshoppers court females. They fly about, snapping their wings to attract mates. The sounds they make are species-specific, according to the Arizona-Sonora Desert Museum. Males also scrape their hind legs against the forewing to create music for a female grasshopper’s ears, which are located on her abdomen, not her head. Mating consists of the male depositing sperm into the vagina, where it heads into the spermatheca before entering the eggs.

Egg Laying

In winter, female grasshoppers lay pods of eggs, with each pod containing 25 eggs or more. Pods, approximately 1 inch long, are laid about 1 inch deep in grassy soils. The nymphs hatch each spring. These little grasshoppers resemble adults except they don’t have wings and their reproductive organs haven’t matured. Depending on the species, nymphs go through several molts before reaching adulthood between the ages of 40 and 60 days, along with the capacity to reproduce. Some grasshopper species produce only one generation annually, while others produce two or three.

Sex Determination: 3 Basic Types of Sex Determination Processes

Read this article to learn about the important types of sex determination by in inheritance:

Homologous chromosomes are pairs of identical chromo­somes with similar gene loci carrying similar or different alleles.

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They occur in somatic cells of animals and vascular plants which possess diploid number of chromosomes. Out of the two homologous chromosomes present in an individual, one is derived from the father parent and the other from the mother parent. The two homologous chromosomes of each type do not occur attached to each other in the nucleus of the cell. They come together only during prophase and metaphase of meiosis I.

Genomes (Gk. genos- offspring):

Genome is the complete but single set of chromo­somes as found in gametes or gametophyte cells where each chromosome (as well as each gene) is represented singly. The condition of having a single genome or set of chromosomes is called monoploid (Gk. monos- single, aplos- one fold, eidos- form). It is briefly written as In. The somatic or body cells of animals and higher plants generally possess two genomes or two sets of chromosomes.

The condition is called diploid (2n). Several modern day crop plants have more than two sets of chromosomes in their somatic cells, viz. triploid (3n, e.g., Banana), tetraploid (4n, e.g., Rice), hexaploid (6n, e.g., Wheat). The condition of having more than two genomes or sets of chromosomes is known as polyploidy. It is quite common in ferns and mosses. Polyploidy seems to be causative agent of large number of chromo­somes present in some organisms, e.g., Amoeba proteus (250), Ophioglossum (Adder’s Tongue Fern, 1262), Geometrid Moth (224).

Gametes possess half the number of chromosomes found in zygote and the cells derived from it. The condition of having half the number of chromosomes is called haploid (Gk. haplos- simple, eidos- form). The gametic number of chromosomes is typically monoploid (In) but in polyploid forms, it is more than monoploid, e.g., 2n, 3n. In order to avoid confusion in this regard the gametic and zygotic conditions are provided with separate symbols of x and 2x.

The somatic cells of several protists, algae and fungi have haploid number of chromosomes. Doubling of chromosomes occurs in the zygote but meiosis occurs in it to restore haploid condition. Male Honey Bee is also haploid because it develops parthenogenetically from an unfertilized egg. The female bee is diploid.

Sex Chromosomes and Autosomes:

Sex chromosomes are those chromosomes which singly or in pair determine the sex of the individual in dioecious or unisexual organisms. They are called allosomes (Gk. alios- other, soma- body) or idiochromosomes (Gk. idios- distinct, chroma- colour, soma- body). A sex chromosome that determines male sex is termed androsome (Gk. ander- male, soma- body), e.g., Y-chromosome in humans.

The normal chromosomes, other than the sex chromosomes if present, of an individual are known as autosomes. Sex chromosomes may be similar in one sex and dissimilar in the other. The two conditions are respectively called homomorphic (= similar, e.g., XX, ZZ) and heteromorphic (= dissimilar, e.g., XY, ZW).

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Individuals having homomorphic sex chro­mosomes produce only one type of gametes. They are, therefore, called homogametic (e.g., human female). Individuals having heteromorphic sex chromosomes produce two types of gametes (e.g., X and Y containing). They are termed as heterogametic (e.g., human male).

Basis of Sex Determination:

Establishment of male and female individuals or male and female organs of an individual is called sex determination. It is of three types— environmental, genic and chromosomal.

A. Environmental or Non-genetic Determination of Sex:

1. Marine mollusc Crepidula becomes female if reared alone. In company of a female, it develops into male (Coe, 1943).

2. Marine worm Bonellia develops into 3 cm long female if its larva settles down in an isolated place. It grows into small (0.3 cm long) parasitic male if it comes closer to an already established female (Baltzer, 1935). The male enters the body of the female and stays there as a parasite.

3. Ophryortocha is male in the young state and female later on.

4. In Crocodiles and some lizards high temperature induces maleness and low tempera­ture femaleness. In turtles, males are predominant below 28°C, females above 33°C and equal number of the two sexes between 28-33°C.

B. Nonallosomic Genic Determination of Sex:

In bacteria, fertility factor present in a plasmid determines sex. Chlamydomonas pos­sesses sex determining genes. Maize possesses separate genes for development of tassel (male inflorescence) and cob (female inflorescence).

C. Chromosomal Determination of Sex:

Henking (1891) discovered an X-body in 50% of the sperms of firefly. Y-body was discovered by Stevens (1902). McClung (1902) observed 24 chromosomes in female Grass­hopper and 23 chromosomes in male Grasshopper. Wilson and Stevens (1905) put forward chromosome theory of sex and named the X- and Y- bodies as sex chromosomes, X and Y.

Chromosomal or allosomic determination of sex is based on heterogamesis or occur­rence of two types of gametes in one of the two sexes. Male heterogamety or digamety is found in allosome complements XX-XY and XX-X0. Female heterogamety or digamety occurs in allosome complements ZW-ZZ and Z0-ZZ. Sex is determined by number of genomes in haplodiploidy. Chromosomal determination of sex is of the following types:

1. XX—XY Type:

In most insects including fruitfly Drosophila and mammals including human beings the females possess two homomorphic (= isomorphic) sex chromosomes, named XX. The males contain two het- eromorphic sex chromosomes, i.e., XY. The Y-chromosome is often shorter and heterochromatic (made of heterochro­matin). It may be hooked (e.g., Drosophila). Despite differences in mor­phology, the XY chromosomes synapse during zygotene. It is because they have two parts, homologous and differential.

Homologous regions of the two help in pairing. They carry same genes which may have different alleles. Such genes present on both X and Y chromosomes are XY-linked genes. They are inher­ited like autosomal genes, e.g., xeroderma pigmentosum, epidermoly­sis bullosa. The differential region of Y-chromosome carries only Y-linked or holandric genes, e.g., testis determin­ing factor (TDF).

It is perhaps the smallest gene occupying only 14 base pairs. Other holandric genes are of hy­pertrichosis (excessive hairiness) on pinna, porcupine skin, keratoderma dissipatum (thickened skin of hands and feet) and webbed toes. Holandric genes are directly inherited by a son from his father.

Genes present on the differential region of X-chromosome also find expression in males whether they are dominant or recessive, e.g., red-green colour blindness, haemophilia. It is be­cause the males are hemizygous for these genes.

Human beings have 22 pairs of autosomes and one pair of sex chromo­somes. All the ova formed by female are similar in their chromosome type (22 + X). Therefore, females are homoga­metic. The male gametes or sperms pro­duced by human males are of two types, (22 + X) and (22 + Y). Human males are therefore, heterogametic (male digamety or male heterogamety).

Sex of Offspring (Fig. 5.23):

Sex of the offspring is determined at the time of fertilization. It cannot be changed later on. It is also not dependent on any characteristic of the female parent because the latter is homogametic and produces only one type of eggs (22 + X), the male gametes are of two types, androsperms (22 + Y) and gynosperms (22 + X). They are produced in equal proportion.

Fertilization of the egg (22 + X) with a gynosperm (22 + X) will produce a female child (44 + XX) while fertilization with an androsperm (22 + Y) gives rise to male child (44 + XY). As the two types of sperms are produced in equal proportions, there are equal chances of getting a male or female child in a particular mating. As Y-chromosome determines the male sex of the individual, it is also called androsome.

In human beings, TDF gene of Y-chromosome brings about differentiation of em­bryonic gonads into testes. Testes produce testosterone that helps in development of male reproductive tract. In the absence of TDF, gonads differentiate into ovaries after sixth week of embryonic development. It is followed by formation of female reproductive tract. Female sex is, therefore, a default sex.

2. XX—X0 Types:

In roundworms and some insects (true bugs, grasshoppers, cock­roaches), the females have two sex chromosomes, XX, while the males have only one sex chromosome, X. There is no second sex chromosome. Therefore, the males are designated as X0. The females are homogametic because they produce only one type of eggs (A+X).

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). The sex ratio produced in the progeny is 1: 1 (Fig. 5.24).

3. ZW—ZZ Type (= WZ—WW Type).

In birds and some reptiles both the sexes possess two sex chromosomes but unlike human beings the females contain heteromorphic sex chromosomes (AA + ZW) while the males have homomorphic sex chromosomes (AA + ZZ). Because of having heteromorphic sex chromosomes, the females are heterogametic (female heterogamety) and produce two types of eggs, (A + Z) and (A + W). The male gametes or sperms are of one type (A + Z). 1: 1 sex ratio is produced in the offspring (Fig. 5.25).

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4. ZO — ZZ Type:

This type of sex determination occurs in some butterflies and moths. It is exactly opposite the condition found in cockroaches and grasshoppers. Here the females have odd sex chromosome (AA + Z) while the males have two homomorphic sex chromo­somes (AA + ZZ). The females are heterogametic.

They produce two types of eggs, male forming with one sex chromosome (A + Z) and female forming without the sex chromosome (A + 0). The males are homogametic, forming similar types of sperms (A + Z). The two sexes are obtained in the progeny in 50 : 50 ratio (Fig. 5.26) as both the types of eggs are produced in equal ratio.

5. Haplodiploidy:

It is a type of sex determination in which the male is haploid while the female is diploid. Haplodiploidy occurs in some insects like bees, ants and wasps. Male insects are haploid because they develop partheno-genetically from unfertilized eggs. The phenomenon is called arrhenotoky or arrhenotokous parthenogenesis. Meiosis does not occur during the formation of sperms.

Females grow from fertilized eggs and are hence diploid. Queen Bee picks up all the sperms from the drone during nuptial flight and stores the same in her seminal vesicle. Formation of worker bees (diploid females) and drones (haploid males) depends upon the brood cells visited by the queen. While visiting the smaller brood cells, the queen emits sperms from its seminal receptacle after laying the eggs.

As it visits the larger brood cells, it lays the eggs but the seminal receptacles fail to emit the sperms due to some sort of pressure on the ducts coming out of them. When a queen is to be formed the workers enlarge one of a small brood cell having fertilized egg and feed the emerging larva on a rich diet.

Males are normally fertile haploids due to development from unfertilized eggs. Occasion­ally diploid infertile males are also produced from heterozygous females through fertilization.

Sex determination in grasshopper

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Sex determination in honeybees involves a multi-allelic locus, such that homozygotes develop as males and heterozygotes as females. In this issue of Cell, Beye and colleagues (2003) report the cloning of the sex-determining gene, csd. It codes for an SR protein, and different alleles have very different amino-acid sequences. Inactivating csd leads to development as a male.

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Modern Theories of Sex Determination (with Diagrams)

The problem of sex determination has been one of the most important biological puzzle up to the year 1900.

A number of theories were postulated from time to time by the biologists to explain this critical phenomenon.

Hippocrates and other theorists believed that the age or vigour of the parents was responsible for determining the sex of the offspring. The older or more vigorous parent tries to impress its sex upon the offspring.

According to some philosophers if an egg is fertilized soon after ovulation it gives rise to female but if it remains in the oviduct for sometime before fertilization it produces male. Galen and various others claim that germ cells from the right ovary produce males while the germ cells from the left ovary produce females.

Professor Shenk of Vienna put forward the Nutrition Theory. He assumed that high degree of nourishment to the mother brings about female offspring while less nutrition causes male offspring’s. These speculations of the early biologists are now replaced by more genetic and scientific theories.

Modern Theories of Sex Determination:

The Modern Theories Given For Sex Determination Are As Follows:

(1) Chromosomal theory or Theory of Heterogamy

(2) Genic balance theory

(3) Hormonal theory

(4) Theory of environmental factors.

(1) Chromosomal Theory or Theory of Heterogamy:

The complete account of chromosomal sex determination was at first worked out by Stevens (1905). This view was later supported by other scientists such as Wilson, Bridge, Goldschmidt and Whitings.

In majority of sexually reproducing animals two types of chromosomes are found:

They are found in all cells. The genes present on autosomes are responsible for determining the somatic characters but sometime influence the sex of the organism. The two members of each homologous pair are similar in shape and size (homomorphic).

(ii) Sex Chromosomes or Allosomes:

They carry genes for sex. A pair of them determines the sex. They are variously named as X and V chromosomes (Man and Drosophila), Z and W chromosomes (Birds and Moth), odd chromosomes, idiosoines, heterosomes or allosomes. The genes which determine the sex are being located on these chromosomes. The two members of this pair arc often dissimilar in male and are represented as X and Y chromosomes or as Z and W chromosomes.

(a) XX Female and XY Male Types:

This type of sex mechanism is found in Drosophila (fruitfly) and majority of mammals including man. In this type the female is homogametic (XX) and male is heterogametic (XY) consisting of two dissimilar chromosomes X and Y. The females produce ova all of one type having X chromosome. Males produce two types of sperms: -50% with X-chromosome and remaining 50% with Y-chromosome. Thus, the sex chromosomes in female are homomorphic and those of male are heteromorphic (Fig. 5.13).

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(b) ZW Female and ZZ Male Type:

In butterflies and birds, the female is heterogametic having dissimilar Z and W chromosomes whereas the male is homogametic having similar ZZ chromosomes (It is a convention to designate female as ZW instead of XY and male as ZZ instead of XX). The situation here is just reverse to first type.

(c) XX Female and XO Male Type:

Mc Clung and Wilson (1903) described this type of sex mechanism in insects especially in grasshopper. In male there is no mate for X chromosome, hence the name XO is given, there is no Y chromosome. They produce sperm of two types, 50% with X chromosome and 50% without X. In females there are two similar or homomorphic sex chromosomes XX.

2. Genic Balance Theory:

This theory was proposed by Calvin Bridges (1921). From his study on Drosophila he suggested that the X chromosomes carry factor for femaleness whereas autosomes “A” carry genes for maleness. Y chromosome does not take part in sex determination. From the Fig. 5.15 it is clear that the genic balance is governed by the ratio of the number of X-chromosomes to the number of sets of autosomes in the zygote at fertilization.

II the ratio is 1.0 the offspring develops into female, but if it is 0.5, then the offspring develops into male. If the ratio is intermediate between 1.0 and 0.5, the resulting individual is neither a male or nor a female but an inter sex. Super females have a ratio of 1.5 and super males have a ratio 0.33.

(3.) Hormonal Theory:

Hormones are the secretion of the endocrine glands which in many instances modify the sex rather determining the sex. They are mainly responsible for the expression of secondary sexual characters. This theory is based upon the observation of Crew in chicks.

In course of his investigation he found a hen which laid fertile eggs, accidentally lost its ovary, stopped laying eggs, and developed male characters such as comb and male plumage
and became a cock. The above case of sex reversal is explained by assuming that destruction or removal of the ovary led to stoppage of production of the ovarian hormones.

But the rudiment of testis (present in all female birds) became functional following the loss of ovary and produced male hormone which is responsible for the appearance of male secondary sexual characters. Such a male produced sperms and became father of two chickens.

Another classical example of sex reversal by the action of hormone is observed in free martin. In cattle, when twin calves of opposite sex are born, the female is usually somewhat abnormal and sterile. Such a calf is called freemartin. Since the male hormone appears earlier in the development, it passes into the body of the under developed female through the circulation and causes partial sex reversal of the female.

(IV) Theory of Environmental Factors:

Baltzer (1935) observed sex determination due to external environment in certain lower animals such as Bonellia. The adult female is several inches long but the male is very small of the size of large protozoa and lives in the reproductive tract of the female. The newly hatched young worm (Bonellia), when reared in isolation, develops into a female. But when, these are released into water containing mature females, some of them attach to the proboscis of female (to suck nourishment) develop into tiny males and come to lie in the oviduct of the female.

Sex Determination in Man:

In case of man the total number of chromosomes is 23 pairs or 46. Of these, 44 chromosomes are autosomes (A) and the other 2 chromosomes are sex-chromosomes (XX in female and XY in male). In male, the diploid cells contain 44 A + XY chromosomes and the same in female contain 44A + XX. So the sperm will contain 22A + X (50%) or 22A + Y (50%) chromosomes and hence are of two types.

On the contrary all the eggs are of one type and always contain 22A + X. When the sperm with 22A + X unites with an egg having 22A + X chromosome, the resultant zygote will be 44A + XX and it will develop into a female baby. But if a sperm with 22A + Y fertilizes an egg with 22A + X chromosome, the zygote will be 44A + XY and the baby will be male one as shown in the figure 5.16.

Thus, in man X-chromosome is female determining and Y-chromosome is male determining.

Role of Sex Chromosomes in Human Diseases:

The presence of extra sex chromosome or absence of any sex chromosome causes certain diseases in man. It further supports the role of X and Y-chromosome in determining sex in human beings.

1. Klinefelter’s Syndrome (2n = 47 or 44+XXY):

This disease is caused in man by the presence of an extra X-chromosome in male individuals. Such males possess 47 chromosomes (44 autosomes plus XXY sex chromosomes). They are sterile (incapable of carrying reproduction) males with under-developed genitalia, sparse body hair and some degree of breast development. They also exhibit mental retardation and limited intelligence. It arises due to non-disjunction (non-separation of XX during meiosis) of XX- chromosomes.

2. Turner’s Syndrome (2n = 45 or 44 + X):

It is a disease caused in female individuals due to the absence of one X-chromosome. They have 45 chromosomes in stead of normal 46 chromosomes. Such females are sterile (unable to produce baby) with poorly developed ovaries and under developed breasts. They have webbed neck and broad chest.

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