NEET Biology Genetics Interaction of Genes and Cytoplasmic Inheritance

Interaction of Genes and Cytoplasmic Inheritance

Category : NEET

Interaction of Genes and Cytoplasmic Inheritance

 

Genes interaction is the influence of alleles and non-alleles on the normal phenotypic expression of genes. It is of two types.

(1) Inter-allelic or intra-genic gene interaction: In this case two alleles (located on the same gene locus on two homologous chromosomes) of gene interact in such a fashion to produces phenotypic expression e.q., co-dominance, multiple alleles.

(i) Incomplete dominance (ratio): After Mendel, several cases were recorded where F1 hybrids were not related to either of the parents but exhibited a blending of characters of two parents. This is called incomplete dominance or blending inheritance.

 

Example : In 4-O’clock plant, (Mirabilis jalapa), when plants with red flowers (RR) are crossed with plants having white flowers (rr) the hybrid F1 plants (Rr) bear pink flowers. When these  plants with pink flowers are self pollinated they develop red (RR), pink (Rr) and white (rr) flowered plants in the ratio of   (  generation).

Example : In Snapdragon or dog flower (Antirrhinum majus) the dominant character of leaf (Broadness) and flower (Red) shows incomplete dominance over recessive characters (Narrowness and white) in dihybrid cross.

(ii) Codominance (ratio): In codominance, both the genes of an allelomorphic pair express themselves equally in  hybrids.  ratio both genotypically as well as phenotypically in  generation.

Example : Codominance of coat colour in cattle.

In cattle gene R stands for red coat colour and gene r stands for white coat colour. When red cattle (RR) are crossed with white cattle (rr), the  hybrids have roan coloured skin (not the intermediate pink). The roan colour is actually expressed by a mixture of red and white hairs, which develop side by side in the heterozygous  hybrid. In  generation red, roan and white appear in the ratio of . The phenotypic ratio equal to genotypic ratio RR, Rr, rr ().

Example: Codominance in andalusian fowl

In andalusian fowl a cross between pure black and pure white varieties results in blue hybrids.

Example: Codominance of blood alleles in man

(a) MN blood type in man is an example of codominance. The persons with MN genotype produce both antigen M and N and not some intermediate product indicating that both the genes are functional at the same time.

(b) In ABO blood group system gene A and B responsible for blood group A and B are codominant. The hybrid has AB blood group.

 

 

Differences between incomplete dominance and codominance

Incomplete dominance

Codominance

Effect of one of the two alleles is more conspicuous.

The effect of both the alleles is equally conspicuous.

It produces a fine mixture of the expression of two alleles.

There is no mixing of the effect of the two alleles.

The effect in hybrid is intermediate of the expression of the two alleles.

Both the alleles produce their effect independently, e.g.,.

 

(2) Non-allelic or inter-genic gene interaction: Here two or more independent genes present on same or different chromosomes, interact to produce a new expression e.g. epistasis, complementary genes, supplementary genes, duplicate genes, inhibitory genes, lethal genes etc.

(i) Complementary genes (9:7 ratio): The complementary genes are two pairs of no allelic dominant genes (i.e. present on separate gene loci), which interact to produce only one phenotypic trait, but neither of them if present alone produces the phenotypic trait in the absence of other.

 

Example: Complementary genes for flower colour in sweet pea. In sweet pea (Lathyrus odoratus) the purple colour of flowers is dependent on two nonallelic complementary genes C and P. Gene C produces an enzyme that catalyzes the formation of colourless chromogen for the formation of anthocyanin pigment. Gene P controls the production of an enzyme, which catalyzes the transformation of this chromogen into anthocyanin. These genes are complementary to each other. It means the pigment anthocyanin is produced by two-biochemical reactions and the end product of first reaction forms the substrate for the other.

If a plant possesses dominant gene C and P, it produces purple flowers. But if a plant has a genotype CCpp, it produces the raw material but is unable to convert it into anthocyanin. Therefore, it produces white flowers. Similarly, if it possesses dominant gene P, but no dominant C (ccPP), it produces white flowers because gene P can convert colourless chromogen into anthocyanin but cannot form chromogen.

 

(ii) Supplementary genes (9 : 3 : 4 ratio) : Supplementary genes are two independent pairs of dominant genes. Which interact in such a way that one dominant gene will produce its effect whether the other is present or not. The second dominant when added changes the expression of the first one but only in the presence of first one. In rats and guinea pigs coat colour is governed by two dominant genes A and C, the agouti-coloured guinea pigs have genotype CCAA. The black mice possess factor for black colour C but not the gene A for agouti colour. If gene for black colour is absent agouti is unable to express itself and mice with a genotype ccAA are albino. Here presence of gene C produced black colour and addition of gene A change its expression to agouti colour.

 

(iii) Epistasis (Inhibiting genes): Epistasis is the interaction between nonallelic genes (Present on separate loci) in which one-gene masks, inhibits or suppresses the expression of other gene. The gene that suppresses the other gene is known as inhibiting or epistatic factor and the one, which is prevented from exhibiting itself, is known as hypostatic. Although, it is similar to dominance and recessiveness but the two factors occupy two different loci. Therefore, while dominance involved intragenic or interallelic gene suppression, the epistasis involves intergenic suppression. Epistasis can be of the following types - dominant epistasis, recessive epistasis.

 

(a) Dominant epistasis (12:3:1 or 13:3 ratio): In dominant epistasis out of two pairs of genes the dominant allele, (i.e., gene A) of one gene masks the activity of other allelic pair (Bb). Since the dominant epistatic gene A exerts its epistatic influence by suppressing the expression of gene B or b, it is known as dominant epistasis.

Example - Dominant epistasis in dogs: In dogs white coat colour appears to be dominant. It develops due to the action of epistatic gene I which prevents the formation of pigment, controlled by hypostatic gene B.

The hypostatic gene B produces black coat while its hypostatic allele b produces brown coat colour only when gene I is recessive. The progeny of dominant gene I does not allow them to function and results in white colour. When two white coat dogs are crossed, they produce white, black and brown in the ratio of 12 : 3 : 1 The white dogs in this case possess gene for black or brown colour but does not produce the pigment because of the presence of gene I in dominant state. Similar phenomena have been seen in fruit colour in cucurbita as summer squash and coat colour in chickens.

 

(b) Recessive epistasis (9:3:4 ratio): Epistasis due to recessive gene is known as recessive epistasis, i.e., out of the two pairs of genes, the recessive epistatic gene masks the activity of the dominant gene of the other gene locus. The dominant A expresses itself only when the epistatic locus C also has the dominant gene if the epistatic locus has recessive gene c, gene A fails to express.

Example : In mice agouti colour, characterised by banding of hairs is controlled by gene A, which is hypostatic to recessive allele c. The dominant epistatic gene C in absence of A gives black coloured mice and in presence of dominant gene A gives agouti, but dominant gene A is unable to produce agouti colour in absence of gene c. Therefore, recessive c gene acts as epistatic gene A.

(iv) Duplicate genes (ratio) : Sometimes two pairs of genes located on different chromosomes determine the same phenotype. These genes are said to be duplicate of each other. The dominant triangular fruit shape of

Capsella bursa pastoris (shepherd’s purse) is determined by two pairs of genes, say A and B. If any of these genes is present in dominant form, the fruit shape is triangular. In double recessive forms the fruits are top shaped and thus we get a 15 (triangular): 1(top shaped) ratio in F2 generation.

(v) Collaborator genes: In collaboration two gene pairs, which are present on separate loci but influence the same trait, interact to produce some totally new trait or phenotype that neither of the genes by itself could produce.

Example: Inheritance of combs in poultry, where two genes control the development of comb.

 

(a) Gene R gives rise to rose comb.

(b) Gene P produces pea comb. Both rose and pea combs are dominant over single comb.

(c) Gene R and P for rose and pea comb together produce a new phenotype the walnut comb.

Wyandotte variety of domestic chicken possesses rose comb, whereas Brahmas have pea comb. Bateson crossed rose-combed Wyandottes and pea-combed Brahmas. The F1 chickens developed walnut comb, a phenotype not expressed in either parent. When F1 chickens mated among themselves, the resultant F2 chickens exhibited the familiar dihybrid ratio 9 : 3 : 3 : 1. These four phenotypes were - walnut comb, rose comb, pea comb and single comb in the ratio of 9 : 3 : 3 : 1. Out of these four phenotypes two phenotypes were different from those expressed in the parents.

The analysis of F2 results indicates that the presence of two dominant genes R and P results in the walnut comb. The double recessive (rrpp) genotype produces single comb. The rose comb develops when dominant gene for rose comb is present and dominant gene for pea comb is absent (RRpp) whereas pea comb develops when gene for rose  comb is recessive and gene for pea comb (P) is dominant (rrPP)

             

(vi) Pleiotropic effect of genes

(a) Lethal genes: Certain genes are known to control the manifestation of some phenotypic trait as well as affect the viability of the organism. Some other genes have no effect on the appearance of the organism but affect the

 

viability alone. These genes are known as lethals or semilethals depending upon their influence. Complete lethal genes in homozygous condition kill all or nearly all homozygous individuals, while in case of semilethal genes some homozygous individuals are able to survive. The lethal genes are always recessive for their lethality and express the lethal effect only in homozygous condition.

Dominant lethals: The dominant lethal genes are lethal in homozygous condition and produce some defective or abnormal phenotypes in heterozygous condition. Their most serious effect in heterozygous may also cause death. Following are the examples of dominant lethal genes.

Example - Yellow lethal in mice: A well-known example of such lethals is from mice, given by Cuenot. He found that the yellow mice never breed true. Whenever the yellow mice were crossed with yellow mice, always yellow and brown were obtained in the ratio of 2:1. A cross between brown and brown mice always produced brown offsprings and a cross between brown and yellow produced yellow and brown in equal proportions.

In 1917, Stiegleder concluded that yellow mice are heterozygous. The homozygous yellow (1/4th of the total offsprings) dies in the embryonic condition. When there unborn ones are added to the 2:1 ratio of yellow and brown, these form typical 3:1 ratio. Cuenot suggested that gene Y has a multiple effect.

  Note : - It controls yellow body colour and has a dominant effect.

                                 - It affects viability and acts as a recessive lethal.

Example - Inheritance of sickle cell anaemia in man: The disease sickle cell anaemia is caused by a gene (HbS), which is lethal in homozygous condition but has a slight detectable effect in the heterozygous condition. The homozygous for this gene (Hbs/ Hbs) generally die of fatal anaemia. The heterozygotes or carriers for Hbs,

(i.e., HbA / Hbs) show signs of mild anaemia as their R.B.C. become sickle shaped in oxygen deficiency.

A marriage between two carriers, therefore, results in carrier and normal offsprings in the ratio of 2:1. The variation in 3:1 ratio is due to the death of homozygous and incomplete dominance of normal gene over recessive gene for sickle cell anaemia in which glutamic acid is substituted by valine in b chain. Which is disorder in Africans that reduce oxygen uptake.

Example - Brachyphalangy: Persons exhibiting brachyphalangy have short fingers apparently having two joints in their fingers, the middle bone being greatly shortened and often fused with one of the other two bones of the finger. Mohr described one case where one child was born without any fingers or toes and did not survive. Two other children showed short fingers and one was normal. This is exact 1 : 2 : 1 ratio.

Example - Huntington’s chorea in man: The gene causing Huntington’s chorea in man can express itself even when a single dominant allele is present. In both homo and heterozygous condition, the gene expresses itself only at middle-age, usually after forty years. The person suffers from muscular failure, mental retardation and finally death. Thus a dominant gene in heterozygous condition may also produce lethal effect. The gene is transmitted to next generation only because it expresses itself only after the start of reproductive period.

Recessive lethals: The recessive lethals produce lethal effect only in homozygous condition. Their heterozygotes are normal. Therefore, recessive lethals remain unnoticed in the population but are established in the population because female are carrier for lethal gene. These are detected only when two heterozygous persons get married.

Example - Tay Sach’s lethal: The recessive lethal gene for Tay Sach’s disease causes death of young children only in homozygotes which are unable to produce enzymes needed for normal fat metabolism. The accumulation of fat in nerve sheaths hampers transmissions of nerve impulse leading to poor muscular control and mental deficiency.

(vii) Qualitative inheritance: Qualitative inheritance or monogenic inheritance is that type of inheritance in which one dominant allele influences the complete trait, so that two such allele do not change the phenotype. Here dominant allele is monogene.

(viii) Quantitative inheritance: Quantitative inheritance or polygenic inheritance can be defined as, 'two or more different pairs of alleles which have cumulative effect and govern quantitative characters. The quantitative inheritance is due to incomplete dominance. It has been suggested that the multiple gene inheritance may have following characteristics:

(a) The effects of each contributing gene are cumulative or additive.

(b) Each contributing allele in a series produces an equal effect.

(c) There is no dominance involved.

(d) Epistasis does not exist among genes at different loci.

(e) No linkage is involved in the process.

(f) Effects of environment are absent or may be ignored.

Example - Human skin colour: This character was studied by Davenport, 1913 in the marriages between negroes and whites. The F1 offsprings arising as a result of these marriages are called as mulattoes. The human skin colour is determined by two pairs of genes, P1 and P2. A negro having very dark skin with four colour genes i.e., P1P1 P2P2, when married to a white with no colour gene (p1p1 p2p2) produce mulattoes with only two colour genes. These mulattoes show intermediate type of skin colour. If this mulatto is married to a similar genotype, the inheritance of pigment forming gene in F2 offspring shall be as under:

Very dark           -           4 Colour genes                -           One

Intermediates      -           3 Colour genes                -           Four

                        -           2 Colour genes                -           Six

                        -           1 Colour genes                -           Four

White                -           No colour gene               -           One

If the mulatto is married to a pure white (test cross), the distribution of skin colour shall be as follows:

25% offsprings with two colour genes (P1 and P2),

50% offsprings with one colour gene (P1 or P2)

25% offsprings with no colour gene

If the mulatto is married to a negro (back cross) the distributions of skin colour shall be as under:

25% offspring with four colour genes                     

50% offspring with three colour genes

25% offsprings with two colour genes

Example - Ear size in maize : Emerson and East (1913) studied the for the ear length in maize. The size difference between two strains of maize is generally due to two or more pairs of genes. If it is due to two pairs of genes, the ratio of different sizes shall be 1 : 4 : 6 : 4 : 1. But, if it is due to three pairs of genes, the size ratio shall be 1 : 6 : 15 : 20 : 15 : 6 : 1.

Example - White spotting in mice: This trait is also polygenic for it is governed by two or more pairs of gene. Depending upon the involvement of the number of gene pairs for determine the trait, the ratios also vary in the manner stated above.

Example - Grain colour in wheat: This character was examined by Nilsson-Ehile 1908, which is similar as polygenic gene of skin colour in human. When a red grain was crossed with a white, the F1 offspring produced light red grains due to incomplete dominance of red over white. The ratio is come out as 1 : 6 : 15 : 20 : 15 : 6 : 1.

(ix) Multiple alleles: The multiple alleles can be defined as a set of three, four or more allelomorphic genes or alleles, which have arisen as a result of mutation of the normal gene and which occupy the same locus in the homologous chromosomes. Characters of multiple alleles are following -

(a) Multiple alleles occupy the same locus with in the homologous chromosomes. It means only one member of the series is present in a given chromosome.

(b) Since only two chromosomes of each type are present in each diploid cell, only two genes of the multiple series are found in a cell and also in a given individual.

(c) The gametes contain only one chromosome of each types, therefore, only one allele of the multiple series in each gamete.

(d) Crossing over does not occur in the multiple alleles.

(e) Multiple alleles control the same character, but each of them is characterised by different manifestation. Sturtevent has summarised it that they carry the same function but with varying degree of efficiency.

(f) The multiple alleles of a series are more often related as dominant and recessive. More commonly, the normal gene is dominant to all other mutant alleles. Even the intermediate members of the series may be related as dominant and recessive, or they may exhibit codominance. Therefore, multiple alleles act in some way to control the various steps in a chemical reaction.

Examples: Coat colour in rabbit, blood group in human beings.

(x) Pedigree analysis: As man is not a suitable material for genetic research, the human genetics is studied from different point of view. Pedigree analysis is one such method based on Mendelism. It was started by Galton.

  

A pedigree is a record of inheritance of certain genetic traits for two or more generations presented in the form of a diagram or family tree or case history or genealogy. Pedigree analysis is a system of analysis of pedigree to find out the possibility of absence/presence of a particular trait in the progeny. It is mainly employed in domesticated animals and men also. The person from whom the case history of a pedigree starts is called Proband (called Propositus or Prosipitus if it is male and Proposita if it is female). The children are called Sibs. Empty/open circles and squares represent normal female (   ) and normal male (  ) solid/shaded (=/<) symbols stand for those which bear the trait under study. or  represent carrier normal female having recessive allele of the trait under studyidentical twins      non-identical twins. ? This is never used as man can never be a carrier. Horizontal line shows marriage line. All siblings are connected to a horizontal line below parents in order of birth. Only X-linked genes show criss cross inheritance.

Important Tips

 

  • Fair child’s sweet William is hybrid flower.
  • In polygenic inheritance some offsprings may exhibit more extremes than either parent or grandparent. For example, some children are shorter or taller than either parent or any of their more remote ancestors. The same is true with respect to intelligence. These are called transgressive variations.
  • Formula of number of genotypes in case of multiple allelism is: \[\frac{n}{2}(n+1)=n\ \ \text{alleles}\].
  • In ABO blood group three alleles regulate blood group leading to the formation of six genotypes. Landsteiner discovered A, B, O, blood groups.
  • During serological test in which antihuman serum is mixed with blood of another animal, blood of chimpanzee gives the thickest precipitate.
  • Dominance is a phenomenon and not a low because of the existence of incomplete dominance and codominance.
  • Heterosis in plants is obtained by crossing in unrelated parents and known as hybrid vigour.
  • Expressivity is the degree of effect produced by penetrant genotype.
  • Nilsson-Ehle (1908) was the first scientist to prove quantitative inheritance.

 

 

Cytoplasmic Inheritance/ Extra Chromosomal Inheritance

 

The fact that nucleus contains the units of inheritance was proposed by Oscar Her twig in 1870's. The mechanism was clearly understood with the development of Mendel's law of inheritance. Further researchers proposed that cytoplasm also contains the hereditary material. The evidence for cytoplasmic inheritance was first presented by Correns in Mirabilis Jalapa and by Baur in Pelargonium zonale in 1908. Later on Ruth Sager (1954) described cytoplasmic inheritance of streptomycin resistance in chlamydomones in other animals and plants certain characters are inherited independent of the chromosomal genes (Non-chromosomal genes). The cytoplasm in such cases contain self-perpetuating hereditary particles formed of DNA. These may be mitochondria, plastids or foreign organism, etc. The total self-duplicating hereditary material of cytoplasm is called plasmon and the cytoplasmic units of inheritance are described as plasmogenes.

 

(1) Criteria for cytoplasmic inheritance: The cases of cytoplasmic inheritance are found to exibit maternal influence. The reason is very simple. Very little cytoplasm is contained in the sperm cell of an animal. Most of the cytoplasm is contributed to the zygote by the ovum or egg. Hence if there are hereditary units in the cytoplasm, these will be transmitted to the offspring’s through the egg. The offspring, therefore will exhibit maternal influence. This could be explained further by following example.

(i) Maternal influence on shell coiling in snail.

(ii) Inheritance of sigma particles in Drosophila.

(iii) Breast tumour in mice.

(iv) Plastid inheritance in Mirabilis (4 O' clock plant).     

(v) Plastid inheritance in Oenothera.

(vi) Male sterility in plants - e.q. maize.

(vii) Inheritance of kappa particles in Paramecium: Sonneborn and his associates have described the transmission of some cytoplasmic particles known as kappa particles and their relation to nuclear genes in Paramecium aurelia. Individuals of particular race of paramecium aurelia called killer strain destroy other races of paramecia by secreating some toxic substance into the water in which they live. This substance is known as paramecin. Although kappa particles are cytoplasmic particles and transmitted strictly through the cytoplasm.

 

Important Terms Used In Inheritance Studies

 

(1) Gene (Mendel called them factor): In modern sense an inherited factor that determines a biological character of an organism is called gene (functional unit of hereditary material).

 

(2) Allelomorphs or alleles: Alleles, the abbreviated form of term allelomorphs (meaning one form or the other) indicates alternative forms of the same gene. e.g., Tall TT and dwarf tt are alternation forms of the same gene etc.

 

(3) Gene locus: It is the portion or region on chromosome representing a single gene. The alleles of a gene are present on the same gene locus on the homologous chromosomes.

 

(4) Wild and mutant alleles: An original allele, dominant in expression and wide spread in the population is called wild allele. An allele formed by a mutation in the wild allele, recessive in expression and less common in the population is termed as mutant allele.

 

(5) Homozygous: Both the genes of a character are identical is said to be homozygous or genetically pure for that character. It gives rise to offspring having the same character on self-breeding e.g. TT (Homozygous dominant) or tt (Homozygous recessive).

 

(6) Heterozygous: Both the genes of a character are unlike is said to be heterozygous or hybrid. Such organisms do not breed true on self-fertilization e.g. Tt

If we know the number of heterozygous pairs we can predict the following:

Number of types of gametes \[=~{{2}^{n}}\]

Number of F2 phenotype \[=~{{2}^{n}}\]             (Where n is the number of heterozygous pairs).

Number of F2 genotype \[=~{{3}^{n}}\]

 

(7) Genotype: The genotype is the genetic constitution of an organism. TT, Tt and tt are the genotypes of the organism with reference to these particular pairs of alleles.

 

(8) Phenotype: Expresses the characters of individuals like form, sex, colour and behaviour etc.

 

(9) Pure line: Generations of homozygous individuals which produce offspring’s of only one type i.e. they breed true for their phenotype and genotype.

 

(10) Monohybrid, dihybrid and polyhybrid: When only one allelic pair is considered in cross breeding, it is called monohybrid cross. Similarly when two allelic pairs are used for crossing, it is called dihybrid cross and more than two allelic pairs in a cross are called polyhybrid cross.

 

(11) Reciprocal cross: The reciprocal crosses involve two crosses concerning the same characteristics, but with reversed sexes.

 

(12) Genome: Total set of genes (DNA instructions) in the haploid set of chromosomes and inherited as unit from parents to offspring is called genome.

 

(13) Gene pool: All the genotypes of all organisms in a population form the gene pool.

(14) \[{{\mathbf{F}}_{\mathbf{1}}}\] Generation: \[{{\mathbf{F}}_{\mathbf{1}}}\] or first filial generation is the generation of hybrids produced from a cross between the genetically different individuals called parents.

 

(15) \[{{\mathbf{F}}_{\mathbf{2}}}\] Generation (Bateson, 1905): \[{{\mathbf{F}}_{\mathbf{2}}}\] or second filial generation is the generation of individuals which arises as a result of inbreeding or interbreeding amongst individuals of \[{{\mathbf{F}}_{\mathbf{1}}}\] generation.

 

(16) Punnet square: It is a checker-board used to show the result of a cross between two organisms, it was devised by geneticist, R.C. Punnet (1927). It depicts both genotypes and phenotypes of the progeny.

 

(17) Back cross: It is cross which is performed between hybrid and one of its parents. In plant breeding, back cross is performed a few times in order to increase the traits of that parent.

 

(18) Test cross: It is a cross to know whether an individual is homozygous or heterozygous for dominant character. The individual is crossed with recessive parent. The ratio will be 50% dominant and 50% recessive in case of hybrid or heterozygous individual. In case of double heterozygote (e.g., RrYy) crossed with recessive (rryy) the ratio will be \[1:1:1:1\] test cross help to find out genotype of parents.

 

(19) Self cross/selfing: It is the process of fertilization with pollen or male gametes of the same individual.

 

(20) Theory of probability: (i) Out of the two alternate events, the probability of occurrence of each one of them is 50%.

(ii) Two events are independent if occurrence of one does not affect the probability of occurrences of the other.

(iii) The probability of joint occurrence of two independent events is the product of their individual probabilities.

(iv) For an event, which can happen through two independent pathways, the probability of its occurrence is the sum of separate probabilities.

 

(21) Observed Vs expected results: Experimental results conform to the ones expected through the theory of probability if the size of the sample is small but they tend to approach the latter if the sample size is large.

 

(22) Hybrid: The organism produced after crossing of two genetically different individuals is called hybrid.

 

 

(23) Heredity and variations in sexual and asexual reproduction

(i) Sexual reproduction: Variations are common in animals and plants which reproduce by sexual means. The reason for this is that the sexual reproduction is biparental, involves meiosis and fertilization, and the offspring receives some traits from father and some from mother.

(ii) Asexual reproduction: Those organisms which reproduce by asexual means eq. bacteria, amoeba, euglena, rose etc. The asexual reproduction is monoparental, involves mitosis and the organism produced by it, and inherits all the traits of its single parent. With the result, it is almost a carbon copy of the parent and is known as ramet. A group of ramets is called a clone.


 

Differences between clone and offspring’s

Characters

Clone

Offspring

Type of reproduction

Clone is the product of asexual reproduction

Offspring is the product of sexual reproduction

Number of parents

Clone is monoparental

Offspring’s is derived from two parents thus biparental

Cell division

Clone is formed by mitosis. Meiosis does not occur.

Meiosis takes place prior to formation of gametes

Resemblance

Clone exactly resembles the parent

Offspring differs from parents.

 

Notes - Interaction of Gene and Cytoplasmic Inheritance
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