roundhead gamefowl stag

Contents

 

Overview

A German scientist, Gregor J. Mendel, had studied the inheritance nature in plants. He presented his paper ‘’Experiments on Plant Hybridization’’ to Society for Research in Nature at Brünn in 1865. Mendel has evaluated the pattern of inheritance for specific traits in the pea plants and presented them mathematically. His discoveries have made the genetics (the science of heredity) basis. Due to this reason, Mendel is called as ‘‘father of genetics”.

Although Mendel had experimented with the varieties of peas. However, his laws apply to the inheritance of different characters in almost every organism like birds, humans, etc.

However, it was not only through the experiments of Mendel that scientists understood how characteristics are inherited. For this purpose, many scientists have contributed to their experimentation.

Theory of Blending Inheritance

The theory of blending Inheritance was famous during Mendel’s time. According to this theory, ‘‘offspring have a mix or blend of their parent’s characteristics’’.

Mendel’s Theory

According to Mendel’s observations, this model was not correct. Mendel noticed that plants grown in his garden weren’t a mix or blended of their parents e.g., a taller plant or a shorter plant had exhibited their offspring either taller or shorter but not the medium. Based on these observations, Mendel questioned the blending inheritance theory and presented his findings.

Law of Segregation

It states that for any individual that produces gametes, the gene copies separate so that each gamete receives only one copy. So, a gamete will gain one allele.

Key Points

Allele pairs are separated when an organism produces gametes.

Explanation

In meiosis, the chromosomes (paternal or maternal origin) are separated, and alleles exhibiting different characters are segregated into two type’s different gametes.

Every gamete has an equal opportunity of receiving any one of the alleles.

Description

As Mendel observed, different traits could come from either parent; every parent exhibits two alleles for a character. Allele separation occurs as a result of gamete formation. For every character, only a single allele is passed by each parent. It recombines the alleles that ultimately lead to fertilization and exhibits the traits genotypes as shown in the figure below.

The universality of Mendel’s laws

Although Mendel had experimented with the varieties of peas. However, his laws apply to the inheritance of different characters in almost every organism like birds, humans, etc.

  1. Bateson and R. Punnett have demonstrated the Mendelian inheritance in poultry. It depicts that Mendelian segregation is universally observed.

For Galliformes, most of the information is obtained from the Gallus gallus, Meleagris gallopavo,  and the chicken’s reproductive biology.

Mendel’s Law of Segregation in relation to game fowls

Mendel’s Law of Segregation in relation to game fowls

Mendel’s law is evidenced as a general inheritance methodology in the breeding experiments of the domestic fowl. This field was made a classical research object by Davenport, Bateson, and Hurst experimentations. The most distinguishable ‘unit character’s poultry is comb form. There are different types of combs e.g., rose, single, pea, etc. These are not to be blended during the cross-breeding. However, they are inherited according to Mendel’s law in an alternative manner. Bateson has studied the inheritance of different comb (rose, single, and pea) types. He proved the application of Mendel’s laws to animals in addition to plants

Important Terminologies

  1. P (or P1) generation: It is the parental generation
  2. F1 generation: ‘F’ derived from Filial, it is the first offspring generation
  3. F2 generation: It is the second offspring generation
  4. Phenotype: It is the appearance or form of a trait of an organism e.g chickens’ comb type, color,
  5. Genotype: An organism’s genetic makeup that defines a phenotype e.g. Bb, BB, and bb all represent potential genotypes.

Genotype may be heterozygous or homozygous.

Homozygous: When the alleles are similar at the locus of homologous chromosomes

Heterozygous: When the alleles are dissimilar at the locus of homologous chromosomes

Gene: It is the smallest unit of inheritance. It is also a part of DNA (a chromosome foundation).

Locus: It determines the particular gene location over a chromosome.

Alleles: It is an alternative gene form.

Dominant: Allele that is predominant  over other alleles and determines a phenotype

Dominant alleles are denoted by capital letter e.g. (C)

Recessive: Allele that did not determine the phenotype in the presence of dominant allele.

Recessive alleles are denoted by lower case letter e.g. (c)

Punnet square:

It is a diagrammatic expression that determines expected genotypes percentages in offspring of the two parents.

Monohybrid cross: It is a cross between heterozygous individuals for a gene. It gives phenotype ratio 3:1 and genotypic ratio 1:2:1

Sex chromosomes

Homogametic sex: Similar pair of sex chromosomes. These types of sex chromosomes are attained by all gametes. In birds ZZ (male homogametic)

Heterogametic sex: It exhibits different sex chromosomes. Gametes are made by different sex chromosomes types. E.g. In birds ZW (female heterogametic).

Autosomes

All the chromosomes are other than sex chromosomes. They did not determine sex. Also called as autosomes

Sex chromosome

Chromosomes that determines sex is called sex chromosome.

Body cells contain diploid (2n) chromosome numbers

Haploid (In) chromosome numbers are present in sex cells

Monohybrid crosses

Mendel’s Experimentation on peas:

Mendel conducted his experiments on various strains of a garden pea. He selected different strains exhibiting opposite characters. E.g., tall/dwarf, round/wrinkled, green/yellow, etc. In every case, Mendel firstly crossed the true-bred strains. After this, he crossed the strains exhibiting the contrasting characters. To evaluate the progeny of the first generation (F1: first filial/Fx), he performed monohybrid crosses. Furthermore, he self-crossed the F1 to get the F2 generation.

When the two strains comprising contrasting characteristics were used for crossing, The Fx individual’s generation did not exhibit a mix or blend of two characteristics. However, it demonstrated the entirely one character. This finding gives a basis for recessive and dominant characteristics.

Moreover, the self-crossing of the F1 generation gives rise to the F2 generation. It exhibited both recessive and dominant types with a ratio 3:1. However, backcrossing of the Fx generation with the dominant type of parent exhibited all dominant progeny. While the backcrossing of the Fx generation with the recessive kind of parent exhibited all 50:50 recessive and dominant, progeny

Bateson and Punnett’s experimentation on birds

Punnet and Bateson discovered the principles of inheritance in fowl. For this purpose, these scientists performed a series of experimentation on animals, particularly domestic fowl. At that time, various types of fowl were present. The distinct character of the domestic fowl was ‘‘the comb shape’’.

In the first round of their experimentation, they crossed the single comb fowls with rose comb fowls for the evaluation of ¥x generation. Afterward, they have done some backcrosses and self-crosses. They have observed similar results to that of Mendel’s experimentation results. It reflects that Fx generation yields rose comb (100%). In comparison, the backcrossing of x generation gives rise to the F2 generation that exhibits 3:1 (rose combed to single combed ratio).

Furthermore, backcrossing of Fx generation with parental rose comb leads to rose combed (100%). While the backcrossing of Fx generation with single parental comb gives rise to 1:1 (50%:50% single comb to rose comb). It shows that the rose comb is a dominant trait while the single comb is a recessive trait. A symbol ‘‘R denotes rose comb,’’ and the single comb is denoted by ‘‘r’’.

 

The two possible backcrosses between the Fx generation and the parents are:

From the above analysis it is clear that a rose comb individual may have either of the two genetic combinations R/R or R/r; the former is referred to as homozygous and the latter heterozygous.

 

More Examples from peafowls:

Peacocks and peahens show extraordinary complexity of plumage. One allele of one gene can alter the entire pattern in unexpected ways–and still, show simple Mendelian inheritance.

More Examples from peafowls

  1. India Blue (B) is dominant to Black Shoulder (b).

Blue Bb x Bb => 3B:1bb

 

  1. Cameo (Zc): It is Z-linked recessive to wild type (Z+)

Cameo Male ZcZc x Wild-type Female Z+W

Wild-type (hybrid) Male Z+Zc and Cameo Female ZcW

Conclusion

Although Mendel had experimented with the varieties of peas. However, his laws are applicable to inheritance of different kinds of characters in almost every organisms like birds, humans etc.

  1. Bateson and R. Punnett has demonstrated the Mendelian inheritance in poultry. The distinct character of the domestic fowl was ‘‘the comb shape’’. For Galliformes, most of the information is obtained from the Gallus gallus, Meleagris gallopavo, and chicken’s reproductive biology. The Fx individual’s generation did not exhibit a mix or blend of two characteristics. The self-crossing of F1 generation gives rise to F2 generation. It exhibited the both recessive and dominant types with ratio 3:1. However, backcrossing of the Fx generation with dominant type of parent, exhibited all dominant progeny. While the backcrossing of the Fx generation with recessive type of parent, exhibited all 50:50 recessive and dominant progeny

References

  • Heredity and Mendel’s law
  • Introduction to genetics and breeding
  • From Mendel to multi-national in poultry breeding
  • Science foundations
  • Mendelian Genetics
  • Recent studies of avian sex ratios
  • Genetics and evolution of the domestic fowl

By Jason M. Davis

My name is Jason M. Davis and this is my website. I am primarily a gamefowl breeder based in the Metropolitan Borough of Sefton United Kingdom and I love to blog everything related to gamefowl chickens and life around the farm in general. Thank you for visiting my site and I hope you all love my content.

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