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Monohybrid cross inheritance one gene

Gregor Mendel solved the genetics enigma in 19th century. He experimented with plants of peas by growing them and examining the inheritance pattern at various phases of generation. Mendel is known as the Father of Genetics. He suggested three laws:

  • Independent assortment law
  • Dominance law
  • Segregation law

Experiments conducted on pea plants with a range of characteristics resulted in the development of these rules. Mendel looked at pairs of pea plants that had one contrasting feature. Mendel investigated the resulting characters with opposing characteristics:

1. Violet/white colour of flower
2. Axial/terminal position of flower
3. Green/yellow colour of pod
4. Inflated/constricted shape of pod
5. Yellow/green colour of seed
6. Round/wrinkled form of seed
7. Tall/dwarf height of stem

He coupled two homozygous varieties, resulting in heterozygous progeny. This was referred to as a monohybrid cross.

Definition of monohybrid cross

“A monohybrid cross is a cross between two individuals with homozygous genotypes that result in the contrasting phenotype for a certain trait of genes.”

“A Monohybrid Cross is a cross between two monohybrid varieties (TT and tt).”

The inheritance of single gene is the result of a monohybrid cross. It is readily demonstrated using a Punnett Square. Geneticists employ monohybrid crosses to study how homozygous progeny express heterozygous genes acquired from their parentages.

How do you perform a monohybrid cross?

The calculated phenotype-to-genotype ratios are just probabilities. The following steps can be used to compute a monohybrid cross:

  • Designate the alleles with the use of characters - recessive alleles should be represented by lesser case letters, whereas dominant alleles should be represented by higher case letters.
  • Make a note of the phenotype as well as the genotype of the parentages or parental group that are selected to be crossed.
  • Make a note of the genotype of the gametes taken from the paternal generation – The gametes will turn out to be haploid as a result of meiotic division.
  • Calculate the possible arrangements of the gametes using a Punnett square – Because fertilisation is a random process, any combination is conceivable.
  • The future offspring's phenotypic and genotype ratios can be transcribed. The resulting result is known as the F1 group. The next generations are formed by the F2, F3, and so on generations.

Peas by Gregor Mendel

Mendel began with a pair of pea plants with two opposing characteristics, one tall and the other one dwarf, for the monohybrid cross. Tall plants developed from the cross between tall and dwarf plants. The hybrid floras were all fairly tall. He referred to this as the first hybrid generation (F1), and the children were known as Filial1 or F1 progeny.

He ran an experimentation with all seven different pairings and discovered that the whole F1 progeny displayed a single behavioural pattern, i.e., they look like one of the parents. Other parent character was conspicuously absent.

He carried on his experiment by self-pollinating F1 offspring plants. Surprisingly, one of the four plants was tiny, while the additional three were tall. The taller plants outnumbered the smaller ones by a factor of three. He also remarked that no children were of intermediate height, indicating that no mixing had occurred. The outcome was the similar for other plant characteristics as well, and he dubbed them the hybrid second generation, with the offspring dubbed Filial2 or F2 progeny.

Mendel noticed that characteristics that were missing in the F1 generation resurfaced in the F2 generation. Such suppressed qualities were referred to as recessive genes, whereas expressed traits were referred to as dominant genes. He also came to the conclusion that some 'factors' were inherited by kids from their parents through several generations.

These 'factors' were later dubbed as genes. Genes were found responsible for the transmission of characteristics from one generation to the next. Genes are made up of two alleles that code for distinct characteristics. If two alleles are the same, for example, TT or tt, they are referred to as homozygous pair, but those with different or non-identical (for example, Tt) are referred to as heterozygous pair.

Huntington's Disease (HD)

Huntington's disease is a deadly hereditary condition. The Huntingtin gene, which causes Huntington's disease, is present in every human. A person's dominant homozygous Huntingtin gene was matched with another person's recessive homozygous Huntingtin gene. The dominant allele for Huntington's disease was found in all of the children. This indicates that the kid will be infested with the illness.

Confirming dominant characteristics

The homozygous characteristics of an individual are crossed in the first phase of a monohybrid cross. When the heterozygous characteristics are crossed, it is determined if the trait is recessive or dominant.

Test cross and dihybrid

To understand the process of genes and analyze the heritance of characteristics from parents and ancestors, there are two types of breeding processes: dihybrid cross and monohybrid cross. The latter happens when the children of the generation F1 vary in two characteristics. It is the result of a cross between two units that are heterozygous for two distinct characteristics. For this cross, Mendel performed the experiment discussed below:

  • He chose a couple of opposing qualities or attributes for crossover.
  • Mendel hybridised round-yellow and green-wrinkled seeds.
  • The generation F1 produced seeds which were yellow and spherical.
  • According to the F1 generation, the round and yellow characteristics are dominant, whereas the green colour and wrinkled form are recessive.
  • Self-pollination of progeny F1 gave rise to four different seed pairings in the following generation, the generation F2.
  • The result and cross-ratio of dihybrid were yellow-round, yellow-wrinkled, green-wrinkled, green-round, and the ratio was 9:3:3:1.

A testcross is defined as the cross that includes mating an unknown genotype with a recognized genotype, resulting in a recessive homozygous genotype. Because of the following, a recessive homozygous genotype is crossed:

  • The effects of recessive alleles are constantly hidden in the presence of dominant alleles.
  • As a result, the offspring's phenotype reflects the genotype of an unidentified father.

The goal of the test cross: They're utilised to figure out if a dominant gene is homozygous or heterozygous.

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