STD 12th/ Ch-5/ Dominance vs Recessive / Homozygous vs Heterozygous / Monohybrid vs Dihybrid.

Dominance vs  Recessive

Dominance and recessiveness are two important concepts in genetics that describe the relationship between alleles of a gene and the resulting expression of a particular trait. The main differences between dominance and recessiveness are:

 

Expression: Dominant alleles are always expressed when present, whereas recessive alleles are only expressed when an individual has two copies of the recessive allele.

 

Effect on phenotype: Dominant alleles have a visible effect on the phenotype, or observable characteristics of an organism, while recessive alleles are not expressed in the phenotype when they are paired with a dominant allele.

 

Inheritance: Dominant alleles are inherited in a straightforward manner, while recessive alleles may be hidden or masked in one generation and expressed in the next generation if both parents pass on the recessive allele.

 

Presence in the population: Dominant alleles are typically more common in a population, while recessive alleles may be less common.

 

In summary, dominance refers to an allele that is always expressed when present, while recessiveness refers to an allele that is only expressed when two copies are present and not masked by a dominant allele. These concepts are crucial in understanding the inheritance of genetic traits and predicting the outcomes of genetic crosses.

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Homozygous vs Heterozygous 

Homozygous and heterozygous are terms used to describe the genetic makeup, or genotype, of an individual concerning a specific gene. The main differences between homozygous and heterozygous are:

Definition: Homozygous refers to having two identical alleles of a gene, while heterozygous refers to having two different alleles of a gene.

Inheritance: Homozygous individuals can only pass on the same allele to their offspring, while heterozygous individuals can pass on either of the two alleles they possess.

Expression of traits: Homozygous individuals will express the trait that is determined by the two identical alleles they possess, while heterozygous individuals may express a dominant trait or a combination of both alleles.

Probability of offspring: Homozygous individuals will always produce offspring that are homozygous for the same allele, while heterozygous individuals may produce offspring that are homozygous for either an allele or heterozygous like themselves.

Symbolism: Homozygous is often represented by two of the same letter (e.g. AA or aa), while heterozygous is represented by two different letters (e.g. Aa).

In summary, homozygous refers to having two identical alleles for a specific gene, while heterozygous refers to having two different alleles. These terms are essential in predicting and understanding the inheritance patterns of genetic traits.

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Monohybrid vs Dihybrid

Monohybrid and dihybrid are terms used to describe genetic crosses involving one or two traits, respectively. The main differences between monohybrid and dihybrid are:

Definition: Monohybrid refers to a genetic cross involving one trait, while dihybrid refers to a genetic cross involving two traits.

Several alleles: In a monohybrid cross, there are two alleles for one gene, while in a dihybrid cross, there are two alleles for each of two different genes.

Inheritance: In a monohybrid cross, the inheritance pattern of one trait is studied, while in a dihybrid cross, the inheritance pattern of two different traits is studied simultaneously.

Probability of offspring: In a monohybrid cross, the Punnett square predicts the probability of the offspring for one trait, while in a dihybrid cross, the Punnett square predicts the probability of the offspring for two different traits.

Complexity: Dihybrid crosses are more complex than monohybrid crosses because they involve the simultaneous study of two different traits, which results in a larger number of possible offspring combinations.

In summary, monohybrid crosses involve the study of one trait with two alleles, while dihybrid crosses involve the study of two different traits with two alleles each. Understanding the difference between monohybrid and dihybrid crosses is essential in predicting and understanding the inheritance patterns of genetic traits.

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