monohybrid crosses

What is a monohybrid cross?

A monohybrid cross is a genetic cross that involves studying the inheritance of a single trait, such as flower color or seed shape, by focusing on the alleles of one gene at a time.

What are the characteristics of the parent organisms used in a monohybrid cross?

In a monohybrid cross, the parent organisms (P1 generation) are typically homozygous for the trait in question: one parent is homozygous dominant (TT), and the other is homozygous recessive (tt). This ensures that the offspring inherit one dominant allele and one recessive allele from each parent.

What gametes do the homozygous dominant (TT) parent produce?

The homozygous dominant parent (TT) can only produce gametes that carry the dominant allele (T), as both alleles on the chromosomes are the same (T).

What gametes do the homozygous recessive (tt) parent produce?

The homozygous recessive parent (tt) can only produce gametes that carry the recessive allele (t), since both alleles on the chromosomes are the same (t).

What is the genotype of the offspring from a cross between TT and tt?

The offspring resulting from a TT × tt cross will all be heterozygous (Tt), meaning they will have one dominant allele (T) and one recessive allele (t).

What phenotype will the F1 generation exhibit?

Since the dominant allele (T) masks the recessive allele (t), all offspring in the F1 generation will display the dominant phenotype, even though they carry one recessive allele. For example, if the trait is flower color and the dominant allele codes for purple flowers, the F1 generation will all have purple flowers.

What are the P1, F1, and F2 generations in a monohybrid cross?

P1 generation: The parental generation, consisting of the homozygous dominant (TT) and homozygous recessive (tt) parents. F1 generation: The first filial generation, which are the offspring of the P1 generation. In this case, all F1 offspring will be heterozygous (Tt). F2 generation: The second filial generation, which are the offspring of the F1 generation, crossed with each other (Tt × Tt).

What happens when two F1 generation organisms (Tt × Tt) are crossed?

When two F1 generation organisms (Tt × Tt) are crossed, the resulting F2 generation will have different combinations of alleles, leading to different genotypes and phenotypes.

What gametes will the F1 generation (Tt) produce?

The F1 generation (Tt) can produce two types of gametes: one carrying the dominant allele (T) and the other carrying the recessive allele (t).

What are the possible genotypes of the F2 generation from a Tt × Tt cross?

The F2 generation from a Tt × Tt cross will have the following possible genotypes: 25% homozygous dominant (TT), 50% heterozygous (Tt), 25% homozygous recessive (tt).

What phenotypes will the F2 generation express?

The phenotypes of the F2 generation will be: 75% will express the dominant phenotype (TT or Tt), because the dominant allele (T) is present in these genotypes. 25% will express the recessive phenotype (tt), as they inherit two recessive alleles, one from each parent.

What is the ratio of genotypes and phenotypes in the F2 generation?

Genotype ratio: 1 TT : 2 Tt : 1 tt. Phenotype ratio: 3 dominant phenotype (purple flowers, for example) : 1 recessive phenotype (white flowers, for example).

Why does the dominant allele mask the recessive allele in a heterozygous organism?

The dominant allele masks the effect of the recessive allele in a heterozygous organism because it is expressed in the phenotype whenever it is present. The recessive allele only shows its effect if two copies of the recessive allele are inherited, meaning the organism is homozygous recessive (tt).

What is the significance of Mendel’s monohybrid cross experiments?

Mendel's monohybrid crosses were fundamental in understanding how traits are inherited. His experiments demonstrated the principles of segregation, independent assortment, and dominance, which became the foundation for modern genetics.