In Mice, The Ability To Run Normally Is A Dominant Trait

In mice, the ability to run normally is a dominant trait

In mice, the ability to run normally is inherited as a dominant trait, designated by R for the dominant allele and r for the recessive allele. Mice with at least one R allele (RR or Rr) can run normally. Mice with two recessive alleles (rr) run in circles only, identified as waltzing mice. Hair color is governed by a separate gene, with black hair (B) being dominant over brown hair (b). This information is essential to constructing Punnett squares and analyzing the inheritance patterns for the given crosses.

Paper For Above instruction

The analysis of genetic inheritance in mice involves understanding dominant and recessive traits and accurately constructing Punnett squares to predict genotypic and phenotypic ratios. This paper discusses monohybrid and dihybrid crosses based on the traits of running ability and hair color, providing detailed calculations and interpretations of genetic inheritance in mice.

Monohybrid Crosses

1. Cross a heterozygous running mouse with a homozygous running mouse

The heterozygous running mouse has a genotype Rr, while the homozygous running mouse has a genotype RR.

Parental genotypes:

  • Rr (heterozygous running mouse)
  • RR (homozygous running mouse)

Punnett Square:

RR
RrRRRR
RrRRRR

Phenotypic ratio:

  • All mice will be able to run normally since all have at least one dominant R allele.
  • Phenotypic ratio: 4 running mice : 0 waltzing mice

2. Cross a heterozygous black mouse with a homozygous brown mouse

The heterozygous black mouse has genotype Bb, and the homozygous brown mouse has genotype bb.

Parental genotypes:

  • Bb (heterozygous black hair)
  • bb (homozygous brown hair)

Punnett Square:

Bb
bBbbb
bBbbb

Phenotypic ratio:

  • Black hair (B_) : brown hair (bb) ratio is 2:2 or simplified to 1:1.
  • Phenotypic ratio: 2 black : 2 brown or 1 black : 1 brown

Dihybrid Crosses

3. Cross a heterozygous running, homozygous black mouse with a heterozygous running, brown mouse

Parental genotypes:

  • Rr B B (hemizygous black mice)
  • Rr bb (brown mice)

Punnett Square would involve crossing Rr B B with Rr bb, considering independent assortment.

Genotypic combinations lead to different phenotypes, with a phenotypic ratio demonstrating the distribution of running ability and hair color.

Expected phenotypic ratio: 9 running black : 3 running brown : 3 waltzing black : 1 waltzing brown

4. Cross a heterozygous running, heterozygous black mouse with a waltzing, brown mouse

Parental genotypes:

  • Rr Bb (heterozygous running black)
  • rr bb (waltzing brown)

This cross involves combining recessive and dominant alleles, and the Punnett square will help determine distribution.

Expected phenotypic ratio: 3 running black : 1 waltzing black : 3 running brown : 1 waltzing brown

5. Cross a heterozygous running, heterozygous black mouse with a heterozygous running, heterozygous black mouse

Parental genotypes:

  • Rr Bb
  • Rr Bb

This classic dihybrid cross assesses the independent assortment of the two traits.

Expected phenotypic ratio: 9 running black : 3 running brown : 3 waltzing black : 1 waltzing brown

These analyses demonstrate the inheritance patterns of the traits in mice, emphasizing the importance of understanding dominant and recessive alleles, constructing accurate Punnett squares, and interpreting phenotypic ratios. Such insights are foundational for genetic studies and breeding strategies.

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