Homozygous

Definition

Homozygous refers to an organism that has two identical alleles for a specific gene, whether they are dominant or recessive. This genetic condition plays a crucial role in inheritance patterns, as it influences the traits expressed in an organism. When both alleles are the same, the offspring's characteristics can be predicted more easily, especially when applying Mendel's principles of heredity and probability.

5 Must Know Facts For Your Next Test

1. Homozygous individuals can be homozygous dominant (two dominant alleles) or homozygous recessive (two recessive alleles), affecting how traits are expressed.
2. In a Punnett square, homozygous parents produce predictable offspring genotypes based on their allele combinations.
3. Mendel's laws of segregation and independent assortment highlight how homozygous traits can be passed down from one generation to the next.
4. Homozygosity can increase the likelihood of certain inherited diseases when both parents carry recessive alleles for those conditions.
5. In plant breeding and genetics, homozygous lines are often desired for their stability and predictability in producing offspring with desired traits.

Review Questions

• How does being homozygous influence the expression of traits in offspring?
  • Being homozygous means that an organism has two identical alleles for a specific gene. This genetic uniformity leads to a consistent expression of traits since there is no variation between alleles. For instance, if both alleles are dominant, the resulting phenotype will display that dominant trait clearly. This predictability makes it easier to anticipate the characteristics of offspring when crossed with other homozygous or heterozygous organisms.
• Discuss how Mendel's experiments with pea plants utilized the concept of homozygosity to understand inheritance.
  • Mendel's experiments involved crossing true-breeding pea plants that were homozygous for specific traits, such as flower color. By starting with homozygous parents, Mendel could track how traits were passed on through generations. He discovered that crossing two homozygous plants with different traits produced heterozygous offspring that exhibited the dominant trait. This foundational work helped establish the principles of heredity and demonstrated how homozygosity contributed to predictable inheritance patterns.
• Evaluate the significance of homozygosity in relation to genetic diseases and breeding programs.
  • Homozygosity plays a significant role in genetic diseases because recessive alleles can manifest only when an individual carries two copies of the defective gene. This increases the risk of inherited conditions when both parents are carriers of such recessive alleles. In breeding programs, especially in agriculture, homozygosity is often targeted to produce stable and uniform offspring that exhibit desired characteristics consistently. However, excessive focus on homozygosity can reduce genetic diversity, which may impact the resilience of populations in changing environments.

Related terms

heterozygous: A condition where an organism has two different alleles for a specific gene, resulting in a mix of traits.

allele: Different forms of a gene that can exist at a specific locus on a chromosome.

phenotype: The observable characteristics or traits of an organism, which result from the interaction of its genotype and the environment.