key term - Heterozygous

Definition

Heterozygous refers to an individual organism that has two different alleles for a specific gene, one inherited from each parent. This condition plays a crucial role in Mendelian genetics as it determines how traits are expressed and inherited across generations. When an organism is heterozygous, the interaction between the different alleles can lead to various phenotypic outcomes, influencing genetic variation and evolutionary processes.

5 Must Know Facts For Your Next Test

1. Heterozygous individuals can exhibit dominant traits, as the presence of a dominant allele will mask the effect of the recessive allele.
2. The genotype of a heterozygous individual is commonly represented as 'Aa', where 'A' is the dominant allele and 'a' is the recessive allele.
3. In Mendelian inheritance, heterozygous individuals can produce gametes with different combinations of alleles, leading to genetic diversity in offspring.
4. The concept of heterozygosity is crucial for understanding concepts like genetic drift, natural selection, and population genetics.
5. Heterozygous advantage occurs when heterozygous individuals have a higher fitness than homozygous individuals, often seen in traits related to disease resistance.

Review Questions

• How does being heterozygous influence the expression of traits in organisms?
  • Being heterozygous means that an individual carries two different alleles for a gene. This can significantly influence trait expression because if one allele is dominant, it will be expressed in the phenotype regardless of the presence of a recessive allele. Thus, heterozygous individuals may show traits associated with the dominant allele, while also contributing to genetic diversity within a population.
• What are the implications of heterozygosity for genetic variation and evolutionary processes?
  • Heterozygosity contributes to genetic variation within populations by allowing for different combinations of alleles to be passed on to future generations. This variation is essential for evolution, as it provides a raw material for natural selection to act upon. Additionally, populations with high levels of heterozygosity are generally more adaptable to changing environments and may have increased survival rates against diseases.
• Evaluate the concept of heterozygous advantage and its significance in understanding evolution.
  • Heterozygous advantage refers to the phenomenon where heterozygous individuals have higher fitness than those who are homozygous for either allele. This concept is significant because it helps explain why certain alleles persist in a population despite being recessive. For example, in cases like sickle cell anemia, individuals who are heterozygous (carrying one normal allele and one sickle cell allele) have increased resistance to malaria. This leads to the maintenance of both alleles in the population, demonstrating how genetic diversity can be beneficial for survival and evolution.

Related terms

homozygous:

A condition where an organism has two identical alleles for a particular gene, either dominant or recessive.

dominant allele:

An allele that expresses its trait even in the presence of a different allele, overshadowing the recessive one.

recessive allele:

An allele that only expresses its trait when paired with an identical allele, being masked by a dominant allele.