Question

Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.

Short answer

Answer: The Mendel's postulate that can only be demonstrated in crosses involving at least two pairs of traits is the Law of Independent Assortment.

Step-by-step solution

Understand Mendel's postulates

Mendel's postulates are the basic principles of inheritance proposed by Gregor Mendel based on his observations in pea plants. There are four postulates: 1. Law of Unit Characters (Principle of Pairs) - Traits are determined by factors (genes) that occur in pairs (alleles) in individual organisms. 2. Law of Dominance - In a heterozygous organism, one allele (dominant) is expressed, and the other (recessive) allele is masked. 3. Law of Segregation (Principle of Separation) - During gamete formation, paired alleles in an organism separate, with each gamete receiving only one allele for each trait. 4. Law of Independent Assortment - Alleles for different traits are inherited independently of each other.

Identify the postulate involving two pairs of traits

Among Mendel's postulates, the Law of Independent Assortment is the one that requires at least two pairs of traits to be demonstrated. This law states that the inheritance of one trait is independent of the inheritance of another trait. It can only be demonstrated when studying crosses involving two or more pairs of traits, as we need to observe how the assortment of alleles for different traits occurs independently.

State the postulate

The Mendel's postulate that can only be demonstrated in crosses involving at least two pairs of traits is the Law of Independent Assortment. It states that alleles for different traits are inherited independently of each other.

Key concepts

Inheritance Patterns

Inheritance patterns in genetics refer to the predictable ways that traits are transmitted from parent to offspring. These patterns follow certain principles laid out by Gregor Mendel in the 19th century, after his experiments with pea plants. Mendel discovered that traits are inherited in distinct patterns, now recognized as autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and mitochondrial inheritance.

Each pattern has unique features: Autosomal dominant traits require only one copy of the dominant allele for the trait to be expressed, whereas autosomal recessive traits require two copies of the recessive allele. X-linked traits are associated with genes located on the X chromosome, and mitochondrial inheritance involves genes in the mitochondria, passed almost exclusively from mother to child. Understanding these patterns is critical in predicting the likelihood of an offspring inheriting a particular trait, and it aids in the diagnosis and management of genetic disorders.

Genetics Principles

The principles of genetics provide the framework for understanding how traits are passed from one generation to the next. These principles include the concepts of genes, alleles, dominance, segregation, and independent assortment. Genes are the fundamental units of heredity and are made up of DNA. They reside on chromosomes which are present in pairs in each cell.

Alleles and Variability

Alleles are different forms of a gene that can exist at a specific locus on a chromosome. Variability in these alleles contributes to the diversity in traits observed among individuals. For example, there are different alleles for eye color, which is why individuals have varying eye colors.

Expression of Traits

The expression of traits involves how these alleles interact, influenced by Mendel's laws, such as dominance, where a dominant allele can mask the presence of a recessive one in determining the physical trait.

Law of Segregation

Mendel's Law of Segregation is the foundation for understanding how alleles are separated during the formation of gametes (sex cells). According to this principle, for each trait, an organism has two alleles, one from each parent, and these alleles segregate, or separate, during gamete formation ensuring that each gamete carries only one allele for each trait.

Meiosis and Gamete Formation

This segregation occurs during a process called meiosis, which is the cellular division specific to gamete formation. During meiosis, paired alleles (located on homologous chromosomes) are separated and distributed into different gametes, reflecting a fundamental genetic mechanism that maintains genetic diversity through sexual reproduction.

Law of Dominance

Mendel's Law of Dominance explains how different forms of a gene (alleles) interact with each other. If an individual carries two different alleles for a certain gene, the dominant allele is expressed while the recessive allele is not, thus 'masking' the recessive trait.

Homozygous and Heterozygous

Individuals carrying two identical alleles (homozygous) will express that trait, be it dominant or recessive. However, in a heterozygous individual, who has one dominant and one recessive allele, the dominant trait will be observed. This law is key to predicting the phenotypic outcome of certain genetic crosses and is essential for understanding patterns of inheritance in an easily visible way.