Video Transcript
Gregor Mendel investigated the inheritance of genes through breeding experiments using his pea plants. From these experiments, he postulated three laws of inheritance. Which of the following best explains Mendel’s law of independent assortment? (A) The combination of alleles in the offspring will be dependent on the combination of alleles in the parents. (B) Genes that are responsible for different characteristics will be inherited independently of each other. (C) Alleles on separate chromosomes will not interact with each other in offspring. (D) A gamete of an organism will carry only one allele for each gene.
This question asks about the key contributions of Gregor Mendel to our current understanding of heredity and inheritance. Heredity is the transmission of characteristics across generations. For instance, if a characteristic is passed from one of your parents to you, we say you have inherited it.
Gregor Mendel studied pea plants in the mid-1850s, and he is considered a pioneer in the field of heredity. Through his experiments, he produced three laws of inheritance.
Mendel’s first law of inheritance was the law of dominance. The law of dominance is used to describe how some alleles conceal the appearance of other alleles. But what is an allele? You may remember that an allele is an alternative form of a gene. For instance, the characteristic of flower color in sweet pea flowers is controlled by purple and white alleles, represented here as uppercase B and lowercase b, respectively. In Mendel’s experiments, he found that crossing a purple flower plant with a white flower plant produced offspring with purple flowers. From this, he concluded that the purple allele was dominant to the white allele.
Mendel’s second law of inheritance was called the law of segregation. This law states that only one allele could exist in each gamete. A gamete is another term for a sex cell. In humans, males produce sperm cells and females produce egg cells. These cells contain half the genetic material of a typical body cell and are referred to as haploid. When a sperm and egg cell come together during fertilization, they form what is called a zygote. The zygote will contain two alleles for every gene, one copy coming from the sperm and the other from the egg. Therefore, in the sperm and egg cell, only one allele can exist. This is the law of segregation.
The last law of inheritance is called the law of independent assortment. During his experiments, Mendel realized that the genes he studied were inherited independently of one another. For the pea plants, Mendel found that the expression of purple or white flowers, indicated here as the letter B, was independent from the expression of smooth or wrinkled seeds, indicated here as the letter T. Therefore, the alleles for these genes must have separated into gametes independently of one another.
It’s important to differentiate between the law of segregation and the law of independent assortment. The law of segregation refers to two alleles of a single gene. On the other hand, the law of independent assortment refers to the alleles of two different genes, which have separated into gametes independently.
Therefore, the option that best explains the law of independent assortment is given by answer choice (B): genes that are responsible for different characteristics will be inherited independently of each other.
