Inheritance and Trait Variation Flashcards

A student is examining a diagram of genetic material. Which of the following statements correctly describes the relationship between DNA, genes, and chromosomes?

Answer: Chromosomes are made of DNA, and genes are specific segments of that DNA that code for traits.

The correct answer accurately represents the hierarchical structure of genetic material. Chromosomes, located in the nucleus of eukaryotic cells, are tightly coiled structures composed of DNA and proteins. A gene is a specific sequence or segment of this DNA that holds the instructions for building a specific protein or functional RNA molecule, which in turn determines a particular trait.

In pea plants, the allele for purple flowers (P) is dominant over the allele for white flowers (p). If a heterozygous purple-flowered plant (Pp) is crossed with a white-flowered plant (pp), what is the probability that an offspring will have white flowers?

Answer: 50%

This is a monohybrid cross. A Punnett square for this cross (Pp x pp) shows that the possible genotypes for the offspring are Pp and pp. The probability of producing a Pp genotype is 2/4 (50%), and the probability of producing a pp genotype is 2/4 (50%). Since the white flower trait is recessive, it is only expressed in the homozygous recessive (pp) genotype. Therefore, there is a 50% probability of an offspring having white flowers.

Which of the following processes is the primary source of new genetic combinations in offspring produced through sexual reproduction?

Answer: Meiosis

Meiosis is the specialized cell division process that produces gametes (sperm and egg cells). During meiosis, processes like crossing over (where chromosomes swap sections) and independent assortment create new combinations of alleles. This recombination of genetic material is a major source of the variation seen in sexually reproducing organisms.

Himalayan rabbits have a gene that codes for fur color. The enzyme produced by this gene is only active at cooler temperatures. In a warm environment, the rabbit's fur is white. However, if an area of its body, like its ears or nose, is exposed to cold, the fur in that area grows black. This scenario is an example of:

Answer: Environmental factors influencing gene expression.

The Himalayan rabbit's fur color is a classic example of how environmental factors can affect the expression of traits (phenotype). The rabbit has the gene for black fur, but its expression is regulated by temperature. This shows that the variation of traits depends on both genetic and environmental factors.

What is a key difference between the outcomes of mitosis and meiosis?

Answer: Mitosis results in diploid cells that are genetically identical to the parent cell, while meiosis results in haploid cells that are genetically unique.

Mitosis is a process of cell division that results in two diploid daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. Meiosis is a process where a single cell divides twice to produce four haploid cells containing half the original amount of genetic information. These cells are our sex cells – sperm in males, eggs in females, and they are genetically unique due to recombination.

Inheritable genetic variation is essential for evolution. Which of the following is a source of such variation?

Answer: A viable error in DNA replication that results in a mutation.

Inheritable variation stems from changes in the genetic code. A mutation is a change in the DNA sequence. If this change occurs in a germ line cell (a cell that produces gametes), it can be passed on to offspring. Errors during DNA replication are one of the primary ways mutations arise, creating new alleles and thus new genetic variation.