- What is a gene?
- A section of DNA that codes for a specific trait or protein
- A protein that controls body functions and chemical reactions
- A chromosome that carries all genetic information in the cell
- An organism’s physical appearance and observable characteristics
A gene is a specific section of DNA that contains instructions for producing a protein or trait. Genes are inherited from parents and determine many characteristics.
- What are alleles?
- Different forms of a gene at the same location on a chromosome
- Identical copies of a parent’s genes passed to offspring
- Mutations that occur during the process of reproduction
- Proteins produced directly by genes during translation
Alleles are different versions of the same gene. For example, a gene for eye color might have alleles for blue eyes and brown eyes. Most organisms inherit two alleles for each gene, one from each parent.
- A trait that only appears when an organism has two copies of the recessive allele is called what?
- A dominant trait
- An inherited trait
- A recessive trait
- A mutated trait
A recessive trait requires two copies of the recessive allele to be expressed because the dominant allele masks it when present. This is why two brown-eyed parents can have a blue-eyed child.
- What is the difference between genotype and phenotype?
- Genotype is an organism’s behavior, while phenotype determines its structure.
- Genotype is inherited from parents, while phenotype is not inherited.
- Genotype is the genetic makeup, while phenotype is the observable physical characteristics.
- Genotype and phenotype refer to the exact same biological concept.
Genotype is an organism’s genetic makeup (the alleles it has), while phenotype is the observable characteristics resulting from both genotype and environment. For example, two organisms can have the same genotype but different phenotypes.
- Which of the following is NOT a characteristic of DNA?
- It contains instructions for making proteins and other molecules.
- It has a double helix structure made of two twisted strands.
- It is made of four different bases: adenine, thymine, guanine, and cytosine.
- It is located only in the cell nucleus and nowhere else in the cell.
While most DNA is in the cell nucleus, DNA is also found in mitochondria and chloroplasts. These organelles have their own DNA separate from nuclear DNA, which they inherited from ancient prokaryotic ancestors.
- Which best describes what happens during meiosis?
- A cell divides once to produce two identical body cells with the same genetic information.
- A cell divides twice to produce four sex cells with half the genetic information.
- A cell duplicates its DNA and then divides once without separating chromosomes.
- Chromosomes exchange genetic material but the cell nucleus remains intact.
Meiosis is the process that produces sex cells (gametes) with half the chromosomes of the parent cell. This ensures that when gametes fuse during fertilization, the offspring has the correct number of chromosomes.
- In humans, more than one gene contributes to the trait of hair color. What is this an example of?
- Pleiotropy
- Polygenic inheritance
- Codominance
- Epistasis
When more than one gene contributes to a trait, inheritance of that trait is said to be polygenic. This type of inheritance does not follow the rules of Mendelian genetics.
- What are chromosomes?
- Structures made of DNA and proteins that carry genes and genetic information
- Individual genes that code for specific proteins and traits
- Cells that can reproduce through division and form new tissues
- Proteins that control chemical reactions in the cell
Chromosomes are thread-like structures found in the nucleus that contain DNA wrapped around protein molecules. Humans have 46 chromosomes arranged in 23 pairs, and each chromosome contains many genes.
- A brown-eyed mother and a brown-eyed father have children, some with brown eyes and some with blue eyes. What must be true about the parents?
- Brown eyes are recessive because both parents express the trait.
- The blue-eyed children must have been adopted or have a different biological father.
- Both parents must be heterozygous carriers of the blue-eye recessive allele.
- Eye color is not inherited genetically in humans.
For two brown-eyed parents to have blue-eyed children, both must carry a recessive allele for blue eyes. They are heterozygous for eye color, carrying both dominant (brown) and recessive (blue) alleles.
- What is a mutation?
- A change in the sequence of DNA that can affect organism traits
- The normal and natural process of sexual reproduction
- A disease caused by inheriting multiple bad genes from parents
- The ability of organisms to adapt to environmental changes
A mutation is a change in DNA sequence. Mutations can be beneficial, harmful, or neutral, and they are a source of genetic variation in populations. Some mutations occur naturally, while others are caused by radiation or chemicals.
- How does sexual reproduction increase genetic variation?
- It creates new mutations in every single offspring produced.
- It combines genetic material from two parents in new combinations.
- It allows organisms to adapt and change during their own lifetime.
- It prevents all harmful alleles from being passed to offspring.
Sexual reproduction shuffles alleles from two parents through processes like crossing over and independent assortment during meiosis. This creates new combinations of alleles in offspring, increasing genetic variation in the population.
- Which statement correctly applies the terms homozygous and heterozygous?
- A homozygous organism has identical alleles and typically expresses the dominant form.
- A heterozygous organism has identical alleles for a trait.
- A homozygous organism has two different alleles for a trait.
- A heterozygous organism cannot inherit alleles from both parents.
An organism that is homozygous has two identical alleles for a trait (both dominant or both recessive). One that is heterozygous has two different alleles, so it typically expresses the dominant trait.
- What is natural selection?
- The process by which humans choose which animals to breed together
- The process where organisms with beneficial traits survive and reproduce
- The random change in allele frequency in populations over time
- A mutation that occurs to help organisms adapt to change
Natural selection is the mechanism of evolution where organisms with traits suited to their environment are more likely to survive and reproduce, passing those advantageous traits to offspring and increasing their frequency in the population.
- What is the key difference between genetic engineering and traditional selective breeding?
- Genetic engineering produces results faster, but selective breeding is more ethical.
- Genetic engineering directly manipulates DNA and can introduce genes from other species.
- Selective breeding can only be used on animals, while genetic engineering works only on plants.
- Genetic engineering relies on natural mutations, while selective breeding requires technology.
Genetic engineering involves the direct manipulation of an organism’s DNA using biotechnology tools like CRISPR, allowing scientists to insert genes from other species or edit existing genes. Traditional selective breeding relies on choosing organisms with desirable traits and breeding them together—a slower process that cannot introduce genes from different species.
- What does genetic variation provide for a population?
- It ensures all offspring are identical to their parents genetically.
- It guarantees that organisms will not develop diseases or illness.
- It provides raw material for natural selection and adaptation.
- It prevents all mutations from occurring in organisms.
Genetic variation within a population means individuals have different traits. This diversity allows populations to adapt when environments change because individuals with beneficial traits are more likely to survive and reproduce.