| Different versions of the same gene, located at the same position on homologous chromosomes. | Alleles |
| What are alleles? | Alleles are different versions of the same gene. |
| A section of DNA that contains the instructions for building a specific protein or RNA molecule. | Gene |
| What is a gene? | A gene is a section of DNA that codes for a protein. |
| Reproduction involving the fusion of gametes from two parents, leading to offspring with a combination of genetic material from both parents. | Sexual Reproduction |
| What type of organisms have a pair of alleles for every trait? | Organisms that reproduce sexually have a pair of alleles for every trait. |
| Thread-like structures made of DNA and proteins that carry genetic information. | Chromosomes |
| Where are alleles located? | Alleles are located at the same position on homologous chromosomes. |
| Sex cells, such as eggs and sperm, that are involved in sexual reproduction. | Gametes |
| What are gametes? | Gametes are the sex cells - eggs in females and sperm in males. |
| The process of fusion of gametes, resulting in the formation of a zygote. | Fertilization |
| What is fertilization? | Fertilization is the process where gametes join together to form a zygote. |
| The cell formed by the fusion of gametes during fertilization; the earliest stage of a multicellular organism's development. | Zygote |
| What is a zygote? | A zygote is a fertilized egg that grows into an embryo. |
| Having two identical alleles for a particular gene. | Homozygous |
| What does it mean if an organism is homozygous for a trait? | If an organism has the same allele from both parents for a trait, it is homozygous for that trait. |
| Having two different alleles for a particular gene. | Heterozygous |
| What does it mean if an organism is heterozygous for a trait? | If an organism has different alleles from each parent for a trait, it is heterozygous for that trait. |
| The genetic makeup of an organism, including all its alleles. | Genotype |
| What is genotype? | Genotype refers to all the alleles an organism has. |
| The genetic makeup of an organism, including all its alleles. | Genotype |
| What does an organism's genotype determine? | An organism's genotype determines its phenotype. |
| The observable physical and physiological traits of an organism, determined by both its genotype and environmental factors. | Phenotype |
| What is phenotype? | Phenotype is all of an organism's physical characteristics. |
| Different versions of the same gene, located at the same position on homologous chromosomes. | Alleles |
| What determines which molecules are made in an organism's body? | The genotype, which includes all the different alleles, determines which molecules are made in an organism's body. |
| Traits or features of an organism that can be seen or measured, such as hair color, eye color, and body mass. | Observable Characteristics |
| What are examples of observable characteristics? | Examples of observable characteristics include hair color, eye color, body mass, and resistance to disease. |
| External influences that can affect an organism's phenotype, such as nutrition, climate, and exposure to toxins. | Environmental Factors |
| What factors can also affect an organism's phenotype besides its genotype? | An organism's phenotype can also be affected by environmental factors. |
| One of the alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. | Allele |
| What are dominant alleles? | Dominant alleles are alleles that are always expressed, even if an organism just has one copy of that allele. |
| Having two identical alleles for a particular gene. | Homozygous |
| How are dominant alleles expressed in homozygous organisms? | Dominant alleles are always expressed, whether an organism is homozygous or heterozygous for the trait. |
| Having two different alleles for a particular gene. | Heterozygous |
| How are dominant alleles expressed in heterozygous organisms? | Dominant alleles are always expressed, whether an organism is homozygous or heterozygous for the trait. |
| The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. | Phenotype |
| What do dominant alleles always affect? | Dominant alleles will always affect an organism's phenotype. |
| Earlobes that are fused directly to the side of the head, without a noticeable free lobe. | Attached Earlobes |
| What is an example of a gene with dominant alleles in humans? | One example is the gene for attached or detached earlobes. |
| Earlobes that hang freely below the point of attachment to the head. | Detached Earlobes |
| How is the allele for attached earlobes and detatched earlobes represented? | We'll call the allele for attached earlobes E and the allele for detached earlobes e. |
| An allele that is always expressed, masking the effect of the recessive allele in heterozygotes. | Dominant Allele |
| What does it mean when an allele is dominant? | It means that the allele is always expressed, even in the presence of a different allele. |
| The genetic constitution of an individual organism. | Genotype |
| What genotypes will result in attached earlobes? | Attached earlobes will result from the genotypes Ee, eE, or EE. |
| Which type of allele is often written using capital letters? | Dominant alleles are often written using capital letters. |
| An allele that is only expressed when an organism has two copies of that allele. | Recessive Allele |
| What are recessive alleles? | Recessive alleles are alleles that are only expressed when an organism has two copies of that allele. |
| Having two identical recessive alleles for a particular gene. | Homozygous Recessive |
| In what condition are recessive alleles expressed? | Recessive alleles are expressed only when an organism is homozygous recessive for the trait. |
| The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. | Phenotype |
| When do recessive alleles affect the phenotype? | Recessive alleles only sometimes affect the phenotype. |
| Earlobes that are fused directly to the side of the head, without a noticeable free lobe. | Attached Earlobes |
| What is an example of alleles for a trait with a recessive allele? | An example is the alleles for attached (E) and detached (e) earlobes. |
| Earlobes that hang freely below the point of attachment to the head. | Detached Earlobes |
| What genotype results in detached earlobes? | Only the genotype ee will result in detached earlobes. |
| The genetic constitution of an individual organism. | Genotype |
| What genotypes lead to attached earlobes? | Genotypes EE, Ee, and eE will lead to attached earlobes. |
| An allele that is always expressed, masking the effect of the recessive allele in heterozygotes. | Dominant Allele |
| How are recessive alleles written? | Recessive alleles are often written using lower case letters. |
| Having two different alleles for a particular gene. | Heterozygous |
| What genotypes result in a mix of phenotypes for a trait with a recessive allele? | Genotypes with one dominant allele and one recessive allele (Ee and eE) result in a mix of phenotypes. |
