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Questions and Answers
What is the main function of chromosomes?
What is a gene?
What is the term for the combination of alleles an organism has for a given characteristic?
What is the term for the outward expression of the genotype in the form of physical characteristics?
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What is the difference between a dominant and recessive allele?
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What is the term for two different alleles that are equally expressed in the phenotype?
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What is the term for the inheritance of a characteristic controlled by more than one gene?
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How many alleles are present in the gene for blood group in humans?
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What is the term for an alternative form of a given gene?
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How many alleles can each human being have for a particular characteristic?
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Study Notes
Chromosomes and Genes
- A chromosome is a DNA thread wrapped in protein that carries inherited information from one generation to the next.
- A gene is a portion/segment of DNA that controls one particular characteristic, e.g., the gene for eye color.
Alleles
- An allele is an alternative form of a given gene.
- Each sexually-reproducing organism has two alleles for each of its characteristics, one inherited from each parent.
- Alleles can be similar or different.
- Multiple alleles are alleles with more than two alternative forms, e.g., the gene for blood group in humans has three alleles (IÂA, IÂB, and IÂO).
Genotype and Phenotype
- Genotype is the combination of alleles an organism has for a given characteristic, written using a pair of letters (e.g., AA, Aa, and aa).
- Phenotype is the outward expression of the genotype in the form of physical characteristics of an organism.
Dominance and Recessiveness
- A dominant allele is one that gets expressed in the phenotype to the exclusion of another, represented by a capital letter (e.g., A, B, T).
- A recessive allele is one that is overshadowed in the phenotype by the presence of a dominant allele, represented by a small/lowercase letter (e.g., a, b, t).
Codominance and Homozygosity
- Codominance occurs when two different alleles are equally expressed in the phenotype when present together (e.g., IÂA and IÂB for blood group).
- Homozygous refers to a genotype where both alleles are the same (e.g., AA, aa, BB, bb), resulting in homozygotes or pure breeds.
Heterozygosity
- Heterozygous refers to a genotype where the two alleles are different, such as one allele is dominant while the other is recessive (e.g., Aa, Tt, Bb), resulting in heterozygotes or hybrids.
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Description
Learn about the basics of genetics, including chromosomes, genes, and inheritance. Understand how chromosomes carry inherited information and genes control characteristics.
