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Questions and Answers
What is the main function of chromosomes?
What is the main function of chromosomes?
What is a gene?
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 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?
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?
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?
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?
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?
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?
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?
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 (IA, IB, and IO).
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., IA and IB 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.
