Section 6.4 Study Guide: Traits, Genes, and Alleles
Vocabulary
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Gene
Allele
Homozygous
Heterozygous
Genome
Genotype
Phenotype
Dominant
Recessive
Review Questions
Main Ideas: The same gene can have many versions and Genes influence the development of traits.
1. What is the relationship between a gene and a protein?
Genes code for proteins
2. What is an allele? Any of the alternative forms of a gene that may occur at a specific locus.
3. What term describes a pair of alleles that are the same? That are different? Homozygous;
Heterozygous.
4. Write a definition of homologous chromosomes using the terms “gene” and “allele.” Homologous
chromosomes are two chromosomes, one from the mother and one from the father, that have the
same length, appearance, and carry the same gene - though each gene may have different alleles.
5. In the space below, draw a pair of homologous chromosomes. Label the chromosomes with two
sets of genes, one with homozygous alleles (Gene A, Gene A) and one with heterozygous alleles
(Gene B, Gene b).
Refer to notes for this.
6. What is the difference between genotype and phenotype?
Genotype is the underlying genetics of an organism, which you cannot see. Phenotype is the
expression of observable physical and behavioral traits. Phenotype is “created” through the
developmental interface of genotype (an organism’s underlying genetics) and environment.
7. How are alleles represented on paper?
Upper case for dominant alleles and lower case for recessive alleles.
8. Fill in the table below with the missing genotype, phenotype (dominant or recessive) or alleles (TT,
Tt, tt).
Genotype
Homozygous dominant
Dominant
Phenotype
TT
Alleles
Homozygous Recessive
Recessive
tt
Heterozygous
Dominant
Tt
9. If an organism has a recessive trait, can you determine its genotype for that trait? Yes but it has to
be homozygous recessive. You can figure out the dominant and recessives of a Mendelian trait
through test crosses.
10. What factors besides alleles affect phenotype? Environment affects phenotype. Again, phenotype is
the result of the combination (or developmental interface) of genotype and environment (example
include nutrients, sunshine for a plant, environmental mutagens, the language spoken in a place,
etc.).
11. What type of alleles are present in an organism with a QQ genotype? Homozygous dominant
12. What is an alternative form of a gene? Allele
13. What is the opposite of homozygous? What is the opposite of dominant? Heterozygous; Recessive