13. Mendelian Genetics

An allele that exerts its effects whenever it is present is:

If the two alleles for a particular gene are identical the gene pair is:

Mendel's pea plants can have yellow peas or green peas. Mendel found the yellow pea color allele to be dominant over the green pea color allele. What does this mean?

If an individual is homozygous for a particular trait:

Complete this concept map to help you review some key concepts of genetics.

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a.

b.

c.

d.

e.

f.

Whether an allele is dominant or recessive depends on

a. How common the allele is, relative to other alleles

b. Whether it is inherited from the mother or the father

c. Whether it or another allele determines the phenotype when both are present

d. Whether or not it is linked to other genes

Why is the pea wrinkle-seed allele a recessive allele?

a. It 'recedes' in the F2 generation when homozygous parents are crossed.

b. The trait associated with the allele is not exhibited in heterozygotes.

c. Individuals with the allele have lower fitness than that of individuals with the dominant allele.

d. The allele is less common than the dominant allele. (The wrinkled allele is a rare mutant.)

The alleles found in haploid organisms cannot be dominant or recessive. Why?

a. Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual.

b. Because only one allele is present, alleles in haploid organisms are always dominant.

c. Alleles in haploid individuals are transmitted like mitochondrial DNA or chloroplast DNA.

d. Most haploid individuals are bacteria, and bacterial genetics is completely different from eukaryotic genetics.

Edward was found to be heterozygous (Ss) for sickle-cell trait. The alleles represented by the letters S and s are

a. Linked

b. On homologous chromosomes

c. Both present in each of Edward's sperm cells

d. On the same chromosome but far apart