General Biology 142
Chapter 12 Part 2 SQP
Mendel’s Experiments and Heredity
Section 12.2 Characteristics and Traits
Question 1: What is incomplete dominance? Provide an example.
Response: when the heterozygous phenotype appears to be intermediate
Incomplete Dominance in Four O’clock Flowers
1:2:1 Phenotypic Ratio produced when crossing 2 pink plants
Question 2: What are multiple alleles? Provide an example.
Response: usually there are more than 2 possible alleles for a given trait in a population
· Diploid organisms inherit 2 alleles out of the possible alleles that exist
· Example: Coat Color in Rabbits
· Four alleles interact to produce four possible phenotypes
· Phenotype: Brown Fur (aka wild type) Genotype: C+C+
· Phenotype: Chinchilla (black-tipped white fur) Genotype: cchcch
· Phenotype: Himalayan (black fur on extremities, white elsewhere) Genotype: chch
· Phenotype: Albino (all white fur) Genotype: cc
Question 3: What are X-linked traits? Provide an example.
Response: There are some genes found on the X chromosome that are not found on the Y chromosome called are X-linked traits
· X-linked trait: Eye color in fruit flies (Drosophila)
· Determined by Thomas Hunt Morgan in 1910
· Phenotype: red eyes or white eyes
· Alleles: XW or Xw
· Red eyed females: XWXW or XWXw
· White eyed females: XwXw
· Red eyed males: XWY
· White eyed males: XwY
Question 4: What are human sex-linked disorders? Provide an example.
· Sex Linked Traits:
· Sex of an organism is often determined by sex chromosomes
· Humans have 23 pairs of chromosomes (46 total)
· 22 pairs are autosomal chromosomes (not involved in determining sex(
· 1 pair determines sex
· Humans: XX female XY male
· X and Y chromosomes (in males only) are homologous even though the Y chromosome is smaller and contains fewer genes
· There are some genes found on the X chromosome that are not found on the Y chromosome
· Called X-linked genes
· Since males only inherit one X chromosome (from their mother), they are hemizygous for X-linked genes
Question 5: What is meant by genetic lethality?
· Lethal alleles:
· A mutation in an allele for a gene that is essential for survival