DNA Structure and Properties
This experiment using smooth and rough strains of pneumonia first hinted that DNA carried genetic information.
What is Griffith's mouse experiment?
A cross with a homozygous recessive individual is called this.
What is a test cross?
What is the ploidy (haploid/diploid) of gametes compared to somatic cells?
Gametes are haploid, somatic cells are diploid.
A gene that influences multiple phenotypes is said to have this property.
What is pleiotropy.
In rabbits, black fur (B) is dominant over white fur (b). A heterozygous black rabbit is crossed with a white rabbit. What is the expected phenotypic ratio?
1 black : 1 white (50% each)
Hershey and Chase used this radioactive element to label DNA.
What is phosphorus?
If R = round seed and r = wrinkled, what proportion of offspring are heterozygotes from a cross of two heterozygotes?
2 out of 4, or 50%
During which phase of meiosis does crossing over occur?
What is Prophase I?
A 2:1 phenotypic ratio is a characteristic of this type of lethal allele.
What is a recessive lethal allele?
In cattle, red coat (R) is dominant to white coat (r). Heterozygotes (Rr) are spotted. If two spotted cows are crossed, what are the expected phenotypes if they have 24 calves, and what is the method of inheritance?
6 red : 12 spotted : 6 white
MOI = Codominance
This property explains why phosphates must face outward in the DNA double helix.
What is hydrophilicity (attraction to water)?
Mendel's true-breeding plants are also called this term.
What is homozygous?
Why do only heterozygotes contribute to variation in gamete combinations?
Homozygotes always pass the same allele, so there's no variation.
A disease persists in populations because its symptoms appear late in life. What type of allele is this?
What is a dominant lethal allele with delayed expression?
In mice, coat color is controlled by a gene where yellow (Y) is dominant to gray (y), but homozygous YY is lethal. Tail length is controlled by a separate gene with simple dominance: long tails (T) are dominant to short tails (t). If two heterozygous yellow, long-tailed mice (YyTt × YyTt) are crossed, what is the phenotypic ratio of the surviving offspring?
6 yellow long : 2 yellow short : 3 gray long : 1 gray short.
Given a species with 40% adenine, calculate the percentages of the other three bases.
40% A, 40% T, 10% G, 10% C
Explain how the reappearnace of a recessive trait in F2 supported Mendel's idea of allele pairs.
Recessive alleles were not lost but hidden in heterozygotes, showing traits exist in pairs.
Mendel's first law corresponds to this meiotic process.
What is segregation of homologous chromosomes in anaphase I and II.
What does incomplete penetrance mean in terms of genotype-to-phenotype expression?
Not all individuals with the genotype express the phenotype.
In dogs, a dominant allele (D) causes deafness, but it shows incomplete penetrance, with only 80% of Dd or DD dogs actually deaf. If two heterozygous dogs are crossed, what fraction of all offspring are expected to be deaf?
3/4 carry at least one D × 0.8 penetrance = 60% expected deaf.
Which form of DNA is left-handed and often associated with specific transcription factor binding?
What is Z-DNA?
Mendel's Law that explains why offspring randomly inherit one allele from each parent.
What is the Law of Segregation?
Using the formula 2^n, calculate the number of zygote combinations possible for a species with 10 pairs of chromosomes.
2^10 * 2^10 = 1,048,576 possible zygotes.
A cross between two heterozygous tailless cats produced fewer kittens than expected. Explain what genetic mechanism accounts for this.
Homozygous offspring carried a recessive lethal allele and did not survive.
A woman with blood type A (IAi) and a man with blood type B (IBi) have a child. What are the possible blood types of the child?
A, B, AB, or O.