Which feature of garden peas made them well suited to Mendel's experiments?
They normally self-fertilize and breed true
✓
They have only one pair of chromosomes
They take several years to mature
They produce only a few seeds per plant
Correct Answer
They normally self-fertilize and breed true
Pea flowers stay sealed until pollination is complete, so the plants self-fertilize and produce true-breeding lines whose offspring match the parent. They have only one pair of chromosomes is wrong; peas have several pairs. They take several years to mature is wrong; peas mature in one season. They produce only a few seeds per plant is wrong; large numbers of peas can be grown, which reduces the effect of chance.
Category: Mendel's Experiments
Question 2
In Mendel's crosses, what is the label for the offspring produced when two true-breeding parent plants are crossed?
P generation
F1 generation
✓
F2 generation
F3 generation
Correct Answer
F1 generation
The F1 (first filial) generation is the offspring of the original parental cross. The P generation is the true-breeding parents themselves. The F2 generation comes from letting F1 plants self-fertilize. The F3 generation comes from the F2 plants.
Category: Mendel's Experiments
Question 3
Mendel crossed true-breeding violet-flowered peas with true-breeding white-flowered peas. What did the first-generation offspring look like?
All had pink flowers
All had white flowers
All had violet flowers
✓
Three-quarters had violet flowers
Correct Answer
All had violet flowers
Violet is dominant to white in peas, so every hybrid offspring showed violet flowers. All had pink flowers would be blending or incomplete dominance, which Mendel did not see. All had white flowers is wrong because white is the recessive trait. Three-quarters had violet flowers describes the next generation, not the first.
Category: Mendel's Experiments
Question 4
Mendel's results contradicted which widely held idea of his time?
Cell theory
Natural selection
Spontaneous generation
Blending inheritance
✓
Correct Answer
Blending inheritance
Blending inheritance predicted that offspring would show a permanent mix of the parents' traits, but Mendel saw a hidden trait reappear unchanged in later generations. Cell theory concerns the cellular makeup of organisms, not inheritance. Natural selection is consistent with Mendel's results. Spontaneous generation concerns the origin of life, not how traits are passed on.
Category: Mendel's Experiments
Question 5
What is the term for the observable traits an organism expresses, such as seed color or plant height?
Phenotype
✓
Genotype
Allele
Karyotype
Correct Answer
Phenotype
The phenotype is what can be seen or measured in an organism. Genotype is the underlying genetic makeup, including alleles that are not expressed. An allele is one version of a gene. A karyotype is a display of an organism's chromosomes.
Category: Genetic Terms
Question 6
An individual with two identical alleles for a gene, such as YY or yy, is described as what?
Heterozygous
Homozygous
✓
Hemizygous
Polygenic
Correct Answer
Homozygous
Homozygous means both alleles of a gene are the same. Heterozygous means the two alleles differ, as in Yy. Hemizygous describes having only one copy of a gene, as for X-linked genes in males. Polygenic describes a trait controlled by several genes.
Category: Genetic Terms
Question 7
What is the term for the most common form of a gene or trait in a natural population, often marked with a plus sign?
Mutant
Hybrid
Wild type
✓
Carrier
Correct Answer
Wild type
The wild type is the typical form found in nature, and other forms are called variants or mutants. Mutant refers to a form that differs from the wild type. Hybrid refers to offspring of parents with different traits. Carrier refers to a heterozygote that holds a hidden recessive allele.
Category: Genetic Terms
Question 8
Two pea plants with the genotype Yy are crossed, and yellow (Y) is dominant to green (y). What ratio of yellow to green offspring is expected?
1:1
1:2:1
2:1
3:1
✓
Correct Answer
3:1
The Punnett square gives YY, Yy, Yy and yy; the first three are yellow and only yy is green, giving 3 yellow to 1 green. The ratio 1:1 is the result of crossing Yy with yy. The ratio 1:2:1 is the genotypic ratio, not the phenotypic one. The ratio 2:1 does not come from a simple cross of two Yy plants.
Category: Monohybrid Crosses
Question 9
In a cross of two Yy pea plants, what fraction of the offspring is expected to have the genotype Yy?
1/2
✓
1/4
3/4
1/3
Correct Answer
1/2
Of the four equally likely combinations (YY, Yy, Yy, yy), two are Yy, so the expected fraction is 2/4, or 1/2. The fraction 1/4 is the share of YY or of yy alone. The fraction 3/4 is the share showing the yellow phenotype. The fraction 1/3 is the share of yellow offspring that are YY, not of all offspring that are Yy.
Category: Monohybrid Crosses
Question 10
Crossing an organism that shows a dominant trait with one that shows the recessive trait, in order to reveal the first organism's genotype, is called what?
Reciprocal cross
Test cross
✓
Dihybrid cross
Self-cross
Correct Answer
Test cross
In a test cross, if any offspring show the recessive trait, the dominant-looking parent must carry a recessive allele. A reciprocal cross swaps which parent supplies the pollen or sperm. A dihybrid cross tracks two characteristics at once. A self-cross fertilizes an organism with its own gametes.
Category: Monohybrid Crosses
Question 11
According to Mendel's law of segregation, what happens to the two copies of a gene when gametes form?
They blend into a single intermediate copy
They stay together in the same gamete
They separate so each gamete gets one copy
✓
They are both copied into every gamete
Correct Answer
They separate so each gamete gets one copy
The law of segregation says the paired copies of a gene separate equally, so each gamete carries only one and an offspring has an equal chance of inheriting either. They blend into a single intermediate copy describes the rejected blending idea. They stay together in the same gamete would give gametes two copies. They are both copied into every gamete would double the gene number each generation.
Category: Laws of Inheritance
Question 12
Which meiotic event is the physical basis of Mendel's law of segregation?
Replication of DNA before meiosis
Fusion of gametes at fertilization
Condensation of chromosomes in prophase
Separation of homologous chromosomes
✓
Correct Answer
Separation of homologous chromosomes
In the first division of meiosis, homologous chromosomes carrying the two versions of a gene move to different cells, so each gamete gets one version. Replication of DNA before meiosis copies genes but does not separate them. Fusion of gametes at fertilization brings alleles together rather than separating them. Condensation of chromosomes in prophase packages chromosomes but does not divide alleles.
Category: Laws of Inheritance
Question 13
Mendel's law of independent assortment always holds for genes that meet which condition?
They sit on different, nonhomologous chromosomes
✓
They sit close together on one chromosome
They are found only on the X chromosome
They control the same characteristic
Correct Answer
They sit on different, nonhomologous chromosomes
Genes on different chromosomes sort into gametes independently because each homologous pair orients randomly in metaphase I. They sit close together on one chromosome describes linked genes, which tend to be inherited together. They are found only on the X chromosome would put them on the same chromosome. They control the same characteristic says nothing about where the genes are located.
Category: Laws of Inheritance
Question 14
Two pea plants with the genotype RrYy are crossed. If the two genes assort independently, what phenotypic ratio is expected?
3:1
9:3:3:1
✓
1:1:1:1
1:2:1
Correct Answer
9:3:3:1
With independent assortment, each parent makes four gamete types, giving 16 equally likely combinations: 9 show both dominant traits, 3 show each single-recessive combination, and 1 shows both recessive traits. The ratio 3:1 is the result of a cross tracking one gene. The ratio 1:1:1:1 is the result of crossing RrYy with rryy. The ratio 1:2:1 is a monohybrid genotypic ratio.
Category: Dihybrid Crosses
Question 15
How many genetically different kinds of gametes can a plant with the genotype RrYy produce if the two genes assort independently?
2
8
4
✓
16
Correct Answer
4
Each gamete gets one allele of each gene, so the possible combinations are RY, Ry, rY and ry, four in all. The value 2 counts the alleles of only one gene. The value 8 would require three heterozygous genes. The value 16 is the number of boxes in the Punnett square for crossing two such plants.
Category: Dihybrid Crosses
Question 16
When neither allele is completely dominant, so a heterozygote shows a trait intermediate between the two homozygotes, the pattern is called what?
Codominance
Epistasis
Linkage
Incomplete dominance
✓
Correct Answer
Incomplete dominance
In incomplete dominance, the heterozygote has an in-between phenotype, as when red and white snapdragons produce pink offspring. Codominance means both alleles are fully expressed at once, as in type AB blood. Epistasis is one gene masking the effect of a different gene. Linkage is the tendency of nearby genes on one chromosome to be inherited together.
Category: Dominance Variations
Question 17
In the ABO blood group system, what blood type does a person with one A allele and one i allele have?
Type A
✓
Type AB
Type O
Type B
Correct Answer
Type A
The A allele is dominant over the i allele, so a person with one of each has type A blood. Type AB requires one A allele and one B allele, which are codominant. Type O requires two i alleles. Type B requires a B allele and no A allele (genotype BB or Bi).
Category: Dominance Variations
Question 18
The human ABO blood group gene has three alleles. How many different genotypes are possible?
3
6
✓
4
9
Correct Answer
6
Three alleles give three homozygous genotypes (AA, BB, ii) and three heterozygous genotypes (AB, Ai, Bi), for six in all. The value 3 counts only the alleles. The value 4 is the number of ABO phenotypes (A, B, AB and O). The value 9 comes from squaring the number of alleles, which counts each heterozygote twice.
Category: Dominance Variations
Question 19
A woman who is a carrier for an X-linked recessive disorder has children with an unaffected man. What fraction of their sons is expected to be affected?
1/4
All of them
1/2
✓
None of them
Correct Answer
1/2
Each son gets his only X chromosome from his mother, and a carrier mother has a 1 in 2 chance of passing the X with the recessive allele. The fraction 1/4 is the chance that any child, son or daughter, will be an affected son. All of them would require the mother to have two copies of the recessive allele. None of them is wrong because a son needs only one copy of the allele to be affected.
Category: Sex-Linked Traits
Question 20
In mice, two recessive alleles at one gene (cc) block all pigment production, giving albino fur no matter which alleles are present at the agouti coat gene. What is this interaction called?
Codominance
Linkage
Polygenic inheritance
Epistasis
✓
Correct Answer
Epistasis
Epistasis occurs when one gene masks or interferes with the expression of a different gene; here the C gene is epistatic to the agouti gene. Codominance is the full expression of two alleles of the same gene. Linkage is the inheritance of nearby genes together. Polygenic inheritance is several genes adding to one trait, not one gene hiding another.
Category: Gene Interactions