What is the difference between heterozygous and homozygous individuals?
All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.
When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______.
gametes, progeny
True or false? The same phenotype can be produced by more than one genotype.
True
True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.
false
If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?
None
Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?
25
A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the “1” in the 9:3:3:1 ratio)?
ttpp
One character in peas that Mendel studied was yellow versus green seeds.
A cross between a homozygous yellow line (YY) and a homozygous green line (yy) will result in F1 plants that are heterozygous (Yy) for this trait and produce yellow seeds.
When an F1 plant undergoes meiosis, what gamete types will it produce, and in what proportions?
Use your understanding of Mendel’s law (or principle) of segregation to label each gamete possibility as “correct” or “incorrect.”
a. incorrect
b. correct
c. incorrect
d. incorrect
e. incorrect
f. incorrect
Punnett squares are convenient ways to represent the types and frequencies of gametes and progeny in experimental crosses.

This Punnett square shows the results of a Yy x Yy cross to form F2 progeny.

Use your understanding of Mendel’s law of segregation and the rules of probability to complete the Punnett square for this cross.
-First identify the gametes. Use pink labels to identify the male and female gamete types and white labels to identify the gamete frequencies.
-Then identify the F2 progeny. Use pink labels to identify the progeny genotypes and white labels to identify the progeny frequencies.

1/2 Y ; 1/2 Y
1/2 Y ; 1/4 YY ; 1/4 Yy
1/2 y ; 1/4 Yy ; 1/4 yy
Use the completed Punnett square in Part B to answer the questions below about the F2 generation.
Answer each question in the table by dragging the correct label to the appropriate location. Labels can be used once, more than once, or not at all.
3/4
1/3
63/64
27/64
The result of the following cross indicates the orange eyes are _____ black eyes.
recessive to
If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the genotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
0 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb)
If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the phenotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
1 black : 1 orange
The result of the following cross indicates that the genotype of the female parent is _____.
RR
The result of the following cross indicates that the genotype of the male parent is _____.
rr
The result of the following cross indicates that genotypically the offspring _____.
are all Rr
Which of these is a testcross?
A? x aa
That each gamete contains a single allele of the eye color gene is an illustration of _____.
Mendel’s law of segregation only
What is the genotype of the parent with orange eyes and white skin? (Note: orange eyes are recessive.)
bbgg
Black eyes are dominant to orange eyes, and green skin is dominant to white skin. Sam, a MendAlien with black eyes and green skin, has a parent with orange eyes and white skin. Carole is a MendAlien with orange eyes and white skin. If Sam and Carole were to mate, the predicted phenotypic ratio of their offspring would be _____.
1 black eyes, green skin : 1 black eyes, white skin : 1 orange eyes, green skin : 1 orange eyes, white skin
In order to determine the genotype of a MendAlien with black eyes and green skin, you would cross this individual with a(n) _____ individual.
bbgg
A cross between an individual with orange eyes and green skin and an individual with black eyes and white skin is an example of a _____ cross.
dihybrid
A phenotypic ratio of 9:3:3:1 in the offspring of a cross indicates that _____.
both parents are heterozygous for both genes
The observed distribution of alleles into gametes is an illustration of _____.
Mendel’s laws of segregation and independent assortment
In a situation in which genes assort independently, what is the ratio of the gametes produced by an AaBB individual?
1 AB : 1 aB
In his breeding experiments, Mendel first crossed true-breeding plants to produce a second generation, which were then allowed to self-pollinate to generate the offspring. How do we name these three generations?
P … F1 … F2
What is an allele?
an alternative version of a gene
Consider pea plants with the genotypes GgTt and ggtt. These plants can each produce how many type(s) of gametes?
four … one
You cross a true-breeding red-flowered snapdragon with a true-breeding white-flowered one. All of the F1 are pink. What does this say about the parental traits?
Red shows incomplete dominance over white.
Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?
a combination of polygenic inheritance and environmental factors
Folk singer Woody Guthrie died of Huntington’s disease, an autosomal dominant disorder. Which statement below must be true?
It is very likely that at least one of Woody Guthrie’s parents also had the allele for Huntington’s disease.
x

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