Mendelian Inheritance

Question 1

The length of stem in the plants that Mendel studied had two alleles: T (tall) and t (short). Using these letters, write the allele for the heterozygous genotype __, the homozygous dominant genotype _
_, and the homozygous recessive genotype __.

Answer 1

Tt
TT
tt

Question 2

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance that either parent will produce a gamete with a dominant allele

Answer 2

1/2

Question 3

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

Using the multiplicative law of probability, calculate the chance of a homozygous dominant offspring (dark hair)?

Answer 3

1/2 x 1/2 = 1/4

Question 4

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance this couple will have a homozygous dominant offspring (dark hair)?

Answer 4

25%

Question 5

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance either parent will produce a gamete with a recessive allele?

Answer 5

1/2

Question 6

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

Using the multiplicative law of probability, calculate the chance of a homozygous recessive offspring (blonde hair)?

Answer 6

1/2 x 1/2 = 1/4

Question 7

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance this couple will have a homozygous recessive offspring (blonde hair)?

Answer 7

25%

Question 8

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance this couple will have a heterozygous offspring (dark hair)?

Answer 8

50%

Question 9

Among humans, the allele for dark hair (D) is dominant to the allele for blonde hair (d). Consider the cross Dd x Dd. To answer these questions, use fractions except when asked for a percentage.

What is the chance that this couple will have offspring with the dominant phenotype (dark hair)?

Answer 9

75%

Question 10

In peas, yellow seed color is dominant to green. The key is: Y = __, y = __.

Answer 10

yellow seed color
green seed color

Question 11

Researchers do a __ (i.e., the dominant phenotype is mated to the recessive phenotype) to determine whether the dominant phenotype is homozygous or heterozygous. If the individual is homozygous dominant, the offspring generation is expected to be __. If the individual is heterozygous, a phenotypic ratio of __ is expected.

Answer 11

Testcross
100% dominant
1 dominant : 1 recessive

Question 12

In humans, widow’s peak (W) is dominant to straight hairline (w). Consider the cross Ww x Ww. The chance of a child with widow’s peak is __%, and the chance of a child with straight hairline is __%.

Answer 12

75
25

Question 13

Consider the cross Ww x ww. The chance of a child with widow’s peak is __%, and the chance of a child with straight hairline is __%.

Answer 13

50
50

Question 14

Among humans, dark eyes (B) is dominant to blue eyes (b). In a family, one parent has dark eyes and the other has blue eyes. Among their offspring, two develop dark eyes and two develop blue eyes. Most likely, the genotypes of the parents are __ (dark-eyed parent) and __ (blue-eyed parent).

Answer 14

heterozygous Bb

homozygous recessive bb

Question 15

In fruit flies, a cross between long-winged (L) flies and short-winged (l) flies produces only long-winged flies. Most likely, the genotypes of the parental flies are __ (long-winged parent) and __ (short-winged parent).

Answer 15

homozygous dominant LL

homozygous recessive ll

Question 16

In pea plants, T = tall and t = short, and G = green pods and g = yellow pods. When Mendel crossed homozygous tall plants having green pods with pure, short plants having yellow pods, the F1 plants all had the genotype __ and the phenotype __. In the F2 plants, Mendel observed a phenotypic ratio of __, which led him to his law of __.

Answer 16

TtGg
tall and green pods
9 dom/dom : 3 dom/rec : 3 rec/dom : 1 rec/rec
independent assortment

Question 17

The process of meiosis explains the law of segregation and the law of independent assortment. Considering the movement of chromosomes,
Why is only one allele for each trait present in the gametes?

Answer 17

Homologous chromosomes are separated in meiosis I, so the cell goes from diploid (two alleles/factors per trait) to haploid (one allele/factor per trait).

Question 18

The process of meiosis explains the law of segregation and the law of independent assortment. Considering the movement of chromosomes,
Why are all combinations of alleles present in the gametes?

Answer 18

Homologous chromosomes separate independently of each other in meiosis I, so the alleles/factors of each trait separate independently.

Question 19

In horses, black (B) is dominant to brown (b) and a trotter (T) is dominant to a pacer (t). Use fractions in your answers.
Consider the cross Bb x bb. Among the offspring, the chance of black coat is __ and the chance of brown coat is __.

Answer 19

1/2

Question 20

In rabbits, black (B) is dominant to brown (b) and spotted coat (S) is dominant to solid coat (s). A black, spotted rabbit is mated to a brown, solid one, and all ten of their offspring are black and spotted. The genotypes of the parents are __ and ___.

Answer 20

BBSS
bbss

Question 21

Two different phenotypes result among the offspring from a genetic cross. The genotypes of the parents are
TT and TT
TT and Tt
Tt and tt
tt and tt

Answer 21

C

Question 22

The phenotypic ratio from a genetic cross is 1:1:1:1. The genotypes of the parents are
TTGG x TtGg
TtGG x Ttgg
TtGg x ttgg
Ttgg x ttgg

Answer 22

C

Question 23

What were the genotypes of the parents in the F1 generation of Mendel’s monohybrid cross for stem length?
Both TT
Both Tt
TT and Tt
Tt and tt

Answer 23

B

Question 24

In guinea pigs, the allele for dark color (B) is dominant to the allele for light color (b). In a cross between two heterozygous organisms, the chance of producing a light-colored offspring is
⅘
¾
½
¼

Answer 24

D

Question 25

The two factors (alleles) for each trait separate when gametes form, so that each gamete contains only one factor (allele) for each trait. This statement is part of Mendel’s law of
dominance
independent assortment
random recombination
segregation

Answer 25

D

Question 26

Select the incorrect association.
Alleles - A and p
Heterozygous - Aa
Homozygous - DD
Homozygous - Pp

Answer 26

D

Question 27

From the cross Aa x Aa, the probability of producing a homozygous dominant offspring is
25%
33%
50%
75%

Answer 27

A

Question 28

From the cross Dd x Dd, the probability of producing the dominant phenotype is
25%
50%
75%
100%

Answer 28

C

Question 29

How many kinds of gametes can an organism with genotype AaBB produce?
One
Two
Three
Four

Answer 29

Two

Question 30

Members of one pair of factors separate independently of the members of another pair of factors. This is a statement of Mendel’s law of
dominant factors
independent assortment
random recombination
segregation

Answer 30

B

Question 31

Two organisms, each with the genotype TtGg, mate. The chance of producing an offspring that has the dominant phenotype for height and the recessive phenotype for color is
9/16
7/16
6/16
3/16

Answer 31

3/16

Question 32

In humans, B = short fingers and b = long fingers, and W = widow’s peak and w = straight hairline. From the cross BbWW x Bbww, the chance of an offspring having both dominant traits is
9/16
3/4
3/8
1/4

Answer 32

3/4