Genetics Problems - Complete Dominance

Question 1

What method should be used when only one gene is studied?

Answer 1

A Punnett Square

Question 2

What method should be used when more than one gene are studied?

Answer 2

Forked Line

Question 3

When you know the genotype of the parents, what should you do to determine other infos?

Answer 3

Determine the possible gamete combinations and analyze the outcomes

Question 4

What is the difference between the sum rule and the multiplication rule in probability?

Answer 4

When either one or the other event need to happen, we add the probability of each event occurring (or). When both need to happen at the same time, we need to multiply their individual probabilities (and).

Question 5

When two or more genes are analyzed, what approach should be used?

Answer 5

Analyze them separately and then use the multiplication rule or sum rule

Question 6

How can we determine the combinations of gametes?

Answer 6

We know that each parent while give either one of its allele to the offspring. We just need to find out all possible combinations.

Question 7

What can be an indication that a trait is dominant?

Answer 7

In the offsprings, a trait that was in the parents disappears. We know that the other one is thus dominant and that this one is recessive. Or proportions match the pattern we know.

Question 8

What can be an indication that a trait is recessive?

Answer 8

When two parents mate and have the dominant phenotype, some of the offsprings have a different phenotype. Then, we know that both are heterozygous and that the new phenotype is recessive. (this offspring is thus homozygous)

Question 9

How should you start a problem if an offspring is recessive?

Answer 9

When it is recessive, it needs to be homozygous to have this phenotype. Thus, we know that BOTH of the parents need to have this allele for it to be in the gametes.

Question 10

What is the maximum number of phenotypes and genotypes for a situation of complete dominance?

Answer 10

2 phenotypes and 3 genotypes maximum.

Question 11

What is a clue that we have complete dominance?

Answer 11

The heterozygotes and the homozygous have the same phenotype.

Question 12

A mother and father both find the taste of the chemical phenylthiourea very bitter. However, two of their three children find the chemical tasteless. Assume this trait is controlled by only one gene. Which of the two phenotypes (tastes bitter vs. tasteless) is dominant?

Answer 12

Dominant = tastes bitter because the two give new phenotypes. Thus, they are heterozygotes.

Question 13

Suppose a man and a woman are both heterozygous for a recessive gene for albinism (no pigment). If they have twins, what is the probability that both of the infants will have the same phenotype with respect to pigmentation?

Answer 13

3/4 or 9/16 (it depends if they are from the same egg or not)…. Same egg is like if they were a complete child, but not same egg is like if they were two children of which we need to multiply the probabilities of 3/4.

Question 14

A dominant allele, B is responsible for wild-type body color in fruit flies; its recessive allele, b, produces black body color. A test cross of a wild-type female gave 52 black and 58 wild-type offspring in the F1 generation. If the wild-type females were crossed with their black F1 male siblings, what genotypic ratios would be expected in the F2?

Answer 14

1/2 Bb 1/2 bb

Question 15

A dominant allele, B is responsible for wild-type body color in fruit flies; its recessive allele, b, produces black body color. A test cross of a wild-type female gave 52 black and 58 wild-type offspring in the F1 generation. If the wild-type females were crossed with their black F1 male siblings, what phenotypic ratios would be expected in the F2?

Answer 15

1 black : 1 wild type

Question 16

Assume that an individual is heterozygous for three independently located pairs of alleles. If this organism is self-fertilized, what proportion of the offspring will carry the genotype AaBbcc? Assume complete dominance

Answer 16

1/16

Question 17

Assume that an individual is heterozygous for three independently located pairs of alleles. If this organism is self-fertilized, what proportion of the offspring will have the same phenotype as the parent? Assume complete dominance

Answer 17

P (A-B-C-) = (3/4)(3/4)(3/4) = 27/64

Question 18

When a pea plant with the genotype AaBb produces gametes, what proportion will be Ab?

Answer 18

1/4

Question 19

In mice the gene for colored coat (P) is dominant to the gene for albino (p) and the gene for straight whiskers (S) is dominant to the allele for bent whiskers (s). Consider a cross between two mice heterozygous for both these alleles: PpSs x PpSs What proportion of the offspring would you expect to be albino?

Answer 19

1/4

Question 20

In mice the gene for colored coat (P) is dominant to the gene for albino (p) and the gene for straight whiskers (S) is dominant to the allele for bent whiskers (s). Consider a cross between two mice heterozygous for both these alleles: PpSs x PpSs. What proportion would be albino with bent whiskers?

Answer 20

1/16

Question 21

Black coat color in Cocker Spaniels is governed by a dominant allele, B, and red coat color by its recessive allele, b. Solid pattern (i.e., one color) is governed by the dominant allele, S, of an independent gene, and spotted pattern (i.e. black and white or black and red) by a its recessive allele, s. A solid, black female is mated to a solid, red male and produces a litter of six pups: 2 solid black, 2 solid red, 1 black and white, 1 red and white. Determine the genotypes of the parents.

Answer 21

the solid black (S-B-)female is SsBb and the solid, red male (S-bb) is Ssbb. Since one puppy is ssbb (spotted, red) BOTH paents must have at least one recessive allele.

Question 22

In tomato plants tall is dominant to short and the phenotype hairy is dominant to hairless. A heterozygous tall, hairy plant is crossed. What is the genotype of this tall hairy plant?

Answer 22

TtHh

Question 23

In tomato plants tall is dominant to short and the phenotype hairy is dominant to hairless. A heterozygous tall, hairy plant is crossed. The F1 offspring were observed to be 118 tall, hairy; 121 dwarf, hairless; 112 tall, hairless; 109 dwarf, hairy. What is the genotype of the unknown parent?

Answer 23

Parent 1 is Tt Hh. half of offspring are hairy. Hh x hh produces 1/2 hairy. same logic for tall.

Question 24

Heterozygous x heterozygous

Answer 24

3/4 dom 1/4 rec.

1/2 homo 1/2 het.

Question 25

Homozygous dom x Homozygous rec.

Answer 25

All het. All dom

Question 26

Het. x Homo dom.

Answer 26

ALL DOMINANT 1/2 homo 1/2 het

Question 27

What is the probable cross if there are equivalent numbers for each phenotype?

Answer 27

Aa x aa (1 trait) or AaBb x aabb (2 traits)

Question 28

What do we do with numbers instead of fractions?

Answer 28

We convert them in fractions to find typical phenotypic ratios

Question 29

What is the number of interest to find quickly the type of pattern we are studying?

Answer 29

Look at the smallest number compared to the largest

Question 30

With 4 phenotypes, what if the largest number is about 9 times more than the smallest? And the two other phenotypes have 3 times more individuals than smallest number?

Answer 30

Probabilities are 9/16, 3/16, 3/16 and 1/16

Question 31

With 2 phenotypes, what if the largest number is 3 times the smallest?

Answer 31

Could be 3/4, 1/4 (COMPLETE DOMINANCE)

Question 32

With 2 phenotypes, what if the largest number is 2 times smallest?

Answer 32

Could be 2/3, 1/3 (lethal recessive)

Question 33

With 3 phenotypes, what if the largest number is 2 times more than smallest?

Answer 33

1/4, 1/2, 1/4 (incomplete dominance or co-dominance)

Question 34

What if we have 3 phenotypes, but not the typical proportions?

Answer 34

It is likely epistasis.