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Chapter 4: Problem 5

The creeper gene in chickens causes short and stunted legs (creeper condition) in the heterozygous state (Cc) and lethality in the homozygous state (CC). The genotype \(c c\) produces normal chickens. What ratio is obtained when creeper chickens are Interbred? Is the \(C\) allele behaving dominantly or recessively in causing lethality?

Short Answer

Expert verified
Also, does the C allele behave dominantly or recessively in causing lethality? Answer: When creeper chickens (Cc) are interbred, the ratio of genotypes of the offspring is 2 creeper (Cc) : 1 normal (cc). The C allele behaves dominantly in causing lethality.

Step by step solution

01

Set up the Punnett Square

A Punnett square is a grid that allows us to visualize the possible offspring genotypes resulting from a given mating event. Since both parents are heterozygous Creeper chickens (Cc), we will represent one parent's alleles on the top row of the grid and the other parent's alleles on the left column. ``` C c C [ ] [ ] c [ ] [ ] ```
02

Fill in the Punnett Square

Now, fill in the empty squares by combining the corresponding alleles from the parents: ``` C c C [CC] [Cc] c [Cc] [cc] ```
03

Determine Offspring Ratios

From the filled-in Punnett Square, we can see the following genotypes: - 1 CC (lethal) - 2 Cc (creeper) - 1 cc (normal) Remember that CC is lethal, so we will not include it in our ratio. Therefore, the ratio of genotypes obtained when creeper chickens are interbred is: 2 creeper (Cc) : 1 normal (cc)
04

Determine Dominant or Recessive Behavior for Lethality

Lethality occurs in the homozygous state (CC). Since the presence of two dominant C alleles leads to lethality and having only one C allele (heterozygous state) does not lead to lethality, the C allele behaves dominantly in causing lethality. In summary, the C allele is dominant in both causing creeper condition in heterozygous state and causing lethality in the homozygous state.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Punnett Square
A Punnett Square is a simple, visual tool used in genetics to predict the genotypes of offspring resulting from a particular genetic cross. It helps us understand how genetic traits might be passed from parents to their offspring. To use a Punnett Square, draw a grid where one parent's alleles are placed along the top and the other parent's alleles are placed along the side. During breeding, the alleles from each parent combine to fill in the squares of the grid, representing potential offspring genotypes.

In our example of the creeper chickens, each parent chicken has a heterozygous genotype, represented as Cc. As shown in the Punnett Square:
  • C from one parent can combine with C from the other parent to give CC.
  • C from one parent can combine with c from the other parent to give Cc.
  • c from one parent can combine with C from the other to give another Cc.
  • c from one parent can combine with c from the other parent to give cc.
This way, the Punnett Square helps us see all possible combinations and predict outcomes such as creeper, normal, or lethal genotypes.
Dominant Allele
In genetics, alleles determine traits and characteristics. A dominant allele demonstrates its trait by overpowering a recessive allele, which means only one dominant allele is needed to express its trait. This is important when determining phenotypes from genotypes.

In the creeper chicken example, the allele C is dominant. When present, even in a single copy (as in Cc), it causes the trait鈥攃reeper condition鈥攖o show in the chicken. Conversely, for traits only to show with recessive alleles, both alleles must be recessive (cc). For lethality due to C, it requires two dominant alleles (CC) because this lethal trait is dominant, causing death in homozygous state.
Lethal Gene
A lethal gene can cause death when present in particular genetic compositions, known as lethal genotypes. These genes can be challenging to work with in genetic breeding as they must be carefully managed to avoid unwanted mortality in offspring.

In our creeper chicken scenario, the gene causing the creeper trait C is lethal in its homozygous form (CC). This means that when both parents pass the allele C to their offspring, the resulting CC genotype is lethal, and the chick will not survive. This fact must always be considered in breeding strategies, as it significantly impacts expected offspring ratios. For creeper chickens, the lethal gene results in a practical ratio of 2 (Cc):1 (cc) as the CC does not survive, highlighting the importance of understanding gene interactions in genetics.

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Most popular questions from this chapter

In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of \(\mathrm{F}_{1}\) cattle were mated to one another, the following \(\mathrm{P}_{2}\) data were obtained: \(3 / 8\) polled Dexters \(1 / 8\) horned Dexters \(3 / 8\) polled Kerrys \(1 / 8\) horned Kerrys A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true-breeding. Dexters, on the other hand, were not true- breeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations.

Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where color can be red, pink (the heterozygote), or white, The second pair leads to the dominant personate or recessive peloric flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed with those that are white, peloric, and dwarf. Determine the \(P_{1}\) genotype(s) and phenotype(s). If the \(F_{1}\) plants are interbred, what proportion of the offspring will exhibit the same phenotype as the \(F_{1}\) plants?

Pigment in the mouse is produced only when the \(C\) allele is pres- ent. Individuals of the ce genotype have no color, If color is present, it may be determined by the \(A\) and \(a\) alleles. AA or Aa results in agouti color, whereas aa results in black coats. (a) What \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) genotypic and phenotypic ratios are obtained from a cross between \(A A C C\) and aace mice? (b) In the three crosses shown here between agouti females whose genotypes were unknown and males of the aacc genotype, what are the genotypes of the female parents for each of the following phenotypic ratios? (1) 8 agouti (2) 9 agouti (3) 4 agouti 8 colorless 10 black \(\quad 5\) black 10 colorless

A geneticist from an alien planet that prohibits genetic research brought with him two true-breeding lines of frogs. One frog line croaks by uttering "rib-it rib-it" and has purple eyes. The other frog line croaks by muttering "knee- deep knee-deep" and has green eyes. He mated the two frog lines, producing \(\mathrm{P}_{1}\) frogs that were all utterers with blue eyes. A large \(\mathrm{F}_{2}\) generation then yielded the following ratios: \(27 / 64\) blue, utterer \(12 / 64\) green, utterer \(9 / 64\) blue, mutterer \(9 / 64\) purple, utterer \(4 / 64\) green, mutterer \(3 / 64\) purple, mutterer (a) How many total gene pairs are involved in the inheritance of both eye color and croaking? (b) Of these, how many control eye color, and how many control croaking? (c) Assign gene symbols for all phenotypes, and indicate the genotypes of the \(P_{1}, F_{1},\) and \(F_{2}\) frogs. (d) After many years, the frog geneticist isolated true-breeding lines of all six \(\mathrm{F}_{2}\) phenotypes. Indicate the \(\mathrm{F}_{1}\) and \(\mathrm{P}_{2}\) phenotypic ratios of a cross between a blue, mutterer and a purple, utterer.

In cattle, coats may be solid white, solid black, or black-andwhite spotted. When true-breeding solid whites are mated with true-breeding solid blacks, the \(\mathrm{F}_{1}\), generation consists of all solid white individuals. After many \(\mathrm{F}_{1} \times \mathrm{F}_{1}\) matings, the following ratio was observed in the \(\mathrm{F}_{2}\) generation: \(12 / 16\) solid white \(3 / 16\) black-and-white spotted \(1 / 16\) solid black Rxplain the mode of inheritance governing coat color by determining how many gene pairs are involved and which genotypes yield which phenotypes. Is it possible to isolate a true-breeding strain of black-and-white spotted cattle? If so, what genotype would they have? If not, explain why not.
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