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Chapter 4: Problem 33

In chickens, congenital baldness is due to a Z-linked recessive gene. A bald rooster is mated with a normal hen. The \(F_{1}\) from this cross are interbred to produce the \(\mathrm{F}_{2},\) Give the genotypes and phenotypes, along with their expected proportions, among the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) progeny.

Short Answer

Expert verified
All F1 are normal (ZZ and ZW); F2 are normal too (ZZ: 50%, ZW: 50%).

Step by step solution

01

Understand the Genetic Inheritance

Chickens have ZW sex-determination system; males are ZZ and females are ZW. Congenital baldness is Z-linked recessive, meaning the gene for baldness is carried on the Z chromosome and baldness is expressed in the presence of two recessive alleles (zz in males, and with only one z in females). A bald rooster (zz) is mated with a normal hen (ZW), with the normal feather allele dominant (Z).
02

Determine F1 Generation Genotypes and Phenotypes

F1 offspring genotypes are determined by mated pairing: - Male genotype from mother (ZW): Z from the male (father) and Z from female = ZZ (normal) - Female genotype from mother (ZW): Z from the male (father) and W from the female = ZW (normal) Therefore, all F1 progeny are phenotypically normal, with male genotype ZZ and female genotype ZW.
03

Determine F2 Generation Genotypes and Phenotypes

When F1 males (ZZ) are interbred with F1 females (ZW), possible gamete combinations are: - Male (ZZ): all contribute Z - Female (ZW): Z or W This results in the following F2 genotypes and phenotypes: - Male: ZZ (normal) : 50% (Z from male, Z from female) - Female: ZW (normal) : 50% (Z from male, W from female) There will be no phenotypically bald F2 progeny as the bald allele from the father (P generation) is not present in F1.

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Key Concepts

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

Chicken Genetics
When we talk about chicken genetics, it's all about understanding the inheritance patterns in birds. Chickens have a unique way of determining the physical traits that are passed down from parents to offspring. By looking at genetic information, known as alleles, scientists and breeders can predict how certain traits might appear in future generations.
  • Chickens exhibit a variety of traits controlled by genes. For instance, feather color, pattern, and even baldness are all traits that can be inherited.
  • Each trait is linked to a specific gene location on a chromosome. In our exercise, the gene for congenital baldness is found on the Z chromosome.
  • The combination of genes from each parent determines the traits of the offspring. This can help breeders understand which animals to select for breeding in order to achieve desired traits.
Understanding these genetic principles is crucial for anyone involved in breeding or studying chickens. It allows for controlled and predictable breeding outcomes.
Sex-Determination Systems
In birds, including chickens, sex-determination is a bit different from what you might find in mammals. Instead of XX (female) and XY (male) as in humans, chickens use a ZW sex-determination system.
  • In chickens, males have two Z chromosomes (ZZ), and females have one Z and one W chromosome (ZW).
  • The presence of W determines femaleness. The male's ZZ contributes to the genetic stability of male traits.
  • This system influences which traits, especially those linked to the Z chromosome, are expressed based on the sex of the chicken.
Understanding sex-determination is key when predicting genetic outcomes, because certain traits can be sex-linked, meaning they appear differently in males and females.
Genotype and Phenotype Ratios
Genotype and phenotype ratios are fundamental components in genetics. They help to predict the physical and genetic characteristics of offspring.
  • The genotype is the genetic makeup of an individual, which includes both visible and non-visible traits. For example, a chicken's genotype might determine if it carries a baldness allele, even if it doesn't express it.
  • The phenotype is the observable physical traits resulting from the combination of genotype and environment. In our case, whether the chicken appears bald or not.
  • Ratios help to understand the likelihood of various genotypes and phenotypes occurring in offspring. This is useful in predicting what the resulting generation will look like.
Accurate predictions depend on correctly understanding the inheritance and expression of traits, as shown by using tools like Punnett squares to map out genetic crosses. This helps demonstrate how likely certain traits are to appear based on parental genetics.

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Most popular questions from this chapter

What is a Barr body? How is it related to the Lyon hypothesis?

A geneticist discovers a male mouse with greatly enlarged testes in his laboratory colony. He suspects that this trait results from a new mutation that is either Y linked or autosomal dominant. How could he determine whether the trait is autosomal dominant or Y linked?

A woman with normal chromosomes mates with a man who also has normal chromosomes. a. Suppose that, in the course of oogenesis, the woman's sex chromosomes undergo nondisjunction in meiosis I; the man's chromosomes separate normally. Give all possible combinations of sex chromosomes that this couple's children might inherit and the number of Barr bodies that you would expect to see in each of the cells of each child. b. What chromosome combinations and numbers of Barr bodies would you expect to see if the chromosomes separate normally in oogenesis, but nondisjunction of the sex chromosomes takes place in meiosis I of spermatogenesis?

Suppose that a recessive gene that produces a short tail in mice is located in the pseudoautosomal region. A short-tailed male mouse is mated with a female mouse that is homozygous for a normal tail. The \(\mathrm{F}_{1}\) mice from this cross are intercrossed to produce the \(\mathrm{F}_{2}\). Give the phenotypes, as well as their proportions, of the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) mice?

Xg is an antigen found on red blood cells. This antigen is caused by an X-linked allele \(\left(X^{a}\right)\) that is dominant over an allele for the absence of the antigen \(\left(\mathrm{X}^{-}\right)\). The inheritance of these X-linked alleles was studied in children with chromosome abnormalities to determine where nondisjunction of the sex chromosomes took place. For each type of mating in parts a through \(d\) indicate whether nondisjunction took place in the mother or in the father and, if possible, whether it took place in meiosis I or meiosis II (assume no crossing over). a. \(X^{a} Y \times X^{-} X^{-} \rightarrow X^{a}\) (Turner syndrome) b. \(X^{a} Y \times X^{a} X^{-} \rightarrow X^{-}\) (Turner syndrome) c. \(X^{a} Y \times X^{-} X^{-} \rightarrow X^{a} X^{-} Y\) (Klinefelter syndrome) d. \(\mathrm{X}^{a} \mathrm{Y} \times \mathrm{X}^{a} \mathrm{X}^{-} \rightarrow \mathrm{X}^{-} \mathrm{X}^{-} \mathrm{Y}\) (Klinefelter syndrome)
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