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Chapter 4: Problem 5

What is the pseudoautosomal region? How does the inheritance of traits encoded by genes in this region differ from the inheritance of other Y-linked characteristics?

Short Answer

Expert verified
PARs allow recombination between X and Y chromosomes, enabling traits to be inherited similarly to autosomal traits, unlike strictly Y-linked traits passed only from father to son.

Step by step solution

01

Understand Pseudoautosomal Regions (PARs)

Pseudoautosomal regions (PARs) are segments of identical nucleotide sequences at the ends of the sex chromosomes (X and Y in humans). These regions allow for the pairing and recombination between the X and Y chromosomes during meiosis, ensuring the proper segregation of the sex chromosomes.
02

Examine Inheritance in Autosomal-like Manner

Traits encoded by genes in the pseudoautosomal regions follow an autosomal-like inheritance because the genes can be present on both the X and Y chromosomes and thus can be passed down to offspring from either parent. This is unlike other regions of the Y chromosome, which contain Y-linked genes that are inherited strictly from father to son.
03

Compare with Y-linked Inheritance

In Y-linked inheritance, characteristics are passed directly from father to son without recombination with the X chromosome. In contrast, genes in the PARs can recombine and thus can be inherited from mothers as well as fathers, similar to autosomal genes.

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Key Concepts

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

Inheritance
Inheritance is the biological process where genetic traits are passed down from one generation to the next. These traits are encoded in the genes found within chromosomes. Most genes follow a typical pattern of inheritance based on whether they are located on autosomal or sex chromosomes. In general, autosomal genes are inherited according to Mendel's laws, with each parent contributing one allele per gene to their offspring. However, some genes are located on sex chromosomes, which creates a different inheritance pattern.
Recombination
Recombination refers to the process where genetic material is rearranged during the formation of gametes in meiosis. This is particularly important for the pseudoautosomal regions (PARs) on sex chromosomes. During meiosis, homologous chromosomes pair and exchange genetic information, a process called crossing over. This recombination ensures genetic diversity among offspring. In the PARs, X and Y chromosomes can pair and recombine, which helps maintain essential sequences on both sex chromosomes and guarantees accurate segregation during cell division.
Sex Chromosomes
Sex chromosomes are a specific pair of chromosomes that determine the sex of an individual. Humans typically have two sex chromosomes: X and Y. Females have two X chromosomes (XX), while males possess one X and one Y chromosome (XY). While most of the Y chromosome doesn鈥檛 recombine with the X chromosome, pseudoautosomal regions (PARs) are exceptions. These regions allow both X and Y chromosomes to participate in recombination, playing a critical role during meiosis by ensuring alignment and proper separation into daughter cells. Unlike typical Y-linked characteristics, genes in the PARs are not restricted to male-to-male transmission.
Autosomal-like Inheritance
Autosomal-like inheritance describes how traits behave similarly to those on autosomes, even when they are located on sex chromosomes, specifically within the pseudoautosomal regions. Genes in PARs follow this type of inheritance because they are found on both the X and Y chromosomes. As a result, they do not strictly adhere to the typical sex-linked inheritance patterns. These genes can be inherited from either parent, regardless of the offspring鈥檚 sex, mirroring the behavior of autosomal genes, where traits are not tied directly to either parent鈥檚 sex.

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Most popular questions from this chapter

Identical twins (also called monozygotic twins) are derived from a single egg fertilized by a single sperm, creating a zygote that later divides into two (see Chapter 6 ). Because identical twins originate from a single zygote, they are genetically identical. Caroline Loat and her colleagues examined nine measures of social, behavioral, and cognitive ability in 1000 pairs of identical male twins and 1000 pairs of identical female twins (C. S. Loat, et al. 2004. Twin Research \(7: 54-61\) ). They found that, for three of the measures (prosocial behavior, peer problems, and verbal ability), the two male twins of a pair tended to be more alike in their scores than were two female twins of a pair. Propose a possible explanation for this observation. What might this observation indicate about the location of genes that influence prosocial behavior, peer problems, and verbal ability?

In certain salamanders, the sex of a genetic female can be altered, changing her into a functional male; these salamanders are called sex-reversed males. When a sex reversed male is mated with a normal female, approximately \(^{2} /_{3}\) of the offspring are female and \(^{1 / 3}\) are male. How is sex determined in these salamanders? Explain the results of this cross.

Coat color in cats is determined by genes at several different loci. At one locus on the X chromosome, one allele \(\left(\mathrm{X}^{+}\right)\) encodes black fur; another allele \(\left(\mathrm{X}^{\circ}\right)\) encodes orange fur. Females can be black \(\left(X^{+} X^{+}\right)\) orange \(\left(\mathrm{X}^{\circ} \mathrm{X}^{\circ}\right),\) or a mixture of orange and black called tortoiseshell \(\left(X^{+} X^{o}\right) .\) Males are either black \(\left(X^{+} Y\right)\) or orange \(\left(X^{o} Y\right) .\) Bill has a female tortoiseshell cat named Patches. One night Patches escapes from Bill's house, spends the night out, and mates with a stray male. Patches later gives birth to the following kittens: one orange male, one black male, two tortoiseshell females, and one orange female. Give the genotypes of Patches, her kittens, and the stray male with which Patches mated.

How does sex determination in the XX-XY system differ from sex determination in the ZZ-ZW system?

Bob has XXY chromosomes (Klinefelter syndrome) and is color blind. His mother and father have normal color vision, but his maternal grandfather is color blind. Assume that Bob's chromosome abnormality arose from non-disjunction in meiosis. In which parent and in which meiotic division did non-disjunction take place? Assume no crossing over has taken place. Explain your answer.
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