Question

In what way are sex-limited traits and sex-influenced traits similar or different from
one another? Can you give more examples of these traits?​

Answer 1

Answer:

Sex-limited genes are genes that are present in both sexes of sexually reproducing species but are expressed in only one sex and have no penetrance, or are simply 'turned off' in the other.[1] In other words, sex-limited genes cause the two sexes to show different traits or phenotypes, despite having the same genotype. This term is restricted to autosomal traits, and should not be confused with sex-linked characteristics, which have to do with genetic differences on the sex chromosomes (see sex-determination system). Sex-limited genes are also distinguished from sex-influenced genes, where the same gene will show differential expression in each sex. Sex-influenced genes commonly show a dominant/recessive relationship, where the same gene will have a dominant effect in one sex and a recessive effect in the other (for example, male pattern baldness). However, the resulting phenotypes caused by sex-limited genes are present in only one sex and can be seen prominently in various species that typically show high sexual dimorphism.[2]

Sex-limited genes are responsible for sexual dimorphism, which is a phenotypic (directly observable) difference between males and females of the same species regardless of genotype.[3] These differences can be reflected in size, color, behavior (ex: levels of aggression), and morphology. An example of sex-limited genes are genes which control horn development in sheep[4]: while both males and females possess the same genes controlling horn development, they are only expressed in males. Sex-limited genes are also responsible for some female beetles' inability to grow exaggerated mandibles,[5] research that is discussed in detail later in this article.

Sex-limited genes were first hypothesized by Charles Darwin and though he was unsuccessful in distinguishing the previously mentioned sex-linked traits, his hypothesis was the starting point for future study of the subject.[6] His studies on sex-limited traits have been further substantiated and supported over time, distinguishing sex-limited genes and sex-linked traits. Modern study of sex-limited genes includes research on epigenetics, which is the study of inheritable phentotypic changes with no change in DNA sequence. Modern research suggests that a substantial portion of the expression of sex-limited genes and sexual dimorphism may be influenced by certain epigenetic marks.[7]

Answer 2

The following are the ways in which sex-limited and sex-influenced traits are similar -

Sex-limited traits -

• Sex-linked inheritance is the trait carried in either the X or the Y chromosome.

• A trait that is due to genes present on the X chromosome is more likely to be  expressed in males as they have only one X chromosome.

• The presence of two X chromosomes in females can suppress its expression  when one of them has the genes for the trait and the other does not.

• Examples of sex-limited traits are in humans, breast development is a trait that is normally limited to females, whereas beard growth is limited to males. A woman does not grow a beard herself but she can descend the genes of heavy beard growth to her sons.

Sex-influenced traits -

• Sex-controlled character, also called Sex-influenced character, a  genetically controlled feature that may appear in organisms of both sexes but  is expressed to a different degree in each.

• Sex-influenced traits are autosomal traits that are influenced by sex.
• The character seems to act as dominant in one sex and a recessive in the
• other. Sex-controlled character, also called Sex-influenced Character, a  genetically controlled feature that may appear in organisms of both sexes but  is expressed to a different degree in each.
• The character seems to act as dominant in one sex and recessive in the  other.
• Examples of sex influenced traits are Male Pattern Baldness,  Length of the index finger,  Body hair , Muscle mass.