Sex-Related Inheritance

• Categories of Sex-Related Inheritance:

  • Sex-linked
  • Sex-influenced
  • Sex-limited
• Sex-related inheritance


  does not follow the laws of Mendelian inheritance.
• Mendelian inheritance


  follows the three concepts proposed by Gregor Mendel: the law of dominance, law of segregation, and law of independent assortment.
• The X and Y chromosomes are the last set of a pair of human genes, and they determine the gender of each individual. These two chromosomes can easily be distinguished because the X chromosome is larger than the Y chromosome.
• Types of Sex-Linked Traits 

  • x-linked traits
  • y-linked traits
• x-linked trait


  the trait is linked to the X chromosome
• y-linked trait


  the trait is linked to the Y chromosome
• Genotypes for Color blindness

  A) XX

  B) X^CX

  C) X^CX^C

  D) XY

  E) X^CY

  
• x-linked Traits for Females

  • It is less common as females have two X chromosomes.
  • It means that before the female expresses the X-linked trait, the trait should be linked in both X chromosomes.
  • If only one of the chromosomes is affected, the female is just a carrier of the trait but does not possess it in her phenotype.
• x-linked Traits for Males

  • As a whole, the X-linked trait is more common in males because they have 1/2 or 50% chance to express the trait, while females only have 1/3 or 33.3% chance of acquiring the trait.
• Examples of Recessive X-linked traits in Humans

  • Hemophilia
  • Color blindness
• Hemophilia


  is a genetic disorder that disallows the body to make blood clots. Hence, bleeding will not stop.
• Color blindness


  is a trait wherein a person cannot distinguish colors properly
• Genotypes for Hemophilia

  A) X^HX^H

  B) X^HX^h

  C) X^hX^h

  D) X^HY

  E) X^hY

  
• y-linked trait


  • the trait is linked to the Y chromosome
  • is only common in males because only they have one Y chromosome.
  • Therefore, if the father possesses the Y-linked trait, all the male offspring will acquire the trait. The female offspring will never acquire the trait.
• hypertrichosis pinnae auris

  • y-linked trait in males
  • This trait is characterized by having a hairy ear.
• Sex-influenced traits

  • autosomal traits
  • not located on the sex chromosomes.
  • the sex of a person influences the trait
  • can be found in both sexes but expressed more in one sex than the other.
• autosome 

  • one of the numbered chromosomes, as opposed to the sex chromosomes
  • Humans have 22 pairs of autosomes and one pair of sex chromosomes (XX or XY)
• Baldness

  • sex-influenced trait
  • is more common in males than in females because they have a 2/3 or 66.7% chance of acquiring the trait.
  • the probability of a male to acquire the trait is 2 (X^BY^B) and (X^BY^b) out of 3 genotypes.
  • females only have 1/3 or 33.3% chance of acquiring the trait. It is because the probability of a female to acquire the trait is 1 (X^BX^B) out of 3 genotypes.
• Sex-Limited Trait

  • an autosomal trait
  • Similar to sex-influenced traits, the sex of a person has something to do with the expression of the trait.
  • can be found in both sexes, but only one sex expresses it on their phenotype.
• Lactation

  • sex-limited trait
  • is a trait that is only seen in females in both humans and animals
  • This trait is both found in males and females. However, only females express it based on their phenotype.
• Genotype and Phenotype for Lactation

  A) X^LX^L

  B) X^LX^l

  C) X^lX^l

  D) Not lactating

  E) Not lactating

  F) Not lactating