Sex Linked Traits

By: Chloe

What are sex-linked traits?

Sex-linked traits are genetic characteristics determined by genes located on sex chromosomes. Sex chromosomes are found within our reproductive cells and determine the sex of an individual. According to http://science.halleyhosting.com "Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual. Usually such genes are found on the X chromosome. " Traits are passed on from one generation to the next by our genes. Genes are segments of DNA found on chromosomes that carry information for protein production and that are responsible for the inheritance of specific traits. Genes exist in alternative forms called alleles. One allele for a trait is inherited from each parent. Like traits that originate from genes on autosomes (non-sex chromosomes), sex-linked traits are passed from parents to offspring through sexual reproduction.
                                        

X-linked inheritance

X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes; males have one X and one Y. Genes on the X chromosome can be recessive or dominant. According to https://www.my46.org "Most X-linked conditions are recessive. This means that in a person with two X chromosomes (most females), both copies of a gene (i.e., one on each X chromosome) must have a change or mutation whereas in a person with one X chromosome (most males), only one copy of a gene must have a mutation."Their expression in females and males is not the same. Genes on the Y chromosome do not exactly pair up with the genes on the X chromosome. X-linked recessive genes are expressed in females only if there are two copies of the gene (one on each X chromosome). However, for males, there needs to be only one copy of an X-linked recessive gene in order for the trait or disorder to be expressed. For example, a woman can carry a recessive gene on one of the X chromosomes unknowingly, and pass it on to a son, who will.
                                                                         

Y-linked inheritance

According to https://www.medicinenet.com"Since only males normally have a Y chromosome, Y-linked genes can only be transmitted from father to son. Y-linked inheritance is also called holandric inheritance." Describes traits that are produced by genes located on the Y chromosome.

Y linkage can be difficult to detect. This is partly because the Y chromosome is small and contains fewer genes than the autosomal chromosomes or the X chromosome. It is estimated to contain about 200 genes. Earlier, the human Y chromosome was thought to have little importance. The Y-chromosome is sex-determining in humans and some other species: not all genes that play a role in sex determination are Y-linked. The Y-chromosome, generally does not undergo genetic recombination and only small regions called pseudoautosomal exhibit recombination. The majority of the Y-chromosome genes that do not recombine are located in the "non-recombining region".

For a trait to be considered Y linkage, it must exhibit these characteristics. Occurs only in males. Appears in all sons of males who exhibit that trait, In addition, is absent from daughters of trait carriers; instead the daughtersthat are phenotypically normal and do not have affected offspring.

                                                                         

What are some examples of sex linked traits? 

Examples of Sex-linked Traits:

• Red-green colorblindness – Inability differentiate between read and green.
• Male Pattern Baldness
• Hemophilia – Causes the blood not to clot.  If get a cut it may take a along time to clot or internal bleeding may result from a bruise.
• Duchenne Muscular Dystrophy – Muscular weakness, progressive deterioration of muscle tissue, and loss of coordination.

How do you know a trait is sex linked?

Autosomal or Sex-linked: To determine whether a trait is autosomal or sex-linked you must look at the males from the F₁ and the reciprocal F₁ crosses. If a trait is sex-linked (on the X-chromosome), then the males from the F₁ crosses will always have the phenotype of their homozyous mothers.