17.11 Pattern of Y-linked inheritance
Y-linked inheritance: Y-Linked traits are passed through Y-chromosome from male to male only. All sons of an affected father are affected. Such traits cannot pass to women because they do not inherit a Y-chromosome (Fig. 17.38).
Fig 17.38: Pedigree indicating Y-linked trait.
17.11.1 Maleness:
In 1991 male-determining gene ‘SRY’ was discovered on Y-chromosome. It is male sex switch that switches on male development process. The process involves many steps in sequence controlled by other genes. ‘SRY’ triggers this process. It forms a protein called ‘’transcription factor’’ that switches on other genes which complete this process in embryo after week 6. Unspecialized gonads are specialized as testes. Testes secrete two types of hormones. One type stops chances of developing into a female; the other type promotes development of male reproductive structures (Fig 17.39).
Fig 17.39: Determination of maleness by ‘SRY’ gene