Reproduction in humans (Bachey ki takhleeq) baap kay sperm aur maan kay baezey kay milaap sey hoti hai baap kay sperm mein X aur Y chromosome hotey hain jab kay maan kay baezey mein sirf X chromosome hotey hain. Y chromosome chotey aur naazuk hotay hain inki quwwat-e-mudafe'at bhi kam hoti hai jab kay X chromosome nisbatan barey aur mazboot hotey hain inn ki quwwat-e-mudafe'at bhi zyada hoti hai yeh sukht jaan bhi hotey hain.

    Jab baap ki taraf sey Y chromosome maan kay X chromosome kay sath milap karta hai to larka paeda hota hai aur jab walid ki taraf sey X chromosome maan kay X chromosome kay sath milap karta hai to larki paeda hoti hai iss sey ma'aloom hua kay aulaad ki jins ka inhisaar mard per hai na kay aurat per.

    Dr. Shettles kay tariqa kaar ki bunyaad iss baat per hai kay mubashrat jitni ovulation (baeza raezi) kay qareeb hogi utna hi betey kay imkaanaat zyada hongey iss kay elawa ba'az doosrey anasir bhi bohut ahem hain maslan sperm ki ta'adaad (sperm count) agar zyada hogi to larkey kay imkaanaat zyada hongey aur agar sperm ki ta'adaad kam hogi to larki kay imkaanaat zyada ho jatey hain. Isi tarah agar aurat mein taezaabiyat zyada ho to naazuk Y chromosome mar jaeingey jab kay X chromosome zinda rahengey to iss surat mein larki kay imkaanaat zyada hongey iss kay elawa mubashrat ka tariqa bhi ahem hai mubashrat ka aisa tariqa ikhtiyar kya jaey jis mein sperm qazif naaliyon mein chaley jaein hum Shettles ka tariqa istaemaal kartey hain humari apni kaamyaabi ki sharah 90% sey zyada hai.