Presentation on theme: "4- X-LINKED GENES, SEX INFLUENCED INHERITANCE, SEX- LIMITED INHERITANCE Compiled by Siti Sarah Jumali Level 3 Room 14 Ext 2123."— Presentation transcript:
4- X-LINKED GENES, SEX INFLUENCED INHERITANCE, SEX- LIMITED INHERITANCE Compiled by Siti Sarah Jumali Level 3 Room 14 Ext 2123
X-LINKED GENES Certain traits are governed by genes that are located on a sex chromosome Outcome of cross depends on the genotypes and sexes of parents and offspring Eg Duchenne Muscular Dystrophy (DMD) – A sign of muscular weakness Eg golden retriever dogs – X-linked recessive Allele on X-chromosome and recessive Rare for female
Who’s having what??
DMD- DUCHENNE MUSCULAR DYSTROPHY
DISCUSS # 4..
CHROMOSOME-LINKED GENES Genes located on mammalian sex chromosomes can be transmitted in an X- limited, Y linked or pseudoautosomal pattern Hemizygous is a condition that describes a single copy of X-linked gene in the male Few genes are located on the X and some other genes are located on the Y chromosome The few genes on Y-chromosome are called holandric genes Y-linked is only transmitted from father to son
SEX-INFLUENCED INHERITANCE Some traits are influenced by the sex of the individual In sex-influenced inheritance: – Allele is dominant in one sex but recessive in opposite sex – Genes for sex-influenced traits are autosomal; not on either X, or Y – Heterozygotes phenomenon Eg baldness – When heterozygote Bb, men will be bald but women don’t.
Baldness MaleFemale BBBald BbBaldNonbald bbNonbaldnonbald When heterozygote Bb, men will be bald but women don’t. Transmitted from father to son but not X- linked because father does not supply X
Baldness cont’d Caused by sex hormone testosterone Overexpression of an ezyme called 5 α- dihydrotestosterone (DHT) which converts testosterone to DHT DHT binds to cellular receptors and affects the expression of many genes including those in the cells of the scalp Because mature men makes more testosterone than female, the allele has greater phenotypic impact on males
SEX-LIMITED INHERITANCE Trait occur only in 1 of the 2 sexes – Eg breast development in female – Beard development in male – Other examples include rooster and hen where allele H for hen is in hen but not in rooster – Just like sex influenced, these are also influenced by hormone
Limitation to gender because of hormone production FemaleMale hhHen-featheredCock-feathered HhHen-feathered HHHen-feathered
Question.. You did relative finger length experiment in the lab. What do you think it is? – X-linked? – Y-linked? – Sex-limited? – Sex-inherited?