Presentation on theme: "4- X-LINKED GENES, SEX INFLUENCED INHERITANCE, SEX-LIMITED INHERITANCE"— Presentation transcript:
14- X-LINKED GENES, SEX INFLUENCED INHERITANCE, SEX-LIMITED INHERITANCE Compiled bySiti Sarah JumaliLevel 3 Room 14Ext 2123
2X-LINKED GENESCertain traits are governed by genes that are located on a sex chromosomeOutcome of cross depends on the genotypes and sexes of parents and offspringEg Duchenne Muscular Dystrophy (DMD)A sign of muscular weaknessEg golden retriever dogsX-linked recessiveAllele on X-chromosome and recessiveRare for female
7CHROMOSOME-LINKED GENES Genes located on mammalian sex chromosomes can be transmitted in an X-limited, Y linked or pseudoautosomal patternHemizygous is a condition that describes a single copy of X-linked gene in the maleFew genes are located on the X and some other genes are located on the Y chromosomeThe few genes on Y-chromosome are called holandric genesY-linked is only transmitted from father to son
8SEX-INFLUENCED INHERITANCE Some traits are influenced by the sex of the individualIn sex-influenced inheritance:Allele is dominant in one sex but recessive in opposite sexGenes for sex-influenced traits are autosomal; not on either X, or YHeterozygotes phenomenonEg baldnessWhen heterozygote Bb, men will be bald but women don’t.
9Baldness Male Female BB Bald Bb Nonbald bb nonbald 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
10Baldness cont’d Caused by sex hormone testosterone Overexpression of an ezyme called 5 α-dihydrotestosterone (DHT) which converts testosterone to DHTDHT binds to cellular receptors and affects the expression of many genes including those in the cells of the scalpBecause mature men makes more testosterone than female, the allele has greater phenotypic impact on males
11SEX-LIMITED INHERITANCE Trait occur only in 1 of the 2 sexesEg breast development in femaleBeard development in maleOther examples include rooster and hen where allele H for hen is in hen but not in roosterJust like sex influenced, these are also influenced by hormone
12Limitation to gender because of hormone production FemaleMalehhHen-featheredCock-featheredHhHH
13Question.. You did relative finger length experiment in the lab. What do you think it is?X-linked?Y-linked?Sex-limited?Sex-inherited?