Sex Linked Traits

14.1 & Sex Linked Traits2/22/2011Human HeredityHuman GenomeA genome is a full set of information that an organism carries in its DNAStudying genomes means studying chromosomesWhen would it be possible to see the chromosomes in order to study them?KaryotypesPictures are taken of cells during mitosis, the chromosomes are cut out of the pictures and arranged into another pictureShow the complete diploid set of chromosomes, grouped together in pairs, and arranged in order of decreasing size

Sex Chromosomes2 of the 46 CHX in the human genome are the sex CHXWhat do these CHX determine?ALL human egg cells contain an X chromosome (designated: 23, X) of all sperm cells contain an X (23, X) and all sperm cells contain a Y (23, Y)

Sex ChromosomesX chromosomes (about 1,200 genes) are larger than Y (about 140 genes)

Human GenomeThe other 44 CHX are called autosomes, and pairs are numbered 1-22 So the complete human genome consists of 44 autosomes and 2 sex chromosomes Cells are labeled as:46, XX (females)46, XY (males)Gene LinkageThink about the karyotype - Can two alleles from different genes be inherited together?Yes! Alleles of different genes tend to be inherited together when they are on the same CHXGene Linkage contThese genes are said to be linkedEach CHX is actually a group of linked genesThe closer together they are, the more likely they are linkedThe further apart they are, the less likelyTransmission of Human TraitsHuman genes follows the same patterns of inheritance as the genes of other organismsDominant / recessive allelesRh blood group (+ or -)Codominant allelesBlood typesMultiple allelesBlood typesPolygenic traitsSkin color, height, metabolism, eye color, intelligenceSex linked inheritanceSex Linked TraitsBecause the X and Y chxs determine sex, the genes located on them show a pattern of inheritance called sex-linkageA sex-linked gene is a gene located on a sex CHXGenes on Y chx are found only in males and passed directly from father to sonGenes on X chx are found in both sexes

Sex Linked TraitsIn humans, three genes control color visionAll three genes are located on the X chxColor blindness is a recessive trait1 in 12 males are red-green color blind1 in 200 females are red-green color blindWhy the difference?END