14.1 & Sex Linked Traits 2/22/2011 Human Heredity

Human Genome A genome is a full set of information that an organism carries in its DNA Studying genomes means studying chromosomes When would it be possible to “see” the chromosomes in order to study them?

Karyotypes Pictures are taken of cells during mitosis, the chromosomes are cut out of the pictures and arranged into another picture Show the complete diploid set of chromosomes, grouped together in pairs, and arranged in order of decreasing size

Sex Chromosomes  2 of the 46 CHX in the human genome are the sex CHX  What do these CHX determine?  ALL human egg cells contain an X chromosome (designated: 23, X)  ½ of all sperm cells contain an X (23, X) and ½ all sperm cells contain a Y (23, Y)

Sex Chromosomes  X chromosomes (about 1,200 genes) are larger than Y (about 140 genes)

Human Genome  The 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 Linkage Think 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 CHX

Gene Linkage con’t… These genes are said to be “linked” Each CHX is actually a group of linked genes The closer together they are, the more likely they are linked The further apart they are, the less likely

Transmission of Human Traits Human genes follows the same patterns of inheritance as the genes of other organisms  Dominant / recessive alleles  Rh blood group (+ or -)  Codominant alleles  Blood types  Multiple alleles  Blood types  Polygenic traits  Skin color, height, metabolism, eye color, intelligence  Sex – linked inheritance

Sex Linked Traits Because the X and Y chxs determine sex, the genes located on them show a pattern of inheritance called sex- linkage A sex-linked gene is a gene located on a sex CHX Genes on Y chx are found only in males and passed directly from father to son Genes on X chx are found in both sexes

Sex Linked Traits In humans, three genes control color vision All three genes are located on the X chx Color blindness is a recessive trait 1 in 12 males are red-green color blind 1 in 200 females are red-green color blind Why the difference?

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