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Published byMiranda Hubbard Modified over 9 years ago
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Sex-linked Traits
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Sex Determination Sex chromosomes – determines the sex of an individual YY XX Males have X and Y Two kinds of gametes Female have two X’s Only one type of gamete
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Which parent determines the sex of the offspring? XY male X Y XX Female X X It is the male that determines the sex of the offspring.
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Sex Linked Traits Traits controlled by genes located on sex chromosomes (X or Y) Most are X-linked The X chromosome is larger and has more genes A Y has very few genes Show inheritance pattern that differs for autosomal traits.
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T.H. Morgan worked with fruit flies Fruit flies normally have red eyes. One day, in one of his cultures of fruit flies, Morgan found a fly with white eyes. This white-eyed fly was male, so Morgan mated it to red-eyed female fly to see if he could determine how this particular trait is inherited. When he mated it with a normal female, the offspring all had red eyes. This was expected in light of Mendel's experiments. The trait reappeared in the F 2 generation. However, there was a twist because the trait only reappeared in males. There were no female flies with white eyes!
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Males only have one copy of the X chromosome (hemizygous), plus a Y Female have two X chromosomes, and may be homozygous or heterozygous for a trait X-linked genes are never passed from father to son. The Y chromosome is the only sex chromosome that passes from father to son.
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Females with one copy of the normal gene and one copy of the mutated gene are called carriers. They don’t show the trait. Males are never carriers – if they have a mutated gene on the X chromosome, it will be expressed
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X-linked disorders Recessive Red-green color blindness Hemophilia Duchenne muscular dystrophy Ichthyosis Dominant Hypertrichosis
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Red-green color blindness Can not distinguish red from green. Normal red-green Red-green colorblind
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What a red-green colorblind person sees NormalRed-green colorblind
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Hemophilia
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X Chromosome Inactivation While females have two X chromosomes, only one is active. The other is turned off. This is random, in some cells the maternal X is turned off and in others the paternal X is turned off. All descents of that cell will have same X turned off It is condensed and known as a Barr Body.
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