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What word is written here?
Most color blind people can easily read what is written in the picture above. That means, if you fail the test, you probably have the full range of color sensitivity that is attributed to color-sighted people.
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Complex Patterns of Inheritance
Topics: Sex Determination Sex Linkage Sex Influenced
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Sex Determination Sex Chromosome was discovered by the work of Thomas Hunt Morgan. He study the fruit flies’ chromosomes.
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Fruit Flies
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He discovered that females have XX chromosomes and males have XY chromosomes.
Sex chromosomes determine the sex of an organism.
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Females have homologous X sex chromosomes while the males have X and Y sex chromosomes.
When gametes are produces each egg in a female will receive one X chromosome. In males, each sperm will either receive an X or Y chromosome.
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Sex Linkage Thomas Hunt Morgan also discovered that genes are also carried on these sex chromosomes. Genes that are carried on either the X or Y chromosome are called sex-linked genes. Genes found on other 44 autosomes are called autosomal genes.
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Fruit Fly Eye Color
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Fruit Fly Eye Color Legend
Order of dominance Phenotype Allele symbol Possible Genotype Dominant Over Wild Type E1 E1E1, E1E2, E1E3, E1E4 Apricot, Honey, White Apricot E2 E2E2, E2E3, E2E4 Honey, White Honey E3 E3E3, E3E4 White E4 E4E4 none
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Morgan’s Conclusion Morgan crossed a white-eyed female (XrXr) with a red eyed male (XRY).
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For example, he noticed that male flies got white eyes way more often than female flies.
Seeing as white eye color is recessive to red eye color the only way white could show up would be if that gene was by itself and not have the dominant red gene to mask it. He concluded that the X chromosome must carry the gene for eye color.
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Sex Linked Traits In Humans
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Color Blindness Color blindness is an example of sex linkage.
People who have the dominant allele for color vision can see all the colors in the visible spectrum. Red-green color blindness is the inability to distinguish red from green which, is a recessive condition.
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For a woman to be color-blind both alleles for red-green color vision must be recessive.
In men however, one recessive allele on the X chromosome will result in color blindness because the Y chromosome does not carry the gene.
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Genotypes for Red-Green Vision
X = the location or loci of the gene A or a = the alternative form of the gene XAXA a woman with normal vision XAXa heterozygous female carrier XaXa a color-blind woman XAY a man with normal vision XaY a color-blind man
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EXAMPLE A woman, that is a carrier for the colorblindness, has a child with a man who has normal color vision. What are the possible genotypes and phenotypes of the offspring?
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SEX INFLUENCED TRAITS A phenotypic characteristics that are controlled by a pair of alleles found on the autosomes chromosomes but not on the sex chromosomes (the X and Y chromosomes). The trait’s expression is influenced by gender (presence of hormones such as: estrogen, progesterone, testosterone, etc.).
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Sex-influences traits can vary in the degree of the phenotypic expression.
Pattern Baldness – the gene for baldness is dominant over the gene for keeping hair. The difference between the sexes expression of this trait is exhibited in the following ways:
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Pattern Baldness
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*Baldness is dominant in males and recessive in females*
B or b = the alternative form of the gene Male BB = baldness Bb = baldness bb = normal hair line FEMALE BB = baldness Bb = normal hair line bb = normal hair line *Baldness is dominant in males and recessive in females*
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EXAMPLE A boy who is wondering if he might be bald later on in his life. When he checks the family gene pool, his mother is not bald but his grandfather is (on his mother’s side) and his dad has a normal hair line. Create two Punnett squares to help him determine the possibility of being bald later in his life.
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Punnett Square 1
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Punnett Square 2
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Check For Understanding
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