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Name: ____________________________ Date:_________________________ Topic: Multiple Alleles, Polygenic and Sex-linked Notes Objective: SWBAT understand the outcome of the cross for multiple alleles, Questions/Main Ideas: polygenic inheritance and sex-linked traits. What is multiple alleles? Why is blood type important? What is Epistasis? Multiple alleles – more than 2 alleles produces 3 or more genotypes. Blood Types: Genotypes Phenotypes IaIa or Iai; AA or AO A IbIb or Ibi; BB or BO B Ii; OO O IaIb; AB AB - Because transfusion of the wrong blood type can cause death Type O is the universal donor, type AB is the universal acceptor - Can be used in parental disputes: Example: if the mother is type A and the child is AB, can the dad be type O? NO why not? Epistasis= One allele hides the effects of another allele Example: Labradors. The dominant allele (E) determines whether the skin will have pigment. The dominant allele (B) determines how dark it is (color). What is polygenic inheritance? What are sex-linked traits? Possible Genotypes Phenotype Explanation BBee Bbee bbee Yellow No Pigment bbEE bbEe Chocolate Recessive Color + Pigment BBEE BbEE BBEe BbEe Black Dominant Color + Pigment Polygenic Inheritance- more than one pair of genes influencing a trait. Examples: hair color, skin color, eye color Sex-linked Traits - 46 chromosomes- 23 pairs ( 22 pairs of autosomes and 1 pair of sex chromosomes) - Male XY - Female XXXX - What is colorblindness? What is Hemophilia? What is Duchenne Muscualr Dystrophy? What is testcross? Summary: Genes located on the X or Y chromosomes Most sex-linked genes are found on the X chromosome - The human Y chromosome is much smaller and appears to contain only few genes. - Father determines the sex of the offspring - The chance is always 50-50 for either sex - A recessive gene has no matching gene on the Y - More Sex linked disorders are found in males Sex linked disorders: 1. Colorblindness- the inability to distinguish certain colors - Three human genes associated with colorvision are located on the X chromosomes - Red-green colorblindness is the most common form - In the US, 1 in 10 males and 1 in 100 females have color- blindness. - Why the difference? Males have just one X chromosome. - Therefore, their genotypes will be XCY or XcY. - Females have two X chromosomes. Therefore, their genotypes would be XCXC (normal), XCXc (carrier), and XcXc is colorblind. 2. Hemophilia - A sex-linked disorder in which a protein for normal blood clotting is missing. - About 1 in 10,000 males has a form of hemophilia. - Hemophiliacs can bleed to death from minor cuts; may suffer internal bleeding from bumps or bruises. 3. Duchenne Muscular Dystrophy - A sex-linked disorder that results in the progressive weakening and loss of skeletal muscle. - 1 in 3000 males (US) has the condition. Testcross – A Way to Determine Certain Genotypes - A testcross is a genetic cross of an organism showing the recessive phenotype with an organism showing the dominant phenotype. - This is done to determine if the organism with the dominant phenotype is homozygous dominant or heterozygous dominant.