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7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture. (dominant). Mendel’s rules of inheritance apply to autosomal genetic disorders.

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7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

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  1. 7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

  2. Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture.

  3. (dominant) • Mendel’s rules of inheritance apply to autosomal genetic disorders. • Recessive disorder requires a homozygous recessive genotype to affect a person. A heterozygote for a recessive disorder is a carrier. • Disorders caused by dominant alleles are uncommon.

  4. Mendel’s rule only apply for autosomal genes(chromosome pairs 1-22). Genes on sex chromosomes are called sex-linked genes. • Y chromosome genes in mammals are responsible for male characteristics. Males have an XY genotype. • X chromosome genes in mammals affect many traits. Females have an XX genotype.

  5. Because males only have one copy of the X chromosome all of a male’s sex-linked genes are expressed. • In females, expression of sex-linked genes is similar to autosomal genes because they have two copies of the X chromosome. Y X

  6. Common examples of sex-linked disorders: • Duchenne’s muscular dystrophy • Hemophilia • Color Blindness

  7. The test to the left is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

  8. X chromosome inactivation randomly “turns off” one X chromosome.

  9. In incomplete dominance, neither allele is completely dominant nor completely recessive.

  10. Codominant alleles will both be completely expressed.

  11. Codominant alleles are neither dominant nor recessive. • The ABO blood types result from codominant alleles. • Codominant alleles will both be completely expressed. • Many genes have more than two alleles.

  12. There are 3 alleles that determine blood type: IA, IB, and i • IA and IB are dominant to i. • IA and IB are codominant.

  13. Codominance

  14. Can receive from: A, O • Can donate to: A, AB • There are 4 blood types: • A : • Genotyple: IAIA or IAi • Antigen: A • Antibody: Anti-B   

  15. Can receive from: B, O • Can donate to: B, AB • B : • Genotyple: IBIB or IBi • Antigen: B • Antibody: Anti-A   

  16. Can receive from: A, B, AB, & O (universal recipient) • Can donate to: AB • AB : • Genotyple: IAIB • Antigen: A & B • Antibody: none  

  17. Can receive from: O • Can donate to: A, B, AB, & O (universal donor) • O : • Genotyple: ii • Antigen: none • Antibody: Anti-A and Anti-B   

  18. Rh Factor: Another surface marker which may or may not be present on the RBC. 

  19. Can receive from: Rh+ & Rh- • Can donate to: Rh+ • Rh+ : • Genotype: Rh+Rh+ or Rh+Rh- • Antigen: Rh • Antibody: none  

  20. Can receive from: Rh- • Can donate to: Rh- & Rh+ • Rh- : • Genotype: Rh-Rh- • Antigen: none • Antibody: Rh+

  21. Many genes have more than two alleles or multiple alleles used to express a trait.

  22. Order of dominance: brown > green > blue. • Polygenic traits are produced by two or more genes.

  23. An epistatic gene can interfere with other genes.

  24. Epistatic: recessive trait blocks another allele Black is dominant to chocolate B or bYellow is recessive epistatic (E or e)

  25. Phenotype can be a combination of genotype and environment. Identical Twins Malnourished Well-fed

  26. 7.4 KEY CONCEPT A combination of methods is used to study human genetics.

  27. X Y • A karyotype is a picture of all chromosomes in a cell.

  28. Karyotypes can show changes in chromosomes. • Nondisjunction: an error in meiosis that results in an extra or a loss of a chromosome • deletion of part of a chromosome or duplication of part of a chromosome

  29. A pedigree is a chart for tracing genes in a family. • Phenotypes are used to infer genotypes on a pedigree. • Autosomal genes show different patterns on a pedigree than sex-linked genes.

  30. If the phenotype is more common in males, the gene is likely sex-linked.

  31. 7.3 KEY CONCEPT Genes can be mapped to specific locations on chromosomes.

  32. Mutant Wild type • Because of their location on a chromosome, some genes travel together and are considered to be linked.

  33. Linkage maps estimate distances between genes. • The closer together two genes are, the more likely they will be inherited together. • Linkage maps show the relative locations of genes.

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