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WHEN HEREDITY FOLLOWS DIFFERENT RULES

WHEN HEREDITY FOLLOWS DIFFERENT RULES. Chapter 12.2. When Heredity Follows Different Rules. Dominant (T) vs recessive (t) is called “simple heredity” There is a more “complex” pattern to some things, and that’s what we’ll study today. Objectives.

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WHEN HEREDITY FOLLOWS DIFFERENT RULES

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  1. WHEN HEREDITY FOLLOWS DIFFERENT RULES Chapter 12.2

  2. When Heredity Follows Different Rules • Dominant (T) vs recessive (t) is called “simple heredity” • There is a more “complex” pattern to some things, and that’s what we’ll study today

  3. Objectives • Distinguish between alleles for “incomplete dominance” and “codominance” • Explain the patterns of “multiple allelic” and “polygenic inheritance” • Analyze the pattern of “sex-linked” inheritance • Summarize how internal/external environmental factors affect gene expression

  4. COMPLEX PATTERNS OF INHERITANCE • Incomplete Dominance • Phenotype of the heterozygous offspring is the intermediate between those of the two homozygous parents (What?) • Example is when red plants cross pollinate with white plants and you get a pink plant • APPEARANCE OF A 3RD PHENOTYPE!!! • F1 = 4:0 , F2 = 1:2:1

  5. Codominance: Expression of Both Alleles • Codominant Alleles: • cause the phenotypes of BOTH homozygous parents to be produced in heterozygous offspring • Best example to relate this to is when a red cow breeds with a white cow, you get “ROAN CATTLE” (red-white combination cow) • “Co”w = “Co”dominant

  6. Multiple Phenotypes from Multiple Alleles • multiple alleles: • traits controlled by more than 2 alleles • it is very common for traits to be controlled by more than 2 alleles (ex: TTt) • Multiple alleles are mostly found to control BLOOD TYPE!!!!

  7. Sex Determination • Autosomes: • 22 pairs of homologous chromosomes (pairs 1-22) • Sex chromosomes: • 23rd pair (is different in males and females) • Chromosomes are either X or Y • Males are XY • Females are XX (homologous)

  8. Sex Linked Inheritance • Sex-linked traits: • Traits controlled by genes on the sex chromosomes • Alleles for sex-linked traits are written as superscripts on the X and Y chromosomes • Do not put alleles on a Y chromosome • Therefore, a recessive alleles on a X chromosome will override the whatever would be on a Y

  9. Sex Linked Inheritance

  10. Polygenic Inheritance • Polygenic inheritance : • Inheritance pattern of a trait that is controlled by 2 or more genes • Skin Color is a good example • Alleles look like AABBCC x aabbcc = AaBbCc

  11. ENVIRONMENTAL INFLUENCES • External Factors • Temperature • Nutrition • Light • Chemicals • Infectious agents • Ex: Arctic Fox in Fig 12.13 on page 321

  12. ENVIRONMENTAL INFLUENCES • Internal Factors: • Hormones • Male-pattern baldness is different in males and females • Dominant in males, recessive in females • Feather color in peacocks is different in males and females • Age

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