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PATTERNS OF HEREDITY AND HUMAN GENETICS CHAPTER 11 ☺ You will compare the inheritance of recessive and dominant traits in humans. ☺ You will analyze the inheritance of incompletly dominant and codominant traits. ☺ You will determine the inheritance of sex linked traits. Mendelian Inheritance of Human Traits Making a Pedigree ▪ Pedigrees illustrate inheritance: a graphic representation of genetic inheritance. ▸Made up of a set of symbols that identify males, females and the trail being studied and family relationships. ☐= male; ❍ = female ☐┬❍ = parents ▄ affected male ┌┴┐ ●affected female ☐ ❍ = siblings Half shaded square or circle means a carrier of trait Simple Recessive Heredity ▪ Most genetic disorders are caused by recessive alleles. Allele must be inherited from both parents. ▪ Many of the alleles are relatively rare. ▪ Few are common in certain ethnic groups ▸Cystic fibrosis - most common genetic disorder among white Americans. 1 in 20 carry, 1 in 2000 inherit disorder. ▸Tay-Sachs - Amish and Ashkenzic Jews. Disorder of the central nervous system. ▸Phenylketnuria (PKU) - Norway, Sweden. Disorder that results from the absence of an enzyme that converts an amino acid to another amino acid. Simple Dominant Heredity ▪ Trait only has to be inherited from one parent ▸Simple dominant traits - Tongue rolling, hitchhiker’s thumb, attached earlobes, and Hunington’s disease. When Heredity Follows Different Rules Complex Patterns of Inheritance ▪ Incomplete dominance: a third genotype: A dominant red flower and a dominant white flower produce a pink flower. ▸Both flowers have incomplete dominance patterns, neither allele is dominant. ▪ Codominance: Expression of both alleles. ▸The phenotype of both homozygotes to be produced in heterozygote individuals. Both alleles are expressed equally. ▪ Traits controlled by more than two alleles have multiple alleles. Sex Determination 1:1 Ratio; 50 - 50 Chance ▪ 22 pairs of matching homologous chromosomes called autosomes; look exactly alike. ▸23rd pair differ in males and females. Females have a “XX” pair males have a “XY” pair. – These are the chromosomes that control the inheritance of sex characteristics. ▸Females only produce the “X” gamete while males produce both the “X” and the “Y” gamete. Sex-linked Traits & Polygenic Inheritance Traits carried on the 23rd pair ▪ Traits dependent on genes that follow the inheritance pattern for a sex chromosome. ▸Color blindness ▪ Traits that are controlled by two or more genes ▸May be on the same chromosome or on different chromosomes – Skin color, height . Environmental Influences External and Internal ▪ External influences: Temperature, nutrition, light, chemicals, infection all can change the way a gene is expressed. ▪ Internal influences: hormones and structural differences, organisms age can change a gene’s expression. Complex Inheritance