Chapter 12 Patterns of Inheritance. What is Inheritance? Who is the Father of Modern Genetics? Answer: The passage of genes from parent to offspring

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1 Chater 12 atterns of Inheritance What is Inheritance? Answer: The assage of genes from arent to offsring Modern Genetic Concets: Locus: Secific location of a gene on a chromosome Locus Locus Allele: Alternate form of a nucleotide sequence for a single gene Heterozygous ( different air ) Homologous chromosomes having different alleles for a given gene Homozygous ( same air ) Homologous chromosomes having the same alleles for a given gene Who is the Father of Modern Genetics? Answer: Johann Gregor Mendel ea lant Ideal for Genetic Work: 1) Normally undergo self-fertilization Same flower rovides ollen and eggs True-breeding (homozygous) 2) Can undergo cross-fertilization (manually) Different flower rovides ollen and eggs Controlled exerimentation Figure 12.3 Audesirk 2 & Byers Inheritance of Single Traits: Mendel raised true-breeders for different forms of a trait and then cross-fertilized the forms: Mendel then allowed F 1 generation to self-fertilize: Inheritance of Single Traits Mendel s Findings: 1) Traits are determined by airs of discrete hysical units hysical units = genes One allele of each gene / homologous chromosome 2) Differing alleles can mask one another if occuying same cell Dominant Allele: Allele exressed (observed) Recessive Allele: Allele mask (not observed) 3) Alleles of a gene segregate from one another during meiosis Law of Segregation Which allele enters which gamete occurs by chance 4) True-breeding individuals have two of the same alleles Hybrids have two different alleles for the gene Figure 12.4 / 12.5 Audesirk 2 & Byers 1

2 Inheritance of Single Traits: Figure 12.8 / Audesirk 2 & Byers Inheritance of Single Traits: Figure Audesirk 2 & Byers Arrgghh! = henotye: Outward exression of a trait (e.g., aearance, behavior) Genotye: Actual combination of alleles carried by an individual Figure Audesirk 2 & Byers unnett Square Method: ( Genetic Bookkeeing ) Mendel s hyothesis can be used to redict cross outcomes: Test Cross: Crossing a dominant henotye individual with a homozygous recessive individual to determine the genotye of the dominant individual henotye: 3 urle : 1 white Genotye: 1 : 2 : 1 or Kee in Mind: redicted roortions will fluctuate in real life 100% urle 50% urle / 50% White Figure Audesirk 2 & Byers Inheritance of Multile Traits: Mendel raised true-breeders for different forms of two traits and then cross-fertilized the forms: YYSS x yyss YySs Inheritance of Multile Traits: Y y Y YY Yy S y Yy yy s 3/4 yellow 1/4 green Resulting ratio of self-fertilization: 9 Yellow, smooth seeds 3 Yellow, wrinkled seeds 3 Green, smooth seeds 1 Green, wrinkled seeds Yy = Seed Color Ss = Seed Texture Mendel then allowed F 1 to self-fertilize: YySs x YySs S s SS Ss Ss ss 3/4 smooth 1/4 wrinkled 9/16 Yellow, smooth seeds 3/16 Yellow, wrinkled seeds 3/16 Green, smooth seeds 1/16 Green, wrinkled seeds 2

3 Egg Figure Audesirk 2 & Byers Inheritance of Multile Traits: Law of Indeendent Assortment: The alleles for one trait may be distributed to the gametes indeendently of the alleles for other traits Occurs via random assortment of chromosomes during meiosis I Traits located on searate chromosomes unnett Square (Multile Traits): Serm YS Ys ys ys YS YYSS Ys YySs x YySs ys ys Figure Audesirk 2 & Byers Figure Audesirk 2 & Byers unnett Square (Multile Traits): Genes on the Same Chromosome Tend to be Inherited Together: Linked Genes: Genes on same chromosome 9 Yellow, smooth seeds 3 Yellow, wrinkled seeds 3 Green, smooth seeds 1 Green, wrinkled seeds Linked genes may be searated via crossing over: Crossing Over: Exchange of homologous chromosome segments (occurs during metahase of meiosis I) Genetic Recombination Figure Audesirk 2 & Byers Sex Chromosomes: Determine sex of individual: Humans = X and Y chromosomes Female = XX : Male = XY Birds / Retiles = W and Z chromosomes Female = WZ : Male = ZZ Only one air er individual in a secies Autosomes: All other chromosome airs other than sex chromosomes Examle of Sex-linked Trait: Sex-linked Genes: Genes resent on one sex chromosome but not the other Human Y chromosome 20 unique genes Human X chromosome 1500 unique genes Examles: Color vision genes / Blood clotting factors Females = Normal dominant / recessive relationshis exist for alleles on X chromosomes Males = Fully exress alleles on X chromosome 3

4 Flower Color in Snadragons Table 12.1 Audesirk 2 & Byers One allele is comletely dominant over another allele Fact: Alleles can dislay incomlete dominance Heterozygous henotye is intermediate between homozygous henotyes There are only two ossible alleles for each gene Fact: Genes can have multile alleles Most genes have > 10 alleles Alleles arise from mutation Remember: An individual will have only a maximum of two unique alleles for a gene (diloid organisms) AA or AO AB Codominance: Both henotyes exressed equally in heterozygotes BB or BO O Each trait is comletely controlled Fact A : Many traits are influenced by several genes Each trait is comletely controlled Fact B : Single genes may have multile henotyic effects (leiotrohy) SRY gene: Codes for rotein that activates other roteins in male cascade olygenic Inheritance: Interaction of two (2) or more genes contribute to a single henotye Fertilization Hormones Sex Determining Region of the Y Gonad Formation Sexual Differentiation of henotye Figure Audesirk 2 & Byers How are Human Genetic Disorders Investigated? Each trait is comletely controlled Fact C : The environment can influence gene exression Examle: Temerature in Himalayan rabbits Enzyme deactivated at high temerature Humans: Skin color (exosure) Height (nutrition) Intelligence (?) Diagrams showing the genetic relationshi among related individuals: Can reveal whether trait is dominant, recessive, or sex-linked Answer: edigrees Dominant Trait Recessive Trait 4

5 Inheritance of Human Disorders (single gene): 1) Recessive Alleles: Disease if individual inherits two recessive alleles Carrier: Heterozygous individual (not affected) Inheritance of Human Disorders (single gene): 2) Dominant Alleles: otential effects: A) roduce abnormal roteins 3) Sex-linked Alleles: B) erform toxic reactions C) roduce overactive roteins Huntington Disease: Deterioration of brain Genes associated with the sex chromosomes Frequently in males; often skis a generation (abnormal rotein roduction) Albinism (no igmentation; ink eyes) Sickle-cell Anemia (defective hemoglobin) Examle 1: Color blindness (defective recetors) Figure Audesirk 2 & Byers Royal Families of Euroe: Examle 2: Hemohilia (defective clotting roteins) Errors in Chromosome Number can Occur: 1) Sex Chromosomes: XO Turner Syndrome ( ; Infertile; lack 2 sexual char.) XXX Trisomy X ( ; Fertile; usually tall; otential IQ) XXY Klinefelter Syndrome ( ; Fertile; often unnoticed) XYY Jacob Syndrome ( ; Fertile; excess testosterone (violent?)) Nondisjunction: Homologous airs do not searate during meiosis Figure Audesirk 2 & Byers Errors in Chromosome Number can Occur: 2) Autosomal Chromosomes: Down Syndrome (Trisomy 21) hysical characteristics Mental retardation Heart malformations Frequency increase with age at regnancy Nondisjunction: Homologous airs do not searate during meiosis 5