Chapter 12: Inheritance

Chapter 12 Who is the Father of Modern ? Patterns of Inheritance

Answer : Johann Gregor Mendel

Definitions:

Character - a heritable feature Trait - each variant for a character

Chapter 12: Inheritance Definitions: 1) Self-fertilization : • Same flower provides • True/pure breeding pollen and eggs • True-breeding (homozygous) consistently gives rise to offspring with same trait x 2) Cross-fertilization : when selfed (or bred with • Different flowers provide same type). pollen and eggs (by hand) • Hybrid cross Carpel cross between parents true- (eggs) breeding for different trait(s) Stamen (pollen) Black lab with a golden lab.

1 Controlled genetic crosses Chapter 12: Inheritance Inheritance of Single Traits: P (parental) • Mendel raised true-breeders Generation for different forms of a trait and then cross-fertilized the forms:

F1 (filial 1) Generation Progeny (offspring) • Mendel then allowed F 1 to self-fertilize: Intercross or self F1 offspring

F2 (filial 2) Generation

Chapter 12: Inheritance Chapter 12: Inheritance Modern Genetic Concepts: Modern Genetic Concepts:

Locus : Specific location of a on : Specific location of a gene on a a chromosome

Locus Locus : Alternate forms of a nucleotide Locus Locus Alleles: Alternate forms of a nucleotide sequence for a single gene sequence for a single gene Heterozygous (“different pair”) Heterozygous (“different pair”) • Homologous have • Homologous chromosomes have different alleles for a gene different alleles for a gene Homozygous (“same pair”) • Homologous chromosomes have same for a gene

Chapter 12: Inheritance Mendel’s Hypothesis : Mendel’s model: 1) Traits are determined by pairs of discrete physical units 1. Hereditary units () come in different forms • Physical units = genes (alleles) • One allele of each gene / homologous chromosome  Gene = hair color 2) Alleles of a gene segregate from one another during  Alleles = blonde hair, red hair, black hair, brown hair. • Law of Segregation 2. Two hereditary units for each trait (per individual) • Which allele enters which gamete occurs by chance One from each parent 3) Differing alleles can mask one another if occupying same • Dominant Allele : Allele expressed (observed) purple • Recessive Allele : Allele mask (not observed) One may be 4) True-breeding individuals have two of the same alleles dominant to purple the other. • Hybrids have two different alleles for the gene white

2 Chapter 12: Inheritance Inheritance of Single Traits: B. The law of segregation • Dominant trait - The trait exhibited by the F1 generation

• Recessive trait - the trait NOT seen in the F1 generation

P x

Phenotype : • Outward expression of a trait (appearance, behavior) Genotype : F1 • Actual combination of alleles carried by an individual

Chapter 12: Inheritance Chapter 12: Inheritance Inheritance of Single Traits: Punnett Square Method: (“Genetic Bookkeeping”)

Individual 1 = Pp Individual 2 = Pp Phenotype : 3 purple : 1 white Genotype : 1 PP : 2 Pp : 1 pp

Keep in Mind : Predicted proportions will fluctuate in real life

Chapter 12: Inheritance Chapter 12: Inheritance Inheritance of Multiple Traits: Mendel’s hypothesis can be used to predict cross outcomes: • Mendel raised true-breeders : for different forms of two traits and then cross-fertilized the Crossing a dominate phenotype individual with a homozygous forms: recessive individual to determine what the genotype of the dominate individual YYSS x yyss

PP P p YySs p Pp Pp p Pp pp PP or Pp • Mendel then allowed F 1 to self-fertilize: p Pp Pp p Pp pp YySs x YySs

pp 100% Purple 50% Purple / 50% White

3 Chapter 12: Inheritance Chapter 12: Inheritance Inheritance of Multiple Traits: • Resulting ratio of self-fertilization: 9 Yellow, smooth seeds Law of Independent Assortment : 3 Yellow, wrinkled seeds Y y • The alleles for one trait may be distributed to the gametes 3 Green, smooth seeds independently of the alleles for other traits 1 Green, wrinkled seeds Y YY Yy • Occurs via random assortment of chromosomes 3/4 yellow 9 : 3 : 3 : 1 during Meiosis I 1/4 green • Traits located on separate chromosomes y Yy yy Yy = Seed Color Ss = Seed Texture S s 9/16 Yellow, smooth seeds S SS Ss 3/16 Yellow, wrinkled seeds 3/4 smooth 3/16 Green, smooth seeds 1/4 wrinkled 1/16 Green, wrinkled seeds s Ss ss 9 : 3 : 3 : 1

Chapter 12: Inheritance Law of independent assortment Punnett Square (Multiple Traits): YySs x YySs Sperm Each pair of alleles segregates independently YS Ys yS ys of other allele pairs. YS as long as they are unlinked Ys Egg yS i.e., not on the same chromosome ys

Independent Chapter 12: Inheritance Assortment Punnett Square (Multiple Traits): of Alleles: YySs x YySs Sperm YS Ys yS ys

YS YYSS

Ys Egg yS

ys (Figure 12.7)

4 Punnett Square Chapter 12: Inheritance for Two 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 9 : 3 : 3 : 1

(Figure 12.6)

Chapter 12: Inheritance Chapter 12: Inheritance

Linked genes may be separated Sex Chromosomes: by crossing over events: • Determine sex of individual: • Crossing Over = Exchange • = X and Y chromosomes of segments of homologous • Female = XX : Male = XY chromosomes • Birds/Reptiles = W and Z chromosomes • Occurs during metaphase • Female = WZ : Male = ZZ of meiosis I • Only one pair per species: • Humans = 23 chromosome pairs (1 pair sex) • Dogs = 39 chromosome pairs (1 pair sex)

• = All other chromosome pairs other than sex chromosomes (usually same size)

Chapter 12: Inheritance Cross: Sex-linked Genes: • Genes present on one but not the other female Bb x male B • ∼ 80 genes B b ∼ X X • Human 1500 genes X • Color vision genes B • Blood clotting factors X XB XB XB Xb

• Females = Normal dominant/recessive relationships A difference in phenotypic ratios exist for alleles on X chromosomes XB Y Xb Y between male and female Y • Males = Fully express alleles on X chromosome progeny always indicates .  i.e., more males have the disorder than females.

5 Example of Sex-linked Chapter 12: Inheritance Trait: Variations on the Mendelian Theme: • Assumptions so far: 1) One allele is completely dominant over another allele Fact : Alleles can display Incomplete : • Heterozygous phenotype is intermediate between homozygous phenotypes

Flower Color in Snapdragons (Figure 12.10) (Figure 12.11)

Chapter 12: Inheritance Chapter 12: Inheritance

Variations on the Mendelian Theme: Variations on the Mendelian Theme: • Assumptions so far: • Assumptions so far: 3) Each trait is completely controlled by a single gene 2) There are only two possible AA or AO BB or BO alleles for each gene Fact : Many traits are influenced by several genes Fact : Genes can have multiple • Polygenic Inheritance : alleles: • Interaction of 2 or more genes contribute to a AB O single phenotype • Most genes have > 10 alleles • Alleles arise from mutation • Skin Color = 3 or 4 genes Codominance : • Eye Color = 2 genes Remember : An individual will • Both phenotypes expressed have only a maximum of two equally in heterozygotes unique alleles for a gene(diploid)

Chapter 12: Inheritance Example of Polygenic Inheritance: Additional Variations on the Mendelian Theme: • Pleiotrophy : Single genes may have multiple phenotypic effects • SRY gene: Codes for protein that activates other proteins in male cascade

Fertilization Sex Determining Region of the Y

Hormones Gonad Formation

Sexual Differentiation of phenotype

(similar idea to Figure 12.12)

6 Pleiotropy Chapter 12: Inheritance Additional Variations on the Mendelian Theme: • Marfan’s syndrome • The Environment influences Gene Expression: Pleiotropic trait that causes • Temperature in Himalayan Rabbits Tall, lanky bodies • Enzyme deactivated at high temperature

Detached retinas

Collapsed lungs Humans:

Aortic dissections • Skin color (exposure) • Height (nutrition) Nearsightedness (myopia) • Intelligence (?)

Chapter 12: Inheritance Pedigrees: Recessive Trait Human Genetic Disorders: How are Human Genetic Disorders Investigated? Answer : Pedigrees

• Diagrams which show the genetic relationship among related individuals • Can reveal whether trait is dominant, recessive, or sex-linked Dominant Trait

(Figure 12.14)

Chapter 12: Inheritance Chapter 12: Inheritance Inheritance of Human Disorders (Single Gene): Inheritance of Human Disorders (Single Gene): 1) Recessive Alleles: 2) Dominant Alleles : • Disease if individual inherits two recessive alleles • Potential Effects: • Carrier = Heterozygous individual (not affected) • Produce abnormal protein • Carry out toxic reactions Albinism (no pigmentation; pink eyes) • Produce “overactive” proteins • Huntington Disease (deterioration of brain) • Abnormal protein production 3) Sex-linked : • Genes associated with sex chromosomes • Frequently in males… often skip generations • Color blindness (defective color receptors) • Hemophilia (defective clotting proteins) Sickle-cell Anemia (defective hemoglobin)

7 Royal Families of Europe: Chapter 12: Inheritance Errors in Chromosome Number can Affect Humans: • : Homologous pairs don’t separate during meiosis (affects gamete chromosome counts) 1) Sex Chromosomes : • XO (Female ) = Turner Syndrome (Infertile; lack 2°sexual char.) • XXX (Female) = X (Fertile; usually tall; potential ↓ IQ) • XXY (Male) = Klinefelter Syndrome (Infertile; often unnoticed) • XYY (Male) = Fertile; Excess testosterone (violent?) ; ↓ IQ)

Chapter 12: Inheritance

Errors in Chromosome Number can Affect Humans: • Nondisjunction: Homologous pairs don’t separate during meiosis (affects gamete chromosome counts) 2) Autosomal Chromosomes : • Down Syndrome (Trisomy 21) • Physical characteristics • Mental retardation • Heart malformations

• Frequency increase with age at pregnancy

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