BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 9 Patterns of Inheritance Modules 9.11 – 9.23

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel’s principles are valid for all sexually reproducing species –However, often the genotype does not dictate the phenotype in the simple way his principles describe VARIATIONS ON MENDEL’S PRINCIPLES 9.11 The relationship of genotype to phenotype is rarely simple

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings When an offspring’s phenotype—such as flower color— is in between the phenotypes of its parents, it exhibits incomplete dominance 9.12 Incomplete dominance results in intermediate phenotypes P GENERATION F 1 GENERATION F 2 GENERATION Red RR GametesRr White rr Pink Rr Rr RR rr 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 SpermEggs Pink Rr Pink rR White rr Red RR Figure 9.12A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Incomplete dominance in human hypercholesterolemia Figure 9.12B GENOTYPES: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors PHENOTYPES: LDL LDL receptor Cell NormalMild diseaseSevere disease

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In a population, multiple alleles often exist for a characteristic –The three alleles for ABO blood type in humans is an example 9.13 Many genes have more than two alleles in the population

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.13 –The alleles for A and B blood types are codominant, and both are expressed in the phenotype Blood Group (Phenotype) O Genotypes Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left OABAB A B ii I A or I A i I B or I B i I A I B Anti-A Anti-B Anti-A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 9.14 A single gene may affect many phenotypic characteristics A single gene may affect phenotype in many ways –This is called pleiotropy –The allele for sickle-cell disease is an example

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells Breakdown of red blood cells Clumping of cells and clogging of small blood vessels Accumulation of sickled cells in spleen Physical weakness Anemia Heart failure Pain and fever Brain damage Damage to other organs Spleen damage Kidney failure Rheumatism Pneumonia and other infections Paralysis Impaired mental function Figure 9.14

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic testing can be of value to those at risk of developing a genetic disorder or of passing it on to offspring 9.15 Connection: Genetic testing can detect disease-causing alleles Figure 9.15B Figure 9.15A Dr. David Satcher, former U.S. surgeon general, pioneered screening for sickle-cell disease

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This situation creates a continuum of phenotypes –Example: skin color 9.16 A single characteristic may be influenced by many genes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.16 P GENERATION F 1 GENERATION F 2 GENERATION aabbcc (very light) AABBCC (very dark) AaBbCc EggsSperm Fraction of population Skin pigmentation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genes are located on chromosomes –Their behavior during meiosis accounts for inheritance patterns THE CHROMOSOMAL BASIS OF INHERITANCE 9.17 Chromosome behavior accounts for Mendel’s principles

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Certain genes are linked –They tend to be inherited together because they reside close together on the same chromosome 9.18 Genes on the same chromosome tend to be inherited together

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.18

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This produces gametes with recombinant chromosomes The fruit fly Drosophila melanogaster was used in the first experiments to demonstrate the effects of crossing over 9.19 Crossing over produces new combinations of alleles

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A B a b TetradCrossing over AB a ba BAb Gametes Figure 9.19A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Crossing over is more likely to occur between genes that are farther apart –Recombination frequencies can be used to map the relative positions of genes on chromosomes 9.20 Geneticists use crossover data to map genes g Figure 9.20B Chromosome cl 17% 9%9.5%

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A partial genetic map of a fruit fly chromosome Figure 9.20C Short aristae Black body (g) Cinnabar eyes (c) Vestigial wings (l) Brown eyes Long aristae (appendages on head) Gray body (G) Red eyes (C) Normal wings (L) Red eyes Mutant phenotypes Wild-type phenotypes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A human male has one X chromosome and one Y chromosome A human female has two X chromosomes Whether a sperm cell has an X or Y chromosome determines the sex of the offspring SEX CHROMOSOMES AND SEX-LINKED GENES 9.21 Chromosomes determine sex in many species

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.21A XY Male (male) Parents’ diploid cells (female) Sperm Offspring (diploid) Egg

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other systems of sex determination exist in other animals and plants Figure 9.21B-D –The X-O system –The Z-W system –Chromosome number

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings All genes on the sex chromosomes are said to be sex-linked –In many organisms, the X chromosome carries many genes unrelated to sex –Fruit fly eye color is a sex-linked characteristic 9.22 Sex-linked genes exhibit a unique pattern of inheritance Figure 9.22A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Their inheritance pattern reflects the fact that males have one X chromosome and females have two Figure 9.22B-D –These figures illustrate inheritance patterns for white eye color (r) in the fruit fly, an X-linked recessive trait FemaleMaleFemaleMaleFemaleMale XrYXrYXRXRXRXR XRXrXRXr XRYXRY XRXR XrXr Y XRXrXRXr XRXR XrXr XRXRXRXR XRXR Y XRYXRY XrXRXrXR XRYXRY XrYXrY XRXrXRXr XRXR XrXr XrXr Y XRXrXRXr XrXrXrXr XRYXRY XrYXrY XrYXrY R = red-eye allele r = white-eye allele

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most sex-linked human disorders are due to recessive alleles –Examples: hemophilia, red-green color blindness –These are mostly seen in males –A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the allele from both parents to be affected 9.23 Connection: Sex-linked disorders affect mostly males Figure 9.23A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A high incidence of hemophilia has plagued the royal families of Europe Figure 9.23B Queen Victoria Albert AliceLouis AlexandraCzar Nicholas II of Russia Alexis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Human Blood Type Blood type is determined by the presence or lack of presence of certain proteins (antigens) on the surface of red blood cells.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings CoDominance - Review Both type A and type B blood are dominant over type O BUT THEY ARE NOT DOMINANT OVER EACH OTHER. Thus an individual with alleles for type A and type B blood expresses both antigens simultaneously and has type AB blood, which demonstrates codominance.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Graphic of cell surface antigens

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How do we express alleles for blood type in genotypes? Type O blood is ii Type A blood is I A I A (homozygous) or I A i (heterozygous) Type B blood is I B I B (homozygous) or I B i (heterozygous) Type AB blood is I A I B You can use these genotypes in Punnett squares.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Codominance Punnett Squares A male is heterozygous for type A blood. A female has type AB blood. If these two have offspring.. draw a Punnett square showing the expected genotype and phenotype results for blood type.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Codomiance Punnet Square What percentage of their offspring would have type O blood? _______ What percentage would have type A blood? ______ What is the probability that their child would have type B blood? _______ If these two parents have four offspring, how many of them would have type AB blood? ______ How many would have type O blood? __________ How many would be a carrier for type O blood? _____

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 32 RH Blood Groups People with Rh agglutinogens on RBC surface are Rh+. Most people are Rh + If an Rh - woman is pregnant and the baby is Rh+, the mother’s body may reject the pregnancy; she must take anti-rejection drugs and be closely monitored.