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 9.1 – 9.10

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetics is the science of heredity These black Labrador puppies are purebred— their parents and grandparents were black Labs with very similar genetic makeups –Purebreds often suffer from serious genetic defects Purebreds and Mutts — A Difference of Heredity

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The parents of these puppies were a mixture of different breeds –Their behavior and appearance is more varied as a result of their diverse genetic inheritance

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The science of heredity dates back to ancient attempts at selective breeding Until the 20th century, however, many biologists erroneously (wrongly!) believed that –characteristics acquired during lifetime could be passed on –characteristics of both parents blended irreversibly in their offspring MENDEL’S PRINCIPLES The science of genetics has ancient roots

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants Experimental genetics began in an abbey garden Figure 9.2A, B Stamen Carpel

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation Figure 9.2C This illustration shows his technique for cross-fertilization 1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF- SPRING (F 1 ) 2 Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel studied seven pea characteristics Figure 9.2D He hypothesized that there are alternative forms of genes – alleles (although he did not use that term), the units that determine heredity FLOWER COLOR FLOWER POSITION SEED COLOR SEED SHAPE POD SHAPE POD COLOR STEM LENGTH PurpleWhite AxialTerminal YellowGreen RoundWrinkled InflatedConstricted GreenYellow TallDwarf

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings From his experimental data, Mendel deduced that an organism has two genes for each inherited characteristic –One characteristic comes from each parent Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION (true-breeding parents) F 1 generation F 2 generation Purple flowersWhite flowers All plants have purple flowers Fertilization among F1 plants (F 1 x F 1 ) 3 / 4 of plants have purple flowers 1 / 4 of plants have white flowers Figure 9.3A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A sperm or egg carries only one gene of each pair –The pairs of genes separate when gametes form –This process describes Mendel’s law of segregation –Alleles can be dominant or recessive GENETIC MAKEUP (ALLELES) P PLANTS F 1 PLANTS (hybrids) F 2 PLANTS PPpp All PAll p All Pp 1/2 P1/2 P 1/2 p1/2 p Eggs P p P PP p Sperm Pp pp Gametes Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Figure 9.3B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Principle of Segregation Homologous pairs of genes segregate (separate) during gamete formation (meiosis). The joining of gametes at fertilization pair the genes once again.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alternative forms of a gene (alleles) reside at the same locus on homologous chromosomes Homologous chromosomes bear the two alleles for each characteristic GENE LOCI Figure 9.4 PaB DOMINANT allele RECESSIVE allele Pab GENOTYPE:PPaaBb HOMOZYGOUS for the dominant allele HOMOZYGOUS for the recessive allele HETEROZYGOUS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Vocabulary Gene – a segment of DNA that contains the instructions that code for a particular trait Locus – specific location of a gene on a chromosome Allele – alternate versions of a gene at a single locus Homozygous – when the alleles of a gene are the same on the homologous chromosomes Heterozygous – when the alleles of a gene are different on the homologous chromosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetics Vocabulary Dominant – the allele that is expressed when the alleles are heterozygous. Represented by an upper case letter Recessive – the allele that is not expressed when the alleles are heterozygous. Represented by a lower case letter. To be expressed the cell must have 2 copies of the recessive allele

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetics Vocabulary Phenotype – the physical appearance of a trait in an organism Genotype – the genetic make up of an organism with respect to a trait. The genotype of a trait can be homozygous dominant, heterozygous or homozygous recessive

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Inheritance follows the rules of probability Mendel’s principles reflect the rules of probability F 1 GENOTYPES Bb female F 2 GENOTYPES Formation of eggs Bb male Formation of sperm 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 1/41/4 1/41/4 1/41/4 BB BB B B b b b b bb Figure 9.7

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Predicting the Outcome of a Monohybrid Cross Predict the results of the following cross (using R to denote tongue-rolling ability): P generation: RR x RR 1.What genotype(s) will be found in the F1 generation? 2.What phenotype(s) will be found in the F1 generation? 3.Explain why you made these predictions.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Predicting the Outcomes of a Monohybrid Cross Predict the results of the following cross: P generation: RR x rr 1.What genotype(s) will be found in the F1 generation? 2.What phenotype(s) will be found in the F1 generation? 3.Explain why you made these predictions.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Predicting the Outcome of a Monohybrid Cross Predict the results of the following cross: P generation = Rr x Rr 1.Draw the Punnett square. 2.What are the possible genotypes in the F1 generation? 3.What is the genotypic ratio of this cross? 4.What are the possible phenotypes in the F1 generation? 5.What is the phenotypic ratio for this cross?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The offspring of a testcross often reveal the genotype of an individual when it is unknown Geneticists use the testcross to determine unknown genotypes TESTCROSS: B_GENOTYPESbb BBBbor Two possibilities for the black dog: GAMETES OFFSPRING All black1 black : 1 chocolate B b B b b Bb bb Figure 9.6

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Test cross A testcross is the mating between an individual of unknown genotype with a homozygous recessive genotype. Usually performed when the phenotype of the unknown individual is dominant.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Understanding Test Cross 1.Brown coat color (B) in rabbits is dominant and white coat color is recessive. Suppose you have a group of rabbits – some brown and some white. a. For which phenotype(s) do you know the genotype(s)? b. For which phenotype(s) are you unsure of the genotype(s)?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Understanding Test Cross Using B and b to symbolize the brown and white alleles a.What are the possible genotypes of a white rabbit in your group? b.What are the possible genotypes of a brown rabbit? Suppose you wanted to find out the genotype of a brown rabbit. What color rabbit would you mate it with?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Understanding Test Cross A brown buck (male) is mated with a white doe (female). In their litter of 11 young, 6 are white and 5 are brown. a.Using a Punnett square to check your answer, what is the genotype of the buck? Use a Punnett square to determine the ratio of brown and white offspring that would have been produced by the above mating if the brown buck had been homozygous.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.5A HYPOTHESIS: DEPENDENT ASSORTMENT HYPOTHESIS: INDEPENDENT ASSORTMENT P GENERATION F 1 GENERATION F 2 GENERATION RRYYrryy GametesRY Yellow round ry RrYy EggsSpermRY ry RY ry 1/21/2 1/21/2 1/21/2 1/21/2 Actual results contradict hypothesis RRYYrryy RY ry Gametes RrYy EggsRY rY 1/41/4 1/41/4 Ry ry 1/41/4 1/41/4 RY rY Ry ry 1/41/4 1/41/4 1/41/4 1/41/4 RRYY RrYY RRYyrrYYRrYy rrYyRRyyrrYy Rryy rryy 9 / 16 3 / 16 1 / 16 Green round Yellow wrinkled Green wrinkled ACTUAL RESULTS SUPPORT HYPOTHESIS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings By looking at two characteristics at once, Mendel found that the genes of a pair segregate independently of other gene pairs during gamete formation –This is known as the principle of independent assortment The principle of independent assortment is revealed by tracking two characteristics at once

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Independent assortment of two genes in the Labrador retriever Figure 9.5B PHENOTYPES Black coat, normal vision B_N_ Blind GENOTYPES MATING OF HETEROZYOTES (black, normal vision) PHENOTYPIC RATIO OF OFFSPRING Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA) Blind BbNn

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Principle of Independent Assortment Dihybrid cross An experimental mating of individuals in which the inheritance of 2 traits is tracked. When the inheritance of 2 traits is tracked in an individual, the dominant/recessive traits does not always appear together. The individual may be dominant in one of the traits and recessive in the other.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Principle of Independent Assortment Genes for different characteristics are not connected and each pair of genes for a characteristic separate independently during meiosis.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Solving Dihybrid Problems 1.List the genotypes of each parent. 2.Make all possible combinations of the gametes 3.Construct a 16 square Punnett square. 4.List the possible genotypes of the offspring and determine the genotypic ratio. 5.List the possible phenotypes of the offspring and determine the phenotypic ratio.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Solving Dihybrid Problems Example: In humans freckles (F) is dominant and no freckles (f) is recessive. Normal arches (A) are dominant and flat feet (a) is recessive. A man who has freckles and flat feet (FFaa) marries a woman without freckles and normal arches (ffAA). What are the possible genotypes and phenotypes of their children?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The inheritance of many human traits follows Mendel’s principles and the rules of probability Connection: Genetic traits in humans can be tracked through family pedigrees Figure 9.8A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Family pedigrees are used to determine patterns of inheritance and individual genotypes Figure 9.8B Dd Joshua Lambert Dd Abigail Linnell D_ Abigail Lambert Female Dd Elizabeth Eddy D_ John Eddy ?D_ Hepzibah Daggett ? ? ddDd ddDd Male Deaf Hearing dd Jonathan Lambert

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most such disorders are caused by autosomal recessive alleles –Examples: cystic fibrosis, sickle-cell disease Connection: Many inherited disorders in humans are controlled by a single gene Figure 9.9A DD dd Normal Dd Normal Dd DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf EggsSperm PARENTS OFFSPRING

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Inherited Single Gene Disorders Recessive disorders Most single gene disorders Relatively harmless disorders to deadly diseases Most born to normal parents who are carriers –Carrier – an individual who is heterozygous for a recessive disorder and does not show symptoms of the disorder Carriers have a 1 in 4 chance of having a child with a recessive disorder

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A few are caused by dominant alleles Figure 9.9B –Examples: achondroplasia, Huntington’s disease

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 9.9

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Karyotyping and biochemical tests of fetal cells and molecules can help people make reproductive decisions –Fetal cells can be obtained through amniocentesis Connection: Fetal testing can spot many inherited disorders early in pregnancy Figure 9.10A Amniotic fluid Fetus (14-20 weeks) Placenta Amniotic fluid withdrawn Centrifugation Fetal cells Fluid UterusCervix Cell culture Several weeks later Karyotyping Biochemical tests

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chorionic villus sampling is another procedure that obtains fetal cells for karyotyping Figure 9.10B Fetus (10-12 weeks) Placenta Chorionic villi Suction Several hours later Fetal cells (from chorionic villi) Karyotyping Some biochemical tests

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Examination of the fetus with ultrasound is another helpful technique Figure 9.10C, D

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 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 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 Incomplete Dominance In a cross between a homozygous dominant parent and a homozygous recessive parent the phenotype of the offspring is in between the phenotypes of the parents. Example: When red snapdragons are crossed with white snapdragons all the offspring have pink flowers

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 Multiple allele traits 3 or more alleles of the same gene code for a single trait Example: the three alleles (I A, I B, i) for ABO blood type in humans Many genes have more than two alleles in the population

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 A single gene may affect many phenotypic characteristics Pleoitropy A single gene may affect phenotype in many ways Example: the allele for sickle-cell disease

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 Polygenic traits Trait that is controlled by 2 or more genes. This situation creates a continuum of phenotypes –When the range of traits is graphed a bell shaped curve is seen Example: skin color, eye color A single characteristic may be influenced by many genes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Match the description with its pattern of inheritance 1.There are 3 different alleles for a blood group, I A, I B, and i, but an individual has only two at a time. 2.The sickle cell allele, s, is responsible for a variety of phenotypic effects, from pain and fever to damage to the heart, lungs, joints, brain or kidneys. 3.If a red shorthorn cow is mated with a white bull, all their offspring are roan, a phenotype that has a mixture of red and white hairs.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 4.Independent genes at 4 different loci are responsible for determining a person’s HLA tissue type, important in organ transplants and certain diseases. 5.When graphed, the number of individuals of various heights forms a bell shaped curve. 6.Chickens homozygous for the black allele are black, and chickens homozygous for the white allele are white. Heterozygous chickens are gray.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The chromosomal basis of Mendel’s principles Figure 9.17

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 Chromosome behavior accounts for Mendel’s principles

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Linked genes Genes that are located close together on the same chromosome tend to be inherited together These genes usually do not follow Mendel’s principle of independent assortment Genes on the same chromosome tend to be inherited together

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 Many animals including humans have a pair of sex chromosomes 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 Chromosomes determine sex in many species

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 Sex Chromosomes and Sex-Linked Genes The genetic basis of sex determination isn’t fully understood: –Gene SRY on the Y chromosome plays a crucial role –SRY triggers testis development –Absence of SRY results in overy development

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 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 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 Sex-Linked Disorders Other sex-linked disorders are –Duchenne muscular dystrophy – weakening and loss of muscle tissue –Fragile X syndrome – abnormal X chromosome, most common cause of mental retardation in boys

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Solving Sex-Linked Problems Example One: Eye color is a sex-linked trait in fruit flies and is carried on the X chromosome. Red eye color (R) is dominant over white eye color (r). What is the sex and eye color of the offsrping of a homozygous red eyed female and a white eyed male? Example Two: What is the sex and eye color of the offspring of a heterozygous red eyed female fruit fly and a red eyed male fruit fly?