Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 9 Patterns of Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Purebreds and Mutts-A Difference of Heredity Genetics is the science of heredity A common genetic background will produce offspring with similar physical and behavioral traits – Purebred dogs show less variation than mutts – True-breeding individuals are useful in genetic research Behavioral characteristics are also influenced by environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings MENDEL'S LAWS 9.1 The science of genetics has ancient roots Early attempts to explain heredity have been rejected by later science – Hippocrates' theory of Pangenesis Particles from each part of the body travel to eggs or sperm and are passed on – Early 19th-century biologists' blending hypothesis Traits from both parents mix in the offspring

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.2 Experimental genetics began in an abbey garden Gregor Mendel hypothesized that there are alternative forms of genes, the units that determine heritable traits Mendel crossed pea plants that differed in certain characteristics – Could control matings – Developed true-breeding varieties – Traced traits from generation to generation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Terminology of Mendelian genetics – Self-fertilization: fertilization of eggs by sperm-carrying pollen of the same flower – Cross-fertilization (cross): fertilization of one plant by pollen from a different plant – True-breeding: identical offspring from self- fertilizing parents – Hybrid: offspring of two different varieties

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – P generation: true-breeding parents – F1 generation: hybrid offspring of true- breeding parents – F2 generation: offspring of self-fertilizing F1 parents

LE 9-2b Petal Stamen Carpel

LE 9-2c Removed stamens from purple flower White Carpel Parents (P) Purple Transferred pollen from stamens of white flower to carpel of purple flower Stamens Pollinated carpel matured into pod Planted seeds from pod Offspring (F 1 )

LE 9-2d Flower color Flower position Seed color Seed shape Pod shape Pod color Stem length PurpleWhite AxialTerminal YellowGreen RoundWrinkled InflatedConstricted GreenYellow Tall Dwarf

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.3 Mendel's law of segregation describes the inheritance of a single characteristic From his experimental data, Mendel developed several hypotheses – There are alternative forms (alleles) of genes that account for variation in inherited characteristics – For each characteristic, an organism inherits two alleles, one from each parent Homozygous: two identical alleles Heterozygous: two different alleles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – If the two alleles of an inherited pair differ The dominant allele determines the organism's appearance The recessive allele has no noticeable effect on the organism's appearance – The law of segregation: A sperm or egg carries only one allele for each inherited trait, because allele pairs separate from each other during gamete production

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An organism's appearance does not always reveal its genetic composition – Phenotype: Expressed (physical) traits – Genotype: Genetic makeup

LE 9-3a P generation (true-breeding parents) Purple flowersWhite flowers  All plants have purple flowers F 1 generation F 2 generation Fertilization among F 1 plants (F 1  F 1 ) of plants have purple flowers 3434 of plants have white flowers 1414

LE 9-3b P plants Gametes Genetic makeup (alleles) All Pp F 1 plants (hybrids) F 2 plants Sperm Phenotypic ratio 3 purple : 1 white Gametes PPpp All PAll p Eggs 1212 Genotypic ratio 1 PP : 2 Pp : 1 pp P 1212 p p P P p PPPp pp

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.4 Homologous chromosomes bear the two alleles for each characteristic Alternative forms of a gene reside at the same locus on homologous chromosomes – Supports the law of segregation

LE 9-4 Gene loci PaB Dominant allele Pab PP Bb Genotype: Homozygous for the dominant allele Homozygous for the recessive allele Heterozygous aa Recessive allele

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.5 The law of independent assortment is revealed by tracking two characteristics at once Dihybrid cross – Mate true-breeding parents differing in two characteristics – The F 1 generation exhibits only the dominant phenotype – The F 2 generation exhibits a phenotypic ratio of 9:3:3:1 Mendel's law of independent assortment: each pair of alleles segregates independently of other allele pairs during gamete formation

LE 9-5a rryy RrYy RRYYrryy RY ry RrYy Sperm Eggs RY rY Ry ry RYrYRyry RRYYRrYYRRYyRrYy RrYYrrYYRrYyrrYy RRYyRrYyRRyyRryy RrYyrrYyRryyrryy Yellow round Green round Yellow wrinkled Green wrinkled Actual results support hypothesis ry RY RRYYrryy P generation RY Hypothesis: Dependent assortment Hypothesis: Independent assortment Gametes  Actual results contradict hypothesis F 1 generation F 2 generation Gametes

LE 9-5b Phenotypes Genotypes Mating of heterozygotes (black, normal vision) Phenotypic ratio of offspring Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Blind Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn BbNn  9 black coat, normal vision 3 black coat, blind (PRA) 1 chocolate coat, blind (PRA) 3 chocolate coat, normal vision

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.6 Geneticists use the testcross to determine unknown genotypes A testcross can reveal an unknown genotype – Mate an individual of unknown genotype and a homozygous-recessive individual – Each of the two possible genotypes (homozygous or heterozygous) gives a different phenotypic ratio in the F 1 generation

LE 9-6 Testcross: Genotypes Gametes Offspring All black 1 black : 1 chocolate Two possibilities for the black dog:  or B_ bb Bb Bb bb B BB Bb bb

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.7 Mendel's laws reflect the rules of probability Events that follow probability rules are independent events – One such event does not influence the outcome of a later such event The rule of multiplication: The probability of two events occurring together is the product of the separate probabilities of the independent events The rule of addition: The probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways

LE 9-7 F 1 genotypes Bb female Bb male Formation of sperm Formation of eggs F 2 genotypes Bb B BBBb b bBbb

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 9.8 Genetic traits in humans can be tracked through family pedigrees The inheritance of many human traits follows Mendel's laws – The dominant phenotype results from either the heterozygous or homozygous genotype – The recessive phenotype results from only the homozygous genotype Family pedigrees can be used to determine individual genotypes

LE 9-8a FrecklesNo freckles Widow’s peakStraight hairline Free earlobeAttached earlobe Recessive TraitsDominant Traits

LE 9-8b Dd Joshua Lambert Dd Abigail Linnell D ? John Eddy D ? Hepzibah Daggett D ? Abigail Lambert dd Jonathan Lambert Dd Elizabeth Eddy Dd ddDd dd FemaleMale Deaf Hearing

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 9.9 Many inherited disorders in humans are controlled by a single gene Thousands of human genetic disorders follow simple Mendelian patterns of inheritance – Recessive disorders Most genetic disorders – Can be carried unnoticed by heterozygotes Range in severity from mild (albinism) to severe (cystic fibrosis) More likely to occur with inbreeding

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominant disorders – Some serious, but nonlethal, disorders (achondroplasia) – Lethal conditions less common than in recessive disorders Cannot be carried by heterozygotes without affecting them Can be passed on if they do not cause death until later age (Huntington's disease)

LE 9-9a Parents Offspring Normal Dd Normal Dd  Sperm Dd D d Eggs DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 9.10 New technologies can provide insight into one's genetic legacy New technologies can provide insight for reproductive decisions Identifying carriers – Tests can distinguish parental carriers of many genetic disorders Fetal testing – Amniocentesis and chorionic villus sampling (CVS) allow removal of fetal cells to test for genetic abnormalities

LE 9-10a Ultrasound monitor Fetus Placenta Uterus Cervix Amniotic fluid Fetal cells Centrifugation Needle inserted through abdomen to extract amniotic fluid Amniocentesis Ultrasound monitor Fetus Placenta Chorionic villi Uterus Fetal cells Cervix Chorionic villus sampling (CVS) Suction tube inserted through cervix to extract tissue from chorionic villi Several hours Several weeks Biochemical tests Karyotyping

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fetal imaging – Ultrasound imaging uses sound waves to produce a picture of the fetus Newborn screening – Some genetic disorders can be detected at birth by routine tests Ethical considerations – How will genetic testing information be used? Video: Ultrasound of Human Fetus 1 Video: Ultrasound of Human Fetus 1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings VARIATIONS ON MENDEL'S LAWS 9.11 The relationship of genotype to phenotype is rarely simple Mendel's principles are valid for all sexually reproducing species However, most characteristics are inherited in ways that follow more complex patterns

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.12 Incomplete dominance results in intermediate phenotypes Complete dominance – Dominant allele has same phenotypic effect whether present in one or two copies Incomplete dominance – Heterozygote exhibits characteristics intermediate between both homozygous conditions – Not the same as blending

LE 9-12a P generation F 1 generation F 2 generation Gametes Eggs White rr Pink Rr R R r r Sperm R 1212 r 1212 Red RR Pink rR Pink Rr White rr Red RR Rr 

LE 9-12b HH Homozygous for ability to make LDL receptors Genotypes: Hh Heterozygous Phenotypes: LDL receptor Cell Normal Mild diseaseSevere disease hh Homozygous for inability to make LDL receptors

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.13 Many genes have more than two alleles in the population In a population, multiple alleles often exist for a single characteristic Example: human ABO blood group – Involves three alleles of a single gene – AB blood group is an example of codominance-both alleles are expressed in heterozygotes

LE 9-13 Blood Group (Phenotype) Genotypes Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left OABAB O A B ii Anti-A Anti-B Anti-A I A or I A i I B or I B i IAIBIAIB

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.14 A single gene may affect many phenotypic characteristics Pleiotropy: a single gene may influence multiple characteristics Example: sickle cell disease – Allele causes production of abnormal hemoglobin in homozygotes Many severe physical effects – Heterozygotes generally healthy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Most common inherited disorder among people of African descent Allele persists in population because heterozygous condition protects against malaria

LE 9-14 Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle-cells 5,555  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 Impaired mental function Paralysis Pneumonia and other infections Rheumatism Kidney failure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.15 A single characteristic may be influenced by many genes Polygenic inheritance is the additive effects of two or more genes on a single phenotypic characteristic Example: human skin color – Controlled by at least three genes

LE 9-15 P generation F 1 generation F 2 generation aabbcc (very light) AABBCC (very dark)   AaBbCc Sperm Eggs Fraction of population Skin color

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.16 The environment affects many characteristics Many characteristics result from a combination of genetic and environmental factors – Nature vs. nurture is an old and hotly contested debate – Only genetic influences are inherited

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 9.17 Genetic testing can detect disease-causing alleles Predictive genetic testing may inform people of their risk for developing genetic diseases – Used when there is a family history but no symptoms – Increased use of genetic testing raises ethical, moral, and medical issues

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE CHROMOSOMAL BASIS OF INHERITANCE 9.18 Chromosome behavior accounts for Mendel's laws Chromosome theory of inheritance – Genes occupy specific loci on chromosomes – Chromosomes undergo segregation and independent assortment during meiosis – Thus, chromosome behavior during meiosis and fertilization accounts for inheritance patterns

LE 9-18 F 1 generation All round yellow seeds (RrYy) Metaphase  of meiosis (alternative arrangements) Anaphase  of meiosis R r Y y R r R r y Y r R Y y R Y y y Metaphase  of meiosis Y R Y r R Y y r Y r y y y Y R R r rr y r y Y R R Y Gametes RY ry 1414 rY 1414 Ry Fertilization among the F 1 plants F 2 generation 9:3 :1 (See Figure 9.5A)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.19 Genes on the same chromosome tend to be inherited together Linked genes – Lie close together on the same chromosome – Tend to be inherited together – Generally do not follow Mendel's law of independent assortment

LE 9-19 Experiment Purple flower Purple long Purple round Red long Red round Explanation: linked genes Parental diploid cell PpLl Most gametes P L p l Meiosis P L p l Fertilization Sperm P L p l P L p l P L p l P L 3 purple long : 1 red round Not accounted for: purple round and red long Most offspring Eggs Long pollen PpLl  Phenotypes Observed offspring Prediction (9:3:3:1)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.20 Crossing over produces new combinations of alleles During meiosis, homologous chromosomes undergo crossing over – Produces new combinations of alleles in gametes – Percentage of recombinant offspring is called the recombination frequency

LE 9-20a TetradCrossing over AB ab AB Ab Gametes ab aB

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thomas Hunt Morgan performed some of the most important studies of crossing over in the early 1900s – Used the fruit fly Drosophila melanogaster – Established that crossing over was the mechanism that "breaks linkages" between genes

LE 9-20c Experiment Gray body, long wings (wild type) GgLl Female Black body, vestigial wings ggll Male Offspring Gray longBlack vestigialGray vestigialBlack long Parental phenotypes Recombinant phenotypes Recombination frequency = 391 recombinants 2,300 total offspring = 0.17 or 17% Explanation GgLl (female) ggll (male) gl gl g l g L G l g l G L g l EggsSperm Offspring G L g l G lg L g l 

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.21 Geneticists use crossover data to map genes Morgan and his students greatly advanced understanding of genetics Alfred Sturtevant used crossover data to map genes in Drosophila – Used recombination frequencies to map the relative positions of genes on chromosomes

LE 9-21b Chromosome gcl 17% 9%9.5% Recombination frequencies

LE 9-21c Short aristae Black body (g) Cinnabar eyes (c) Vestigial wings (l) Brown eyes Red eyes Normal wings (L) Red eyes (C) Gray body (G) Long aristae (appendages on head) Mutant phenotypes Wild-type phenotypes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings SEX CHROMOSOMES AND SEX-LINKED GENES 9.22 Chromosomes determine sex in many species Many animals have a pair of chromosomes that determine sex – Humans: X-Y system Male is XY; the Y chromosome has genes for the development of testes Female is XX; absence of a Y chromosome allows ovaries to develop

LE 9-22a (male) 44  XY (female) Parents’ diploid cells 22  X 22  Y 22  X 44  XX Sperm Egg Offspring (diploid) 44  XY 44  XX

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other animals have other sex-determination systems – X-O (grasshopper, roaches, some other insects) – Z-W (certain fishes, butterflies, birds) – Chromosome number (ants, bees) Different plants have various sex- determination systems

LE 9-22b 22  X 22  XX

LE 9-22c 76  ZW 76  ZZ

LE 9-22d 3216

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9.23 Sex-linked genes exhibit a unique pattern of inheritance Sex-linked genes are genes for characteristics unrelated to sex that are located on either sex chromosome – In humans, refers to a gene on the X chromosome Because of linkage and location, the inheritance of these characteristics follows peculiar patterns – Example: eye color inheritance in fruit flies follows three possible patterns, depending on the genotype of the parents

LE 9-23b FemaleMale  XRXRXRXR X r Y Sperm XRXrXRXr XRYXRY XrXr Y XRXR Eggs R = red-eye allele r = white-eye allele

LE 9-23c FemaleMale  XRXrXRXr XRYXRY Sperm XRXRXRXR XRYXRY XRXR Y XRXR Eggs XrXr XrXRXrXR X r Y

LE 9-23d FemaleMale  XRXrXRXr X r Y Sperm XRXrXRXr XRYXRY XrXr Y XRXR Eggs XrXr X r X r Y

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 9.24 Sex-linked disorders affect mostly males In humans, recessive sex-linked traits are expressed much more frequently in men than in women – Most known sex-linked traits are caused by genes (alleles) on the X chromosome – Because the male has only one X chromosome, his recessive X-linked characteristic will always be exhibited – Females with the allele are normally carriers and will exhibit the condition only if they are homozygous – Examples: red-green color blindness, hemophilia, Duchenne muscular dystrophy

LE 9-24b Queen Victoria Albert AliceLouis Alexandra Czar Nicholas  of Russia Alexis