Chapter 9 Patterns of Inheritance Power Point Lectures

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

Purebreds and Mutts–A Difference of Heredity • Purebred dogs – Are very similar on a genetic level due to selective breeding Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Mutts, or mixed breed dogs on the other hand – Show considerably more genetic variation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

MENDEL’S LAWS 9. 1 The science of genetics has ancient roots • The historical roots of genetics, the science of heredity – Date back to ancient attempts at selective breeding Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

9. 2 Experimental genetics began in an abbey garden • Modern genetics – Began with Gregor Mendel’s quantitative experiments with pea plants Petal Stamen Figure 9. 2 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Carpel Figure 9. 2 B

• Mendel crossed pea plants that differed in certain characteristics – And traced traits from generation to generation 1 Removed stamens from purple flower White Stamens Carpel Parents (P) 2 Transferred pollen from stamens Purple of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F 1) Figure 9. 2 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Mendel hypothesized that there alternative forms of genes – The units that determine heritable traits Flower color White Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Yellow Tall Dwarf Flower position Figure 9. 2 D Purple Stem length 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 deduced that an organism has two genes (alleles) for each inherited characteristic P generation (true-breeding parents) Purple flowers F 1 generation White flowers All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 generation 3 1 4 of plants have purple flowers have white flowers Figure 9. 3 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• For each characteristic – An organism inherits two alleles, one from each parent Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• If the two alleles of an inherited pair differ – Then one determines the organism’s appearance and is called the dominant allele • The other allele – Has no noticeable effect on the organism’s appearance and is called the recessive allele Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Mendel’s law of segregation – Predicts that allele pairs separate from each other during the production of gametes P plants Genetic makeup (alleles) pp PP Gametes All p All P F 1 plants (hybrids) All Pp 1 P 2 Gametes 1 p 2 Sperm F 2 plants Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp: 1 pp Figure 9. 3 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings P p P PP Pp pp Eggs

9. 4 Homologous chromosomes bear the two alleles for each characteristic • Alternative forms of a gene – Reside at the same locus on homologous Dominant chromosomes allele Gene loci a B P a b PP Homozygous for the dominant allele aa Homozygous for the recessive allele Bb Heterozygous P Genotype: Figure 9. 4 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Recessive allele

9. 5 The law of independent assortment is revealed by tracking two characteristics at once • By looking at two characteristics at once – Mendel tried to determine how two characteristics were inherited Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Mendel’s law of independent assortment – States that alleles of a pair segregate independently of other allele pairs during gamete formation P generation Hypothesis: Dependent assortment RRYY rryy Hypothesis: Independent assortment RRYY ry Gametes RY rryy ry Gametes RY Rr. Yy F 1 generation Sperm 1 2 RY 1 2 ry 1 RY 2 F 2 generation Eggs 1 ry 2 Actual results contradict hypothesis Figure 9. 5 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1 1 ry RY 4 4 1 RY 4 1 ry 4 Eggs 1 Ry 4 1 ry 4 1 RY 4 1 ry 4 RRYY Rr. YY RRYy Rr. YY rr. YY Rr. Yy rr. Yy RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Actual results support hypothesis 9 16 3 16 1 16 Yellow round Green round Yellow wrinkled Green wrinkled

• An example of independent assortment Blind Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) Chocolate coat, normal vision Chocolate coat, blind (PRA) B_nn bb. N_ bbnn Mating of heterozygotes (black, normal vision) Phenotypic ratio of offspring 9 black coat, normal vision Bb. Nn 3 black coat, blind (PRA) Figure 9. 5 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Bb. Nn 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA)

9. 6 Geneticists use the testcross to determine unknown genotypes • The offspring of a testcross, a mating between an individual of unknown genotype and a homozygous recessive individual – Can reveal the unknown’s genotype Testcross: Genotypes bb B_ Two possibilities for the black dog: BB Gametes Offspring Bb B b Figure 9. 6 or Bb All black Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings b Bb bb 1 black : 1 chocolate

9. 7 Mendel’s laws reflect the rules of probability • Inheritance follows the rules of probability Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• The rule of multiplication – Calculates the probability of two independent events • The rule of addition – Calculates the probability of an event that can occur in alternate ways F genotypes 1 Bb male Formation of sperm Bb female Formation of eggs 1 2 B 1 2 b Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings B B b 1 4 b B 1 4 F 2 genotypes Figure 9. 7 1 2 B b b 1 4

CONNECTION 9. 8 Genetic traits in humans can be tracked through family pedigrees • The inheritance of many human traits – Follows Mendel’s laws Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe Figure 9. 8 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Family pedigrees – Can be used to determine individual genotypes Dd Joshua Lambert D? John Eddy Dd Abigail Linnell dd Jonathan Lambert D? Abigail Lambert Dd Dd dd D? Hepzibah Daggett Dd Elizabeth Eddy Dd Dd Dd dd Female Male Deaf Hearing Figure 9. 8 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

CONNECTION 9. 9 Many inherited disorders in humans are controlled by a single gene • Some autosomal disorders in humans Table 9. 9 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Recessive Disorders • Most human genetic disorders are recessive Parents Normal Dd Sperm D D Offspring DD Normal d Dd Normal (carrier) Eggs d Figure 9. 9 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Dd Normal (carrier) dd Deaf

Dominant Disorders • Some human genetic disorders are dominant Figure 9. 9 B 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 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Identifying Carriers • For an increasing number of genetic disorders – Tests are available that can distinguish carriers of genetic disorders Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Fetal Testing • Amniocentesis and chorionic villus sampling (CVS) – Allow doctors to remove fetal cells that can be tested for genetic abnormalities Chorionic villus sampling (CVS) Amniocentesis Needle inserted through abdomen to Ultrasound extract amniotic fluid monitor Ultrasound monitor Fetus Placenta Uterus Suction tube inserted through cervix to extract tissue from chorionic villi Placenta Chorionic villi Cervix Uterus Amniotic fluid Centrifugation Fetal cells Several weeks Figure 9. 10 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Biochemical tests Karyotyping Several hours

Fetal Imaging • Ultrasound imaging – Uses sound waves to produce a picture of the fetus Figure 9. 10 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Newborn Screening • Some genetic disorders can be detected at birth – By simple tests that are now routinely performed in most hospitals in the United States Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Ethical Considerations • New technologies such as fetal imaging and testing – Raise new ethical questions 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 – But genotype often does not dictate phenotype in the simple way his laws describe Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

9. 12 Incomplete dominance results in intermediate phenotypes • When an offspring’s phenotype is in between the phenotypes of its parents – It exhibits incomplete dominance P generation Red RR Gametes R White rr r F 1 generation Pink Rr Gametes 1 R 2 1 r 2 Sperm 1 1 r R 2 2 F 2 generation Eggs 1 R 2 Red RR Pink r. R 1 r 2 Pink Rr White rr Figure 9. 12 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Genotypes: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors Phenotypes: LDL receptor Cell Normal Figure 9. 12 B Mild disease Severe disease

9. 13 Many genes have more than two alleles in the population • In a population – Multiple alleles often exist for a characteristic Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• The ABO blood type in humans – Involves three alleles of a single gene • The alleles for A and B blood types are codominant – And both are expressed in the phenotype Blood Group (Phenotype) Genotypes Antibodies Present in Blood O ii Anti-A Anti-B A IAIA or IAi Anti-B B IBIB or IBi Anti-A AB IAIB — Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left Figure 9. 13 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings O A B AB

9. 14 A single gene may affect many phenotypic characteristics • In pleiotropy – A single gene may affect phenotype in many ways Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Clumping of cells and clogging of small blood vessels Breakdown of red blood cells Physical weakness Anemia Impaired mental function 5, 555 Sickle cells Heart failure Paralysis Figure 9. 14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Pain and fever Pneumonia and other infections Accumulation of sickled cells in spleen Brain damage Damage to other organs Rheumatism Spleen damage Kidney failure

9. 15 A single characteristic may be influenced by many genes • Polygenic inheritance – Creates a continuum of phenotypes P generation aabbcc (very light) AABBCC (very dark) F 1 generation Aa. Bb. Cc 1 64 Sperm 1 8 1 8 1 8 1 Eggs 8 1 8 1 8 1 8 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 15 64 20 64 Fraction of population F 2 generation Figure 9. 15 6 64 15 64 6 64 1 64 Skin color 15 64 6 64 1 64

9. 16 The environmental affects many characteristics • Many traits are affected, in varying degrees – By both genetic and environmental factors Figure 9. 16 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 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

THE CHROMOSOMAL BASIS OF INHERITANCE 9. 18 Chromosome behavior accounts for Mendel’s laws • Genes are located on chromosomes – Whose behavior during meiosis and fertilization accounts for inheritance patterns Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• The chromosomal basis of Mendel’s laws All round yellow seeds (Rr. Yy) F 1 generation R r R Y R r Y y Y Metaphase I of meiosis (alternative arrangements) y Y R R Y y r F 2 generation 9 ry Y y R Y y r 1 4 r. Y Fertilization among the F 1 plants : 3 Figure 9. 18 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings : 3 : 1 (See Figure 9. 5 A) y y Y r r 1 4 R r Y y RY r Metaphase II of meiosis y Y Y R Anaphase I of meiosis y r Gametes r r R 1 4 y R R 1 4 Ry

9. 19 Genes on the same chromosome tend to be inherited together Experiment Purple flower • Certain genes are linked Pp. LI – They tend to be inherited together because they reside close together on the same chromosome Pp. LI Long pollen Phenotypes Observed offspring Prediction (9: 3: 3: 1) Purple long Purple round Red long Red round 284 21 21 55 215 71 71 24 Explanation: linked genes PL Parental diploid cell Pp. LI PI Meiosis Most gametes PL PI Fertilization Sperm Most offspring PL PI PL PL PL PI PI PI PL Eggs PI 3 purple long : 1 red round Not accounted for: purple round and red long Figure 9. 19 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

9. 20 Crossing over produces new combinations of alleles • Crossing over can separate linked alleles – Producing gametes with recombinant chromosomes A B a b A b a B A B a Tetrad b Crossing over Figure 9. 20 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Gametes

• Thomas Hunt Morgan – Performed some of the early studies of crossing over using the fruit fly Drosophila melanogaster Figure 9. 20 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Morgan’s experiments – Demonstrated the role of crossing over in inheritance Experiment Black body, vestigial wings Gray body, long wings (wild type) Gg. LI ggll Male Female Offspring Gray long Black vestigial Gray vestigial Black long 965 944 206 Parental phenotypes Recombinant phenotypes Recombination frequency = Explanation Gg. LI (female) GL 391 recombinants = 0. 17 or 17% 2, 300 total offspring GL g l gl g l Gl g. L Eggs GL gl gl gl Offspring Figure 9. 20 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 185 Gl gl ggll (male) gl Sperm g. L gl

9. 21 Geneticists use crossover data to map genes • Morgan and his students – Used crossover data to map genes in Drosophila Figure 9. 21 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Recombination frequencies – Can be used to map the relative positions of genes on chromosomes. Mutant phenotypes Short aristae Chromosome g Black body (g) Cinnabar eyes (c) Vestigial wings (l) Brown eyes Red eyes (C) Normal wings (L) Red eyes l c 17% 9% 9. 5% Recombination frequencies Figure 9. 21 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Long aristae (appendages on head) Figure 9. 21 C Gray body (G) Wild-type phenotypes

SEX CHROMOSOMES AND SEX-LINKED GENES 9. 22 Chromosomes determine sex in many species • In mammals, a male has one X chromosome and one Y chromosome – And a female has two X chromosomes (male) 44 Parents’ + diploid XY cells 22 + X Figure 9. 22 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings (female) 44 + XX 22 + Y Sperm 22 + X 44 + XY Offspring (diploid) Egg

• The Y chromosome – Has genes for the development of testes • The absence of a Y chromosome – Allows ovaries to develop Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Other systems of sex determination exist in other animals and plants 22 + XX 22 + X 76 + ZW 76 + ZZ 32 16 Figure 9. 22 B Figure 9. 22 C Figure 9. 22 D Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

9. 23 Sex-linked genes exhibit a unique pattern of inheritance • All genes on the sex chromosomes – Are said to be sex-linked • In many organisms – The X chromosome carries many genes unrelated to sex Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• In Drosophila – White eye color is a sex-linked trait Figure 9. 23 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• The inheritance pattern of sex-linked genes – Is reflected in females and males Female XR XR Male Female Xr Y XR Xr Eggs XR Y XR Xr XR Y Female XR Y XR Xr XR Figure 9. 23 B Xr Y Sperm XR Y XR XR XR Y XR Xr XR Y Xr Xr Xr Y Eggs R = red-eye allele r = white-eye allele Male Sperm Xr Male Xr Xr XR Figure 9. 23 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Xr Y Xr Figure 9. 23 D

CONNECTION 9. 24 Sex-linked disorders affect mostly males • Most sex-linked human disorders – Are due to recessive alleles – Are mostly seen in males Queen victoria Albert Alice Louis Alexandra Figure 9. 24 A Figure 9. 24 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Czar Nicholas II of Russia Alexis

• A male receiving a single X-linked allele from his mother – Will have the disorder • A female – Has to receive the allele from both parents to be affected Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings