Chapter 9 Patterns of Inheritance PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko 203 Pearson Education, Inc.
Biology and Society: Our Longest-Running Genetic Experiment: Dogs People have selected and mated dogs with preferred traits for more than 5,000 years. Over thousands of years, such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today. The biological principles underlying genetics have only recently been understood. 203 Pearson Education, Inc.
Figure 9.0
HERITABLE VARIATION AND PATTERNS OF INHERITANCE Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel worked in the 860s, was the first person to analyze patterns of inheritance, and deduced the fundamental principles of genetics. 203 Pearson Education, Inc.
Figure 9.
In an Abbey Garden Mendel studied garden peas because they were easy to grow, came in many readily distinguishable varieties, are easily manipulated, and can self-fertilize. 203 Pearson Education, Inc.
Figure 9.3-3 Removed stamens from purple flower. Parents (P) Carpel 2 Stamens Transferred pollen from stamens of white flower to carpel of purple flower. 3 Pollinated carpel matured into pod. Offspring (F ) 4 Planted seeds from pod.
In an Abbey Garden A character is a heritable feature that varies among individuals. A trait is a variant of a character. Each of the characters Mendel studied occurred in two distinct traits. 203 Pearson Education, Inc.
In an Abbey Garden Mendel created purebred varieties of plants and crossed two different purebred varieties. 203 Pearson Education, Inc.
In an Abbey Garden Hybrids are the offspring of two different purebred varieties. The parental plants are the P generation. Their hybrid offspring are the F generation. A cross of the F plants forms the F 2 generation. 203 Pearson Education, Inc.
Mendel s Law of Segregation Mendel performed many experiments. He tracked the inheritance of characters that occur as two alternative traits. 203 Pearson Education, Inc.
Figure 9.4 Dominant Recessive Dominant Recessive Flower color Flower position Purple White Pod shape Pod color Inflated Green Constricted Yellow Axial Terminal Stem length Seed color Seed shape Yellow Round Green Wrinkled Tall Dwarf
Figure 9.4a
Monohybrid Crosses A monohybrid cross is a cross between purebred parent plants that differ in only one character. 203 Pearson Education, Inc.
Figure 9.5-3 P Generation (purebred parents) Purple flowers White flowers F Generation All plants have purple flowers Fertilization among F plants (F F ) F 2 Generation 3 4 of plants have purple flowers 4 of plants have white flowers
Figure 9.5a
Monohybrid Crosses Mendel developed four hypotheses from the monohybrid cross, listed here using modern terminology (including gene instead of heritable factor ).. The alternative versions of genes are called alleles. 203 Pearson Education, Inc.
Monohybrid Crosses 2. For each inherited character, an organism inherits two alleles, one from each parent. An organism is homozygous for that gene if both alleles are identical. An organism is heterozygous for that gene if the alleles are different. 203 Pearson Education, Inc.
Monohybrid Crosses 3. If two alleles of an inherited pair differ, then one determines the organism s appearance and is called the dominant allele and the other has no noticeable effect on the organism s appearance and is called the recessive allele. 203 Pearson Education, Inc.
Monohybrid Crosses 4. Gametes carry only one allele for each inherited character. The two alleles for a character segregate (separate) from each other during the production of gametes. This statement is called the law of segregation. 203 Pearson Education, Inc.
Monohybrid Crosses Do Mendel s hypotheses account for the 3: ratio he observed in the F 2 generation? A Punnett square highlights the four possible combinations of gametes and the four possible offspring in the F 2 generation. 203 Pearson Education, Inc.
Figure 9.6 P Generation Genetic makeup (alleles) Alleles carried by parents Gametes Purple flowers PP All P White flowers pp All p F Generation (hybrids) Alleles segregate Gametes 2 P Purple flowers All Pp 2 p F 2 Generation (hybrids) Sperm from F plant P p Eggs from F plant P p PP Pp Phenotypic ratio 3 purple : white Pp pp Genotypic ratio PP : 2 Pp : pp
Monohybrid Crosses Geneticists distinguish between an organism s physical appearance and its genetic makeup. An organism s physical appearance is its phenotype. An organism s genetic makeup is its genotype. 203 Pearson Education, Inc.
Genetic Alleles and Homologous Chromosomes A gene locus is a specific location of a gene along a chromosome. Homologous chromosomes have alleles (alternate versions) of a gene at the same locus. 203 Pearson Education, Inc.
Figure 9.7 Homologous chromosomes Gene loci Dominant allele P a B Genotype: P PP Homozygous for the dominant allele a aa Homozygous for the recessive allele b Bb Recessive allele Heterozygous with one dominant and one recessive allele
Figure 9.UN0 Fertilization Alleles Diploid cell (contains paired alleles, alternate forms of a gene) Meiosis Haploid gametes (allele pairs separate) Gamete from other parent Diploid zygote (contains paired alleles)
Mendel s Law of Independent Assortment A dihybrid cross is the mating of parental varieties differing in two characters. What would result from a dihybrid cross? Two hypotheses are possible:. dependent assortment or 2. independent assortment. 203 Pearson Education, Inc.
Figure 9.8 (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent assortment P Generation RRYY rryy RRYY rryy Gametes RY ry Gametes RY ry F Generation RrYy RrYy F 2 Generation 2 Sperm RY 2 ry 4 RY 4 RY RRYY 4 Sperm ry RrYY 4 Ry 4 ry RRYy RrYy 2 RY Eggs 2 ry Eggs 4 4 ry Ry RrYY rryy RrYy rryy RRYy RrYy RRyy Rryy 9 6 3 6 Yellow round Green round Predicted results (not actually seen) 4 ry RrYy rryy Rryy rryy Actual results (support hypothesis) 3 6 6 Yellow wrinkled Green wrinkled
Mendel s Law of Independent Assortment Mendel s dihybrid cross supported the hypothesis that each pair of alleles segregates independently of the other pairs during gamete formation. Thus, the inheritance of one character has no effect on the inheritance of another. This is called Mendel s law of independent assortment. Independent assortment is also seen in two hereditary characters in Labrador retrievers. 203 Pearson Education, Inc.
Figure 9.9 Blind dog Blind dog Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbn_ (a) Possible phenotypes of Labrador retrievers Mating of double heterozygotes (black coat, normal vision) BbNn BbNn Chocolate coat, blind (PRA) bbnn Blind Blind Phenotypic ratio of offspring 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, normal vision chocolate coat, blind (PRA) (b) A Labrador dihybrid cross
Using a Testcross to Determine an Unknown Genotype A testcross is a mating between an individual of dominant phenotype (but unknown genotype) and a homozygous recessive individual. 203 Pearson Education, Inc.
Figure 9.UN02 Phenotype Genotype Dominant P? Recessive pp Phenotype or Conclusion All dominant Unknown parent is PP dominant : recessive Unknown parent is Pp
Figure 9.0 Testcross Genotypes B_ bb Two possible genotypes for the black dog: BB or Bb Gametes B B b b Bb b Bb bb Offspring All black black : chocolate
The Rules of Probability Mendel s strong background in mathematics helped him understand patterns of inheritance. The rule of multiplication states that the probability of a compound event is the product of the separate probabilities of the independent events. 203 Pearson Education, Inc.
Female gametes Figure 9. F Genotypes Bb female Bb male Formation of eggs Formation of sperm F 2 Genotypes Male gametes 2 B 2 b 2 B B B B 2 4 2 ( ) 4 b 2 b b B b b 4 4
Family Pedigrees Mendel s principles apply to the inheritance of many human traits. 203 Pearson Education, Inc.
Figure 9.2 DOMINANT TRAITS RECESSIVE TRAITS Freckles Widow s peak Free earlobe No freckles Straight hairline Attached earlobe
Family Pedigrees Dominant traits are not necessarily normal or more common. Wild-type traits are those seen most often in nature and not necessarily specified by dominant alleles. 203 Pearson Education, Inc.
Family Pedigrees A family pedigree shows the history of a trait in a family and allows geneticists to analyze human traits. 203 Pearson Education, Inc.
Figure 9.3 First generation (grandparents) Aaron Ff Betty Ff Cletus ff Debra Ff Second generation (parents, aunts, and uncles) Third generation (brother and sister) Evelyn FF or Ff Fred ff Gabe ff Hal Ff Kevin ff Ina Ff Lisa FF or Ff Jill ff Female Male Attached Female Male Free
Figure 9.3a
Human Disorders Controlled by a Single Gene Many human traits show simple inheritance patterns and are controlled by single genes on autosomes. 203 Pearson Education, Inc.
Table 9.
Recessive Disorders Most human genetic disorders are recessive. Individuals who have the recessive allele but appear normal are carriers of the disorder. 203 Pearson Education, Inc.
Figure 9.4 Parents Hearing Dd Hearing Dd Offspring D Sperm d D Eggs d DD Hearing Dd Hearing (carrier) Dd Hearing (carrier) dd Deaf
Recessive Disorders Cystic fibrosis is the most common lethal genetic disease in the United States and caused by a recessive allele carried by about one in 3 Americans. 203 Pearson Education, Inc.
Recessive Disorders Prolonged geographic isolation of certain populations can lead to inbreeding, the mating of close relatives. Inbreeding increases the chance of offspring that are homozygous for a harmful recessive trait. 203 Pearson Education, Inc.
Dominant Disorders Some human genetic disorders are dominant. Achondroplasia is a form of dwarfism. The homozygous dominant genotype causes death of the embryo. Thus, only heterozygotes have this disorder. Huntington s disease, which leads to degeneration of the nervous system, does not usually begin until middle age. 203 Pearson Education, Inc.
Figure 9.5
Figure 9.6 Normal (no achondroplasia) dd Parents Dwarf (achondroplasia) Dd Molly Jo Jeremy d Sperm d D Dd Dwarf Dd Dwarf Jacob Zachary Matt Amy Eggs d dd Normal dd Normal
The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs? Observation: Dogs come in a wide variety of physical types. Question: What is the genetic basis for canine coats? Hypothesis: A comparison of genes of a wide variety of dogs with different coats would identify the genes responsible. 203 Pearson Education, Inc.
The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs? Prediction: Mutations in just a few genes account for the coat appearance. Experiment: Compared DNA sequences of 622 dogs from dozens of breeds. Results: Three genes in different combinations produced seven different coat appearances, from very short hair to full, thick, wired hair. 203 Pearson Education, Inc.
Figure 9.7
Genetic Testing Today many tests can detect the presence of disease-causing alleles. Most genetic tests are performed during pregnancy. Amniocentesis collects cells from amniotic fluid. Chorionic villus sampling removes cells from placental tissue. Genetic counseling helps patients understand the results and implications of genetic testing. 203 Pearson Education, Inc.
VARIATIONS ON MENDEL S LAWS Some patterns of genetic inheritance are not explained by Mendel s laws. 203 Pearson Education, Inc.
Incomplete Dominance in Plants and People In incomplete dominance, F hybrids have an appearance between the phenotypes of the two parents. 203 Pearson Education, Inc.
Figure 9.UN03 Dominant phenotype (RR) Recessive phenotype (rr) Intermediate phenotype (incomplete dominance) (Rr)
Figure 9.8-3 P Generation Red RR White rr Gametes R r F Generation Pink Rr Gametes 2 R 2 r F 2 Generation 2 Sperm R 2 r 2 Eggs 2 R r RR Rr Rr rr
Incomplete Dominance in Plants and People Hypercholesterolemia is a human trait that is an example of incomplete dominance and is characterized by dangerously high levels of cholesterol in the blood. 203 Pearson Education, Inc.
Incomplete Dominance in Plants and People In hypercholesterolemia, heterozygotes have blood cholesterol levels about twice normal, and homozygotes have about five times the normal amount of blood cholesterol and may have heart attacks as early as age 2. 203 Pearson Education, Inc.
Figure 9.9 PHENOTYPE GENOTYPE HH Hh hh Heterozygous Homozygous for ability to make LDL receptors Homozygous for inability to make LDL receptors LDL LDL receptor Cell Normal Mild disease Severe disease
ABO Blood Groups: An Example of Multiple Alleles and Codominance The ABO blood groups in humans are an example of multiple alleles. The immune system produces blood proteins called antibodies that bind specifically to foreign carbohydrates. 203 Pearson Education, Inc.
ABO Blood Groups: An Example of Multiple Alleles and Codominance If a donor s blood cells have a carbohydrate (A or B) that is foreign to the recipient, the blood cells may clump together, potentially killing the recipient. The clumping reaction is the basis of a bloodtyping lab test. The human blood type alleles I A and I B are codominant, meaning that both alleles are expressed in heterozygous individuals who have type AB blood. 203 Pearson Education, Inc.
Figure 9.20 Blood Group (Phenotype) Genotypes Red Blood Cells Antibodies Present in Blood Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB A I A I A or I A i Carbohydrate A Anti-B B I B I B or Carbohydrate B Anti-A I B i AB I A I B O ii Anti-A Anti-B
Pleiotropy and Sickle-Cell Disease Pleiotropy is when one gene influences several characters. Sickle-cell disease exhibits pleiotropy, results in abnormal hemoglobin proteins, and causes disk-shaped red blood cells to deform into a sickle shape with jagged edges. 203 Pearson Education, Inc.
Figure 9.UN04 Single gene Pleiotropy Multiple traits (e.g., sickle-cell disease)
Colorized SEM Figure 9.2 Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes into long flexible chains, causing red blood cells to become sickle-shaped. Sickled cells can lead to a cascade of symptoms, such as weakness, pain, organ damage, and paralysis.
Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotype. 203 Pearson Education, Inc.
Figure 9.UN05 Polygenic inheritance Single trait (e.g., height) Multiple genes
Figure 9.22 Fraction of population P Generation aabbcc (very short) AABBCC (very tall) short allele tall allele F Generation F 2 Generation AaBbCc (medium height) AaBbCc (medium height) Sperm 8 8 8 8 8 8 8 8 8 20 64 8 8 5 64 Eggs 8 8 8 6 64 8 8 64 Very short Adult height Very tall 64 6 64 5 64 20 64 5 64 6 64 64
Figure 9.22a P Generation aabbcc (very short) AABBCC (very tall) short allele tall allele F Generation AaBbCc (medium height) AaBbCc (medium height)
The Role of Environment Many human characters result from a combination of heredity and environment. Only genetic influences are inherited. 203 Pearson Education, Inc.
Figure 9.23
THE CHROMOSOMAL BASIS OF INHERITANCE The chromosome theory of inheritance states that genes are located at specific positions (loci) on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns. 203 Pearson Education, Inc.
THE CHROMOSOMAL BASIS OF INHERITANCE It is chromosomes that undergo segregation and independent assortment during meiosis and account for Mendel s laws. 203 Pearson Education, Inc.
Figure 9.24 P Generation Round-yellow seeds (RRYY) Y R Y R MEIOSIS y r y r Wrinkled-green seeds (rryy) Gametes R Y FERTILIZATION y r F Generation Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. The R and r alleles segregate in anaphase I of meiosis. Only one long chromosome ends up in each gamete. Gametes Y R R Y R R Y r y r r y R r Y y MEIOSIS Metaphase I (alternative arrangements) Metaphase II All round-yellow seeds (RrYy) Y y y Y Y y y r r r r Y r Y R y R Law of Independent Assortment: Follow both the long and the short chromosomes. They are arranged in either of two equally likely ways at metaphase I. R y R They sort independently, giving four gamete types. Fertilization recombines the r and R alleles at random. F 2 Generation 4 4 RY ry ry Ry FERTILIZATION AMONG THE F PLANTS 9 : 3 : 3 : 4 4 Fertilization results in the 9:3:3: phenotypic ratio in the F 2 generation.
Linked Genes Linked genes are located close together on a chromosome and tend to be inherited together. Thomas Hunt Morgan used the fruit fly Drosophila melanogaster and determined that some genes were linked based on the inheritance patterns of their traits. 203 Pearson Education, Inc.
Figure 9.25-2 Dihybrid testcross Gray body, long wings (wild-type) Black body, short wings (mutant) GgLl ggll Female Male Results Gray-long GgLl Black-short ggll Offspring Gray-short Ggll Black-long ggll 965 944 206 85 Parental phenotypes 83% Recombinant phenotypes 7%
Genetic Recombination: Crossing Over Crossing over can separate linked alleles, produce gametes with recombinant gametes, and produce offspring with recombinant phenotypes. The percentage of recombinant offspring among the total is called the recombination frequency. 203 Pearson Education, Inc.
Figure 9.26 A B a b A B Parental gametes a b Pair of homologous chromosomes Crossing over A b a B Recombinant gametes
Figure 9.27 GgLl (female) G L g l g l g l ggll (male) CROSSING OVER G L g l G l g L g l Parental gametes Recombinant gametes Eggs FERTILIZATION Sperm Offspring G L g l G l g L g l g l g l g l Parental Recombinant
Linkage Maps Early studies of crossing over were performed using the fruit fly Drosophila melanogaster. Alfred H. Sturtevant, a student of Morgan, developed a method for mapping the relative gene locations, which resulted in the creation of linkage maps. 203 Pearson Education, Inc.
Figure 9.28 Chromosome g c l 7% 9% 9.5% Recombination frequencies
SEX CHROMOSOMES AND SEX-LINKED GENES Sex chromosomes influence the inheritance of certain traits. For example, humans that have a pair of sex chromosomes designated X and Y are male or X and X are female. 203 Pearson Education, Inc.
Figure 9.29 Colorized SEM Y X Male 44 XY Somatic cells Female 44 XX 22 X 22 Y Sperm Egg 22 X 44 XX Female Offspring 44 XY Male
Sex Determination in Humans Nearly all mammals have a pair of sex chromosomes designated X and Y. Males have an X and Y. Females have XX. 203 Pearson Education, Inc.
Figure 9.UN06 Male Female 44 XY Somatic cells 44 XX
Sex-Linked Genes Any gene located on a sex chromosome is called a sex-linked gene. Most sex-linked genes are found on the X chromosome. Red-green colorblindness is a common human sex-linked disorder and caused by a malfunction of light-sensitive cells in the eyes. 203 Pearson Education, Inc.
Figure 9.UN07
Figure 9.30
Figure 9.3 X N X N X n Y X N X n X N Y X N X n X n Y X n Y Sperm X N Y Sperm X n Y Sperm Eggs X N X N X n X N Y Eggs X N X N X N X N Y Eggs X N X N X n X N Y X N X N X n X N Y X n X N X n X n Y X n X n X n X n Y (a) Normal female colorblind male (b) Carrier female normal male (c) Carrier female colorblind male Key Unaffected individual Carrier Colorblind individual
Sex-Linked Genes Hemophilia is a sex-linked recessive blood-clotting trait that may result in excessive bleeding and death after relatively minor cuts and bruises and has plagued the royal families of Europe. 203 Pearson Education, Inc.
Figure 9.32 Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis
Evolution Connection: Barking Up the Evolutionary Tree About 5,000 years ago in East Asia, people began to cohabit with ancestral canines that were predecessors of modern wolves and dogs. As people settled into geographically distinct populations, different canines became separated and eventually became inbred. 203 Pearson Education, Inc.
Evolution Connection: Barking Up the Evolutionary Tree A 200 study indicated that small dogs were developed within the first permanent agricultural settlements of the Middle East around 2,000 years ago. Continued over millennia, genetic tinkering has resulted in a diverse array of dog body types and behaviors. 203 Pearson Education, Inc.
Figure 9.33 Ancestral canine Wolf Chinese shar-pei Akita Basenji Siberian husky Alaskan malamute Afghan hound Saluki Rottweiler Sheepdog Retriever