Chapter 9 Patterns of Inheritance Power Point Lectures

Chapter 9 Patterns of Inheritance Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

Introduction Dogs are one of man’s longest genetic experiments. – Over thousands of years, humans have chosen and mated dogs with specific traits. – The result has been an incredibly diverse array of dogs with distinct – body types and – behavioral traits. © 2012 Pearson Education, Inc.

Figure 9. 0_1 Chapter 9: Big Ideas Mendel’s Laws The Chromosomal Basis of Inheritance Variations on Mendel’s Laws Sex Chromosomes and Sex-Linked Genes

MENDEL’S LAWS © 2012 Pearson Education, Inc.

9. 1 The science of genetics has ancient roots Pangenesis, proposed around 400 BCE by Hippocrates, was an early explanation for inheritance that suggested that – particles called pangenes came from all parts of the organism to be incorporated into eggs or sperm and – characteristics acquired during the parents’ lifetime could be transferred to the offspring. Aristotle rejected pangenesis and argued that instead of particles, the potential to produce the traits was inherited. © 2012 Pearson Education, Inc.

9. 1 The science of genetics has ancient roots The idea that hereditary materials mix in forming offspring, called the blending hypothesis, was – suggested in the 19 th century by scientists studying plants but – later rejected because it did not explain how traits that disappear in one generation can reappear in later generations. © 2012 Pearson Education, Inc.

9. 2 Experimental genetics began in an abbey garden Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel – began the field of genetics in the 1860 s, – deduced the principles of genetics by breeding garden peas, and – relied upon a background of mathematics, physics, and chemistry. © 2012 Pearson Education, Inc.

9. 2 Experimental genetics began in an abbey garden In 1866, Mendel – correctly argued that parents pass on to their offspring discrete “heritable factors” and – stressed that the heritable factors (today called genes), retain their individuality generation after generation. A heritable feature that varies among individuals, such as flower color, is called a character. Each variant for a character, such as purple or white flowers, is a trait. © 2012 Pearson Education, Inc.

9. 2 Experimental genetics began in an abbey garden True-breeding varieties result when self-fertilization produces offspring all identical to the parent. The offspring of two different varieties are hybrids. The cross-fertilization is a hybridization, or genetic cross. True-breeding parental plants are the P generation. Hybrid offspring are the F 1 generation. A cross of F 1 plants produces an F 2 generation. © 2012 Pearson Education, Inc.

Figure 9. 2 B Petal Carpel Stamen

Figure 9. 2 C_s 1 White 1 Removal of stamens Stamens Carpel Parents (P) 2 Transfer Purple of pollen

Figure 9. 2 C_s 2 White 1 Removal of stamens Stamens Carpel Parents (P) 2 Transfer Purple of pollen 3 Carpel matures into pea pod

Figure 9. 2 C_s 3 White 1 Removal of stamens Stamens Carpel Parents (P) 2 Transfer Purple of pollen 3 Carpel matures into pea pod 4 Seeds from pod planted Offspring (F 1)

Figure 9. 2 D Traits Character Dominant Recessive Purple White Axial Terminal Yellow Green Round Wrinkled Inflated Constricted Green Yellow Tall Dwarf Flower color Flower position Seed color Seed shape Pod color Stem length

9. 3 Mendel’s law of segregation describes the inheritance of a single character A cross between two individuals differing in a single character is a monohybrid cross. Mendel performed a monohybrid cross between a plant with purple flowers and a plant with white flowers. – The F 1 generation produced all plants with purple flowers. – A cross of F 1 plants with each other produced an F 2 generation with ¾ purple and ¼ white flowers. © 2012 Pearson Education, Inc.

Figure 9. 3 A_s 1 The Experiment P generation (true-breeding parents) Purple flowers White flowers

Figure 9. 3 A_s 2 The Experiment P generation (true-breeding parents) Purple flowers F 1 generation White flowers All plants have purple flowers

Figure 9. 3 A_s 3 The Experiment 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 4 1 of plants 4 have purple flowers have white flowers

9. 3 Mendel’s law of segregation describes the inheritance of a single character The all-purple F 1 generation did not produce light purple flowers, as predicted by the blending hypothesis. Mendel needed to explain why – white color seemed to disappear in the F 1 generation and – white color reappeared in one quarter of the F 2 offspring. Mendel observed the same patterns of inheritance for six other pea plant characters. © 2012 Pearson Education, Inc.

9. 3 Mendel’s law of segregation describes the inheritance of a single character Mendel developed four hypotheses, described below using modern terminology. 1. Alleles are alternative versions of genes that account for variations in inherited characters. 2. For each characteristic, an organism inherits two alleles, one from each parent. The alleles can be the same or different. – A homozygous genotype has identical alleles. – A heterozygous genotype has two different alleles. © 2012 Pearson Education, Inc.

9. 3 Mendel’s law of segregation describes the inheritance of a single character 3. If the alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele. The other has no noticeable effect on the organism’s appearance and is called the recessive allele. – The phenotype is the appearance or expression of a trait. – The genotype is the genetic makeup of a trait. – The same phenotype may be determined by more than one genotype. © 2012 Pearson Education, Inc.

9. 3 Mendel’s law of segregation describes the inheritance of a single character 4. A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation. Mendel’s hypotheses also explain the 3: 1 ratio in the F 2 generation. – The F 1 hybrids all have a Pp genotype. – A Punnett square shows the four possible combinations of alleles that could occur when these gametes combine. © 2012 Pearson Education, Inc.

Figure 9. 3 B_s 1 The Explanation P generation Genetic makeup (alleles) White flowers Purple flowers PP pp Gametes All P All p

Figure 9. 3 B_s 2 The Explanation P generation Genetic makeup (alleles) White flowers Purple flowers PP pp Gametes All P All p F 1 generation (hybrids) All Pp Gametes 1 2 P 1 2 p

Figure 9. 3 B_s 3 The Explanation P generation Genetic makeup (alleles) White flowers Purple flowers PP pp Gametes All P All p F 1 generation (hybrids) All Pp Gametes 1 2 P Alleles segregate 1 2 p Fertilization Sperm from F 1 plant F 2 generation P Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp P Eggs from F 1 plant p p PP Pp Pp pp

Figure 9. 3 B_4 F 2 generation Phenotypic ratio 3 purple : 1 white Sperm from F 1 plant P Eggs from F 1 plant Genotypic ratio p 1 PP : 2 Pp : 1 pp P p PP Pp Pp pp

9. 4 Homologous chromosomes bear the alleles for each character A locus (plural, loci) is the specific location of a gene along a chromosome. For a pair of homologous chromosomes, alleles of a gene reside at the same locus. – Homozygous individuals have the same allele on both homologues. – Heterozygous individuals have a different allele on each homologue. © 2012 Pearson Education, Inc.

Figure 9. 4 Gene loci P a B P a b Dominant allele Homologous chromosomes Genotype: PP Homozygous for the dominant allele aa Homozygous for the recessive allele Recessive allele Bb Heterozygous, with one dominant and one recessive allele

9. 5 The law of independent assortment is revealed by tracking two characters at once A dihybrid cross is a mating of parental varieties that differ in two characters. Mendel performed the following dihybrid cross with the following results: – P generation: round yellow seeds wrinkled green seeds – F 1 generation: all plants with round yellow seeds – F 2 generation: – 9/16 had round yellow seeds – 3/16 had wrinkled yellow seeds – 3/16 had round green seeds – 1/16 had wrinkled green seeds © 2012 Pearson Education, Inc.

Figure 9. 5 A P generation RRYY Gametes RY F 1 generation rryy ry Sperm Rr. Yy 1 4 RY 1 4 r. Y 1 4 Ry 1 4 ry Sperm 1 2 F 2 generation RY 1 2 ry RY Eggs 1 2 ry 1 4 RY 1 4 r. Y Eggs 1 4 The hypothesis of dependent assortment Data did not support; hypothesis refuted RRYY Rr. YY RRYy Rr. YY Rr. Yy rr. YY Ry RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy ry 9 16 Yellow round 3 16 Green round 3 16 Yellow wrinkled 1 16 Green wrinkled The hypothesis of independent assortment Actual results; hypothesis supported

Figure 9. 5 B Blind Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, normal vision bb. N_ Chocolate coat, blind (PRA) bbnn Mating of double heterozygotes (black coat, normal vision) Bb. Nn Blind Phenotypic ratio of the offspring 9 Black coat, normal vision 3 Black coat, blind (PRA) 3 Chocolate coat, normal vision 1 Chocolate coat, blind (PRA)

9. 5 The law of independent assortment is revealed by tracking two characters at once Mendel needed to explain why the F 2 offspring – had new nonparental combinations of traits and – a 9: 3: 3: 1 phenotypic ratio. Mendel – suggested that the inheritance of one character has no effect on the inheritance of another, – suggested that the dihybrid cross is the equivalent to two monohybrid crosses, and – called this the law of independent assortment. © 2012 Pearson Education, Inc.

9. 5 The law of independent assortment is revealed by tracking two characters at once The following figure demonstrates the law of independent assortment as it applies to two characters in Labrador retrievers: – black versus chocolate color, – normal vision versus progressive retinal atrophy. © 2012 Pearson Education, Inc.

9. 6 Geneticists can use the testcross to determine unknown genotypes A testcross is the mating between an individual of unknown genotype and a homozygous recessive individual. A testcross can show whether the unknown genotype includes a recessive allele. Mendel used testcrosses to verify that he had truebreeding genotypes. The following figure demonstrates how a testcross can be performed to determine the genotype of a Lab with normal eyes. © 2012 Pearson Education, Inc.

Figure 9. 6 What is the genotype of the black dog? Testcross Genotypes B_? bb Two possibilities for the black dog: BB Gametes B b Offspring Bb or Bb All black b Bb bb 1 black : 1 chocolate

9. 7 Mendel’s laws reflect the rules of probability Using his strong background in mathematics, Mendel knew that the rules of mathematical probability affected – the segregation of allele pairs during gamete formation and – the re-forming of pairs at fertilization. The probability scale ranges from 0 to 1. An event that is – certain has a probability of 1 and – certain not to occur has a probability of 0. © 2012 Pearson Education, Inc.

9. 7 Mendel’s laws reflect the rules of probability The probability of a specific event is the number of ways that event can occur out of the total possible outcomes. Determining the probability of two independent events uses the rule of multiplication, in which the probability is the product of the probabilities for each event. The probability that an event can occur in two or more alternative ways is the sum of the separate probabilities, called the rule of addition. © 2012 Pearson Education, Inc.

Figure 9. 7 F 1 genotypes Bb male Bb female Formation of eggs Formation of sperm 1 2 B b Sperm 1 1 (2 2 ) 1 2 F 2 genotypes B b b 1 4 B 1 4 b B 1 4 Eggs 1 2 B B b b 1 4

9. 8 CONNECTION: Genetic traits in humans can be tracked through family pedigrees In a simple dominant-recessive inheritance of dominant allele A and recessive allele a, – a recessive phenotype always results from a homozygous recessive genotype (aa) but – a dominant phenotype can result from either – the homozygous dominant genotype (AA) or – a heterozygous genotype (Aa). Wild-type traits, those prevailing in nature, are not necessarily specified by dominant alleles. © 2012 Pearson Education, Inc.

Figure 9. 8 A Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe

9. 8 CONNECTION: Genetic traits in humans can be tracked through family pedigrees The inheritance of human traits follows Mendel’s laws. A pedigree – shows the inheritance of a trait in a family through multiple generations, – demonstrates dominant or recessive inheritance, and – can also be used to deduce genotypes of family members. © 2012 Pearson Education, Inc.

Figure 9. 8 B First generation (grandparents) Ff Second generation (parents, aunts, FF and uncles) or Ff Third generation (two sisters) Female Male Attached Free ff Ff ff ff Ff Ff Ff ff ff FF or Ff

9. 9 CONNECTION: Many inherited disorders in humans are controlled by a single gene Inherited human disorders show either 1. recessive inheritance in which – two recessive alleles are needed to show disease, – heterozygous parents are carriers of the disease-causing allele, and – the probability of inheritance increases with inbreeding, mating between close relatives. 2. dominant inheritance in which – one dominant allele is needed to show disease and – dominant lethal alleles are usually eliminated from the population. © 2012 Pearson Education, Inc.

Figure 9. 9 A Normal Dd Parents D D Offspring Normal Dd Sperm d DD Normal Dd Normal (carrier) dd Deaf Eggs d

9. 9 CONNECTION: Many inherited disorders in humans are controlled by a single gene The most common fatal genetic disease in the United States is cystic fibrosis (CF), resulting in excessive thick mucus secretions. The CF allele is – recessive and – carried by about 1 in 31 Americans. Dominant human disorders include – achondroplasia, resulting in dwarfism, and – Huntington’s disease, a degenerative disorder of the nervous system. © 2012 Pearson Education, Inc.

Table 9. 9

9. 10 CONNECTION: New technologies can provide insight into one’s genetic legacy New technologies offer ways to obtain genetic information – before conception, – during pregnancy, and – after birth. Genetic testing can identify potential parents who are heterozygous carriers for certain diseases. © 2012 Pearson Education, Inc.

9. 10 CONNECTION: New technologies can provide insight into one’s genetic legacy Several technologies can be used for detecting genetic conditions in a fetus. – Amniocentesis extracts samples of amniotic fluid containing fetal cells and permits – karyotyping and – biochemical tests on cultured fetal cells to detect other conditions, such as Tay-Sachs disease. – Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests. © 2012 Pearson Education, Inc.

Figure 9. 10 A Amniocentesis Amniotic fluid extracted Ultrasound transducer Fetus Chorionic Villus Sampling (CVS) Tissue extracted from the Ultrasound chorionic villi transducer Fetus Placenta Chorionic villi Placenta Uterus Cervix Centrifugation Amniotic fluid Fetal cells Several hours Cultured cells Several weeks Karyotyping Biochemical and genetics tests Cervix Uterus Fetal cells Several hours

9. 10 CONNECTION: New technologies can provide insight into one’s genetic legacy Blood tests on the mother at 14– 20 weeks of pregnancy can help identify fetuses at risk for certain birth defects. Fetal imaging enables a physician to examine a fetus directly for anatomical deformities. The most common procedure is ultrasound imaging, using sound waves to produce a picture of the fetus. Newborn screening can detect diseases that can be prevented by special care and precautions. © 2012 Pearson Education, Inc.

9. 10 CONNECTION: New technologies can provide insight into one’s genetic legacy New technologies raise ethical considerations that include – the confidentiality and potential use of results of genetic testing, – time and financial costs, and – determining what, if anything, should be done as a result of the testing. © 2012 Pearson Education, Inc.

VARIATIONS ON MENDEL’S LAWS © 2012 Pearson Education, Inc.

9. 11 Incomplete dominance results in intermediate phenotypes Mendel’s pea crosses always looked like one of the parental varieties, called complete dominance. For some characters, the appearance of F 1 hybrids falls between the phenotypes of the two parental varieties. This is called incomplete dominance, in which – neither allele is dominant over the other and – expression of both alleles occurs. © 2012 Pearson Education, Inc.

Figure 9. 11 A P generation Red RR White rr Gametes R r F 1 generation Pink hybrid Rr Gametes 1 2 R 1 2 r Sperm 1 1 R 2 2 r F 2 generation 1 R 2 RR r. R 1 r 2 Rr rr Eggs

9. 11 Incomplete dominance results in intermediate phenotypes Incomplete dominance does not support the blending hypothesis because the original parental phenotypes reappear in the F 2 generation. One example of incomplete dominance in humans is hypercholesterolemia, in which – dangerously high levels of cholesterol occur in the blood and – heterozygotes have intermediately high cholesterol levels. © 2012 Pearson Education, Inc.

Figure 9. 11 B HH Homozygous for ability to make LDL receptors Genotypes Hh Heterozygous hh Homozygous for inability to make LDL receptors Phenotypes LDL receptor Cell Normal Mild disease Severe disease

9. 12 Many genes have more than two alleles in the population Although an individual can at most carry two different alleles for a particular gene, more than two alleles often exist in the wider population. Human ABO blood group phenotypes involve three alleles for a single gene. The four human blood groups, A, B, AB, and O, result from combinations of these three alleles. The A and B alleles are both expressed in heterozygous individuals, a condition known as codominance. © 2012 Pearson Education, Inc.

9. 12 Many genes have more than two alleles in the population In codominance, – neither allele is dominant over the other and – expression of both alleles is observed as a distinct phenotype in the heterozygous individual. – AB blood type is an example of codominance. © 2012 Pearson Education, Inc.

Figure 9. 12 Blood Group (Phenotype) Genotypes Carbohydrates Present on Red Blood Cells A IAIA or IAi Carbohydrate A Carbohydrate B B IBIB or IBi AB IAIB O ii Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB Anti-A Carbohydrate A and Carbohydrate B Neither None Anti-A Anti-B No reaction Clumping reaction

9. 13 A single gene may affect many phenotypic characters Pleiotropy occurs when one gene influences many characteristics. Sickle-cell disease is a human example of pleiotropy. This disease – affects the type of hemoglobin produced and the shape of red blood cells and – causes anemia and organ damage. – Sickle-cell and nonsickle alleles are codominant. – Carriers of sickle-cell disease are resistant to malaria. © 2012 Pearson Education, Inc.

Figure 9. 13 A

Figure 9. 13 B An individual homozygous for the sickle-cell allele Produces sickle-cell (abnormal) hemoglobin The abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickled cell The multiple effects of sickled cells Damage to organs Other effects Kidney failure Heart failure Spleen damage Brain damage (impaired mental function, paralysis) Pain and fever Joint problems Physical weakness Anemia Pneumonia and other infections

9. 14 A single character may be influenced by many genes Many characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes. Human skin color is an example of polygenic inheritance. © 2012 Pearson Education, Inc.

Figure 9. 14 P generation aabbcc AABBCC (very light) (very dark) F 1 generation Aa. Bb. Cc Sperm 1 8 F 2 generation 1 8 1 8 1 8 Fraction of population Eggs 1 8 1 8 1 8 1 64 6 64 15 64 20 64 15 64 6 64 1 64 Skin color

9. 15 The environment affects many characters Many characters result from a combination of heredity and the environment. For example, – skin color is affected by exposure to sunlight, – susceptibility to diseases, such as cancer, has hereditary and environmental components, and – identical twins show some differences. Only genetic influences are inherited. © 2012 Pearson Education, Inc.

THE CHROMOSOMAL BASIS OF INHERITANCE © 2012 Pearson Education, Inc.

9. 16 Chromosome behavior accounts for Mendel’s laws The chromosome theory of inheritance states that – genes occupy specific loci (positions) on chromosomes and – chromosomes undergo segregation and independent assortment during meiosis. © 2012 Pearson Education, Inc.

9. 16 Chromosome behavior accounts for Mendel’s laws correlate with chromosome separation in meiosis. – The law of segregation depends on separation of homologous chromosomes in anaphase I. – The law of independent assortment depends on alternative orientations of chromosomes in metaphase I. © 2012 Pearson Education, Inc.

Figure 9. 16_s 1 F 1 generation R r y All yellow round seeds (Rr. Yy) Y R Y r y Metaphase I of meiosis r R Y y

Figure 9. 16_s 2 F 1 generation R r y All yellow round seeds (Rr. Yy) Y r R Y R y Metaphase I of meiosis r R Y y r r R Y y Anaphase I Y y R r Y y Metaphase II r R Y y

Figure 9. 16_s 3 F 1 generation R r All yellow round seeds (Rr. Yy) y Y r R Y R y Metaphase I of meiosis r R Y y r r R Y y Anaphase I Y y R r Y y Metaphase II r R Y y Gametes Y Y R R 1 4 RY y y r r 1 4 Y Y r r ry F 2 generation 9 Fertilization : 3 : 1 1 4 r. Y y y R R 1 4 Ry

Figure 9. 16_4 Sperm 1 1 4 RY 4 r. Y 4 Ry 4 ry 1 4 RY RRYY Rr. YY RRYy Rr. Yy 1 4 r. Y Eggs 1 Ry 4 1 ry 4 Rr. YY rr. YY Rr. Yy rr. Yy RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy 9 16 Yellow round 3 16 Green round 3 16 Yellow wrinkled 1 16 Green wrinkled

9. 17 SCIENTIFIC DISCOVERY: Genes on the same chromosome tend to be inherited together Bateson and Punnett studied plants that did not show a 9: 3: 3: 1 ratio in the F 2 generation. What they found was an example of linked genes, which – are located close together on the same chromosome and – tend to be inherited together. © 2012 Pearson Education, Inc.

Figure 9. 17_1 The Experiment Purple flower Pp. Ll Phenotypes Purple long Purple round Red long Red round Pp. Ll Observed offspring 284 21 21 55 Long pollen Prediction (9: 3: 3: 1) 215 71 71 24

Figure 9. 17_2 The Explanation: Linked Genes PL Parental diploid cell Pp. Ll pl Meiosis Most gametes pl PL Fertilization Sperm pl PL PL PL Most PL offspring Eggs pl pl PL PL pl pl pl 3 purple long : 1 red round Not accounted for: purple round and red long

9. 18 SCIENTIFIC DISCOVERY: Crossing over produces new combinations of alleles Crossing over between homologous chromosomes produces new combinations of alleles in gametes. Linked alleles can be separated by crossing over, forming recombinant gametes. The percentage of recombinants is the recombination frequency. © 2012 Pearson Education, Inc.

Figure 9. 18 A p L p l PL Parental gametes pl Tetrad Crossing over (pair of homologous chromosomes) p L P l Recombinant gametes

Figure 9. 18 C_1 The Experiment Gray body, long wings (wild type) Black body, vestigial wings Gg. Ll ggll Female Male Offspring: Gray long Black vestigial Gray vestigial Black long 965 944 Parental phenotypes Recombination frequency 206 185 Recombinant phenotypes 391 recombinants 0. 17 or 17% 2, 300 total offspring

Figure 9. 18 C_2 The Explanation Gg. Ll Female GL gl gl gl ggll Male Crossing over g l GL Gl gl g. L Eggs Sperm Offspring GL g l G l g. L g l g l Parental Recombinant

9. 19 Geneticists use crossover data to map genes When examining recombinant frequency, Morgan and his students found that the greater the distance between two genes on a chromosome, the more points there are between them where crossing over can occur. Recombination frequencies can thus be used to map the relative position of genes on chromosomes. © 2012 Pearson Education, Inc.

Figure 9. 19 A Section of chromosome carrying linked genes g c l 17% 9% 9. 5% Recombination frequencies

Figure 9. 19 B Mutant phenotypes Short aristae Black body (g) Cinnabar Vestigial wings eyes (l) (c) Red Long aristae Gray Normal eyes (appendages body wings (C) on head) (G) (L) Wild-type phenotypes Brown eyes Red eyes

SEX CHROMOSOMES AND SEX-LINKED GENES © 2012 Pearson Education, Inc.

9. 20 Chromosomes determine sex in many species Many animals have a pair of sex chromosomes, – designated X and Y, – that determine an individual’s sex. In mammals, – males have XY sex chromosomes, – females have XX sex chromosomes, – the Y chromosome has genes for the development of testes, and – an absence of the Y allows ovaries to develop. © 2012 Pearson Education, Inc.

Figure 9. 20 A X Y

Figure 9. 20 B Male 44 XY Parents (diploid) Gametes (haploid) Offspring (diploid) 22 X 22 Y Sperm 44 XX Female 44 XX 22 X Egg 44 XY Male

Figure 9. 21 A

Figure 9. 21 A_1

Figure 9. 21 A_2

Figure 9. 21 B Female Male X RX R X r. Y Sperm Eggs XR Xr Y X RX r X RY R red-eye allele r white-eye allele

Figure 9. 21 C Female Male X RX r X RY Sperm Y x. R XR X RX R X RY X r. X R X r. Y Eggs Xr R red-eye allele r white-eye allele

Figure 9. 21 D Female Male XRXr Xr. Y Sperm Xr Y XR XRXr XRY Xr Xr. Y Eggs R red-eye allele r white-eye allele

9. 22 CONNECTION: Human sex-linked disorders affect mostly males Most sex-linked human disorders are – due to recessive alleles and – seen mostly in males. A male receiving a single X-linked recessive allele from his mother will have the disorder. A female must receive the allele from both parents to be affected. © 2012 Pearson Education, Inc.

9. 22 CONNECTION: Human sex-linked disorders affect mostly males Recessive and sex-linked human disorders include – hemophilia, characterized by excessive bleeding because hemophiliacs lack one or more of the proteins required for blood clotting, – red-green color blindness, a malfunction of lightsensitive cells in the eyes, and – Duchenne muscular dystrophy, a condition characterized by a progressive weakening of the muscles and loss of coordination. © 2012 Pearson Education, Inc.

Figure 9. 22 Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Female Male Hemophilia Carrier Normal

9. 23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolution because – Y chromosomes are passed intact from father to son and – mutations in Y chromosomes can reveal data about recent shared ancestry. © 2012 Pearson Education, Inc.