CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman

CAMPBELL BIOLOGY TENTH EDITION Reece  Urry  Cain  Wasserman

CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson 14 Mendel and the Gene Idea Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick 2014 Pearson Education, Inc. Drawing from the Deck of Genes What principles account for the passing of traits from parents to offspring? The blending hypothesis is the idea that genetic material from the two parents blends together

(like blue and yellow paint blend to make green) 2014 Pearson Education, Inc. The particulate hypothesis is the idea that parents pass on discrete heritable units (genes) Mendel documented a particulate mechanism through his experiments with garden peas 2014 Pearson Education, Inc. Figure 14.1 2014 Pearson Education, Inc. Figure 14.1a Mendel (third from right, holding a sprig of fuchsia) with his fellow monks. 2014 Pearson Education, Inc. Concept 14.1: Mendel used the scientific

approach to identify two laws of inheritance Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments 2014 Pearson Education, Inc. Mendels Experimental, Quantitative Approach Mendels approach allowed him to deduce principles that had remained elusive to others 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 color for flowers, is called a trait Peas were available to Mendel in many different varieties 2014 Pearson Education, Inc. Other advantages of using peas Short generation time Large numbers of offspring

Mating could be controlled; plants could be allowed to self-pollinate or could be cross pollinated 2014 Pearson Education, Inc. Figure 14.2 Technique 1 2 Stamens Parental generation (P) Carpel 3 4 Results First filial generation

offspring (F1) 2014 Pearson Education, Inc. 5 Mendel chose to track only those characters that occurred in two distinct alternative forms He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate) 2014 Pearson Education, Inc. In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F1 generation When F1 individuals self-pollinate or crosspollinate with other F1 hybrids, the F2 generation is produced

2014 Pearson Education, Inc. The Law of Segregation When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation 2014 Pearson Education, Inc. Figure 14.3-1 Experiment P Generation (true-breeding parents) 2014 Pearson Education, Inc.

Purple flowers White flowers Figure 14.3-2 Experiment P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids)

All plants had purple flowers Self- or cross-pollination 2014 Pearson Education, Inc. Figure 14.3-3 Experiment P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids)

All plants had purple flowers Self- or cross-pollination F2 Generation 705 purple-flowered plants 2014 Pearson Education, Inc. 224 white-flowered plants Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids Mendel called the purple flower color a dominant trait and the white flower color a recessive trait The factor for white flowers was not diluted or destroyed because it reappeared in the F 2 generation 2014 Pearson Education, Inc.

Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits What Mendel called a heritable factor is what we now call a gene 2014 Pearson Education, Inc. Table 14.1 2014 Pearson Education, Inc. Table 14.1a 2014 Pearson Education, Inc. Table 14.1b 2014 Pearson Education, Inc. Mendels Model

Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes 2014 Pearson Education, Inc. First: alternative versions of genes account for variations in inherited characters For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers These alternative versions of a gene are called alleles Each gene resides at a specific locus on a specific chromosome 2014 Pearson Education, Inc. Figure 14.4 Enzyme

C T A A A T C G G T Allele for purple flowers Locus for flower-color gene G A T T T A G C C A CTAAATCGGT Pair of homologous chromosomes Allele for white flowers A T A A A T C G G T T A T T T A G C C A ATAAATCGGT

2014 Pearson Education, Inc. Enzyme that helps synthesize purple pigment Absence of enzyme One allele results in sufficient pigment Second: for each character, an organism inherits two alleles, one from each parent Mendel made this deduction without knowing about chromosomes The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendels P generation Alternatively, the two alleles at a locus may differ,

as in the F1 hybrids 2014 Pearson Education, Inc. Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organisms appearance, and the other (the recessive allele) has no noticeable effect on appearance In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant 2014 Pearson Education, Inc. Fourth (the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Thus, an egg or a sperm gets only one of the two alleles that are present in the organism This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis

2014 Pearson Education, Inc. The model accounts for the 3:1 ratio observed in the F2 generation of Mendels crosses Possible combinations of sperm and egg can be shown using a Punnett square A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele 2014 Pearson Education, Inc. Figure 14.5-1 P Generation Appearance: Purple flowers White flowers Genetic makeup: PP pp Gametes:

2014 Pearson Education, Inc. P p Figure 14.5-2 P Generation Appearance: Purple flowers White flowers Genetic makeup: PP pp Gametes: p P F1 Generation Appearance:

Genetic makeup: Gametes: 2014 Pearson Education, Inc. Purple flowers Pp 1 2 P 1 2 p Figure 14.5-3 P Generation

Appearance: Purple flowers White flowers Genetic makeup: PP pp Gametes: p P F1 Generation Appearance: Genetic makeup: Purple flowers Pp Gametes: 1

2 P 1 2 p Sperm from F1 (Pp) plant F2 Generation Eggs from F1 (Pp) plant P p 3 2014 Pearson Education, Inc.

P p PP Pp Pp pp :1 Useful Genetic Vocabulary An organism with two identical alleles for a character is homozygous for the gene controlling that character An organism that has two different alleles for a gene is heterozygous for the gene controlling that character Unlike homozygotes, heterozygotes are not truebreeding

2014 Pearson Education, Inc. Because of the different effects of dominant and recessive alleles, an organisms traits do not always reveal its genetic composition Therefore, we distinguish between an organisms phenotype, or physical appearance, and its genotype, or genetic makeup In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes 2014 Pearson Education, Inc. Figure 14.6 3 Phenotype Genotype

Purple PP (homozygous) Purple Pp (heterozygous) 1 2 1 2014 Pearson Education, Inc. Purple Pp (heterozygous)

White pp (homozygous) Ratio 3:1 Ratio 1:2:1 1 The Testcross An individual with the dominant phenotype could be either homozygous dominant or heterozygous To determine the genotype we can carry out a testcross: breeding the mystery individual with a homozygous recessive individual If any offspring display the recessive phenotype, the mystery parent must be heterozygous 2014 Pearson Education, Inc.

Figure 14.7 Technique Recessive phenotype, known genotype: pp Dominant phenotype, unknown genotype: PP or Pp? Predictions If purple-flowered or parent is PP Sperm p p P Pp Eggs

If purple-flowered parent is Pp Sperm p p P Pp Eggs P p Pp Pp Pp Pp

pp pp Results or All offspring purple 2014 Pearson Education, Inc. 1 2 offspring purple and 1 2 offspring white The Law of Independent Assortment Mendel derived the law of segregation by following a single character The F1 offspring produced in this cross were monohybrids, heterozygous for one character A cross between such heterozygotes is called a monohybrid cross

2014 Pearson Education, Inc. Mendel identified his second law of inheritance by following two characters at the same time Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently 2014 Pearson Education, Inc. Figure 14.8 Experiment YYRR P Generation

yyrr Gametes YR yr F1 Generation Predictions YyRr Hypothesis of dependent assortment Predicted offspring of F2 generation Hypothesis of independent assortment Sperm

or 1 Sperm 1 2 YR 1 2 2 YR YYRR Eggs 1

2 YyRr 1 4 YR 4 Yr 4 yR 4 yr

Eggs yr YyRr 3 4 yyrr 1 YR 1 4 Yr 1

4 yR 1 4 yr yr 1 1 4 1 YYRR

YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr

YyRr Yyrr yyRr yyrr 4 Phenotypic ratio 3:1 1 9 16 3 16

3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 2014 Pearson Education, Inc. 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 14.8a

Experiment P Generation YYRR Gametes YR F1 Generation 2014 Pearson Education, Inc. yyrr yr YyRr Figure 14.8b Hypothesis of dependent assortment Hypothesis of

independent assortment Sperm Predicted offspring of F2 generation 1 Sperm 1 2 YR 1 2 yr 1

1 2 YR YYRR YyRr Eggs 1 2 1 4 YR 4

Yr 4 yR 4 yr Eggs yr yyrr YyRr 3 4 1

1 4 YR 1 4 Yr 1 4 yR 1 4

yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr

yyrr 4 Phenotypic ratio 3:1 1 9 16 3 16 Yyrr 3 16 1

16 Phenotypic ratio 9:3:3:1 Results 315 108 2014 Pearson Education, Inc. 101 32 Phenotypic ratio approximately 9:3:3:1 Using a dihybrid cross, Mendel developed the law of independent assortment It states that each pair of alleles segregates independently of each other pair of alleles during gamete formation

This law applies only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome Genes located near each other on the same chromosome tend to be inherited together 2014 Pearson Education, Inc. Concept 14.2: Probability laws govern Mendelian inheritance Mendels laws of segregation and independent assortment reflect the rules of probability When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss In the same way, the alleles of one gene segregate into gametes independently of another genes alleles 2014 Pearson Education, Inc. The Multiplication and Addition Rules Applied to Monohybrid Crosses The multiplication rule states that the probability

that two or more independent events will occur together is the product of their individual probabilities Probability in an F1 monohybrid cross can be determined using the multiplication rule Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele 2014 Pearson Education, Inc. Figure 14.9 Rr Segregation of alleles into eggs Rr Segregation of alleles into sperm Sperm

1 R 2 R 1 2 1 1 4 R r 1

2014 Pearson Education, Inc. r R r 2 r 2 R R Eggs 1 1

4 4 r r 1 4 The addition rule states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous 2014 Pearson Education, Inc.

Solving Complex Genetics Problems with the Rules of Probability We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters A multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously In calculating the chances for various genotypes, each character is considered separately, and then the individual probabilities are multiplied 2014 Pearson Education, Inc. Figure 14.UN01 2014 Pearson Education, Inc. Figure 14.UN02 2014 Pearson Education, Inc.

Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics The relationship between genotype and phenotype is rarely as simple as in the pea plant characters Mendel studied Many heritable characters are not determined by only one gene with two alleles However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance 2014 Pearson Education, Inc. Extending Mendelian Genetics for a Single Gene Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: When alleles are not completely dominant or recessive When a gene has more than two alleles

When a gene produces multiple phenotypes 2014 Pearson Education, Inc. Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways 2014 Pearson Education, Inc. Figure 14.10-1 P Generation Red CRCR Gametes

2014 Pearson Education, Inc. White CWCW CR CW Figure 14.10-2 P Generation Red CRCR White CWCW Gametes CR

CW F1 Generation Pink CRCW Gametes 2014 Pearson Education, Inc. 1 2 CR 1 2 CW

Figure 14.10-3 P Generation Red CRCR White CWCW Gametes CR CW F1 Generation Pink CRCW Gametes 1

2 1 2 CW Sperm F2 Generation 1 1 Eggs 1 2014 Pearson Education, Inc. CR

2 CR 2 CW 2 CR 1 2 CW CRCR CRCW

CRCW CWCW The Relation Between Dominance and Phenotype A dominant allele does not subdue a recessive allele; alleles dont interact that way Alleles are simply variations in a genes nucleotide sequence For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype 2014 Pearson Education, Inc. Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain At the organismal level, the allele is recessive At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant

At the molecular level, the alleles are codominant 2014 Pearson Education, Inc. Frequency of Dominant Alleles Dominant alleles are not necessarily more common in populations than recessive alleles For example, one baby out of 400 in the United States is born with extra fingers or toes 2014 Pearson Education, Inc. The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage In this example, the recessive allele is far more prevalent than the populations dominant allele 2014 Pearson Education, Inc. Multiple Alleles Most genes exist in populations in more than two

allelic forms For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither 2014 Pearson Education, Inc. Figure 14.11 (a) The three alleles for the ABO blood groups and their carbohydrates Allele Carbohydrate IA IB

A i none B (b) Blood group genotypes and phenotypes Genotype IAIA or IAi IBIB or IBi IAIB ii A B

AB O Red blood cell appearance Phenotype (blood group) 2014 Pearson Education, Inc. Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease 2014 Pearson Education, Inc. Extending Mendelian Genetics for Two or More Genes

Some traits may be determined by two or more genes 2014 Pearson Education, Inc. Epistasis In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus For example, in Labrador retrievers and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair 2014 Pearson Education, Inc. Figure 14.12 BbEe BbEe

Sperm 1 4 BE 1 4 bE 1 Be 4 1

4 Eggs 1 1 1 1 4 BE 4 bE 4 Be

4 be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe

BbEe BBee Bbee BbEe bbEe Bbee bbee 9 2014 Pearson Education, Inc. : 3 : 4

be Polygenic Inheritance Quantitative characters are those that vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance 2014 Pearson Education, Inc. Figure 14.13 AaBbCc AaBbCc Sperm 1 1

1 1 1 Eggs 1 1 1 1 Phenotypes: Number of dark-skin alleles: 2014 Pearson Education, Inc. 1 8 8 1

8 1 1 8 8 1 8 1 1 8 8

8 8 8 8 8 8 8 8 1 64 0 6 64 1

15 64 2 20 64 3 15 64 4 6 64

5 1 64 6 Nature and Nurture: The Environmental Impact on Phenotype Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype The phenotypic range is broadest for polygenic characters Traits that depend on multiple genes combined with environmental influences are called multifactorial 2014 Pearson Education, Inc. Figure 14.14

2014 Pearson Education, Inc. Figure 14.14a 2014 Pearson Education, Inc. Figure 14.14b 2014 Pearson Education, Inc. A Mendelian View of Heredity and Variation An organisms phenotype includes its physical appearance, internal anatomy, physiology, and behavior An organisms phenotype reflects its overall genotype and unique environmental history 2014 Pearson Education, Inc. Concept 14.4: Many human traits follow Mendelian patterns of inheritance

Humans are not good subjects for genetic research Generation time is too long Parents produce relatively few offspring Breeding experiments are unacceptable However, basic Mendelian genetics endures as the foundation of human genetics 2014 Pearson Education, Inc. Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees 2014 Pearson Education, Inc. Figure 14.15

Key Male Female 1st generation (grandparents) Ww Affected male ww Affected female ww 2nd generation (parents, aunts,

Ww ww ww Ww and uncles) Ww Ww ww Offspring, in birth order (first-born on left) Mating Ff FF or Ff ff Ff ff

ff Ff Ff Ff ff ff FF or Ff 3rd generation (two sisters) WW or Ww

ww Widows peak No widows peak (a) Is a widows peak a dominant or recessive trait? Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait? 2014 Pearson Education, Inc. Figure 14.15a Key Male Female

1st generation (grandparents) 2nd generation (parents, aunts, and uncles) Affected male Affected female Ww Mating Offspring, in birth order (first-born on left) ww Ww ww ww Ww

ww Ww Ww ww 3rd generation (two sisters) WW or Ww ww Widows peak No widows peak (a) Is a widows peak a dominant or recessive trait? 2014 Pearson Education, Inc. Figure 14.15aa

Widows peak 2014 Pearson Education, Inc. Figure 14.15ab No widows peak 2014 Pearson Education, Inc. Figure 14.15b Key Male Female 1st generation (grandparents) Affected male

Affected female Ff 2nd generation (parents, aunts, and uncles) FF or Ff ff Mating Offspring, in birth order (first-born on left) Ff ff ff Ff

Ff ff FF or Ff Ff ff 3rd generation (two sisters) Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait? 2014 Pearson Education, Inc.

Figure 14.15ba Attached earlobe 2014 Pearson Education, Inc. Figure 14.15bb Free earlobe 2014 Pearson Education, Inc. Pedigrees can also be used to make predictions about future offspring We can use the multiplication and addition rules to predict the probability of specific phenotypes 2014 Pearson Education, Inc. Recessively Inherited Disorders Many genetic disorders are inherited in a

recessive manner These range from relatively mild to life-threatening 2014 Pearson Education, Inc. The Behavior of Recessive Alleles Recessively inherited disorders show up only in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair 2014 Pearson Education, Inc. Figure 14.16 Parents Normal Aa

Normal Aa Sperm A a A AA Normal Aa Normal (carrier) a Aa Normal

(carrier) aa Albino Eggs 2014 Pearson Education, Inc. Figure 14.16a 2014 Pearson Education, Inc. If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele Most societies and cultures have laws or taboos against marriages between close relatives

2014 Pearson Education, Inc. Cystic Fibrosis Cystic fibrosis is the most common lethal genetic disease in the United States, striking one out of every 2,500 people of European descent The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine 2014 Pearson Education, Inc. Sickle-Cell Disease: A Genetic Disorder with Evolutionary Implications Sickle-cell disease affects one out of 400 AfricanAmericans The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells In homozygous individuals, all hemoglobin is

abnormal (sickle-cell) Symptoms include physical weakness, pain, organ damage, and even paralysis 2014 Pearson Education, Inc. Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms About one out of ten African Americans has sicklecell trait, an unusually high frequency Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous in regions where malaria is common 2014 Pearson Education, Inc. Figure 14.17 Sickle-cell alleles Low O2 Sickle-cell hemoglobin proteins

Part of a fiber of sickle-cell hemoglobin proteins Sicklecell disease Sickled red blood cells (a) Homozygote with sickle-cell disease: Weakness, anemia, pain and fever, organ damage Sickle-cell allele Normal allele Very low O2 Sickle-cell and normal hemoglobin proteins Part of a sickle-cell fiber and normal hemoglobin proteins

Sicklecell trait Sickled and normal red blood cells (b) Heterozygote with sickle-cell trait: Some symptoms when blood oxygen is very low; reduction of malaria symptoms 2014 Pearson Education, Inc. Dominantly Inherited Disorders Some human disorders are caused by dominant alleles Dominant alleles that cause a lethal disease are rare and arise by mutation Achondroplasia is a form of dwarfism caused by a rare dominant allele 2014 Pearson Education, Inc. Figure 14.18

Parents Dwarf Dd Normal dd Sperm D d d Dd Dwarf dd Normal d

Dd Dwarf dd Normal Eggs 2014 Pearson Education, Inc. Figure 14.18a 2014 Pearson Education, Inc. The timing of onset of a disease significantly affects its inheritance Huntingtons disease is a degenerative disease of the nervous system The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age Once the deterioration of the nervous system begins the condition is irreversible and fatal

2014 Pearson Education, Inc. Multifactorial Disorders Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components No matter what our genotype, our lifestyle has a tremendous effect on phenotype 2014 Pearson Education, Inc. Genetic Testing and Counseling Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease 2014 Pearson Education, Inc. Counseling Based on Mendelian Genetics and Probability Rules Using family histories, genetic counselors help

couples determine the odds that their children will have genetic disorders It is important to remember that each child represents an independent event in the sense that its genotype is unaffected by the genotypes of older siblings 2014 Pearson Education, Inc. Tests for Identifying Carriers For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately The tests enable people to make more informed decisions about having children However, they raise other issues, such as whether affected individuals fully understand their genetic test results 2014 Pearson Education, Inc. Fetal Testing

In amniocentesis, the liquid that bathes the fetus is removed and tested In chorionic villus sampling (CVS), a sample of the placenta is removed and tested Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero 2014 Pearson Education, Inc. Figure 14.19 (a) Amniocentesis Ultrasound monitor (b) Chorionic villus sampling (CVS) Amniotic fluid withdrawn 1

Fetus Placenta Uterus Cervix Fluid Fetal cells Ultrasound monitor Fetus Placenta Chorionic villi Uterus Centrifugation Several hours

Biochemical 2 Several and genetic tests weeks 1 Cervix Several hours Fetal cells 2 Several weeks Several hours

3 Karyotyping 2014 Pearson Education, Inc. Suction tube inserted through cervix Video: Ultrasound of Human Fetus 2014 Pearson Education, Inc. 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 One common test is for phenylketonuria (PKU), a recessively inherited disorder that occurs in one of every 10,00015,000 births in the United States

2014 Pearson Education, Inc. Figure 14.UN03a Phenotypes: Number of dark-skin alleles: 2014 Pearson Education, Inc. 1 64 0 6 64 1

15 64 2 20 64 3 15 64 4 6 64

5 1 64 6 Figure 14.UN03b 2014 Pearson Education, Inc. Figure 14.UN04 Rr Segregation of alleles into sperm Sperm 1

2014 Pearson Education, Inc. 2 R 1 2 r Figure 14.UN05 Relationship among alleles of a single gene Description Complete dominance

of one allele Heterozygous phenotype same as that of homozygous dominant Incomplete dominance of either allele Heterozygous phenotype intermediate between the two homozygous phenotypes Codominance Multiple alleles Pleiotropy 2014 Pearson Education, Inc.

Example PP Pp CRCR CRCW CWCW Both phenotypes expressed in heterozygotes IA IB In the population some genes have more than two alleles ABO blood group alleles One gene affects multiple phenotypic

characters Sickle-cell disease IA, IB, i Figure 14.UN06 Relationship among two or more genes Epistasis Description The phenotypic expression of one gene affects the expression of another gene Example BbEe

BbEe BE bE Be be BE bE Be be 9 Polygenic inheritance 2014 Pearson Education, Inc. A single phenotypic character is affected AaBbCc by two or more genes

:3 :4 AaBbCc Figure 14.UN07 Ww Ww ww ww ww Widows peak 2014 Pearson Education, Inc. ww

Ww Ww WW or Ww ww Ww ww No widows peak Figure 14.UN08 Sickle-cell alleles Low O2 Sickle-cell

hemoglobin proteins 2014 Pearson Education, Inc. Part of a fiber of sickle-cell hemoglobin proteins Sicklecell disease Sickled red blood cells Figure 14.UN09 2014 Pearson Education, Inc. Figure 14.UN10 George Sandra

Tom Sam Arlene Wilma Ann Michael Carla Daniel Alan Tina Christopher

2014 Pearson Education, Inc. Figure 14.UN11 2014 Pearson Education, Inc.

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