Biology, 9th ed,Sylvia Mader

Biology, 9th ed,Sylvia Mader
Chapter 11 Outline Mendelian Inheritance 11.1 Gregor Mendel 11.2 Mendel’s Laws 11.3 Mendelian Patterns of Inheritance and Human Disease 11.4 Beyond Mendelian Inheritance 1

Phenylketonuria: A Human Genetic Disorder
Biology, 9th ed,Sylvia Mader Chapter 11 Phenylketonuria: A Human Genetic Disorder Mendelian Inheritance Phenylalanine is an amino acid found in many foods. Phenylketonurics are people who lack the enzyme that breaks down phenylalanine. Excess phenylalanine accumulates in their bodies, causing nervous system disorders. Phenylketonuria is a recessively inherited trait, which means people have to inherit two copies of the gene to have the disorder. Food labels inform phenylketonurics which foods they should avoid.

11.1 Gregor Mendel Chapter 11 Mendelian Inheritance The Blending Concept of Inheritance: Parents of contrasting appearance produce offspring of intermediate appearance. Over time, variation would decrease as individuals became more alike in their traits. Blending was a popular concept during Mendel’s time. Mendel’s findings were in contrast with this. He formulated the particulate theory of inheritance. Mendel proposed the laws of segregation and independent assortment. Inheritance involves reshuffling of genes from generation to generation.

Chapter 11 Gregor Mendel Mendelian Inheritance Austrian monk Studied science and mathematics at the University of Vienna Conducted breeding experiments with the garden pea Pisum sativum Carefully gathered and documented mathematical data from his experiments Formulated fundamental laws of heredity in the early 1860s Had no knowledge of cells or chromosomes Did not have a microscope Experiments on the inheritance of simple traits in the garden pea disproved the blending hypothesis

Chapter 11 Mendelian Inheritance Gregor Mendel

Mendel Worked with the Garden Pea
Biology, 9th ed,Sylvia Mader Chapter 11 Mendel Worked with the Garden Pea Mendelian Inheritance The garden pea: Organism used in Mendel’s experiments A good choice for several reasons: Easy to cultivate Short generation Normally self-pollinating, but can be cross-pollinated by hand Pollen was transferred from the male (anther) of one plant to the female (stigma) parts of another plant. True-breeding varieties available Simple, objective traits 6

Garden Pea Anatomy Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flower Structure anther stamen filament stigma style carpel ovules in ovary a.

Garden Pea Anatomy Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cutting away anthers Brushing on pollen from another plant All peas are yellow when one parent produces yellow seeds and the other parent produces green seeds.

Chapter 11 11.2 Mendel’s Laws Mendelian Inheritance Mendel performed cross-breeding experiments. Used “true-breeding” (homozygous) plants Chose varieties that differed in only one trait (monohybrid cross) Performed reciprocal crosses Parental generation = P First filial generation offspring = F1 Second filial generation offspring = F2 Formulated the law of segregation

Monohybrid Cross Done by Mendel
Biology, 9th ed,Sylvia Mader Chapter 11 Slide #10 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation TT tt P gametes T t F1 generation Tt eggs F1 gametes T t T sperm TT Tt F2 generation t Tt tt Offspring Allele Key Phenotypic Ratio T = tall plant 10 3 tall t = short plant 1 short

Mendel’s Laws Chapter 11 Mendelian Inheritance Law of Segregation: Each individual has a pair of factors (alleles) for each trait. The factors (alleles) segregate (separate) during gamete (sperm & egg) formation. Each gamete contains only one factor (allele) from each pair of factors. Fertilization gives the offspring two factors for each trait. Results of the monohybrid cross: All F1 plants were tall, disproved blending hypothesis.

Chapter 11 Mendel’s Laws Mendelian Inheritance Classical Genetics and Mendel’s Cross: Each trait in a pea plant is controlled by two alleles (alternate forms of a gene). Dominant allele (capital letter) masks the expression of the recessive allele (lowercase). Alleles occur on a homologous pair of chromosomes at a particular gene locus. Homozygous = identical alleles Heterozygous = different alleles

Homologous Chromosomes
Biology, 9th ed,Sylvia Mader Chapter 11 Homologous Chromosomes Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sister chromatids alleles at a gene locus G g G G g g Replication R r R R r r S s S S s s a. Homologous chromosomes have alleles for same genes at specific loci. b. Sister chromatids of duplicated chromosomes have same alleles for each gene. t T t t T T

Relationship Between Observed Phenotype and F2 Offspring
Biology, 9th ed,Sylvia Mader Chapter 11 Relationship Between Observed Phenotype and F2 Offspring Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics F2Results Trait Dominant Recessive Dominant Recessive Ratio Stem length Tall Short 787 277 2.84:1 Inflated Pod shape Constricted 882 299 2.95:1 Seed shape Round Wrinkled 5,474 1,850 2.96:1 Seed color Yellow Green 6,022 2,001 3.01:1 Flower position Axial Terminal 651 207 3.14:1 705 224 3.15:1 Flower color Purple White Pod color Green Yellow 428 152 2.82:1 Totals: 14,949 5,010 2.98:1

Chapter 11 Mendel’s Laws Mendelian Inheritance Genotype It refers to the two alleles an individual has for a specific trait. If identical, genotype is homozygous. If different, genotype is heterozygous. Phenotype It refers to the physical appearance of the individual.

Mendel’s Cross Viewed by Modern Genetics
Biology, 9th ed,Sylvia Mader Chapter 11 Mendel’s Cross Viewed by Modern Genetics Mendelian Inheritance The dominant and recessive alleles represent DNA sequences that code for proteins. The dominant allele codes for the protein associated with the normal gene function within the cell. The recessive allele represents a “loss of function.” During meiosis I the homologous chromosomes separate. The two alleles separate from each other. The process of meiosis explains Mendel’s law of segregation and why only one allele for each trait is in a gamete.

Chapter 11 Mendel’s Laws Mendelian Inheritance A dihybrid cross uses true-breeding plants differing in two traits. Mendel tracked each trait through two generations. It started with true-breeding plants differing in two traits. The F1 plants showed both dominant characteristics. F1 plants self-pollinated. He observed phenotypes among F2 plants. Mendel formulated the law of independent assortment. The pair of factors for one trait segregate independently of the factors for other traits. All possible combinations of factors can occur in the gametes. P generation is the parental generation in a breeding experiment. F1 generation is the first-generation offspring in a breeding experiment. F2 generation is the second-generation offspring in a breeding experiment.

Dihybrid Cross Done by Mendel
Biology, 9th ed,Sylvia Mader Dihybrid Cross Done by Mendel Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × P generation TTGG ttgg P gametes TG tg F1 generation TtGg eggs F1 gametes TG Tg tG tg TG TTGG TTGg TtGG TtGg F2 generation Tg TTGg TTgg TtGg Ttgg sperm tG TtGG TtGg ttGG ttGg tg TtGg Ttgg ttGg ttgg Offspring Allele Key Phenotypic Ratio T = tall plant 9 tall plant, green pod t = short plant 3 tall plant, yellow pod G = green pod 3 short plant, green pod g = Yellow pod 1 short plant, yellow pod

Independent Assortment and Segregation during Meiosis
Biology, 9th ed,Sylvia Mader Independent Assortment and Segregation during Meiosis Chapter 11 Slide #19 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A B A A AB B B A B A A a a B B b b a a a b b b ab either a b A a B b A A A b or b b Ab A Parent cell has two pairs of homologous chromosomes. b A A a a b b B B a a a B B B aB a B All orientations of homologous chromosomes are possible at metaphase I in keeping with the law of Independent assortment. At metaphase II, each daughter cell has only one member of each homologous pair in keeping with the law of segregation All possible combi - tions of chromosomes and alleles occur in the gametes as suggested by Mendel's two laws. 19

Chapter 11 Mendel’s Laws Mendelian Inheritance Punnett Square Table listing all possible genotypes resulting from a cross All possible sperm genotypes are lined up on one side. All possible egg genotypes are lined up on the other side. All possible zygote genotypes are placed within the squares.

Mendel and the Laws of Probability
Biology, 9th ed,Sylvia Mader Mendel and the Laws of Probability Chapter 11 Mendelian Inheritance Punnett Square It allows us to easily calculate probability of genotypes and phenotypes among the offspring. Punnett square in next slide shows a 50% (or ½) chance. The chance of E = ½ The chance of e = ½ An offspring will inherit: The chance of EE = ½  ½ = ¼ The chance of Ee = ½  ½ = ¼ The chance of eE = ½  ½ = ¼ The chance of ee = ½  ½ = ¼ The sum rule allows us to add the genotypes that produce the identical phenotype to find out the chance of a particular phenotype.

Punnett Square Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents Ee Ee eggs E e E EE Ee spem Punnett square e Ee ee Offspring Allele key Phenotypic Ratio E = unattached earlobes 3 unattached earlobes e = attached earlobes 1 attached earlobes

Chapter 11 Mendel’s Laws Mendelian Inheritance Testcrosses Individuals with recessive phenotype always have the homozygous recessive genotype. However, individuals with dominant phenotype have indeterminate genotype. May be homozygous dominant, or Heterozygous A testcross determines the genotype of an individual having the dominant phenotype.

One-Trait Testcrosses
Biology, 9th ed,Sylvia Mader One-Trait Testcrosses Chapter 11 Mendelian Inheritance

Chapter 11 Mendel’s Laws Mendelian Inheritance Two-trait testcross: An individual with both dominant phenotypes is crossed with an individual with both recessive phenotypes. If the individual with the dominant phenotypes is heterozygous for both traits, the expected phenotypic ration is 1:1:1:1. 25

11.3 Mendelian Patterns of Inheritance and Human Disease
Biology, 9th ed,Sylvia Mader Chapter 11 11.3 Mendelian Patterns of Inheritance and Human Disease Mendelian Inheritance Genetic disorders are medical conditions caused by alleles inherited from parents. Autosome is any chromosome other than a sex chromosome (X or Y). Genetic disorders caused by genes on autosomes are called autosomal disorders. Some genetic disorders are autosomal dominant. An individual with AA has the disorder. An individual with Aa has the disorder. An individual with aa does NOT have the disorder. Other genetic disorders are autosomal recessive. An individual with AA does NOT have the disorder. An individual with Aa does NOT have the disorder, but is a carrier. An individual with aa DOES have the disorder.

Autosomal Recessive Pedigree
Biology, 9th ed,Sylvia Mader Autosomal Recessive Pedigree Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I aa A? II A? Aa Aa A? Generations * III Aa Aa A? A? IV aa aa A? Key aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) Autosomal recessive disorders • Most affected children have unaffected parents. • Heterozygotes (Aa) have an unaffected phenotype. • Two affected parents will always have affected children. • Close relatives who reproduce are more likely to have affected children. • Both males and females are affected with equal frequency.

Autosomal Dominant Pedigree
Biology, 9th ed,Sylvia Mader Chapter 11 Autosomal Dominant Pedigree Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I Aa Aa * Generations II aa Aa A? aa aa aa III Aa Aa aa aa aa aa Key AA = affected Aa = affected A? = affected (one allele unknown) aa = unaffected Autosomal dominant disorders • Affected children will usually have an affected parent. • Heterozygotes (Aa) are affected. • Two affected parents can produce an unaffected child. • Two unaffected parents will not have affected children. • Both males and females are affected with equal frequency.

Mendelian Patterns of Inheritance and Human Disease
Biology, 9th ed,Sylvia Mader Mendelian Patterns of Inheritance and Human Disease Chapter 11 Mendelian Inheritance Autosomal Recessive Patterns of Inheritance and Disorders: If both parents carry one copy of a recessive gene they are unaffected but are capable of having a child with two copies of the gene who is affected. Methemoglobinemia It is a relatively harmless disorder. Accumulation of methemoglobin in the blood causes skin to appear bluish-purple. Cystic Fibrosis Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous.

Chapter 11 Cystic Fibrosis Mendelian Inheritance

Mendelian Patterns of Inheritance and Human Disease
Biology, 9th ed,Sylvia Mader Mendelian Patterns of Inheritance and Human Disease Chapter 11 Mendelian Inheritance Autosomal Dominant Patterns of Inheritance and Disorders Two parents with a dominantly inherited disorder will be affected by one copy of the gene. It is possible for them to have unaffected children. Osteogenesis Imperfecta Characterized by weakened, brittle bones. Most cases are caused by mutation in genes required for the synthesis of type I collagen. Hereditary Spherocytosis It is caused by a mutation in the ankyrin-1 gene. Red blood cells become spherical, are fragile, and burst easily.

11.4 Beyond Mendelian Inheritance
Biology, 9th ed,Sylvia Mader Chapter 11 11.4 Beyond Mendelian Inheritance Mendelian Inheritance Some traits are controlled by multiple alleles (multiple allelic traits). The gene exists in several allelic forms, but each individual only has two alleles. ABO blood types The alleles: IA = A antigen on red blood cells, anti-B antibody in plasma IB = B antigen on red blood cells, anti-A antibody in plasma i = Neither A nor B antigens on red blood cells, both anti-A and anti-B antibodies in plasma The ABO blood type is also an example of codominance. More than one allele is fully expressed. Both IA and IB are expressed in the presence of the other.

Chapter 11 ABO Blood Type Mendelian Inheritance Phenotype A B AB O Genotype IAIA, IAi IBIB, IBi IAIB ii

(a) The three alleles for the ABO blood groups and their carbohydrates
Figure 14.11 (a) The three alleles for the ABO blood groups and their carbohydrates Allele IA IB i Carbohydrate A B none Figure Multiple alleles for the ABO blood groups. (b) Blood group genotypes and phenotypes Genotype IAIA or IAi IBIB or IBi IAIB ii Red blood cell appearance Phenotype (blood group) A B AB O

Beyond Mendelian Inheritance
Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Incomplete Dominance Heterozygote has a phenotype intermediate between that of either homozygote. Homozygous red has red phenotype. Homozygous white has white phenotype. Heterozygote has pink (intermediate) phenotype. Phenotype reveals genotype without a testcross.

Chapter 11 Incomplete Dominance Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R R R R 1 2 1 2 eggs R R 1 2 R 1 R R R R 1 1 1 2 sperm Key 1 R R red 1 1 R 2 R R pink 2 1 2 1 R R white 2 2 R R R R 1 2 2 2 Offspring

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Human examples of incomplete dominance: Familial Hypercholesterolemia (FH) Homozygotes for the mutant allele develop fatty deposits in the skin and tendons and may have heart attacks during childhood. Heterozygotes may suffer heart attacks during early adulthood. Homozygotes for the normal allele do not have the disorder. 38

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Human examples of incomplete dominance: Incomplete penetrance The dominant allele may not always lead to the dominant phenotype in a heterozygote. Many dominant alleles exhibit varying degrees of penetrance. Example: polydactyly There are extra digits on hands, feet, or both. Not all individuals who inherit the dominant polydactyly allele will exhibit the trait. 39

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Pleiotropy occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits. Marfan syndrome has been linked to a mutated gene FBN1 on chromosome 15 which codes for the fibrillin protein. Marfan syndrome is pleiotropic and results in the following phenotypes: Disproportionately long arms, legs, hands, and feet A weakened aorta Poor eyesight

Marfan Syndrome Chapter 11 Mendelian Inheritance

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Polygenic Inheritance: Occurs when a trait is governed by two or more sets of alleles. Each dominant allele has a quantitative effect on the phenotype. These effects are additive. It results in continuous variation of phenotypes within a population. The traits may also be affected by the environment. Examples Human skin color Height Eye color

Polygenic Inheritance
Biology, 9th ed,Sylvia Mader Polygenic Inheritance Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation F1 generation F2 generation 20 — 64 15 — 64 Proportion of Population 6 — 64 1 — 64 aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC Genotype Examples

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance X-Linked Inheritance In mammals The X and Y chromosomes determine gender. Females are XX. Males are XY.

Extending the Range of Mendelian Genetics
Biology, 9th ed,Sylvia Mader Chapter 11 Extending the Range of Mendelian Genetics Mendelian Inheritance X-Linked Inheritance The term X-linked is used for genes that have nothing to do with gender. X-linked genes are carried on the X chromosome. The Y chromosome does not carry these genes. It was discovered in the early 1900s by a group at Columbia University, headed by Thomas Hunt Morgan. Performed experiments with fruit flies They can be easily and inexpensively raised in simple laboratory glassware. Fruit flies have the same sex chromosome pattern as humans. Morgan’s experiments with X-linked genes apply directly to humans.

X-Linked Inheritance Chapter 11 Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation XrY XRXR P gametes Xr Y XR F1 generation XRY XRXr eggs F1 gametes XR Xr XR XRXR XRXr F2 generation sperm Y XRY XrY Offspring Phenotypic Ratio Allele Key females: XR = red eyes all red-eyed males: 1 red-eyed Xr = white eyes 1 white-eyed

Chapter 11 X-Linked Inheritance Mendelian Inheritance

Biology, 9th ed,Sylvia Mader Chapter 11 Beyond Mendelian Inheritance Mendelian Inheritance Several X-linked recessive disorders occur in humans: Color blindness The allele for the blue-sensitive protein is autosomal. The alleles for the red- and green-sensitive pigments are on the X chromosome. Menkes syndrome It is caused by a defective allele on the X chromosome. It disrupts movement of the metal copper in and out of cells. Phenotypes include kinky hair, poor muscle tone, seizures, and low body temperature. Muscular dystrophy Causes wasting away of the muscle It is caused by the absence of the muscle protein dystrophin. Adrenoleukodystrophy It is an X-linked recessive disorder. It is a failure of a carrier protein to move either an enzyme or very long chain fatty acid into peroxisomes. Hemophilia It is an absence or minimal presence of clotting factor VIII or clotting factor IX. An affected person’s blood either does not clot or clots very slowly.

Hemophilia and the Royal Families of Europe
Biology, 9th ed,Sylvia Mader Chapter 11 Hemophilia and the Royal Families of Europe Mendelian Inheritance Hemophilia is called the bleeder’s disease because the affected person’s blood either doesn’t clot correctly or doesn’t clot at all. People with hemophilia bleed internally and externally after injury. Blood transfusions or clotting factor injections help with the disorder. The pedigree shows why hemophilia is referred to as “the royal disease.” Queen Victoria was the first of the royals to carry the gene. Eventually it was spread throughout the royal families of Europe through arranged marriages between the English, Spanish, Prussian, and Russian royal families.

X-Linked Recessive Pedigree
Biology, 9th ed,Sylvia Mader Chapter 11 X-Linked Recessive Pedigree Mendelian Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XBXB XbY grandfather XBY XBXb daughter XBY XbXb XbY XBY XBXB XBXb XbY grandson Key XBXB = Unaffected female XBXb = Carrier female XbXb = Color-blind female XbY = Unaffected male XbY = Color-blind male X-Linked Recessive Disorders • More males than females are affected. • An affected son can have parents who have the normal phenotype. • For a female to have the characteristic, her father must also have it. Her mother must have it or be a carrier. • The characteristic often skips a generation from the grandfather to the grandson. • If a woman has the characteristic, all of her sons will have it.

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 C for color and c for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc.

BbEe BbEe Sperm 1/4 1/4 1/4 1/4 Eggs 1/4 1/4 1/4 1/4 9 : 3 : 4 BE bE
Figure 14.12 BbEe BbEe Sperm 1/4 1/4 BE 1/4 1/4 bE Be be Eggs 1/4 BE Figure An example of epistasis. BBEE BbEE BBEe BbEe 1/4 bE BbEE bbEE BbEe bbEe 1/4 Be BBEe BbEe BBee Bbee 1/4 be BbEe bbEe Bbee bbee 9 : 3 : 4

Linked Genes

Mapping the Distance Between Genes Using Recombination Data: Scientific Inquiry
Alfred Sturtevant, one of Morgan’s students, constructed a genetic map, an ordered list of the genetic loci along a particular chromosome Sturtevant predicted that the farther apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency © 2011 Pearson Education, Inc.

A linkage map is a genetic map of a chromosome based on recombination frequencies
Distances between genes can be expressed as map units; one map unit represents a 1% recombination frequency Map units indicate relative distance and order, not precise locations of genes © 2011 Pearson Education, Inc.

Recombination frequencies
Figure 15.11 RESULTS Recombination frequencies Figure Research Method: Constructing a Linkage Map 9% 9.5% Chromosome 17% b cn vg

Sturtevant used recombination frequencies to make linkage maps of fruit fly genes
Using methods like chromosomal banding, geneticists can develop cytogenetic maps of chromosomes Cytogenetic maps indicate the positions of genes with respect to chromosomal features © 2011 Pearson Education, Inc.

Long aristae (appendages on head) Gray body Red eyes Normal wings
Figure 15.12 Mutant phenotypes Short aristae Black body Cinnabar eyes Vestigial wings Brown eyes Figure A partial genetic (linkage) map of a Drosophila chromosome. 48.5 57.5 67.0 104.5 Long aristae (appendages on head) Gray body Red eyes Normal wings Red eyes Wild-type phenotypes

X Inactivation in Female Mammals
In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development The inactive X condenses into a Barr body If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character © 2011 Pearson Education, Inc.

Cell division and X chromosome inactivation
Figure 15.8 X chromosomes Allele for orange fur Early embryo: Allele for black fur Cell division and X chromosome inactivation Figure 15.8 X inactivation and the tortoiseshell cat. Two cell populations in adult cat: Active X Inactive X Active X Black fur Orange fur

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