mendelian genetics

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Figure 14.1

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Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments © 2011 Pearson Education, Inc. Advantages of pea plants for genetic study…….. distinct heritable features- characters (ex: flower color) character variants (purple or white flowers) are called traits Each flower has sperm-producing organs (stamens) and egg-producing organ (carpel) Can easily manipulate and control mating Short generation time and many off-spring

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Table 14.1 What Mendel called a “heritable factor” is what we now call a gene

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Parental generation (P) Stamens Carpel 2 1 3 4 Mendel mated two contrasting, true-breeding varieties = hybridization

Wingdings:

Figure 14.2b First filial generation offspring (F 1 ) RESULTS 5

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Figure 14.3-1 P Generation EXPERIMENT (true-breeding parents) Purple flowers White flowers

Figure 14.1:

Figure 14.3-2 P Generation EXPERIMENT (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers

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Figure 14.3-3 P Generation F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers 705 purple 224 white F 1 individuals cross with other F 1 hybrids- F 2 generation Mendel developed hypothesis to explain the 3:1 inheritance pattern

Table 14.1:

Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes These alternative versions of a gene are now called alleles Each gene resides at a specific locus on a specific chromosome 1st: alternative versions of genes account for variations in inherited characters

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2nd : an organism inherits two alleles for each character ……… one from each parent two alleles at a particular locus may be identical - homozygous (AA or aa) Or the two alleles at a locus may differ – heterozygous (Aa) © 2011 Pearson Education, Inc. 3rd : if the two alleles at a locus differ ………….. then one ( dominant allele ) determines appearance the other ( recessive allele ) has no noticeable effect

Figure 14.2b:

4th: ( law of segregation ): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Each gamete gets only one of the two alleles that are present in the parent producing the gamete © 2011 Pearson Education, Inc.

Figure 14.3-1:

Figure 14.5-1 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP pp P p PP pp Phenotype - physical appearance Genotype - genetic makeup

Figure 14.3-2:

Figure 14.5-2 P Generation F 1 Generation Gametes: Gametes: Pp PP pp P P p p 1 / 2 1 / 2 The possible combinations of gametes can be shown using a Punnett square to predict the results of a cross between individuals of known genetic makeup

Figure 14.3-3:

Figure 14.5-3 P Generation F 1 Generation F 2 Generation Gametes: Gametes: Sperm from F 1 ( Pp ) plant Pp PP pp P P P P p p p p Eggs from F 1 ( Pp ) plant PP pp Pp Pp 1 / 2 1 / 2 3 : 1

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Phenotype Purple Purple Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous) Figure 14.6

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testcross : breeding a mystery individual with a homozygous recessive individual If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.

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unknown genotype: PP or Pp ? known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Sperm Eggs Eggs or All offspring purple 1 / 2 offspring purple and 1 / 2 offspring white Pp Pp Pp Pp Pp Pp pp pp p p p p P P P p TECHNIQUE RESULTS TEST CROSS

Figure 14.5-1:

The Law of Independent Assortment pairs of chromosomes (alleles) segregate independently of other pairs of chromosomes (alleles) during meiosis (gamete formation)

Figure 14.5-2:

P Generation F 1 Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yr YR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F 2 generation Sperm Sperm or Eggs Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1 315 108 101 32 1 / 2 1 / 2 1 / 2 1 / 2 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 9 / 16 3 / 16 3 / 16 1 / 16 YR YR YR YR yr yr yr yr 1 / 4 3 / 4 Yr Yr yR yR YYRR YyRr YyRr yyrr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr The Law of Independent Assortment

Figure 14.5-3:

The laws of probability govern Mendelian inheritance When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss Similarly….the alleles of one gene segregate into gametes independently of another gene’s alleles © 2011 Pearson Education, Inc.

Figure 14.6:

Segregation of R and r alleles into eggs Segregation of R and r alleles into sperm Sperm Eggs 1 / 2 1 / 2 1 / 2 1 / 2 1 / 4 1 / 4 1 / 4 1 / 4 Rr Rr R R R R R R r r r r r  r 1/2 x 1/2= 1/4 multiplication rule - the probability that two or more independent events will occur together is the product of their individual probabilities

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Sperm Eggs 1 / 2 1 / 2 1 / 2 1 / 2 1 / 4 1 / 4 1 / 4 1 / 4 Rr Rr R R R R R R r r r r r  r ¼ + ¼ = 2/4  1/2 addition rule - probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities the probability that an F 2 offspring from a cross will be heterozygous rather than homozygous (when the F 1 parents are both heterozygous)

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Inheritance patterns are usually more complex than predicted by simple Mendelian genetics The relationship between genotype and phenotype is rarely as simple as the pea 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 © 2011 Pearson Education, Inc.

The Law of Independent Assortment:

Degrees of Dominance Complete dominance - phenotypes of the heterozygote and dominant homozygote are identical Incomplete dominance - the phenotype of heterozygote is somewhere between the phenotypes of the two homozygote varieties Codominance - two dominant alleles affect the phenotype in separate, distinguishable ways © 2011 Pearson Education, Inc.

The Law of Independent Assortment:

Figure 14.10-1 P Generation Red White Gametes C W C W C R C R C R C W

The laws of probability govern Mendelian inheritance:

Figure 14.10-2 P Generation F 1 Generation 1 / 2 1 / 2 Red White Gametes Pink Gametes C W C W C R C R C R C W C R C W C R C W Incomplete dominance

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Figure 14.10-3 P Generation F 1 Generation F 2 Generation 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 Red White Gametes Pink Gametes Sperm Eggs C W C W C R C R C R C W C R C W C R C W C W C R C R C W C R C R C R C W C R C W C W C W Incomplete dominance

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Homozygous for ability to make LDL receptors Severe disease Mild disease Cell Normal LDL receptor LDL Homozygous for inability to make LDL receptors Heterozygous HH Hh hh GENOTYPE PHENOTYPE Figure 9.19 Hypercholesterolemia - incompletely dominant . Heterozygotes -blood cholesterol levels about twice normal. Homozygotes - blood cholesterol levels about 5x normal.

Inheritance patterns are usually more complex than predicted by simple Mendelian genetics:

Multiple Alleles and Codominance Most genes actually exist in more than two allelic forms For example - four phenotypes of blood type in humans ( A, B, AB, and O ) ……. determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A , I B , and i . The enzyme encoded by the I A allele adds the A carbohydrate, the enzyme encoded by the I B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither carbohydrate © 2011 Pearson Education, Inc.

Degrees of Dominance :

Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O I A I B i ii I A I B I A I A or I A i I B I B or I B i

Figure 14.10-1:

Anti-A serum Anti-B serum Blood type clumps None Type A None Clumps Type B Clumps Clumps Type AB none None Type O Recipient Donor Type O Can receive…… Type O Type A Can receive…… Type A or O Type B Can receive…… Type B or O Type AB Can receive…… Type A, B, AB or O Type AB – no antibodies ………. universal recipient Type O – no antigens ……..….. Universal donor

Figure 14.10-2:

Pleiotropy Most genes have multiple phenotypic effects ……… pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease © 2011 Pearson Education, Inc.

Figure 14.10-3:

Polygenic Inheritance Quantitative characters - vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance = additive effect of two or more genes on a single phenotype © 2011 Pearson Education, Inc.

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Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 1 2 3 4 5 6 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 64 6 / 64 15 / 64 20 / 64 15 / 64 6 / 64 1 / 64 AaBbCc AaBbCc Polygenic Inheritance

Multiple Alleles and Codominance:

Epistasis a gene at one locus alters the phenotypic expression of a gene at a second locus Example: - in many other mammals, coat color depends on two genes - One gene determines the pigment color ( B for black and b for brown) - another gene (E, e) determines whether the pigment will be deposited in the hair or not © 2011 Pearson Education, Inc.

Figure 14.11:

Figure 14.12 Sperm Eggs 9 : 3 : 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 BbEe BbEe BE BE bE bE Be Be be be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee Epistasis

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Nature and Nurture: Environmental Impact on Phenotype phenotype often depends on environment as well as genotype hydrangea flowers of the same genotype range from blue to pink, depending on soil acidity © 2011 Pearson Education, Inc. characters called multifactorial - genetic and environmental factors collectively influence phenotype

Pleiotropy:

Recessively Inherited Disorders © 2011 Pearson Education, Inc. Recessively inherited disorders show up only in individuals homozygous for the allele Carriers - heterozygous individuals carry the recessive allele but are phenotypically normal

Polygenic Inheritance:

Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a Albinism - a recessive condition ( lack of pigmentation )

Figure 14.13:

Sickle-cell disease (recessive disorder) Homozygous (aa) - all hemoglobin is abnormal (sickled) Symptoms include physical weakness, pain, organ damage, and even paralysis © 2011 Pearson Education, Inc. Heterozygotes ( Aa ) (sickle-cell trait) - mostly healthy but may suffer some symptoms Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous

Epistasis:

Some disorders are caused by dominant alleles Dominant alleles that cause a lethal disease are rare © 2011 Pearson Education, Inc. Achondroplasia - form of dwarfism Heterozygous (Aa) – have achondroplasia Homozygous dominant (AA) – embryo dies Homozygous recessive (aa) – normal stature

Figure 14.12:

Figure 14.17 Parents Dwarf Dd Sperm Eggs Dd Dwarf dd Normal Dd Dwarf dd Normal D d d d Normal dd

Nature and Nurture: Environmental Impact on Phenotype:

timing of onset of disease can significantly affect its inheritance Huntington’s disease - degenerative disease of the nervous system (irreversible and fatal) no obvious phenotypic signs until the individual is about 35 to 40 years of age When signs show………..have usually already reproduced Late-Onset Lethal Disease © 2011 Pearson Education, Inc.

Recessively Inherited Disorders:

Homologous chromosomes P Genotype: Gene loci P a aa b B Dominant allele Recessive allele Bb PP Homozygous for the dominant allele Homozygous for the recessive allele Heterozygous for B and b alleles a Figure 9.7 Homologous chromosomes have……. Genes at specific loci Alleles of a gene at the same locus

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Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes These alternative versions of a gene are now called alleles Each gene resides at a specific locus on a specific chromosome 1st: alternative versions of genes account for variations in inherited characters

PowerPoint Presentation:

2nd : an organism inherits two alleles for each character ……… one from each parent two alleles at a particular locus may be identical - homozygous (AA or aa) Or the two alleles at a locus may differ – heterozygous (Aa) © 2011 Pearson Education, Inc. 3rd : if the two alleles at a locus differ ………….. then one ( dominant allele ) determines appearance the other ( recessive allele ) has no noticeable effect

PowerPoint Presentation:

4th: ( law of segregation ): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Each gamete gets only one of the two alleles that are present in the parent producing the gamete © 2011 Pearson Education, Inc.

Figure 14.17:

The Law of Independent Assortment pairs of chromosomes (alleles) segregate independently of other pairs of chromosomes (alleles) during meiosis (gamete formation)

Late-Onset Lethal Disease:

Figure 14.5-3 P Generation F 1 Generation F 2 Generation Gametes: Gametes: Sperm from F 1 ( Pp ) plant Pp PP pp P P P P p p p p Eggs from F 1 ( Pp ) plant PP pp Pp Pp 1 / 2 1 / 2 3 : 1

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P Generation F 1 Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yr YR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F 2 generation Sperm Sperm or Eggs Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1 315 108 101 32 1 / 2 1 / 2 1 / 2 1 / 2 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 9 / 16 3 / 16 3 / 16 1 / 16 YR YR YR YR yr yr yr yr 1 / 4 3 / 4 Yr Yr yR yR YYRR YyRr YyRr yyrr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr The Law of Independent Assortment

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Figure 14.10-3 P Generation F 1 Generation F 2 Generation 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 Red White Gametes Pink Gametes Sperm Eggs C W C W C R C R C R C W C R C W C R C W C W C R C R C W C R C R C R C W C R C W C W C W Incomplete dominance

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Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O I A I B i ii I A I B I A I A or I A i I B I B or I B i

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Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 1 2 3 4 5 6 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 8 1 / 64 6 / 64 15 / 64 20 / 64 15 / 64 6 / 64 1 / 64 AaBbCc AaBbCc Polygenic Inheritance

The Law of Independent Assortment:

Figure 14.12 Sperm Eggs 9 : 3 : 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 1 / 4 BbEe BbEe BE BE bE bE Be Be be be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee Epistasis

Figure 14.5-3:

Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a Albinism - a recessive condition ( lack of pigmentation )

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Male Sperm Somatic cells 44  XY 44  XX Female 22  X 44  XY 44  XX 22  Y Egg 22  X Male Female Offspring Figure 9.29 gametes

Figure 14.10-3:

Unaffected individual Sperm Eggs X N X N X n Y X n Y Sperm X N X n X N Y X N Y Sperm X N X n X n Y X n Y X N X n X N Y X N X N X N X n X N Y Eggs X N X N X N Y X N X n X n Y X N X n Eggs X N X n X N Y X N X n X n Y X n X n Normal female  colorblind male Key (a) Carrier female  normal male (b) Carrier female  colorblind male (c) Colorblind individual Carrier Figure 9.31

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