Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 14 Mendel and the Gene Idea

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

LE 14-2 Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Carpel Stamens Parental generation (P) Pollinated carpel matured into pod Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F 1 )

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendel chose to track only those characters that varied in an “either-or” manner He also used varieties that were “true-breeding” (plants that produce offspring of the same variety when they self-pollinate)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Law of Segregation When any individual produces gametes, the copies of a gene separate, so that each gamete receives only one copy. P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers PP x pp Pp x Pp

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendel called the purple flower color a dominant trait and white flower color a recessive trait “heritable factor” is what we now call a gene

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendel’s Model Mendel developed four related concepts to explain the 3:1 inheritance pattern he observed in F 2 offspring. First Concept – alternate versions of genes, alleles, exist and explain for inherited variations. Allele for purple flowers Homologous pair of chromosomes Allele for white flowers Locus for flower-color gene

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Second concept - for each character an organism inherits two alleles, one from each parent P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Third concept - if the two alleles at a locus differ, then the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect on appearance P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fourth concept – The Law of Segregation states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

LE 14-5_2 Appearance: P Generation Genetic makeup: Gametes F 1 Generation Appearance: Genetic makeup: Gametes: F 2 Generation Purple flowers Pp P p P p F 1 sperm F 1 eggs PPPp pp P p 3: 1 Purple flowers PP White flowers pp P p

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Useful Genetic Vocabulary Homozygous - An organism with two identical alleles for a character. Heterozygous - An organism that has two different alleles for a gene. – Unlike homozygotes, heterozygotes are not true-breeding

LE 14-6 Phenotype Purple 3 Genotype PP (homozygous Pp (heterozygous Pp (heterozygous pp (homozygous Ratio 1:2:1 White Ratio 3:1 1

LE 14-7 Dominant phenotype, unknown genotype: PP or Pp? If PP, then all offspring purple: pp P P Pp If Pp, then 1 2 offspring purple and 1 2 offspring white: pp P P pp Pp Recessive phenotype, known genotype: pp Test Cross

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Law of Independent Assortment Monohybrids - individuals that are heterozygous for one character A cross between such heterozygotes is called a monohybrid cross Yy x Yy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dihybrids - heterozygous for two characters A dihybrid cross, a cross between F 1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently YyRr x YyRr ?

LE 14-8

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Law of Independent Assortment - each pair of alleles segregates independently of other pairs of alleles during gamete formation – This law applies only to genes on different, non-homologous chromosomes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 14.2: The laws of probability govern Mendelian inheritance Mendel’s laws of segregation and independent assortment reflect the rules of probability The alleles of one gene segregate into gametes independently of another gene’s alleles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Multiplication and Addition Rules Applied to Monohybrid Crosses Multiplication rule - the probability that two or more independent events will occur together is the product of their individual probabilities Rr x Rr – Probability of gamete having: RR? rr?

LE 14-9 Segregation of alleles into eggs Rr Sperm Rr R r R R R r Eggs r R r r Segregation of alleles into sperm Rr

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rule of addition - the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities Rr x Rr – Probability of gamete having: Rr?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Solving Complex Genetics Problems with the Rules of Probability A dihybrid cross is equivalent to two or more independent monohybrid crosses occurring simultaneously Cross: YyRr x YyRr What is the probability of YYRR? – of Yyrr?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetics Problems PPYyRrTt x PpyyRrtt What is the probability of PpyyrrTt?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetics Problems PpYyRr x Ppyyrr What fraction of the offspring from this cross would exhibit the recessive phenotypes for at least two of the three characteristics?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Spectrum of Dominance Complete dominance – PP=Purple Pp=Purple Codominance – BB=Black Fur WW=White Fur BW=Black & White Fur Incomplete dominance – RR=Red WW=White RW=Pink

Red C R Gametes P Generation CRCR CWCW White C W Pink C R C W CRCR Gametes CWCW F 1 Generation F 2 Generation Eggs CRCR CWCW CRCR CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW CWCW Sperm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 – this unusual trait is dominant Known as polydactyly Natural Selection at work!

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multiple Alleles Most genes exist in populations in more than two allelic forms Four phenotypes of the ABO blood group – three alleles for the enzyme (I): I A, I B, and i

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy For example, the multiple symptoms of – cystic fibrosis and sickle-cell disease

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Epistasis Epistasis - a gene at one locus alters the phenotypic expression of a gene at a second locus In mice and many other mammals, coat color depends on two genes – One gene determines the pigment color – The other gene determines whether the pigment will be deposited in the hair

LE Sperm BC bCBc bc BbCcBBCcBbCCBBCC BbCC bbCCBbCc bbCc BbccBBcc BbCcBBCc BbCc bbCc Bbcc bbcc BC bC Bc bc BbCc

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polygenic Inheritance Quantitative characters are those that vary in the population along a continuum usually indicates polygenic inheritance Skin color in humans is an example of polygenic inheritance aabbccAabbccAaBbccAaBbCcAABbCcAABBCcAABBCC AaBbCc 20 / / 64 6 / 64 1 / 64 Fraction of progeny

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nature and Nurture: The Environmental Impact on Phenotype Norm of reaction - the phenotypic range of a genotype influenced by the environment Hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 14.4: Many human traits follow Mendelian patterns of inheritance Pedigree - 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

LE 14-14a Wwww Ww wwWwww Ww WWww or Ww No widow’s peak Third generation (two sisters) Widow’s peak Second generation (parents plus aunts and uncles) First generation (grandparents) Dominant trait (widow’s peak)

LE 14-14b First generation (grandparents) Ff FF or Ffff Ff ff Ff Second generation (parents plus aunts and uncles) Third generation (two sisters) Attached earlobe Free earlobe ffFF or Ff Recessive trait (attached earlobe)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pedigrees can also be used to make predictions about future offspring

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominantly Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Recessively Inherited Disorders Recessively inherited disorders show up only in individuals homozygous for the allele – Carriers are heterozygous individuals who carry the recessive allele but appear normal

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Recessively Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings X-Linked Recessive Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings X-Linked Dominant Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitochondrial Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 – Common symptom - abnormal mucus buildup

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sickle-Cell Disease Sickle-cell disease affects one out of 400 African- Americans Symptoms include physical weakness, pain, organ damage, and even paralysis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominantly Inherited Disorders Some human disorders are due to dominant alleles One example is achondroplasia, a form of dwarfism that is lethal when homozygous for the dominant allele

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Video: Ultrasound of Human Fetus I Video: Ultrasound of Human Fetus I

LE 14-17a Amniocentesis Amniotic fluid withdrawn Fetus A sample of amniotic fluid can be taken starting at the 14th to 16th week of pregnancy. Centrifugation PlacentaUterusCervix Fluid Fetal cells Biochemical tests can be performed immediately on the amniotic fluid or later on the cultured cells. Biochemical tests Several weeks Karyotyping Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping.

LE 14-17b Chorionic villus sampling (CVS) PlacentaChorionic villi Fetus Suction tube inserted through cervix Fetal cells Biochemical tests Karyotyping and biochemical tests can be performed on the fetal cells immediately, providing results within a day or so. Several hours A sample of chorionic villus tissue can be taken as early as the 8th to 10th week of pregnancy. Karyotyping