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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece.

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece."— Presentation transcript:

1 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 11 – law of segregation, law of ind. assortment Mendel and the Gene Idea

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

3 LE 14-4 Allele for purple flowers Homologous pair of chromosomes Allele for white flowers Locus for flower-color gene

4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Testcross How can we tell the genotype of an individual with the dominant phenotype? Could be DD or Dd The answer is to 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. Same thing for a 2 trait but testcross would involve the double recessive.

5 LE 14-8 P Generation F 1 Generation YYRR Gametes YR yr yyrr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Sperm Eggs YR Yr yrYR yr Eggs YYRRYyRr yyrr yR yr Phenotypic ratio 3:1 F 2 Generation (predicted offspring) YYRR YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr Phenotypic ratio 9:3:3:1 YRYryRyr Sperm

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Using a dihybrid cross, Mendel developed the law of independent assortment This principle states that the alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.allelesfertilization Genes located near each other on the same chromosome tend to be inherited together – these are called linked genes and we will do work them!

7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Spectrum of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In codominance, two dominant alleles affect the phenotype – both expressed! In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties

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

9 LE aabbccAabbccAaBbccAaBbCcAABbCcAABBCcAABBCC AaBbCc 20 / / 64 6 / 64 1 / 64 Fraction of progeny

10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Males = squares, females = circles The trait is shaded in

11 LE 14-14a Wwww Ww wwWwww Ww WWww or Ww No widows peak Third generation (two sisters) Widows peak Second generation (parents plus aunts and uncles) First generation (grandparents) Dominant trait (widows peak)

12 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)

13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner Recessively inherited disorders show up only in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically (look) normal, so they dont know they have bad genes!

14 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 - why??? The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes –so lungs full of mucus Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine (so stunted growth)

15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sickle-Cell Disease – Watch HHMI video Sickle-cell disease affects one out of 400 African- Americans The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells Symptoms include physical weakness, pain, organ damage, and even paralysis

16 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

17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blue Fugates of Kentucky: mutant enzyme

18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Marfans – Defective connective tissue

19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Color blindness inheritance – mostly seen in males. How would females get it??

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Are you color blind? Try to read these!


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