Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


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 14 Mendel and the Gene Idea

2 LE 14-3 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

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

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

5 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

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Testcross How can we tell the genotype of an individual with the dominant phenotype? Such an individual must have one dominant allele, but the individual could be either homozygous dominant or heterozygous 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

7 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

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

9 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

10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Using a dihybrid cross, Mendel developed the law of independent assortment The law of independent assortment states that each pair of alleles segregates independently of other pairs of alleles during gamete formation Genes located near each other on the same chromosome tend to be inherited together

11 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 in separate, distinguishable ways In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties

12 LE 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

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

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

15 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

16 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)

17 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)

18 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 normal

19 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 The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sickle-Cell Disease 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

21 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

22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Huntingtons disease is a degenerative disease of the nervous system – Dominant gene on chromosome 4 The disease has no obvious phenotypic effects until about 35 to 40 years of age

23 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.

24 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


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

Similar presentations


Ads by Google