© 2010 Pearson Education, Inc. Imagine a family with two parents who both maintain low fat levels through a combination of aerobic activity and weight training. Which of the following statements is/are most likely to apply to their two children? 1.The parents’ fat levels are irrelevant to the fat levels of the children. 2.One child is likely to have low fat levels but the other is more likely to have high fat levels because of independent assortment of genes. 3.The children may not have the same fat levels as their parents because genes independently assort during meiosis.

© 2010 Pearson Education, Inc. DEVISING HYPOTHESES TO EXPLAIN  What genetic principles account for the passing of traits from parents to offspring?  The “blending” hypothesis - genetic material from the two parents blends together  (example – paints - blue+ yellow=green)  The “particulate” hypothesis - parents pass on discrete heritable units (genes) can explain the reappearance of traits after several generations  Mendel documented a particulate mechanism through his experiments with garden peas

© 2010 Pearson Education, Inc. Mendel laws of inheritance  Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments  Advantages of pea plants for genetic study  Distinct heritable features, or characters –(such as flower color) character variants –(such as purple or white flowers) or traits Controlled Mating –Each flower has sperm-producing organs (stamens) and egg-producing organ (carpel) –Cross-pollination (fertilization between different plants)

Removed stamens from purple flower. White Stamens Purple Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel Offspring (F 1 ) Pollinated carpel matured into pod. Planted seeds from pod. Figure 9.3-3

White Purple Recessive Dominant Green Yellow Terminal Axial Wrinkled Round Green Yellow Seed shape Seed color Flower position Flower color Pod color Recessive Dominant Pod shape Stem length Inflated Constricted Tall Dwarf Figure 9.4

Purple flowers White flowers P Generation (true-breading parents) Figure 9.5-1

Purple flowers F 1 Generation White flowers P Generation (true-breading parents) All plants have purple flowers Figure 9.5-2

Purple flowers F 1 Generation White flowers P Generation (true-breading parents) All plants have purple flowers F 2 Generation Fertilization among F 1 plants (F 1  F 1 ) of plants have purple flowers of plants have white flowers Figure 9.5-3

© 2010 Pearson Education, Inc. Mendel developed four hypotheses from the monohybrid cross: There are alternative versions of genes, called alleles. 2. For each character, an organism inherits two alleles, one from each parent. –An organism is homozygous for that gene if both alleles are identical. –An organism is heterozygous for that gene if the alleles are different. 3. If two alleles of an inherited pair differ –The allele that determines the organism’s appearance is the dominant allele –The other allele, which has no noticeable effect on the appearance, is the recessive allele 4. Gametes carry only one allele for each inherited character. –The two members of an allele pair segregate (separate) from each other during the production of gametes. –This statement is the law of segregation.

Purple flowers F 1 Generation (hybrids) White flowers P Generation Genetic makeup (alleles) Gametes Alleles carried by parents PP P pp p All All Pp Purple flowers Gametes Alleles segregate P p F 2 Generation (hybrids) Sperm from F 1 plant P p P p PP pp Pp Eggs from F 1 plant Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Figure 9.6-3

© 2010 Pearson Education, Inc. Geneticists distinguish between an organism’s physical traits and its genetic makeup. –An organism’s physical traits are its phenotype. –An organism’s genetic makeup is its genotype. Homologous chromosomes have –Genes at specific loci –Alleles of a gene at the same locus

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 a Figure 9.7

© 2010 Pearson Education, Inc. Mendel’s Law of Independent Assortment A dihybrid cross is the crossing of parental varieties differing in two characters. What would result from a dihybrid cross? Two hypotheses are possible: 1. Dependent assortment 2. Independent assortment

F 1 Generation F 2 Generation RRYY Predicted results (not actually seen) P Generation Gametes RY rryy ry (a) Hypothesis: Dependent assortment RrYy RY ry Sperm Eggs RY ry

Eggs Actual results (support hypothesis) RRYY RY rryy ry RrYy (b) Hypothesis: Independent assortment Gametes RY ry Sperm RY ry Ry rY Ry rY RRYY Rryy RRyy RrYy RRYy RrYy rrYy Rryy rryy RrYY rrYY RrYyrrYy RRYy RrYy Yellow round Yellow wrinkled Green wrinkled Green round

© 2010 Pearson Education, Inc. Mendel’s dihybrid cross supported the hypothesis that each pair of alleles segregates independently of the other pairs during gamete formation. Thus, the inheritance of one character has no effect on the inheritance of another. This is the law of independent assortment.

© 2010 Pearson Education, Inc. A cross between homozygous purple- flowered and homozygous white-flowered pea plants results in offspring with purple flowers. This demonstrates a)the blending model of genetics. b)true-breeding. c)dominance. d)a dihybrid cross. e)the mistakes made by Mendel.

Female Male Attached Free Third generation (brother and sister) Second generation (parents, aunts, and uncles) First generation (grandparents) Ff FF ff or Ff ff FF or Ff ff Ff ff Figure 9.13 What can you say about dominance here?

Parents Offspring Ee Hearing Ee Sperm Eggs E Hearing E Ee e Hearing (carrier) EE Ee Hearing (carrier) ee Deaf e Figure 9.14 What can you say about dominance here?

© 2010 Pearson Education, Inc.  If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low  Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele  Most societies and cultures have laws or taboos against marriages between close relatives

Parents Sperm Eggs d Dwarf D Dd d dd d Normal (no achondroplasia) Molly Jo Dwarf (achondroplasia) Dd dd Normal dd Normal Dwarf Matt Amy JakeZachary Jeremy Figure 9.16 What is the difference from previous example?

© 2010 Pearson Education, Inc. Biology and Society  Early in the history of genetics a movement developed known as eugenics. The goal of eugenics was to “breed” a better human race by using social pressures to encourage reproduction for those with “good” genes and discourage those with “bad” genes. Eugenics led to bad legislation in the United States and eventually was used by the Nazis in Europe to justify many of their atrocities. Today, genetic research is providing ever-greater detail into the workings of each and every one of us, including genetic influences on behavior and personality. For some this is an opportunity to fully realize our individual potentials; for others this research dredges up memories of eugenics. As a member of society, do you think it is important to heed the lessons to be learned from eugenics as we explore more deeply into the genetics of human beings? Strongly Agree Strongly Disagree A. E. C. B. D.

RRrr P Generation Gametes Red White R r Figure

F 1 Generation RRrr Gametes P Generation Gametes Red White R r Rr Pink R r Figure

F 1 Generation RRrr Gametes P Generation F 2 Generation Sperm Gametes Red White R r Rr Pink R r R r R r RRRr rr Rr Eggs Figure Incomplete dominance

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

Blood Group (Phenotype) Genotypes Red Blood Cells O A B AB ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Figure 9.20a

Blood Group (Phenotype) O Genotypes Antibodies Present in Blood Red Blood Cells Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left AB AB O A B ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Anti-A Anti-B Anti-A Anti-B — Figure 9.20

Multiple genes Polygenic inheritance Single trait (e.g., skin color) Figure 9.UN5

F 1 Generation P Generation F 2 Generation Sperm AABBCC (very dark) Eggs aabbcc (very light) AaBbCc Figure 9.22a

Skin pigmentation Fraction of population Figure 9.22b

F 1 Generation P Generation Round-yellow seeds (RRYY) Wrinkled-green seeds (rryy) Gametes MEIOSIS FERTILIZATION R R R Y Y Y y y y r r r All round-yellow seeds (RrYy) R r y Figure

F 1 Generation Law of Independent Assortment: Follow both the long and the short chromosomes. P Generation Round-yellow seeds (RRYY) Wrinkled-green seeds (rryy) Gametes MEIOSIS FERTILIZATION R R R Y Y Y y y y r r r All round-yellow seeds (RrYy) R r y Y MEIOSIS They are arranged in either of two equally likely ways at metaphase I. R r y Y R r y Y Metaphase I (alternative arrangements) Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. Figure

F 1 Generation Law of Independent Assortment: Follow both the long and the short chromosomes. P Generation Gametes Round-yellow seeds (RRYY) Wrinkled-green seeds (rryy) Gametes MEIOSIS FERTILIZATION R R R Y Y Y y y y r r r All round-yellow seeds (RrYy) R r y Y MEIOSIS They are arranged in either of two equally likely ways at metaphase I. They sort independently, giving four gamete types. R r y Y R r yY R r y Y Metaphase I (alternative arrangements) Metaphase II r y R Y Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. Only one long chromosome ends up in each gamete. The R and r alleles segregate in anaphase I of meiosis. R Y R Y R Y r y r r y Y r RY ry rY Ry R y y Figure

F 1 Generation Law of Independent Assortment: Follow both the long and the short chromosomes. P Generation Gametes Round-yellow seeds (RRYY) Wrinkled-green seeds (rryy) Gametes MEIOSIS FERTILIZATION R R R Y Y Y y y y r r r All round-yellow seeds (RrYy) R r y Y MEIOSIS They are arranged in either of two equally likely ways at metaphase I. They sort independently, giving four gamete types. Fertilization results in the 9:3:3:1 phenotypic ratio in the F 2 generation. R r y Y R r yY R r y Y Metaphase I (alternative arrangements) Metaphase II r y R Y Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. Only one long chromosome ends up in each gamete. The R and r alleles segregate in anaphase I of meiosis. R Y R Y R Y r y r y r y Y r Fertilization recombines the r and R alleles at random. F 2 Generation RY ry rY Ry 9 : 3 : 1 FERTILIZATION AMONG THE F 1 PLANTS R y Figure

© 2010 Pearson Education, Inc. For any species the total number of chromosome combinations that can appear in the gametes due to independent assortment is: –2 n where n is the haploid number. For a human: –n = 23 –2 23 = 8,388,608 different chromosome combinations possible in a gamete

© 2010 Pearson Education, Inc. Albinism in humans occurs when both alleles at a locus produce defective enzymes in the biochemical pathway leading to melanin. Given that heterozygotes are normally pigmented, which of the following statements is/are correct? 1.One normal allele produces as much melanin as two normal alleles. 2.Each defective allele produces a little bit of melanin. 3.Two normal alleles are needed for normal melanin production. 4.The two alleles are codominant. 5.The amount of sunlight will not affect skin color of heterozygotes.

Crossing over Pair of homologous chromosomes A Recombinant gametes B A B ab a b Parental gametes A Ba b Figure 9.26

© 2010 Pearson Education, Inc. Genetic Recombination: Crossing Over Crossing over can –Separate linked alleles –Produce gametes with recombinant chromosomes –Produce offspring with recombinant phenotypes –The percentage of recombinant offspring among the total is called the recombination frequency.

Crossing over Recombinant gametes Parental gametes GgLl (female) G L g l G l g L ggll (male) g g l Sperm Eggs l g l g l Figure 9.27a

Recombinant gametes Parental gametes G L g l G lg L g l Sperm Recombinant Parental Eggs Offspring FERTILIZATION G L g l g L g l G l g l Figure 9.27b

Chromosome gc Recombination frequencies l 17% 9.5% 9% Figure 9.28

Unaffected individual Sperm Eggs XNXNXNXN XnYXnY XnXn Y Sperm XNXnXNXn XNYXNY XNXN Y XNXnXNXn XnYXnY XnXn Y XNXnXNXn XNYXNY XNXN XNXN XNXnXNXn XNYXNY Eggs XNXNXNXN XNYXNY XNXN XnXn XnYXnY XNXnXNXn XNXnXNXn XNYXNY XNXN XnXn XnYXnY XnXnXnXn Normal female  colorblind male Key (a) Carrier female  normal male (b) Carrier female  colorblind male (c) Colorblind individual Carrier Figure 9.31 Sex-linked inheritance

Albert Queen Victoria Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9.32 Hemophelia

© 2010 Pearson Education, Inc. Biology and Society  Assume that you have a history of Huntington’s chorea in your family. (Though the disease is not common, obviously there’s a chance that for a few of you this is a very real dilemma.) Huntington’s is a fatal condition that strikes during middle age and is inherited as a dominant trait—you only need one copy of the HD allele. Today, DNA screening tests are available but currently there is no way to stop the course of the disease. Some people at risk take the test—others do not. Would you take the screening test for Huntington’s if you were at risk? Strongly Agree Strongly Disagree A. E. C. B. D.

© 2010 Pearson Education, Inc. Figure (a) Amniocentesis (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta UterusCervix Centrifugation Fluid Fetal cells Several hours Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 11223