Scheman

Gregor Mendel Austrian Monk, mid- 19 th century. Worked with Pea plants. 1 st to succeed in predicting the passage of traits from parent to offspring. Utilized Scientific Method with controlled experimentation. Both Stamens and Carpels Control cross-pollination

What genetic principles account for the passing of traits from parents to offspring? The “ blending ” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) The “ particulate ” hypothesis is the idea that parents pass on discrete heritable units (genes) Mendel documented a particulate mechanism through his experiments with garden peas

EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers  F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants Particulate Hypothesis Proven (no blending)

Mendel’s Key Points Hybrid = The offspring of parents that have different forms for the same trait. Two Factors that control gene activation for any particular trait. (Alleles) Dominant vs. Recessive Law of Segregation Law of Independent Assortment What Mendel called a “heritable factor” is what we now call a gene!

Mitosis and meiosis were first described in the late 1800s The chromosome theory of inheritance states: –Mendelian genes have specific loci (positions) on chromosomes –Chromosomes undergo segregation and independent assortment The behavior of chromosomes during meiosis was said to account for Mendel ’ s laws of segregation and independent assortment

0.5 mm Meiosis Metaphase I Anaphase I Metaphase II Gametes LAW OF SEGREGATION The two alleles for each gene separate during gamete formation. LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation. 1 4 yr 1 4 Yr 1 4 YR 3 3 F 1 Generation 1 4 yR R R R R R R R R R R R R Y Y Y Y Y Y Y Y Y Y YY y rr r r r r r r r r r r y y y y y y y y y y y All F 1 plants produce yellow-round seeds (YyRr)

Punnett Squares Technique for predicting offspring from one generation to the next. Homozygous vs. Heterozygous

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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

EXPERIMENT RESULTS P Generation F 1 Generation Predictions Gametes Hypothesis of dependent assortment YYRRyyrr YR yr YyRr  Hypothesis of independent assortment or Predicted offspring of F 2 generation Sperm YR yr Yr YR yR Yr yR yr YR YYRR YyRr YYRr YyRR YYrr Yyrr yyRR yyRr yyrr Phenotypic ratio 3:1 Eggs Phenotypic ratio 9:3:3:1 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 yr 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 3/43/4 9 / 16 3 / 16 1 / 16 Phenotypic ratio approximately 9:3:3:

Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics The relationship between genotype and phenotype is rarely as simple as in the pea plant 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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

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

Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Red P Generation Gametes White CRCRCRCR CWCWCWCW CRCR CWCW F 1 Generation Pink CRCWCRCW CRCR CWCW Gametes 1/21/2 1/21/2 F 2 Generation Sperm Eggs CRCR CRCR CWCW CWCW CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW 1/21/2 1/21/2 1/21/2 1/21/2 incomplete dominance

Multiple Alleles Most genes exist in populations in more than two allelic forms For example, the four phenotypes of the ABO blood group in humans are 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, whereas the enzyme encoded by the I B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Blood Typing

IAIA IBIB i A B none (a) The three alleles for the ABO blood groups and their associated carbohydrates Allele Carbohydrate Genotype Red blood cell appearance Phenotype (blood group) I A I A or I A i A B I B I B or I B i IAIBIAIB AB iiO (b) Blood group genotypes and phenotypes

Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus For example, in mice and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair

Quantitative characters are those that vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance 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

Punnett Square Practice Great Punnett Square Problem Web Site Go to Mendelian Genetics

Meiosis The process of making gametes (sex cells such as sperm and egg). Purpose = to reduce the chromosome number in half! 1 Diploid(2N) cell becomes 4 Haploid(N) cells.

Human Meiosis Spermatogenesis produces 4 viable sperm every meiosis. Oogenesis produces 1 viable egg every meiosis and 4 polar bodies. Zygote = fertilized egg which contains the standard number of chromosomes. 46 Zygote

Most of the time, meiosis occurs flawless. However, sometimes, chromosomes, parts of chromosomes, or specific nucleotides get messed up! Genetic disorders are inherited from the parents and can be found in the DNA of every cell.

Nondisjunction Non disjunction results when an entire chromosome does not separate from its sister chromosome. Thus, both chromosomes travel together. Trisomy 21

Cystic Fibrosis Common disorder in Caucasians. Mutation in amino acids that make up a specific transport protein. Thick mucus builds up in respiratory and digestive systems.

Sickle Cell Anemia & PKU Minor changes in the sequence of nucleotides can lead to extreme genetic disorders. Sickle cell anemia PKU

Sex-Linked Inheritance Some inherited traits are located on the X and Y (sex) chromosomes. Hemophilia Pattern baldness Color blindness Duchenne muscular dystrophy

Dominant Inheritance 6-Fingers Huntington’s Disease

Morgan’s Experimental Evidence: Scientific Inquiry The first solid evidence associating a specific gene with a specific chromosome came from Thomas Hunt Morgan, an embryologist Morgan ’ s experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel ’ s heritable factors

Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type) –The F 1 generation all had red eyes –The F 2 generation showed the 3:1 red:white eye ratio, but only males had white eyes Morgan determined that the white-eyed mutant allele must be located on the X chromosome Morgan ’ s finding supported the chromosome theory of inheritance

Eggs F1F1 CONCLUSION Generation P X X w Sperm X Y Eggs Sperm Generation F2F2  w w w w w w w w w w w w w w w

44 + XY Parents 44 + XX 22 + X 22 + X 22 + Y or XX or Sperm Egg 44 + XY Zygotes (offspring) (a) The X-Y system 22 + XX 22 + X (b) The X-0 system 76 + ZW 76 + ZZ (c) The Z-W system 32 (Diploid) 16 (Haploid) (d) The haplo-diploid system

X chromosomes Early embryo: Allele for orange fur Allele for black fur Cell division and X chromosome inactivation Two cell populations in adult cat: Active X Inactive X Black furOrange fur X Inactivation in Female Mammals In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development The inactive X condenses into a Barr body If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character

Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structure: –Deletion removes a chromosomal segment –Duplication repeats a segment –Inversion reverses a segment within a chromosome –Translocation moves a segment from one chromosome to another Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Deletion A B C D E F G HA B C E F G H (a) (b) (c) (d) Duplication Inversion Reciprocal translocation A B C D E F G H A B C B C D E F G H A D C B E F G H M N O C D E F G H M N O P Q RA B P Q R

DNA Technology

TRANSFORMATION

Protein Synthesis The making of Proteins! DNA carries the “blueprints” for the making of every molecule and cellular structure. Transcription Translation