DNA Lecture 009

Gregor Mendel

Rosalind FranklinFrances Crick & James Watson X-ray diffraction photograph of DNA, 1953 Proposed double helix model 1953

Cell

Nucleus

DNA

What is DNA? DNA, or deoxyribonucleic acid, is the genetic instruction set. It is composed of a linear sequence of units called nucleotides. There are four different kinds of nucleotides (designated by the letters A, G, C, & T; sometimes called “bases”). An individual DNA strand (or chromosome) may consist of 100,000’s of nucleotides. The sequence of the nucleotides of a DNA strand determines the genetic code.

Polymers made up of individual nucleotides Nucleotides contain Phosphate group Five carbon sugar Ring shaped nitrogen base DNA contains information for almost all cell activities

Nitrogen Base

adenineguanine Purines

cytosine thymine Pyrimidines

Deoxyribose

DNA is Double Stranded

Base Pairing in DNA

Chromosomes

Chromosomes Come in Pairs

Beliefs about Heredity Fig. 1. De la propagation du genre humain, ou manuel indispensable pour ceux qui veulent avoir de beaux enfants de l’un ou l’autre sexe (Paris, Year VII). Image courtesy of the Bibliothèque Interuniversitaire de Médecine, Paris.

Homunculus How is “heredity passed on: Spermist vs Ovists Spermist conception of a human sperm

Homunculus Leeuwenhoek’s black male and white female rabbit experiments: spermist “proof”

Darwin What he got right.What he got wrong. Acquired characteristics Ex. Blind cave animals Sex. Repro.- gemmules from all over body are packed in sperm and egg Blended inheritance Likes produce likes Change can be permanent There is no limit to cumulative change

Mendel’s Three Principles Dominance Segregation Independent Assortment The foundation of “classical” science ( )

Genes- genetic material on a chromosome that codes for a specific trait Genotype- the genetic makeup of the organism Phenotype- the expressed trait Allel- an alternative form of a gene Genetic Definitions

Dominance Mechanism Two alleles are carried for each trait In true-breeding individuals, both alleles are the same (homozygous). Hybrids, on the other hand, have one of each kind of allele (heterozygous). One trait is dominant, the other trait is recessive

Dominance Traits of both parents inherited, but one shows over the other Traits are not blended

Segregation Half the gametes (egg or sperm) will carry the traits of one parent and half the traits for the other parent Pairs of alleles are separated (=segregated) during meiosis

Two different parental characteristics will be inherited independently of one another during gamete formation. Independent Assortment Example: flower color and leaf shape

Complexities Multiple genes for one trait Example: eye color Blended traits (“incomplete dominance”) Influence of the environment (UV, smoking, alcoholism)

Complexities Co-dominance-neither allele is recessive and the phenotypes of both alleles are expressed. Blood types- AB (not O); sickle cell anemia heterochromia

Disorders Down’s Syndrome (chrom 21) Huntington’s (chrom 4) Alzheimer’s (chrom 1, 10, 14, 19, 21)

Genetic Information Genes are traits “Eye color” Ear lobe connectedness Genes produce proteins Enzymes are proteins

Homologous Chromosomes allele: specific trait gene: location

Allele Example Gene = “eye color” Alleles brown blue green lavender

Allele Examples appearance eye color: homozygous

Allele Examples appearance eye color: heterozygous, brown dominant over blue

Genotype vs Phenotype homozygous (dominant) heterozygous homozygous (recessive) genotype phenotype appearance Phaner = visible

Punnett Square If male & female are heterozygous for eye color X brown:3/4 offspring blue:1/4 offspring male female

Sickle Cell Anemia Each parent carries one gene for sickle cell Ss Ss X S s sS S S S s s S s s Possible genotypes: 1SS 2Ss 1ss Possible phenotypes:no sickle cellsickle cell

Autosomes and Sex Chromosomes

Red-Green Color Blindness Sex-linked trait XCXC Y XCXC XcXc X XCXC XcXc YXCXC XCXC XCXC XCXC Y XcXc XCXC Y XcXc Normal male Normal female recessive gene Possible outcomes:X C X C X C X c X C YX c Y Normal female Normal Female (carrier) Normal male Color-blind male

Eunconnected earlobe econnected earlobe Eunconnected earlobe econnected earlobe allele gene PEE x ee gametes E e F1F1 unconnected connected

F1F1 Ee x Ee gametes 1/2 E 1/2 e E e Ee EEEe ee F2F2 1 EE 2 Ee 1 ee Punnett Square

Genotypes Phenotypes Experiment to determine dominant vs. recessive

Genetic Sleuthing My eye color phenotype is brown. What is my genotype?

Where Does Genetic Diversity Come From? MutationMutation Chromosomal AberrationsChromosomal Aberrations Genetic Recombination (e.g., from sexual reproduction)Genetic Recombination (e.g., from sexual reproduction)

mutation Sickle Cell Mutation CTG ACT CCT GAG GAG AAG TCT Leu Thr Pro Glu Glu Lys Ser CTG ACT CCT GAG GTG AAG TCT Leu Thr Pro Glu Val Lys Ser NORMAL Hb SICKLE CELL

Difference between Meiosis and Mitosis

Meiosis I Interphase Prophase IMetaphase IAnaphase ITelephase I

Crossing Over of Nonsister Chromatids between Homologous Chromosomes

Meiosis II Prophase IIMetaphase IIAnaphase IITelephase II

Genetic Testing

Predisposition to disease Alzheimer's case (Feb. 2002) Amniocentesis & Chorionic villa Family history >35 years old Donor match Paternity Forensics

Gel electrophoresis

PCR way of copying specific DNA fragments from small sample DNA material "molecular photocopying" It’s fast, inexpensive and simple Polymerase Chain Reaction

Genetic Testing Paternity Test $99 $299, looks at specific diseases 23 and me

Genetic Testing Would you want to know? Ethical concerns Cost Insurance companies

Tongue Roller R = Tongue Roller r = Unable to Roll Tongue

Widow’s Peak W = Widows Peak w = Lack of Widow’s Peak

Free Ear Lobe Attached Ear Lobe E = Free Ear Lobe e = Attached Ear Lobe

Hitchhiker’s Thumb Hi = Straight Thumb hi = Hitchhiker’s Thumb

Bent Little Finger Bf = Bent Little Finger bf = Straight Little Finger

Mid-digital Hair M = Mid-Digital Hair m = Absence of Mid-Digital Hair

Dimples D = Dimples d = Absence of Dimples

Short Hallux Ha = Short Hallux ha = Long Hallux

Short Index Finger S s = Short Index Finger S 1 = Long Index Finger *Sex-Influenced Trait

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