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Mendel and the Gene Idea Chapter 14 http: //sps. k 12. ar. us/massengale/genetics%20 tutorial. htm http: //www. jic. bbsrc. ac. uk/germplas/pisum/zgs 4 f. htm
Transmission of characteristics from parents to offspring = __________ heredity The science that studies how those Genetics characteristics are passed on = _____
Two ideas about how genes are passed: ______Blending genetic material from parents mix (like mixing paint: blue + yellow → green) http: //www. digitalartform. com/archives/images/grad. Color. Mix. jpg Problems: Predicts over time a freely mating population will result in a uniform population of individuals Doesn’t explain traits skipping a generation Particulate parents pass _______on discrete heritable units that keep their separate identities http: //www. magicbob 2000. com/resources/Svengali%20 cards. jpg
http: //strongbrains. com/science/biology/default. htm Gregor Mendel _______________ • • • Father of Genetics Looked at one trait at a time Made experimental crosses Large sample size Kept careful records http: //www. jic. bbsrc. ac. uk/germplas/pisum/zgs 4 f. htm
MENDEL’S PEA EXPERIMENTS Peas are “self pollinating” ie. , egg and sperm come from same plant Mendel’s experiments Allowed him to experiment and observe offspring produced from a variety of known genetic crosses http: //hus. yksd. com/distanceedcourses/YKSDbiology/lessons/Fourth. Quarter/Chapter 11/11 -1/images/Mendel. Experiment. gif
MENDEL’S EXPERIMENTS P 1 generation ____ (_____) parental F 1 ____ generation (______= offspring) filial F 2 ___ generation
PATTERNS ARE THE KEY Image modified from: http: //www. laskerfoundation. org/rprimers/gnn/timeline/1866. html http: //www. accessexcellence. org/AB/GG/mendel. html
Image modified from: http: //www. newtonswindow. com/problem-solving. htm Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 genotype Genetic makeup of organism = _____ phenotype Appearance of organism = ______
MENDEL’S MODEL 1. Alternative versions of genes account for variations in inherited traits. 2. For each trait, an organism inherits TWO alleles. 3. If the two alleles at a locus differ, one determines the organism’s appearance; the other has no effect. 4. The two alleles for a character separate during gamete formation and end up in different gametes.
Image modified from: http: //www. newtonswindow. com/problem-solving. htm 1. Alternative versions of genes account for variations in inherited traits. Trait = ______ Observable characteristic Ex: flower color, height, pod shape From Biology; Miller and Levine; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pearson Education Inc ______ Allele = choices for a trait Ex: blue eyes, green eyes, brown eyes) http: //sps. k 12. ar. us/massengale/genetics%20 tutorial. htm
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 2. For each trait, an organism inherits TWO alleles. Organisms with two identical alleles for a gene HOMOZYGOUS PURE BREEDING = ______OR _______ Organism with two different alleles for a gene HETEROZYGOUS ______ HYBRID = ________OR
3. If the two alleles at a locus differ, one determines the organism’s appearance; the other has no effect. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 _________ = allele that masks DOMINANT the presence of another allele RECESSIVE _________ = An allele that is hidden
4. The two alleles for a trait separate during gamete formation and end up in different gametes. = MENDEL’S LAW OF SEGREGATION Image modified from: http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Crossover. gif
http: //www. tokyo-med. ac. jp/genet/anm/mimov. gi
Mendel’s Law of Independent Assortment http: //fig. cox. miami. edu/~cmallery/150/mitosis/c 13 x 9 independent-assortment. jpg Two or more pairs of alleles segregate independently of one another during gamete formation.
PROBABILITY ________ is the likelihood that a particular event will occur EX: If you close your eyes and pick a disk, what is the probability you will pick the white one? It can be written as a: Fraction ____ 1/4 25% Percent ____ Ratio ____ 1: 3
http: //www. arborsci. com/Cool. Stuff/Coin. Flip. jpg COIN FLIP capital There are 2 possible outcomes: HEADS TAILS The chance the coin will land on either one is: ____ 1/2 ____ 50% ____ 1: 1 Alleles segregate randomly just like a coin flip. . . So can use probability to predict outcomes of genetic crosses.
PROBABILITIES Past outcomes DON’T affect future ones! If last coin flip was heads… there is still a 50/50 chance the next flip will be heads too. Probability works best in predicting a large number of events. The more flips. . . The closer results will be to the expected 50: 50 average.
MULTIPLICATION & ADDITION RULES To determine the probability of two or more independent events: MULTIPLICATION RULE: Multiply the probability of one event by the probability of the other What is the probability two coins tossed simultaneously will both end up on heads? ½X½ =¼ http: //www. arborsci. com/Cool. Stuff/Coin. Flip. jpg
MULTIPLICATION RULE WORKS FOR PREDICTING GENETIC CROSSES, TOO Tt X Tt What is the probability offspring will be tt ? Each egg has a ½ chance of passing on t. Each sperm has ½ chance of passing on t. ½X½ =¼ Punnett by Riedell
ADDITION RULE To figure out the probability of an offspring being heterozygous (Tt) T can come from mom and t from dad OR t can come from the mom and T from the dad but not both (events are mutually exclusive) 1 st probability T from mom t from dad ½X½ =¼ 2 nd probability t from mom T from dad ½X½ =¼ ¼+¼=½ Punnett by Riedell
HOW CAN YOU TELL THE GENOTYPE? Tall plant has two possible genotypes ___ TT OR ___ Tt TEST CROSS Make a ______ with a ___________ HOMOzygous recessive t t T T Tt Tt t T Tt t tt t Tt tt Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing © 2006
GENES are more complicated than Mendel thought 1. Environment influences gene expression 2. Spectrum of dominance 3. Multiple allele traits 4. Polygenic traits 5. Gene Linkage 6. Pleiotropy 7. Epistasis
Environment influences Phenotype “Nature vs Nurture” • Siamese cats and Himalayan rabbits have dark colored fur on their extremities • Allele that controls pigment production is only able to function at the lower temperatures of those extremities. Images from slide show by Tracy Nelson
Environment influences Phenotype “Nature vs Nurture” • Color of hydrangea flowers varies depending on p. H of soil Images from: http: //www. gardensablaze. com/Shrubs. Hydrangea. htm
GENES are more complicated than MENDEL thought Spectrum of DOMINANCE COMPLETE DOMINANCE ____________________ INCOMPLETE DOMINANCE CO-DOMINANCE __________
COMPLETE DOMINANCE If two alleles are present DOMINANT allele masks the RECESSIVE allele Recessive trait shows again in F 2 generation in 3: 1 ratio http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Bio. Book. TOC. html
INCOMPLETE DOMINANCE Heterozygous snapdragons show a blended intermediate trait Image modified from: http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Bio. Book. TOC. html
CO-DOMINANCE BOTH traits are expressed at the same time side by side in heterozygote A ROAN HORSE has both RED and WHITE hair side by side
CO-DOMINANCE Both traits are expressed together (NO BLENDING) in heterozygote Persons with an A allele AND a B allele have AB blood type
REMEMBER • Membrane proteins with sugars attached that help cells “recognize self” GLYCOPROTEINS = _______ • Type of sugars attached gives cell its “Blood type” • I is used for blood type alleles http: //www. mannanw. com/super-sugars. htm
BLOOD TYPES Person with IA IA OR IA i genotype has cells with a certain glycoprotein “A” on its surface TYPE “A” BLOOD
BLOOD TYPES Person with IB IB OR IB i genotype has cells with a different glycoprotein “B” on its surface TYPE “B” BLOOD
BLOOD TYPES Person with i i genotype have neither “A” nor “B” glycoproteins on their surface TYPE “O” blood Note: Cells have other glycoproteins… just not A or B
A and B are CO-DOMINANT Person with IA IB genotype has BOTH “A” and “B” glycoproteins on its surface TYPE “AB” Blood
BLOOD TYPE FREQUENCY IN USA A B AB O 40% 10% 4% 46% http: //www. reachoutmichigan. org/funexperiments/agesubject/lessons/newton/Bld. Typing. html
BLOOD TYPES DONOR BLOOD YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from: http: //www. new-fitness. com/images/body_shapes. jpg See A blood cells as DIFFERENT! IMMUNE SYSTEM ATTACKS!
BLOOD TYPES DONOR BLOOD YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from: http: //www. new-fitness. com/images/body_shapes. jpg A and O see B cells as DIFFERENT! IMMUNE SYSTEM ATTACKS!
BLOOD TYPES DONOR BLOOD YOU’RE LIKE ME! Body images modified from: http: //www. new-fitness. com/images/body_shapes. jpg A, B, and O see AB cells as DIFFERENT! IMMUNE SYSTEM ATTACKS!
BLOOD TYPES YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from: http: //www. new-fitness. com/images/body_shapes. jpg ____ O can donate to EVERY BLOOD TYPE = ___________ UNIVERSAL DONOR NO A’s or B’s on surface to recognize as “NOT SELF”
BLOOD TYPES AB can RECEIVE FROM ______ EVERY BLOOD TYPE UNIVERSAL RECIPIENT = ____________ Body image modified from: http: //www. new-fitness. com/images/body_shapes. jpg
ABO SYSTEM is NOT THE ONLY ONE + Rh Rh
OTHER BLOOD TYPES NO PROBLEMS IF: Rh+ MOM is _____ & BABY is _____ Rh+ Image modified from: http: //www. wsd 1. org/lessonplans/images/Body. gif MOM is _____ Rh+ & BABY is ____ Rh-
PROBLEM IF: Can be a ______ Mom is _____ Rh- Baby is _____ Rh+ Image modified from: http: //www. wsd 1. org/lessonplans/images/Body. gif 1 st baby OK but few baby cells entering mom’s bloodstream put mom’s immune system on alert for + cells. Next + baby, mom’s immune system can attack baby as it is growing = ERYTHROBLASTOSIS FETALIS Mom given shot (Rho. GAM) after birth to prevent this
GENES are more complicated than Mendel thought MULTIPLE ALLELE TRAITS have MORE THAN 2 allele choices EX: blood type A ___ B ___ O Allele choices ___
GENES are more complicated than MENDEL thought POLYGENIC TRAITS are governed by the cumulative effect of MORE THAN ONE GENE Polygenic traits show a whole range of in-between phenotypes EX: human height. intelligence, skin & eye color http: //www. bcps. org/offices/lis/models/life/images/grow. JPG
POLYGENIC traits are recognizable by their expression as a gradation of small differences (a continuous variation). The results form a bell shaped curve. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Linked Genes • Genes close together on same chromosome are called linked genes • Linked genes do not exhibit independent assortment and they move together during crossing over if they are very close together on the chromosome. http: //anthro. palomar. edu/biobasis/bio_3. htm
Sex Linked Genes carried on the X chromosome are called X-linked traits. • Red-green colorblindness, hemophilia, an Duchenne muscular dystropy are examples of X-linked traits. http: //gizmodo. com/gadgets/peripherals/samsung-develops-lcd-for-colorblind-036306. php
Y-LINKED GENES: Genes carried on the Y chromosome Y-linked genes only show up in MALES Hairy pinnae SRY gene initiates male sex determination http: //www. ndpteachers. org/perit/hairears. gif http: //content. answers. com/main/content/wp/en/thumb/f/fb/200 px-YChrom. Showing. SRY 2. png
X and y chromosomes NON-HOMOLOGOUS partners
PLEIOTROPY Most genes have multiple phenotypic effects Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
EPISTASIS • Gene at one locus alters the phenotypic expression of a gene at another locus EX: Coat color in mice B = Black b = brown C = color deposited in coat c = color NOT deposited cc-mouse looks white even though it has color genes Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Pedigrees are diagrams that show genes are passed on in families over several generations Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pedigrees can be used to predict future offspring in families with genetic disorders
Drawing a pedigree chart
http: //www. ikm. jmu. edu/Buttsjl/ISAT 493/Hemophilia/hemophiliaeurope. html
Human Genetic Disorders
THINK ABOUT IT What does a can of Diet Coke and this song have to do with human genetics? (Answers to come in this slide show!)
MANY HUMAN GENES HAVE BECOME KNOWN THROUGH THE STUDY OF GENETIC DISORDERS result from Many genetic ______ changes in the DNA code so NON-FUNCTIONING _________ proteins are produced. http: //patentdocs. typepad. com/photos/uncategorized/2007/05/28/dna 1. gif
A mutation in an allele that causes a protein to be NON-FUNCTIONAL would appear ________ to the normal working allele. RECESSIVE Examples of _____________ AUTOSOMAL RECESSIVE GENETIC DISORDERS: PHENYLKETONURIA (PKU) __________ TAY-SACHS DISEASE ____________________ CYSTIC FIBROSIS
Phenylketonuria (PKU) CAUSE: Mutation in gene for an enzyme the breaks down an amino acid called phenylalanine MENTAL RETARDATION Build up causes ____________ http: //biology. clc. uc. edu/courses/bio 104/protein. htm
Phenylketonuria (PKU) ALL babies are tested for PKU before they leave the hospital. Treatment: Need a diet low in phenylalanine to extend life and prevent mental retardation Amino acid If phenylalanine is an _______, what type of foods should PKU patients avoid? PROTEINS ! _________
THINK ABOUT IT What does a can of Diet Coke have to do with human genetics? LOOK AT THE WARNING LABEL ! NUTRASWEET is made with phenylalanine _______
CYSTIC FIBROSIS CAUSE: • Loss of 3 DNA bases in a gene for the ion channe protein that transports Cl- ions • Salt balance is upset • Causes a build up of thick mucous in lungs and digestive organs thick mucous Image from: BIOLOGY by Miller and Levine; Prentice Hall Publishing © 2006
CYSTIC FIBROSIS Leads to: Respiratory and digestive complications, increased susceptibility to infections; “Salty skin” is a symptom More common in Caucasians but can affect all races. 30, 000 people in U. S. have cystic fibrosis 1 in 31 people are carriers
CARRIER Heteroygous individual That carries one recessive allele for a genetic disorder Doesn’t show the disorder themselves, but can pass it on to offspring http: //www. biochem. arizona. edu/classes/bioc 460/spring/rlm/RLM 36. 1. html
TAY-SACHS DISEASE AUTOSOMAL RECESSIVE __________ CAUSE: Mutation in gene for an enzyme the breaks down a kind of lipid in the developing brain As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death. Found more frequently in people with Jewish, Mediterranean, or Middle Eastern ancestry Image from: http: //www. djsfoundation. org/images/Steeler%20 pics%20 Dylan. jpg
DISORDERS CAUSED AUTOSOMAL CODOMINANT ALLELES BY __________ SICKLE CELL DISEASE __________ CAUSE: A changed to T in gene for HEMOGLOBIN _________ (protein in red blood cells that carries oxygen in blood)
SICKLE CELL DISEASE SYMPTOMS: Red blood cells become sickle shaped under low oxygen condition in persons with two sickle cell alleles (ss) Ss=Sickle cell trait Normally healthy, but can suffer some sickle cell episodes
SICKLE CELL DISEASE Circulatory problems Cells stick in capillaries Loss of blood cells (anemia) Organ damage (brain, heart, spleen) Can lead to DEATH
SICKLE CELL DISEASE AFRICAN AMERICANS More common in _________ 1 in 400 = have sickle cell disease 1 in 10 = carriers for allele MEDITERRANEAN Also affects persons of ________ MIDDLE EASTERN and _________ descent Why do so many African Americans carry the sickle cell allele?
SICKLE CELL DISEASE Many can trace their ancestry to west MALARIA central Africa where ______, a serious parasitic disease that infects red blood cells is common. Watch a video about sickle cell and malaria Images from: http: //en. wikipedia. org/wiki/Malaria
AT MOLECULAR LEVEL Sickle cell allele is CODOMINANT ss- has abnormal hemoglobin; unhealthy SS-has normal hemoglobin and can be infected with malaria Ss-makes both normal and abnormal hemoglobin; resistant to malaria infection Sickle cell disease is a trade off for malaria resistance
GENETIC LINK TO DISEASE • Many human genetic disorders may be the small “price we pay” for mutations that provide protection from otherwise lethal diseases • Persons heterozygous for cystic fibrosis are resistant to typhoid • Changes in Vitamin D receptors confer resistance to tuberculosis, but result in greater susceptibility to osteoporosis
CLOSER LOOK AT RELATIONSHIP BETWEEN DOMINANCE AND PHENOTYPE REVEALS AN INTRIGUING FACT: DOMINANCE ? CODOMINANCE? INCOMPLETE DOMINANCE ? Depends on how you look at it!
Image from: http: //www. djsfoundation. org/images/Steeler%20 pics%20 Dylan. jpg TAY-SACHS DISEASE Human genetic disorder in which brain cells are unable to metabolize certain lipids because a crucial enzyme does not work properly. As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death. At ORGANISMAL LEVEL acts as a recessive trait. Child with two copies of Tay-Sachs allele (tt-homozygous) has the disorder. Child with Tt or TT does not (COMPLETE DOMINANCE) At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level in between the TT and tt person (INCOMPLETE DOMINANCE ? ) At the MOLECULAR LEVEL – Tt individual makes equal number of normal and dysfunctional enzyme molecules (CODOMINANT ? )
HUNTINGTON’S DISEASE AUTOSOMAL DOMINANT ___________ CAUSE: CAG repeats at end of gene Extra 40 -100 _______ on chromosome 4 more repeats. . . the more _____ severe The _______ the symptoms. http: //www. healthsystem. virginia. edu/internet/huntdisease/images/cag. gif
HUNTINGTON’S DISEASE Huntington’s brain Begins in middle age Causes progressive loss of muscle control and mental function 1 in 10, 000 people in U. S. have Huntington’s disease Normal brain http: //www. scielo. br/img/revistas/bjmbr/v 39 n 8/html/6233 i 01. htm
A person with Huntington’s disease 50% chance of has a _____ passing the disorder on to their offspring. Problem: Symptoms of disorder usually don’t show until ______ MIDDLE AGE. . . so you don’t know you have it until ____ AFTER you have had children.
THINK ABOUT IT Click to hear Woody’s song What does the song have to do with human genetics? “This Land is My Land” was written by a musician named Woody Guthrie before he began to show the symptoms of Huntington’s disease.
Woody Guthrie had a son named Arlo that was a popular musician during the 70’s Click to hear one of Arlo’s songs Before 1993 there was no test for Huntington’s. If one of your parents showed symptoms, you had to wait to see if it had been passed on to you.
http: //www. jimdirden. com/woodyfest 2004/artists/index_3. htm Arlo Guthrie is still performing today. He never developed symptoms for Huntington’s disease. If there is no cure, would you want to be tested and find out if you have the gene? http: //webs. wichita. edu/depttoolsmemberfiles/accomp/question_mark%20(Win. CE). jpg
ACHONDROPLASIA (One kind of Dwarfism) AUTOSOMAL DOMINANT CAUSE: ______________ gene 1 in 25, 000 births DD = lethal Dd = dwarf phenotype dd= = normal height 200, 000 “little people” worldwide One of oldest known disorders – seen in Egyptian art
ACHONDROPLASIA (One kind of Dwarfism) Normal size head and torso; short arms and legs Problem with way cartilage changes to bone as bones grow
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006
KARYOTYPE is a picture of A _____ an organism’s chromosomes
SEX DETERMINATION XX = female Xy = male
• • Karyotype can show: Sex of baby Missing or extra chromosomes Major deletions or translocations Can’t see individual gene changes http: //content. answers. com/main/content/wp/en/1/11/Down_Syndrome_Karyotype. png http: //content. answers. com/main/content/wp/en/thumb/f/f 3/220 px-Down_syndrome_translocation. png