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Genetics - PowerPoint PPT Presentation

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Genetics. Genetics. Molecular Genetics: study of the structure and function of chromosomes and genes Heredity: transmission of characteristics from parents to offspring Trait: two contrasting choices Genotype: genetic makeup of organism (TT, Tt, tt)

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Molecular Genetics:study of the structure and function of chromosomes and genes

Heredity:transmission of characteristics from parents to offspring

Trait:two contrasting choices

Genotype:genetic makeup of organism (TT, Tt, tt)

Phenotype:what is physically observed (tall, short)

Heterozygous:two different alleles (Tt); hybrid

Homozygous:two identical alleles (TT, tt); purebred


Gregor Mendel

  • Austrian Monk, born in 1822
  • University of Vienna
  • Job at monastery was to teach science and tend the garden
  • Major study done on characteristics of pea plants


  • Pollination:pollen grains from male part of plant fertilize the egg from the female portion of the plant
  • Self-Pollination:pollen and egg from same plant; all offspring characteristics the same as parent (Pea Plants)
  • Cross- Pollination:pollen and eggs from different plants; offspring characteristics formed from a combination of parental genes

Parts of the Flower

  • Male:
    • Stamen:anther + filament
    • Anther:produces pollen grains
    • Filament:holds up anther
  • Female:
    • Stigma:top of pistil, sticky to catch pollen
    • Style:tube leading from stigma to ovary
    • Ovary:contains ovules
    • Ovules:when fertilized will become seeds

Pea Plants

  • Closed petals
  • Always self-pollination
  • Purebred:if allowed to self-pollinate, all offspring identical to parents
    • EX:all short, tall
  • Experiment:Mendel prevented self-pollination by removing stamen and using a paint brush to transfer pollen grains to stigma
  • Results
  • Hybrids:produced by crossing parents with different characteristics


  • Dominant Traits:characteristic that when present is always expressed
  • Recessive Traits:masked by dominant trait; only appears if there are two copies
  • P-Generation:purebred parent generation; produce offspring identical to themselves
    • Ex:Mendel found: tall/tall produced only tall, short/short only short
  • F1- Generation:first filial generation; produced by cross-pollination
    • Ex:Mendel found tall/short produced tall plants
  • F2- Generation:second filial generation; offspring of crossed F1
    • Ex:tallF1/tallF1 = tall and short plants

Parent Generation

TT or tt

F1 Generation

TT x tt

Punnett Squares

  • A diagram to aid in predicting the probability that certain traits will be inherited.
  • Monohybrid Cross:Punnett square involving only one trait (2x2)

F2 Generation:Tt x Tt


T t

Genotypic Ratio:


Genotypic Ratio:

4:0 Tt





Phenotypic Ratio:


Phenotypic Ratio:

4:0 tall


Mendel's Conclusions

  • Gene:individual factors that do not blend with one another; control traits in living things
  • Allele:each alternative for a gene; genes/chromsomes occur in pairs; Ex: T and t
  • Law of Segregation:Alleles are segregated (separated) during meiosis. Only one allele from parent is present in gamete. Occurs during anaphase when chromatids separate.
  • Law of Independent Assortment:factors for different traits are separated during meiosis; dominant traits are not necessarily inherited together


  • How can you tell if a phenotypically dominant organism is homozygous or heterozygous?
  • Cross with a recessive
  • If homozygous: offspring will all be dominant.
  • If heterozygous: offspring will be both dominant and recessive.

Gene Interactions

  • Complete Dominance:when one allele totally masks the other allele
    • Dominant trait occurs with TT or Tt, recessive only tt
    • Ex:Tall plants, rolling tongue upwards, crossing hands
    • Ratio when crossing two heterozygous: 3:1

Gene Interactions

  • Incomplete Dominance:occurs when two or more alleles influence the phenotype; when heterozygous, results in a third BLENDED phenotype
    • Ex:Red and white flowers = pink
    • Ratio: 1:2:1

Gene Interactions

  • Codominance:occurs when both alleles for a gene are expressed in a herterozygous offspring; DO NOT BLEND, both are equally dominant
    • Ex: Roan Horse
    • Ratio: 1:2:1

Sickle Cell Anemia

  • Recessive
  • Defective Hemoglobin on RBCs
  • Anemia (loss of blood cells)
  • Damage to brain, heart, lungs
  • Primarily in African Americans; 1/10 in US is a carrier

Cystic Fibrosis

  • Recessive
  • Point mutation stops production of a protein in the lungs and pancreas
    • Prevents cells from transporting Cl- ions out of the cell
  • Lung Congestion
    • Abnormally thick mucus lining in lungs
    • Chronic Bacterial Infections (pneumonia)
    • Treated with antibiotics, lung transplant, and new genetic engineering treatments

Tay Sachs

  • Recessive
  • Lack of enzyme hexosaminidase A (hex A), which breaks down fatty acids in brain in nervous tissue
  • Symptoms appear at 4-6 months
  • Death by 5 years
  • Found primarily in those descendants of Ashkenazi Jews
    • 1/30 American Jews carry the gene

Huntington's Disorder

  • Autosomal- Dominant
  • Lethal
  • Begins around ages 35-45
  • First symptoms; mild forgetfulness and irritability
  • Lose control over muscles
  • Genetic Marker: short section of DNA that has a close association with a known gene
    • Presence of gene marker can indicate the presence of huntington’s allele
    • People with marker have 90% chance of developing Huntington’s
    • Gene Marker and gene so close on chromosome rarely separated by crossing over during meiosis

Marfan's Syndrome

  • Dominant Disorder
    • 1/20,000 people
  • Believed to be caused by a mutation in the fibrillin gene on chromosome 15
  • Connective Tissue defects
  • Dislocation of lens in eye
  • Rupture of aorta (weak vessel walls)
  • Arachnodactyly – “spider fingers”
  • Elongated body, face
  • Pectus Excavatum (caved in chest)

Marfan's Syndrome

  • Abraham Lincoln?
  • Descendents of Lincoln’s great-great grandfather (8th generation) diagnosed with Marfan’s
    • Lincoln could have had a mild form of Marfan’s
  • Should we test Lincoln’s DNA?

Phenylketonuria (PKU)

  • Do not contain enzyme phenylalanine hydroxlyase (PAH) that breaks down amino acid phenylalanine into amino acid tyrosine
    • Phenylalanine builds up in brain
    • Toxic to central nervous system (CNS)
    • Mental Retardation
  • Tested at birth
  • PKU – 1/10,000
    • U.S.  1/50 carry PKU allele
  • Regulated by Strict diet
    • Low protein: no meat, eggs, dairy
    • No Aspartame: sugar substitute sold as Equal or NutraSweet
      • Contains amino acid phenylalanine – 50%

Dihybrid Cross

  • Cross that involves two traits; more allele combinations possible; 4x4 Punnett Square
    • Ex: Peas  Green/Yellow & Round/Wrinkled
    • Ratio: 9:3:3:1

Multiple Alleles

  • 3 or more alleles for a single trait
  • EX:ABO blood groups – blood types
  • Characterized by the presence or absence of antigens
    • 4 Types: A, B, AB, o
    • A Blood has A antigen but no B, AB has both, O has neither
    • Represented by I (isoagglutination)
  • Codominant

Sex-Influenced Traits

  • Sex- Influenced:
    • Presence of male or female hormones influences the expression of the trait
    • Males and females with the same genotype will have different phenoypes
      • Ex: baldness; B=baldness, B’=normal hair
      • BB=bald (male/female)
      • B’B’=normal hair (male/female)
      • BB’= bald (male) normal (female)

Sex Linkage

  • Presence of gene on a sex chromosome (X or y)
  • X chromosome is larger than y  more genes carried on the X
  • X-Linked Genes:genes found on X chromosome
    • Appear mostly in males
    • Only one copy of X; nothing to counteract “bad gene”
    • Females would need two copies to express trait


  • X-linked recessive
  • Cannot distinguish between different colors
  • Most common type is red/green colorblindness
  • Heterozygous females have mosaic retinas in which they have patches of color vision
  • Heterozygous female is considered a carrier


  • X-linked recessive
  • Most Common in males
  • “Bleeder’s Disease”
  • Missing clotting factor
  • Bleeding spontaneously and in joints
  • Queen Victoria: descendents affected with hemophilia
    • Alexei Romanov

Duchenne Muscular Dystrophy

  • X-linked recessive
  • Most Common in males
    • 1/3500
  • Muscle Enlargement
  • Dystrophin
    • Protein that provides support for the cell; without it, cell enlarges and explodes


  • X-linked recessive
  • Most Common in males
  • “Lorenzo’s Oil”
  • Degradation of myelin sheath surrounding nerves (insulation)
  • Current News:
    • Oil not as effective as previously thought
    • Cholesterol lowering drug, Lovastatin seems to work
    • Bone Marrow Transplants work in some cases
    • Lorenzo Odone turned 27 on May 29, 2005 (Still completely paralyzed)


  • Barr Body
    • Only in females
    • Inactivated X chromosome
    • Random whether mom’s or dad’s X
    • Dark staining mass in nucleus
    • Allows for equal genetic expression between males and females (both express 1 X)
  • X-inactivation:
    • EX:Calico Cat
      • Coat color is X-linked recessive
      • Large patches of color (Black or orange)
      • Not in males because they only have 1 X

Genomic Imprinting

  • Genomic Imprinting: variation in phenotype expression depending on which parent gave the chromosome
    • Chromosome “remembers” which parent it came from
    • EX: Deletion of Chromosome 15
    • Prader-Willi: uncontrollable eating, diabetes, mental retardation
      • Deletion of portion of paternal 15
    • Angleman’s: behavior problems, some mental retardation
      • Deletion of portion of maternal 15

Holandric Traits

  • Holandric Traits: genes on the y chromosome; carry genes for male sexual characteristics
    • Absence of these genes causes female development
    • Small arm of y chromosome responsible for individuals that have a sex chromosome combination that does not match their appearance
      • XX males and XY females due to absence or presence of SRY factor
    • Ghengis Khan
      • Mongolian warrior 13th century
      • 8% of men living in region that was once Mongolian empire have same y chromosome

Mitochondrial DNA

  • mDNA inherited strictly from the mother
  • 600 bp region that is extremely different in unrelated individuals
  • Romanovs:
    • Tsar Nickolas II of Russia murdered during Bolshevik Revolution in 1918
    • Remains identified by comparing mDNA to maternal descendants
    • Anna Anderson: pretended to be Anastasia
      • Proved false by mDNA

Marriage Line:





Fraternal Twins:

Identical Twins:

Pedigree Charts

  • Pedigree:family record that shows how a trait is inherited over several generations
    • Shows both recessive and dominant traits
    • First Step in genetic counseling
  • Symbols:

Point Mutations

  • Gene Mutation: affects either one nucleotide or one codon
  • Substitution: one nucleotide is replaced with a different nucleotide resulting in a new codon
    • If new codon codes for same amino acid – no effect
    • If new codon codes for a different amino acid or stop codon – incorrect protein
    • Ex: Sickle Cell Anemia
      • Substitution: Adenine replaced by Thymine in a single codon; results in a defective form of hemoglobin
  • Frame-shift Mutation: caused by additions and deletions of one nucleotide; all codons after mutation are grouped incorrectly
    • Mutation at beginning of gene is worse than near the end of gene

Chromosomal Mutations

  • Germ-Cell: occurs in gametes; only affect offspring
  • Somatic Cell: affects body cells; only affects organism
  • Lethal: causes death; often before birth (miscarriages)
  • Chromosome: changes to part or the whole chromosome; cannot be repaired by enzymes
  • Deletion: loss of a piece or whole chromosome
  • Inversion: segment of chromosome breaks off and reattaches in the reverse order on same chromosome
  • Translocation: piece of chromosome breaks off and reattaches to a nonhomologous chromosome
    • Down’s Syndrome: Trisomy 21; 3rd 21 can translocate to chromosome 13 (young mothers)
  • Duplication:part of chromosome attaches to homologous chromosome giving two copies of gene on that chromosome
  • Nondisjunction: failure of a chromosome to separate from its homologous chromosome during anaphase of meiosis; one gamete receives extra copy of chromosome other gamete does not receive one


  • Karyotype: chromosomes are stained and photographed under the microscope, cut from photo and arranged by size and shape; can detect chromosomal abnormalities
  • Monosomy: a zygote with only 45 chromosomes; one copy of a chromosome
  • Trisomy: three copies of a chromosome; 47 chromosomes total
    • Both result from nondisjunction

Down's Syndrome

  • Trisomy 21
  • Mild to severe mental retardation
  • Distinct Facial Features
  • Heart Defects
  • Fingerprints – Sworl
  • Most Common Birth Defect – 1/700 births
  • Mother’s Age over 40 – 1/80
    • Problems during Oogenesis

Klinefelter's Syndrome

  • Trisomy of sex chromosomes; XXy male
  • Feminine Characteristics, Infertile
  • George Washington?
    • No Children – Sterile?
    • Dental Problems
    • Height – Very tall for generation
    • Still Inconclusive

Turner's Syndrome

  • Monosomy of Sex Chromosomes; XO female
  • Infertile
  • Dwarfism
  • Overweight
  • Some mental retardation
  • Webbed Neck

Edward's Syndrome

  • Trisomy 18
  • Elfin Appearance
  • Low set ears
  • Malformation of many organs – specifically heart/lungs
    • “Blue Babies” due to lack of oxygen
  • 90% die within first 6 months

Patau's Syndrome

  • Trisomy 13
  • Cleft Lip and Palate
  • Polydactyl – more than ten fingers/toes
  • 1/6000 births
  • Most die within first year


  • “Cat’s Cry” Syndrome
  • Deletion of a portion of Chromosome 5
  • Mental Retardation

Reproductive Technology

  • Invitrofertilization (IVF):“test tube babies”
  • Procedure:
    • Woman treated with fertility drugs to regulate menstrual cycle and develop high quality eggs
    • Eggs collected using a needle
    • Fertilization occurs in a Petri dish
    • Within 72 hours embryos transferred to uterus
    • Multiple births often occur
  • Artificial Insemination: fertilization occurs within uterus (in vivo)
    • Sperm inserted through a catheter passing through the cervix into the uterus

Ultra Sound

  • High frequency sound waves with computer produce image
  • Locate fetus during amniocentesis and CVS
  • Estimate fetal age, sex, twins
  • 600 disorders can be diagnosed prenatally
  • Spina bifida, heart defects, dwarfism, hydrocephalus (water on brain)

Fetal Cells

  • Fetal Cells obtained from either amniocentesis or chorionic villi sampling (CVS)
  • Cultured and a karyotype created to diagnose genetic disorders
  • Alphafetoproteins (AFP) levels indicated in sample; different levels signal defects
    • Low AFP levels
      • Down’s Syndrome
    • High AFP levels
      • Spina Bifida: spinal cord not contained within spinal column
      • Twins

Genetic Screening

  • Genetic Screening: a person with family history for genetic disorders are screened before deciding to have children
    • Karyotype of individual created to check for any chromosomal abnormalities
  • Genetic Counseling:couples at risk for having children with genetic disorder seek medical guidance to determine their chances of having a child with a disorder
    • Punnett Squares


  • Needle removes small amount of amniotic fluid from sac surrounding baby
  • 14th – 16th week
  • Fetal cells and proteins are analyzed
  • Karyotype

Chorionic Villi Sampling (CVS)

  • Through cervix and vagina, remove sample of chorion (tissue between uterus and placenta)
  • Same DNA as baby
  • 8th – 10th week
  • Fast results since cells grow faster
  • Dangerous to fetus

Preimplantation Genectic Diagnosis (PGD)

  • Identify embryos that do not carry gene for inherited disease
    • Cystic Fibrosis, sickle cell anemia
  • Reduces the risk diseases are passed on to children
  • Genetic Analysis of one cell from embryo before implantation
    • Biopsied with needle under microscope; doesn’t harm development of healthy fetuses (cells – blastomeres)
    • Only healthy embryos implanted; some are saved for later use
    • DOES NOT ALTER genetic material
    • DOES NOT always occur prior to in vitro
  • PGD for X-Linked: sex determination
    • Only not at risk females are implanted
    • Gender selection and family balancing
    • Check for Huntington’s disease, CF, chromosomal translocation when one parent has a translocation and they cause miscarriages in those babies produced

Sources: Pictures (Gregor Mendel) (Pea Plants) (Flower Diagram) (Incomplete Dominance) (Roan horse) (Dihybrid Cross) (Lincoln) (Blood Types) (x-linked inheritance) (romanovs) (Nondisjuntion) (Mutations) (Sickle Cell) (Blood Typing) (Colorblindness Retina) (Y Chromosome) (Hemophilia Punnett Square) (Hemophilia Knee) (Queen Victoria’s Pedigree) (DMD Photo) (Lorenzo Odone) (Barr Body) (Calico Cat)


Sources: Pictures conti. (Sickle Cell) (Cystic Fibrosis Chest Scan) (Tay Sachs Tissue Sample) (Marfan’s Diagram) ency/esp_imagepages/2927.htm (Pectus Excavatum) GettysburgAddress.htm (Abraham Lincoln) 11nondisjunction.gif (Nondisjunction) mutations3_rev.shtml (Down’s Syndrome Karyotype) issue7329/twib.shtml (Down’s Syndrome) 18258/ped-karyo2.htm (Klinefelter’s Karyotype) portraits/presidents/ (George Washington) default.html (Turner’s Syndrome Karyotype) 2002/2155/slide17.gif (Turner’s Syndrome) or3/edwardssyndrome/ (Edward’s Karyotype) album11.htm (Patau’s Syndrome) (Patau’s Karyotype) June/DSCN0558.JPG (Polydactyl) ped/topic504.htm (Cri-du-chat karyotype) ../criduchat.cfm (Cri-du-Chat person) kirk/cory/babyscans.html (Ultra Sound) pregnancyepilepsy_index.shtml (UltraSound) Ultrasound-Sept_17-2.jpg (Ultra Sound Image) AMO_whatis.html (Amniocentesis Diagram) 050214/full/050214-6.html (Amniocentesis) health/health-info/do... (Chorionic Villi Sampling) designer-children2.htm (PGD) ivf/pgd.php (PGD) IBhuntingtons.shtml (Huntington’s Inheritance) (3D ultrasound) (Fish cartoon)