CHAPTER 8
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CHAPTER 8. Mendel and Heredity. I. The Origins of Genetics:. A. Terms Trait : A characteristic determined by a genes INHERITANCE - The passing of traits by heredity HEREDITY - The transmission of traits from parents to offspring. B. The History of Genetics. Gregor Mendel :

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CHAPTER 8

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Chapter 8

CHAPTER 8

Mendel and Heredity


Chapter 8

I. The Origins of Genetics:

A. Terms

  • Trait:

    A characteristic determined by a genes

  • INHERITANCE-

    The passing of traits by heredity

  • HEREDITY-

    The transmission of traits from parents to offspring


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B. The History of Genetics

Gregor Mendel:

  • An Austrian monk in the mid-1800’s

  • Studied math and science

  • “Father of Genetics”


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  • Mendel made observations within the monastery's garden.

  • Noticed that in pea plants, seven specific traits could be seen.

  • Mendel was interested in testing the predictability of the traits


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C. Mendel’s Breeding Experiments

  • Crossed pea plants with purple flowers with plants with white flowers

  • Mendel counted all offspring and analyzed the data


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The Genetic Work of Mendel


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Traits Expressed as Simple Ratios


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D. Monohybrid Crosses

  • Cross involving only one pair of contrasting traits.

    STEP 1:

  • Produce TRUE BREEDING strains

  • Ex: Purple plants only produce purple offspring

  • These plants make up the “P Generation” (parental)


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Step 2:

  • Cross-pollinate two P generation plants with contrasting traits

  • F1- First Filial Generation:

  • The offspring of the P generation

  • Record the number of F1 plants with each trait


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STEP 3:

  • F1plants self-pollinate

  • The offspring are called F2 Second Filial

  • Each plant was counted


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E. Mendel’s Results

  • F1 showed only one form of the trait

  • Missing trait reappeared in some of the F2 generation

  • 3:1 ratio in the F2 generation


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Mendel’s Work


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II. Mendel’s Theory

A. Mendel’s 4 Hypotheses:

1. For each trait an individual has 2 copies of the gene (one from each parent)

2. There are alternative versions of genes called ALLELES


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Mendel’s Hypotheses Continued

  • Dominance and Recessiveness:

  • One factor isDominant, and hides, the other factorRecessive

  • Segregation:

  • Theeggandspermcarry only one of the possible alleles


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B. Mendel’s Findings in Modern Times

  • Dominant-

    First letter of the trait in capital (P- purple),

  • Recessive-

    First letter of the dominant trait in lower case (p- white)


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Homozygous vs. Heterozygous

  • Homozygous: 2 alleles are the same

    - Homozygous Dominant(PP) ”Pure”

    - Homozygous Recessive(pp)

  • Heterozygous: alleles are different (Pp)

    - Display the characteristics of the dominant trait

  • A genetic trait that appears in every generation of offspring is called dominant.


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Genotype vs. Phenotype

Genotype:

  • The genetic makeup of an organism

    Phenotype:

  • External “physical” appearance of an organism(trait)


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C. The Laws of Heredity

1. Law of Segregation:

  • The 2 alleles for a trait segregate when gametes are formed

    2. Law of Independent Assortment:

  • Dominant factorsdon’talways go with other dominant factors

  • Recessive factorsdon’talways go with other recessive factors


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III. Studying Heredity

A. Punnet Squares

  • Diagram that predicts the outcome of a monohybrid cross

  • Four Boxes in a square


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Monohybrid Crosses


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Simulating a Dihybrid Cross


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Dihybrid Crosses:

compares 2 contrasting traits at one time


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Test Crosses

  • Used to determine the genotype of an individual

  • A procedure in which an individual of unknown genotype is crossed with a homozygous recessive individual


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B. Probability:

  • Likelihood that a specific event will occur

    Probability = # of one kind of outcome total # of all possible outcomes


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C. Inheritance of Traits

Pedigree :

  • History of how a trait has been inherited over several generations


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1. Autosomal Traits

  • Autosomal will appear in both sexes equally

  • It affects a chromosome other than the 23rd pair


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2. SEX-LINKED TRAITS

-Traits with alleles found on the “X” chromosome

-Males are more likely to express recessive sex-linked alleles because the single “X” has nothing to hide/mask the trait

  • Red/Green most common form of

  • color deficiency

    Ex: Colorblindness

    Hemophilia


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3. SEX-INFLUENCED TRAITS

-A trait that is expressed because of the presence of male or female sex hormones

-Alleles that code for these are on the autosomes

-Both males and females have same allele, but the trait is only expressed in one of the sexes

Ex: Pattern Baldness

B = dominant in males

B’ = recessive in females


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IV. Complex Patterns of Inheritance

A.) Polygenic Traits:

-Trait that is controlled by two or more genes.

Examples:

  • skin color

  • eye color

  • fingerprints


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B. Incomplete Dominance

  • Individual displays a phenotype intermediate “blending of genetic information” between the two parents

    Ex: Red Snapdragon + White Snapdragon = Pink Snapdragon

    Ex: Straight hair + Curly hair = Wavy hair


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C. Multiple Alleles

  • Genes with 3 or more alleles

    EX: Blood … A-B-O


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D. Codominance:

  • Two dominant alleles are expressed at the same time

  • Ex: IA + IB = AB blood type


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  • Genetic Disorders

Mutation: A change in a gene due to damage or being copied incorrectly.


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A. SICKLE-CELL ANEMIA

  • Change in the shape of the RBC:

  • Results in anemia, clogs, pain, decreased blood flow, death….

  • Primarily effects the black population

  • 1 in 500 births in USA

    A = Normal

    A’ = Sickle Cell


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B. HUNTINGTONS DISEASE

  • Dominant Disorder

  • 30-40’s, forgetfulness, loss of muscle control,mental illness, death

  • genetically programmed degeneration of brain cells

    *Can be detected by identifying short sections of DNA known as GENETIC MARKERS


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C. TAY-SACHS DISEASE

  • Recessive Disorder

  • fatty substance accumulate in the nerve cells of the brain

  • A child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in

  • Children usually die by age 5


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D. CYSTIC FIBROSIS

  • Body produces an abnormally thick, sticky mucus

  • Faulty transport of salt within cells of organs such as the lungs and pancreas

  • very salty-tasting skin;

  • persistent coughing,

  • wheezing or pneumonia;

  • excessive appetite but poor weight gain


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D. CYSTIC FIBROSIS

  • 1 in 2500 people are born with it

  • More than 10 million people


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NONDISJUNCTIONS

  • Failure of chromatids to separate during Meiosis

  • Results in an egg or sperm with extra or missing chromosomes


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A. MONOSOMY

Condition where the zygote has only 45 chromosomes

Examples:

  • Turner Syndrome (XO)

  • CRI-DU-CHAT SYNDROME


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B. TRISOMY-

  • A condition where the zygote has 47 chromosomes

  • Examples:

  • Supermale (XYY)

  • Klinefelters Syndrome (XXY)


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-DOWN SYNDROME (trisomy) - Extra 21


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PATAU SYNDROME (trisomy 13)


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DETECTING GENETIC DISORDERS

  • Genetic Screening-

  • The examination of a persons genetic make-up…

  • especially if they have a history of problems in their family


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Fetoscopy

  • Tiny camera into the uterus


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Karyotyping-

  • Picture of a persons chromosomes


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Amniocentesis-

  • Removal of amniotic fluid


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Ultrasound

  • High frequency sound waves = picture


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