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Other Laws of Inheritance. Mendelian Genetics : characteristics controlled by dominant and recessive paired alleles Many traits follow the patterns outlined by Mendel’s Laws, many do not. Incomplete Dominance. Offspring heterozygous for a trait have an intermediate appearance .

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Other Laws of Inheritance

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Other laws of inheritance

Other Laws of Inheritance

  • Mendelian Genetics: characteristics controlled by dominant and recessive paired alleles

    • Many traits follow the patterns outlined by Mendel’s Laws, many do not.

Incomplete dominance

Incomplete Dominance

  • Offspring heterozygous for a trait have an intermediate appearance.

  • Neither allele is completely dominant over the other

  • Ex: Snapdragon flowers

    • Homozygous Red x Homozygous White

    • Results in all PINK flowers

Other laws of inheritance

Showing a Cross for Incomplete Dominance

  • Use a capital letter for each allele since each influence trait equally

  • RR (homozygous red) x WW (homozygous white)

  • What is phenotype ratio of offspring?

  • RW x RW (heterozygous pink)

  • What is phenotype ratio of offspring?

    • How is this ratio different from the offspring

      of Mendel’s Monohybrid cross? (Tt xTt)

  • Codominance


    • If individual is heterozygous, both alleles for gene are expressed.

    • Ex: Chickens

      • Black feathers (BB) x White Feathers (WW)

      • Offspring (BW) are checkered and have both black and white feathers

    Other laws of inheritance

    • Try a codominant cross:

    • Checkered (BW) x checkered (BW)

    • Checkered (BW) x white (WW)

    • Checkered (BW) x black (BB)

    Other laws of inheritance

    • Ex: Roan Cattle

      • Offspring of pure red and pure white cows

      • Have both red and white hair

    Multiple alleles

    Multiple Alleles

    • A gene that has more than two alleles.

    • Each individual can only have two alleles

    • Ex: Human Blood Types

    Other laws of inheritance

    Possible Blood Types:

    A, B, AB, O

    • There are 3 alleles for blood type (A, B, O)

    • A and B are codominant alleles (IA, IB)

    • O is a recessive allele (i)

    Other laws of inheritance

    Six genotypes are possible for blood:

    • IA IA

    • IA IB

    • IB IB

    • IA i

    • IB i

    • i i

    • What blood types would they have?

    Other laws of inheritance

    • Ex: Type A (homozygous) x Type B

    • What are the blood types of the offspring?

    Other laws of inheritance

    • Try a Cross:

    • What blood types do the offspring have?

      • IB IB xIA IA

      • IA i x i i

      • IA IB x i i

  • If a Type A mother and a Type B Father produce a type O child, what are the parent’s genotypes?

  • Environmental influences on gene expression

    Environmental Influences on Gene Expression

    • Ex: temperature, nutrition, light etc.

  • Ex: Coat color in Himalayan rabbits

    • Black fur present only on areas of body that are colder. (ear, nose, feet and tail)

  • Other laws of inheritance

    • Ice Pack placed on fur = fur turns black

    • If rabbit kept in warm environment, all fur is white.

    Genetic research and testing

    Genetic Research and Testing

    • Genetic Research:

      • To study genes for different traits it is best to use an organism that grows and reproduces quickly an produces many offspring.

      • Can do controlled breeding experiments

      • Can do forced “inbreeding”

        • Ex: Drosophila melanogaster (fruit fly)

    Genetic tests

    Genetic Tests

    • Test Cross:

      • To determine if an individual is homo or heterozygous for a trait.

      • Breed to a homozygous recessive.

      • Ex:

        • Drosophila: red eyes dominant over white.

        • To see if red eyed fly is hetero/homo, breed to white eyed fly

    Sex determination

    Sex Determination

    • Humans have 23 pairs of chromosomes

    • 22 pairs are autosomes

    • 1 pair are sex chromosomes

    These pictures are called karyotypes!

    I’m a BOY!

    I’m a GIRL!

    Sex determination1

    Sex Determination

    • XX = female, XY = male

    • Males can give Y chromosome or X chromosome

    • Females can only contribute X

    • There is always a 50% chance of being boy or girl

    Sex linked traits

    Sex Linked Traits

    • If allele is found on an X or a Y chromosome it is inherited differently in males and females.

    • Ex:

      • Calico Cats

      • Color Blindness

      • Hemophilia

      • Duchenne Muscular Dystrophy

    Other laws of inheritance

    Calico Cats: (Codominant X Linked Trait)

    • X chromosome has gene for black or orange fur (codominant)

    • Only females can be “Calico” XBlackXOrange

    • Males can only be Black or Orange

      they have only one X chromosome and one Y

    I’m always a girl!

    Other laws of inheritance

    Colorblindness: (Recessive X linked trait)

    • Certain colors cannot be distinguished from others (usually red or green)

    • Most often seen males

    • Females are more likely to be “carriers”

    • Father cannot pass gene to son, only mother

    Other laws of inheritance

    Hemophilia: (Recessive X-linked trait)

    • Blood has trouble clotting

  • XHXhCarrier female

  • XHYNormal Male

  • XhYAffected Male

  • XhXhAffected Female

  • XHXHNormal Female

  • Other laws of inheritance

    • Examples of Crosses for Hemophilia

    Other laws of inheritance

    • Queen Victoria of England passed this gene onto some of the royal family offspring

    She must have been a “carrier”

    Queen Victoria

    Chromosomal disorders

    Chromosomal Disorders

    • Due to the presence of absence of an entire chromosome or part of a chromosome.

    • Can be determined by doing a Karyotype from blood or amniotic fluid

    Other laws of inheritance

    • Amniocentesis:

      • Prenatal test

      • Grow cells from amniotic fluid around fetus.

      • Helps to rule out major chromosomal abnormalities



    • Nondisjunction:

      • homologous chromosomes fail to separate properly during meiosis.

      • Results in egg or sperm with one or more extra chromosomes.

    Other laws of inheritance


    Normal Meiosis

    What is wrong

    What is Wrong?

    Other laws of inheritance

    Nondisjunction of Sex Chromosomes

    • Klinefelter’s Syndrome (XXY)

      • 2 X’s from mother, Y from father

      • Often tall, long arms and legs

      • May have some gynomastia and small testicles

    Other laws of inheritance

    • Turner’s Syndrome (XO)

      • Offspring has only one X (always female)

      • Usually sterile, short, thick neck

    Other laws of inheritance

    Nondisjunction of Autosomes

    • Trisomy 21 (Down’s Syndrome) (47, +21)

      • Most commonly seen chromosomal disorder resulting in live birth

      • Extra Chromosome 21

    Other laws of inheritance

    • Other trisomys can happen as well

    • Babies may make it to term but usually don’t live very long (nonviable)

      • Ex: Trisomy 18, Trisomy 13

    Gene linkage

    Gene Linkage

    • When alleles for different traits are located on the same chromosome

    • They tend get inherited together.

      • They are “linked”

      • They do no “assort independently”

    Other laws of inheritance

    • Ex: Red hair and freckles

    Other laws of inheritance

    Crossing Over and Linked Genes

    Crossing Over: homologous chromosomes

    line up during synapsis and exchange


    • Increases variation in offspring.

    Other laws of inheritance

    Sometimes linked

    genes will separate

    when crossing over


    The closer genes are

    on the chromosome,

    the less chance they

    will be separated during

    crossing over

    Autosomal genetic disorders

    Autosomal Genetic Disorders

    • Caused by defective alleles on autosomes

    • Can be recessive or dominant

    Other laws of inheritance

    Sickle Cell Anemia: (Autosomal recessive)

    • Red blood cells have a sickle shape

    • Very fragile and break easily

    • Clump up on blood vessels (causing pain)

    Other laws of inheritance

    • Reduces oxygen carrying capacity of red blood cells

    • Caused by a single flaw in gene

    • One nitrogenous base in DNA sequence is different

    • Cause wrong amino acid in protein chain for hemoglobin, changing it’s shape

    • Hemoglobin doesn’t transport oxygen as well

    Other laws of inheritance

    • Mostly found in people of African American descent

      • (1 in 500 births heterozygous)

    • If disorder has negative effects why so common in population?

      • Malaria is a deadly disease common in Africa

      • Heterozygous individuals for sickle cell have malarial resistance, more likely to survive than people who aren’t carriers.

    I spread malaria!

    Other laws of inheritance

    Phenylketonuria (PKU):(Autosomal recessive)

    • Enzyme that breaks down amino acid phenylalanine doesn’t function

    • Chemical builds up in system and eventually forms substances that can damage the brain and cause mental retardation

    • Can test for it at birth and treat with a low phenylalanine diet

    Other laws of inheritance

    Tay-Sachs Disease: (Autosomal Recessive)

    • Incurable inherited disorder that damages the brain

    • Enzyme doesn’t function that helps breakdown lipid in brain.

    • Brain tissue deteriorates

    • Most often found in eastern European Jews

    • Death occurs several years after birth

    • http://www.youtube.com/watch?v=SeoPF74QSms&safe=active

    Gene chromosome theory

    Gene-Chromosome Theory

    • Explains the hereditary patterns that Mendel and others observed.

    • The genetic characteristics of an organism are determined by the genes for different traits present on their chromosomes.



    • Sometimes a genetic disorder is caused by a mutation of a gene.

    • The mutation can only be passed to the next generation if it happens in a sex cell.

    • Mutagenic Agents:

      • Exposure to x-rays

      • Radiation

      • Certain chemical toxins

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