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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
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
slide3
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
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
slide5
Try a codominant cross:
  • Checkered (BW) x checkered (BW)
  • Checkered (BW) x white (WW)
  • Checkered (BW) x black (BB)
slide6
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
slide8
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)
slide9
Six genotypes are possible for blood:
  • IA IA
  • IA IB
  • IB IB
  • IA i
  • IB i
  • i i
  • What blood types would they have?
slide10
Ex: Type A (homozygous) x Type B
  • What are the blood types of the offspring?
slide11
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)
slide13
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
slide19
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!

slide20
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
slide22
Hemophilia: (Recessive X-linked trait)
    • Blood has trouble clotting
  • XHXh Carrier female
  • XHY Normal Male
  • XhY Affected Male
  • XhXh Affected Female
  • XHXH Normal Female
slide24
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
slide26
Amniocentesis:
    • Prenatal test
    • Grow cells from amniotic fluid around fetus.
    • Helps to rule out major chromosomal abnormalities
nondisjuction
Nondisjuction
  • Nondisjunction:
    • homologous chromosomes fail to separate properly during meiosis.
    • Results in egg or sperm with one or more extra chromosomes.
slide28

Nondisjunction

Normal Meiosis

slide31
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
slide32
Turner’s Syndrome (XO)
    • Offspring has only one X (always female)
    • Usually sterile, short, thick neck
slide33
Nondisjunction of Autosomes
  • Trisomy 21 (Down’s Syndrome) (47, +21)
    • Most commonly seen chromosomal disorder resulting in live birth
    • Extra Chromosome 21
slide34
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”
slide37
Crossing Over and Linked Genes

Crossing Over: homologous chromosomes

line up during synapsis and exchange

material.

  • Increases variation in offspring.
slide38
Sometimes linked

genes will separate

when crossing over

occurs.

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
slide40
Sickle Cell Anemia: (Autosomal recessive)
  • Red blood cells have a sickle shape
  • Very fragile and break easily
  • Clump up on blood vessels (causing pain)
slide41
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
slide42
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!

slide43
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
slide45
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.
mutations
Mutations
  • 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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