Patterns of Inheritance


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  • If Adam and Eve did not have all three blood type alleles, then there must have been a mutation creating the O allele while the human race was still very small and before humans dispersed across the globe. Whether the origin of blood type O was in Adam and Eve at Creation or whether it arose as a mutational event that took place shortly before or after the Flood, it strongly supports that all humans today are descendants of two individuals or a small group of people that eventually populated the globe. Both scenarios are consistent with the biblical model of human origins.
  • Chickens also display codominance in their feather color. Instead of gray feathers from a black/white hybrid, both black AND white feathers are expressed.
  • Probable # of genes responsible is around 40! additive = not clearly dominant/recessive, and not equally codominant either, but each gene contributes a degree of pigment that combines to produce a variety (or full spectrum) of skin color
  • Each gene of every human chromosome is now know by location and trait.
  • So who determine's a baby's sex? The Father!
  • sex-linked recessive trait
  • multiple incomplete dominant alleles
  • Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers and/or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia). Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life. Only five percent to 10 percent of children with this condition live past their first year. Trisomy 13 occurs in about 1 in 16,000 newborns. Although women of any age can have a child with trisomy 13, the chance of having a child with this condition increases as a woman gets older.
  • Down syndrome is a genetic disorder that includes a combination of birth defects, including some degree of mental retardation, characteristic facial features and, often, heart defects, visual and hearing impairment, and other health problems. The severity of all of these problems varies greatly among affected individuals. Down syndrome is one of the most common genetic birth defects, affecting approximately one in 800 to 1,000 babies. In this country, there are more than 350,000 individuals with Down syndrome, according to the National Down Syndrome Society. Life expectancy among adults with Down syndrome is about 55 years, though average lifespan varies.   The name "Down syndrome" comes from the physician, Dr. Langdon Down, who first described the collection of findings in 1866. It was not until 1959 that the cause of Down syndrome (the presence of an extra #21 chromosome) was identified.
  • Patterns of Inheritance

    1. 1. Patterns ofInheritance How genes interact and are influenced to produce different traits.
    2. 2. Review - Simple Mendelian Genetics Dominant gene covers other allele • Ss or SS genotype yields smooth coat Recessive gene is only expressed when dominant allele is not inherited • ss genotype yields long coat
    3. 3. Lethal Allele Combinations The yellow fur color allele is dominant (Y) • however, its only expressed in heterozygous Yy mice Homozygous dominant (YY) mice never appear (they die before birth) Homozygous recessive (yy) mice are white Even though the fur color Y is dominant, the lethal allele is considered recessive because it only appears in the homozygous YY genotype.
    4. 4. Incomplete Dominance Heterozygotes (CRCW) express an intermediate phenotype (pink) Instead of overpowering one another, both traits are partially expressed Flower color traits separate again during meiosis and can be seen in the F2 generation
    5. 5. Codominance The inheritance of ABO • Two alleles are dominant blood groups demonstrates • Type A and Type B codominant inheritance • (Type O is recessive) • Both phenotypes are expressed in the heterozygote (Type AB)
    6. 6. Codominance  B = black X  W = white  What would the genotype of each of these chickens have to be?
    7. 7. Multiple Alleles The ABO blood type is an example of a trait that has more than just two different alleles (A, B, and O) Most genes have multiple alleles (different forms of the same gene) • hair, eye, and fur color genes all have many different alleles • multiple alleles usually exhibit some sort of incomplete dominance
    8. 8. Polygenic Traits The control of a trait by more than one gene • Skin color is controlled by at least 6 genes Each gene product is additive to the others The hallmark of a polygenic traits phenotype expression is: • A bell curve distribution • A continuous distribution
    9. 9. The Human Genome Project In the 1950s, scientists were first able to view a set of human chromosomes In 2003, scientists finished mapping the human genome Now every gene of each human chromosome is know by location and trait
    10. 10. Human Karyotype: 23 homologouspairs
    11. 11. Sex Chromosomes The X and Y chromosomes determines genderX + Y = BOY X + X = GIRL The mother always donates an X chromosome. Why? The father gives either an X (female) or a Y (male).
    12. 12. Sex-Linked Recessive Inheritance The pattern of inheritance still follows Mendels predictions Genes found on the X chromosome: • Hemophilia • Color blindness Males are more often affected than females because they inherit only one X chromosome
    13. 13. Pedigree Pedigrees help track the appearance of one trait (or disease) • Very useful for determining the type of inheritanceDoes the whirling trait appear to be sex-linked?Are there multiple alleles for the whirling trait?Is it recessive or dominant?
    14. 14. Multiple Alleles
    15. 15. Autosomal Dominant Inheritance Genes on non-sex chromosomes are autosomes • Huntington’s disease is an autosomal dominant trait • It only take one copy of the Huntington gene to have the disease Some individuals in every generation are affected regardless of gender This pedigree shows the affected individuals of each generation as ablack circle or square
    16. 16. Autosomal Recessive
    17. 17. Environmental Influences Genes are often influenced by environmental factors • leaf & stem size is dictated by genes, but also affected by sunlight • black fur color genes can be "turned on" by changes in temperature • conditions such as baldness can be triggered by hormones (internal environment) • both men and women inherit baldness genes, but the gene is only expressed when exposed to high levels of testosterone
    18. 18. Different levels of hormones affect the thickness and length of horns in bighorn sheep, even though their genotype is identical.Diet, exercise, and other environmental factors have beenproven to influence the expression of genes causingheart disease, diabetes and other serious illnesses. Exposure to chemicals during pregnancy and early infancy can trigger severe genetic abnormalities.
    19. 19. Abnormal Chromosome Number many miscarriages  this zygote has 3 copies of a are the result of chromosome instead extra or missing of 2 chromosomes due  instead of a to nondisjunction homologous pair, there is a trisomy
    20. 20. Trisomy 13 - also known as PatausSyndrome An individual with full trisomy 13 at age 7 years (survival beyond the first year is uncommon). He is deaf and legally blind
    21. 21. Trisomy 21 - (Down Syndrome)