Understanding Inheritance
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Understanding Inheritance

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Understanding Inheritance Understanding Inheritance Presentation Transcript

  • Understanding inher itance
  • What controls traits? • Mendel concluded that two factors control each trait. • He also concluded that they can be dominant or recessive. • One factor comes from the egg cell and one factor comes from the sperm cell. • What are these factors? How are they passed from parents to offspring?
  • What controls traits? chromosomes • Inside each cell is a nucleus that has chromosomes. Chromosomes contain genetic information that controls traits. • What Mendel called “factors” are parts of chromosomes. We know them as genes.
  • What controls traits? chromosomes • Each cell in an offspring contains chromosomes from both parents. • These chromosomes exist in pairs — one chromosome from each parent.
  • What controls traits? genes & alleles • Each chromosome can have information about 100’s or 1000’s of traits. • A gene is a section on a chromosome that has genetic information for one trait.
  • What controls traits? genes & alleles • An offspring inherits two genes for each trait, one from each parent. • The genes can be the same or different, such as purple or white for pea flower color. XX
  • What controls traits? genes & alleles • Another example of a trait and its forms is having dimples or not having dimples.
  • What controls traits? genes & alleles • The different forms of a gene are called alleles.
  • What controls traits? genot ype & phenot ype • Geneticists call how a trait appears, or is expressed, the trait’s phenotype. • A person’s eye color is an example of phenotype. The trait of eye color can be expressed as blue, brown, green, or other colors.
  • What controls traits? genot ype & phenot ype • Mendel concluded that there were two alleles that controlled the phenotype of each trait. • The two alleles that control the phenotype of a trait are called the trait’s genotype. • You cannot see an organism’s genotype. But you can make guesses about a genotype based on its phenotype.
  • What controls traits? genot ype & phenot ype
  • What controls traits? genot ype & phenot ype • Scientists use symbols to represent the alleles in a genotype. • Uppercase letters represent dominant alleles and lowercase letters represent recessive alleles. • The dominant allele, if present, is written first.
  • What controls traits? genot ype & phenot ype
  • What controls traits? homoz ygous & het er oz ygous homozygous: heterozygous: RR rr Rr
  • modeling inheritance • Plant breeders and animal breeders use two tools to help them predict how often traits will appear in offspring. • These tools, Punnett squares and pedigrees, can be used to predict and identify traits among genetically related individuals.
  • modeling inheritance Punnet t Square Pedigree
  • modeling inheritance Punnet t Squar es • If the genotypes of the parents are known, then the different genotypes and phenotypes of the offspring can be predicted. • A Punnett square is a model used to predict possible genotypes and phenotypes of offspring.
  • modeling inheritance Punnet t Squar es
  • modeling inheritance Pedigr ees • A pedigree shows phenotypes of genetically related family members. • It can also help determine genotypes.
  • modeling inheritance Pedigr ees • Let’s look at the phenotypes of the children.....
  • complex patterns of inheritance t ypes of dominance: • Mendel studied traits influenced by only one gene with two alleles. • We know now that not all traits are inherited this way. Some traits have more complex inheritance patterns.
  • complex patterns of inheritance t ypes of dominance: incomplete dominance • Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes. • Here is an example with 4 o’clock flowers.
  • complex patterns of inheritance t ypes of dominance: incomplete dominance
  • complex patterns of inheritance t ypes of dominance: incomplete dominance
  • complex patterns of inheritance t ypes of dominance: codominance • When both alleles can be observed in a phenotype, this type of interaction is called codominance.
  • complex patterns of inheritance t ypes of dominance: codominance • For example, if a cow inherits the allele for white coat color from one parent and the allele for red coat color from the other parent, the cow will have both red and white hairs.
  • complex patterns of inheritance mul t iple alleles • Unlike the genes in Mendel’s pea plants, some genes have more than two alleles, or multiple alleles. • Human ABO blood type is an example of a trait that is determined by multiple alleles. • There are three alleles for the ABO blood type—IA, IB, and i.
  • complex patterns of inheritance mul t iple alleles • In the pea plants there were two possible phenotypes, ie round pea or wrinkled pea. • The way the alleles combine for blood types, results in one of four blood types—A, B, AB, or O.
  • complex patterns of inheritance mul t iple alleles • The IA and IB alleles are codominant to each other, but they both are dominant to the i allele. • Even though there are multiple alleles, a person inherits only two of these alleles, one from each parent.
  • complex patterns of inheritance mul t iple alleles
  • complex patterns of inheritance polygenic inher i tance • Mendel concluded that only one gene determined each trait. We now know that more than one gene can affect a trait. • Polygenic inheritance occurs when multiple genes determine the phenotype of a trait.
  • complex patterns of inheritance polygenic inher i tance
  • complex patterns of inheritance polygenic inher i tance • Because several genes determine a trait, many alleles affect the phenotype even though each gene has only two alleles. • Therefore, polygenic inheritance has many possible phenotypes. • Eye color, height, weight and skin color are all examples of traits that are determined by polygenic inheritance.
  • complex patterns of inheritance polygenic inher i tance
  • genes and the environment • Genes are not the only factors that can affect phenotypes. An organism’s environment can also affect its phenotype. • For example, the flower color of one type of hydrangea is determined by the soil in which the hydrangea plant grows. • Acidic soil produces blue flowers. Basic soil produces pink flowers.
  • genes and the environment • The flower color of one type of hydrangea is determined by the soil in which the hydrangea plant grows. • Acidic soil produces blue flowers. Basic soil produces pink flowers.
  • genes and the environment • Himalayan rabbits have alleles for dark-coloured fur, which is only displayed at lower temperatures. • The fur in areas further from the rabbit’s body heat i.e. nose, ears, feet, are therefore darkly coloured.
  • genes and the environment • For humans, healthful choices can also affect phenotype. • Many genes affect a person’s chances of having heart disease. • However, what a person eats and the amount of exercise he or she gets can influence whether heart disease will develop.
  • recessive genetic disorders • Disorders caused by recessive genes. You must have both recessive alleles in order to have the disorder.
  • recessive genetic disorders
  • sex-linked disorders • Red-green colour blindness is a recessive sex-linked disorder. • It occurs on the X chromosome. XX XX XX XY XY female not color blind female not color blind male not color blind female color blind male color blind
  • sex-linked disorders
  • recessive genetic disorders