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Genetics Notes


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  • 1.  
  • 2. What is Genetics Genetics is a branch of biology that deals with characteristics that are inherited from one generation to the next. Genetics is the study of genes.
  • 3. Molecular Basis of Inheritance
    • The blueprint for the development and appearance of each individual is contained within the chromosomes of our cells. All of this information is efficiently organized and tightly packed into pairs of chromosomes located inside the cell nucleus.
    • Chromosomes are made up of a molecule called DNA (deoxyribonucleic acid)
  • 4. Molecular Basis of Inheritance Genetics
  • 5. Molecular Basis of Inheritance Take A Tour (Can be found in the outbox) Genetics
  • 6. Phenotypes vs Genotypes
    • Inherited characteristics that can be seen; looks, functions or behaviors are called phenotypes . The genes making up the chromosomes that demonstrate a characteristic are called genotypes.
    • A child has blue eyes. Blue eyes are her phenotype and the genes inherited from her parents that are responsible for her blue eyes are called the genotype.
  • 7. Single Trait Inheritance
  • 8. Genes
    • Genes are a piece of chromosome that contain the actual code for a certain trait.
    • Every characteristic we have must have a corresponding gene in our chromosome.
    Homologous Chromosomes D d Dark hair colour gene Light hair colour gene
  • 9. Alleles
    • An allele is a form of a gene.
    • Variations of a gene that relate to the same characteristic are called alleles .
    • Alleles for hair color could be dark (D) or light (d).
    Homologous Chromosomes D d Dark hair colour allele (D) Light hair colour allele (d)
  • 10. Dominant and Recessive Genes
    • Scientists have found that there are two kinds of genes. One type of gene is called recessive and the other type is called dominant .
    • Brown eye colour is a dominant gene and blue eye colour is a recessive gene. If you inherited a blue eye colour gene from one parent and a brown eye colour gene from the other parent, you would have brown eyes.
  • 11. Law of Dominance
    • The rule for inherited traits follows:
      • Whenever a recessive trait combines with a dominant trait, the dominant trait always shows as the phenotype. A recessive trait will only show in the offspring when two recessive traits combine.
  • 12.  
  • 13. Hereditary Traits
    • Traits are closely related to phenotype.
    • Traits refer to the single characteristic of the individual whereas phenotype refers to all the observable characteristics that make up the individual.
  • 14.
    • Specific genes determine hereditary traits. A gene specifies a single inherited characteristic. There are genes for height, weight, eye colour, earlobe attachment and so on.
    • Each person carries two genes for a given characteristic. One gene comes from the mother’s egg and one from the father’s sperm.
    • One of the two genes is dominant over the other. The dominant allele will mask the other recessive allele. For example, if the mother provides a blue eye-colour allele and the father a brown eye-colour allele, the off spring will have brown eyes since brown eye-colour is dominant.
    Hereditary Traits
  • 15. Punnet Squares
    • A punnett square is a method of predicting what characteristics to expect from offspring if you know the parents genotype.
    Tt Tt t TT TT T T T
  • 16.
    • A punnett square assigns two alleles to each parent and predicts the outcome for each trait .
    • For example tallness.
    Punnet Squares The mother is called homozygous since she has two alleles that are the same. The TT represents the two dominant alleles for tallness. The father is called heterozygous since he has two different alleles. The Tt represents the one dominant( T ) and one recessive( t ) allele for tallness.
  • 17. Punnet Squares
  • 18.
    • Each parent contributes one allele to form the trait in the offspring
    • Notice how gametes from the father combine with gametes from the mother to form offspring with two gametes, one from each parent.
    • The possible offspring with the tallness trait are shown below.
    • Two homozygous tall TT
    • Two heterozygous tall Tt
    Punnet Squares T t T t t T T T T T T T
  • 19. Punnet Squares
    • Punnett Squares give us three types of information.
      • They show us the gametes each parent can produce
      • They show us the genotype combinations that are possible
      • They tell us the probability that a given genotype will occur
    Punnet Squares
  • 20. Punnet Squares - Question
    • Complete the Punnett Square for a cross between the following parents.
    • ff x Ff
    • Describe the probable phenotypes and genotypes that come from the Punnett Square. Indicate the percentage probability of each.
    • F – free earlobes
    • F – attached earlobes
    Punnet Squares _ _ _ _ __ _ _ _ _ __ __ __
  • 21. Punnet Squares - Answer
    • Phenotype
      • ½ free earlobes
      • ½ attached earlobes
    • Genotype
      • ½ heterozygous
      • ½ homozygous recessive
    Punnet Squares ff ff f Ff Ff F f f
  • 22. Beaker Babies
  • 23. Beaker Babies
  • 24. Sex Linked Inheritance
  • 25.
    • Sex-linked traits are traits carried on sex chromosomes (X and Y).
    • The male determining chromosome (Y) has no corresponding alleles on the X chromosome to mask its effects. The presence of the Y chromosome causes maleness. The female determining chromosome (X) does not carry "male" genes of the Y chromosome.
    Sex Linked Inheritance
  • 26. Sex Linked Inheritance
    • A male has XY homologous chromosomes for sex determination.
    • The male has one X and one Y sex chromosome. Since Y (male) genes can't be masked by genes on the X chromosome, he is male.
    Sex Linked Inheritance
  • 27. Sex Linked Inheritance
    • A female has XX homologous chromosomes for sex determination.
    • The female has two X sex chromosomes. Since there are no male, Y-based genes, she is female.
    Sex Linked Inheritance
  • 28. Sex Linked Inheritance
    • Males are (XY) and females are (XX). That makes it easy to predict offspring gender probability and trace the pattern of X Y chromosome inheritance.
    • What percent of the time will parents produce a female offspring?
    Sex Linked Inheritance
  • 29. Sex Linked Inheritance
    • The X and Y chromosomes carry genes that code for traits other than gender. Traits determined by genes on the X chromosome are called sex-linked. Some genes are also carried on the Y chromosome and they are called sex-limited traits. An example is hairy ears that many older men have.
    • Some sex-linked traits that show up as disorders are hemophilia and colour blindness.
    • Recall also the father contributes either an X or Y chromosome to the mother's X chromosome.
    Sex Linked Inheritance
  • 30. Sex Linked Inheritance
    • Some other considerations
      • Fathers can only pass on X-linked (sex-linked) alleles to daughters, not to sons
      • Males always receive their X chromosome from the mother
      • Mothers can pass sex-linked alleles to daughters and sons.
      • Females receive two X chromosomes - one from mother and one from father
    Sex Linked Inheritance
  • 31. Males & Sex Linked Traits
    • Sex-linked traits are always on the X chromosome.
    • A male has one X chromosome only. If he receives an X chromosome with a sex-linked allele on it, he will demonstrate that trait because there is no corresponding allele on the Y chromosome to mask it.
    Sex Linked Inheritance
  • 32. Females & Sex Linked Traits
    • Females receive X chromosomes from both parents and therefore can inherit sex linked traits from either parent.
    • If a female is to show a sex-linked trait, she must have one dominant allele on an X chromosome or two recessive alleles on both X chromosomes.
    • If a female receives one recessive sex-linked allele from her mother or father she will not show the trait, but she is a carrier and there is a probability that she will pass the sex-linked trait one-half of her sons. The same probability exists for her daughters. If masked by a corresponding allele on their other x chromosome, they won't show the trait.
    Sex Linked Inheritance
  • 33. Sex Linked Traits & Punnett Squares
  • 34. Sex Linked Traits & Punnett Squares
  • 35. Pedigrees
    • A pedigree is a diagram representing the phenotype history of a family. A phenotype history is used since we have traits only of ancestors to work with. Genotypes would not have been known for any ancestors.
    • Symbols can be used to represent female and male ancestors. If the symbols are empty, the trait is dominant; if the symbol is filled, the trait is recessive. Traits shown by the offspring help determine whether the trait in the parent is dominant or recessive.
  • 36. Pedigrees
    • An example of a pedigree is shown below.
  • 37. Pedigrees
    • There are several pieces of information that relate to pedigrees.
      • The genetic information about ancestors is determined through their offspring. The genetic information about the parents in this example can only be obtained through their children and grandchildren.
      • We only know the phenotype and must interpret traits in the offspring to derive the genotype.
  • 38. Pedigrees
    • There are two types of pedigrees.
      • Autosomal pedigrees These pedigrees are ones that demonstrate a trait that is not attached to a sex (X,Y) chromosome. The example is an autosomal pedigree.
        • If an offspring demonstrates a recessive trait, then both parents must have at least one recessive allele. This means the parents can be either homozygous or heterozygous recessive.
        • If the offspring is dominant then at least one of the parents must have the dominant allele. The parent can be either homozygous dominant or heterozygous.
        • If both parents are recessive, all the offspring will be recessive also.
  • 39. Automsomal Pedigrees
  • 40. Pedigrees
    • There are two types of pedigrees.
      • The second type of pedigree is sex-linked. These pedigrees are ones that demonstrate a trait that is attached to a sex (X,Y) chromosome. A common sex-linked pedigree is the one for hemophilia in European aristocracy. Recall that sex-linked traits are inherited through the allele located on the X sex chromosome.
  • 41. Sex Linked Traits & Pedigrees
  • 42. Hemophilia
  • 43. Sex Linked Pedigree
  • 44. Conclusion