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Human Genetics


Human Genetics. BIOL 151. Winthrop University. Genetics ... Genetics ... And finally, there will be a genetics handout for you to turn in for participation credit. ... – PowerPoint PPT presentation

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Title: Human Genetics

Human Genetics
  • BIOL 151
  • Winthrop University

  • Genetics is the branch of biology that studies
    the storage, duplication, and transfer of
  • This information is encoded in a chemical form
  • DNA stands for deoxyribonucleic acid.

  • Genes are sections of the DNA that code for
    specific characteristics of an organism.
  • The DNA is packaged up into chromosomes.
  • Chromosomes come in pairs where did each member
    of each pair come from in any individual that was
    created by sexual reproduction?

  • So, genes are physical structures that lie in
    segments along a strand of DNA.
  • In humans, genes come in pairs, and they reside
    on homologous chromosomes.
  • These variant forms of a gene are called alleles.

Homologous chromosomes
From Dad
From Mom
  • For example, in humans, there is a gene that
    codes for whether or not the child will have long
    eyelashes or short eyelashes.
  • This gene will be in the babys genetic library
    as a PAIR, one copy of the gene came from its
    mother, one came from its father.
  • Maybe the babys mother gave it the long
    eyelashes allele, and its father gave it the
    short eyelashes allele.

The genes code for the same characteristic
(eyelashes), but they are variant forms of that
characteristic (long or short)!
  • An organisms phenotype is the combination of
    physical features, characteristics, and
  • The phenotype of an organism is determined by the
    genotype, or, the genetic makeup of the
  • Some examples of human phenotypic traits
  • Hair color.
  • Eye color.
  • Freckles.
  • Dimples.
  • Free or attached earlobes.

Image from http//
  • So, if we have two alleles for every
    characteristic, what decides which characteristic
    the baby is going to have?
  • Go back to the eyelashes example what
    determined whether the baby had moms long
    eyelashes or dads short ones, since the baby had
    both alleles in its genotype?

  • The characteristic that is expressed (the one we
    SEE) is called the dominant allele.
  • The allele that has no visible effect on the
    organisms phenotype is the recessive allele.

  • In the case of the eyelashes, long eyelashes are
    dominant, short ones are recessive.
  • So, since we know that dominant alleles are the
    ones that code for the phenotype that we SEE in
    an individual, what kind of eyelashes will our
    baby have?

  • We can write alleles as dominant or recessive
    using capital or lowercase letters.
  • Lets use L for long eyelashes, l for short.

  • Since the baby inherited the dominant (L) from
    its mother, and the recessive (l) from its
    father, we can write the babys phenotype as Ll.
  • Having both the dominant and recessive alleles
    for this characteristic, we say that the baby is
    heterozygous for eyelash length.
  • Again, the presence of that dominant allele
    masks the recessive from being seen, so our baby
    will have LONG eyelashes!

  • If the baby had inherited two dominant alleles
    (LL) or two recessive alleles (ll) from its
    parents, we would say that they are homozygous
    for that characteristic.
  • What kind of eyelashes would the LL baby have?
  • What about the ll baby?

Terminology Review
  • This brings up a good point a recessive allele
    can be present in an organisms genotype, but it
    is not expressed if it is paired with the
    dominant allele.
  • The only way we will see a recessive
    characteristic is if the person is ___________!

Gender Determination
  • Gender in humans is determined by chromosomes.
  • Females will have two X chromosomes, and males
    have an X and a Y chromosome.

Gender Determination
  • The sex of a baby is determined by what
    chromosome is carried by the sperm that
    fertilizes the egg so it is up to the father.
  • Each egg will have one X chromosome, since
    females only have two X chromosomes.
  • Conversely, sperm may have either X or Y
  • So, if an egg is fertilized by a sperm with an X
    chromosome, it will be a female child.
  • If the egg is fertilized by a sperm with a Y
    chromosome, the child will be male.

Todays Lab (Monday)
  • In todays lab, you will be making a baby.
  • You will flip a coin to determine which allele
    from each parent is being inherited for 15
    characteristics (page 71-75), as well as for the
    sex of the baby.
  • For simplicitys sake, both parents will be
    heterozygous for each trait.

Todays Lab (Monday)
  • Heads will represent the dominant allele, tails
    will represent the recessive allele.
  • Record your findings in table 14.4 on page 76 of
    your lab manual.
  • Once you finish your table, you will draw and
    name your baby and share it with the class.

  • We can do pedigrees to track genetic connections
    between generations.
  • Squares represent males, ovals represent females.
  • If we know some genotypes of some individuals, we
    can predict or guess the genotypes of their
    offspring or their parents.
  • See examples on the board.

X-linked Disorders
  • X-linked disorders are caused by problems with
    the genes that lie along the X sex chromosome.
  • Example color blindness.
  • X-linked disorders more commonly affect males
    more so than females why do you think this is?

Blood Types
  • Humans can have four different blood types
  • A
  • B
  • AB
  • O
  • Blood type refers to the type of protein
    present on the surface of their blood cells.
  • There are three different alleles that code for
    blood type IA, IB, and i.

Blood Types
  • People with the A allele have type-A blood,
    people with the B allele have type-B blood, and
    type O individuals have inactive alleles and
    therefore no proteins on their blood cells.
  • Type-A and Type-B individuals can be
    heterozygous or homozygous dominant.
  • Type-O blood is recessive, so what does their
    genotype have to be?

Blood Types
  • What happens when an individual inherits the A
    allele and the B allele?
  • This is an example of codominance A is not
    dominant over B, and B is not dominant over A.
  • These people have both A and B proteins on the
    surface of their blood cells!

Todays Lab (Wednesday)
  • You will be looking at pedigrees and filling in
    examples (pages 78-81).
  • You will also do a blood type exercise on page
  • And finally, there will be a genetics handout for
    you to turn in for participation credit.