Human Genetics

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Human Genetics

• BIOL 151
• Winthrop University

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Genetics

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

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Genetics

• 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?

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Genetics

• 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
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Genetics

• 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)!
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Genetics

• An organisms phenotype is the combination of
  physical features, characteristics, and
  behaviors.
• The phenotype of an organism is determined by the
  genotype, or, the genetic makeup of the
  individual.
• Some examples of human phenotypic traits
• Hair color.
• Eye color.
• Freckles.
• Dimples.
• Free or attached earlobes.

Image from http//www.bbc.co.uk/
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Genetics

• 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?

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Genetics

• 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.

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Genetics

• 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?

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Genetics

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

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Genetics

• 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!

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Genetics

• 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?

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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 ___________!

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Gender Determination

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

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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
  chromosomes.
• 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.

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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.

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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.

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Pedigrees

• 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.

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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?

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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.

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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?

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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!

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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
  82.
• And finally, there will be a genetics handout for
  you to turn in for participation credit.