GENETICS

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GENETICS
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Gregor Mendel

• Genetics the branch of biology that deals with
  heredity.
• A great deal of what we know about genetics began
  with the work of a monk named Gregor Mendel, who
  experimented with sweet pea plants in the 1800s.

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Mendels Work

• Mendel studied the patterns of inheritance in pea
  plants.
• He chose seven traits to follow.

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• Mendel needed to make sure he had plants that
  always gave the same offspring-called true
  breeding.
• He self-pollinated plants until he got seeds
  that always gave the same offspring.

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• He took a purple flower plant and crossed it with
  a white flower plant.
• He called these the parent generation (P1
  generation)
• What do you think the offspring (the F1
  generation) looked like?

Pollen
X
ALL PURPLE
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POLLEN
F1
SAY WHAT???????
F2
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Mendel concluded

• Something is being passed from parent to
  offspring.
• Sometimes you can see it and sometimes you
  cant.
• If you can see it- it is dominant.
• If its there and you cant see it- its
  recessive.

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• Dominant alleles are shown using a capital letter
  (R)
• Recessive alleles are shown using a lower case
  letter (r)
• Examples Rred rpink
• RR - ?
• Rr - ?
• rr- ?
• Each version is called an allele.

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Alleles are located on genes on chromosomes.
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Law of Dominance

• States that the dominant allele will prevent the
  recessive allele from being expressed. The
  recessive allele will only appear when it is
  paired with another recessive allele in the
  offspring.

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WHAT WE KNOW NOW
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We have two copies of all of our chromosomes Why?
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BOY OR GIRL?
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What is a gene?

• A segment on the chromosome that codes for a
  protein.
• People have two copies of each gene, one copy
  inherited from the mother and the other copy
  inherited from the father.
• There are many versions of each gene-alleles

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If the two alleles in the pair are identical,
then the condition called homozygous.

If the 2 alleles are different, the condition is
called heterozygous. The term hybrid is
sometimes used to refer to heterozygous.
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Genotype the genes or alleles (RR, Rr, rr)
Phenotype an organisms physical appearance (Red,
White)
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How did you end up with the traits and genes that
you got? During meiosis, each egg or sperm only
gets one copy of each chromosome.
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A b
a B
Law of Segregation (separation) states that gene
pairs separate when gametes (sex cells) are
formed, so each gamete has only one allele of
each gene pair.
A b
a B
A b
a B
A b
a B
A b
a B
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• Law of Independent Assortment
• states that different pairs of genes separate
• independently of each other when gametes are
  formed.

Example Just because you get the gene for brown
hair does not mean you will get the gene for blue
eyes.
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REVIEW

1. A trait is a characteristic an individual
   receives from its parents.
2. Genes carry the instructions responsible for the
   expression of traits.
3. A pair of inherited genes controls a trait.
4. One member of the pair comes from each parent.
5. Alternative versions of genes are known as
   alleles.

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REVIEWMendels Principles of Inheritance

• Inherited traits are transmitted by genes which
  occur in alternate forms called alleles
• Principle of Dominance - when 2 forms of the same
  gene are present the dominant allele is expressed
• Principle of Segregation - in meiosis two alleles
  separate so that each gamete receives only one
  form of the gene
• Principle of Independent Assortment - each trait
  is inherited independent of other traits (chance)

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Punnett Squares

• Used to determine the probability of a
  combination of alleles
• Example If a heterozygous black rabbit is
  crossed with a heterozygous black rabbit, what
  are the chances the offspring will be black?

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• BBlack
• b Brown
• Genotypes?
• Phenotypes?

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Example EOCT Question

• Earlobe shape is a human trait. Some people have
  free earlobes while others have attached
  earlobes. Two parents with free earlobes have
  four children. Three children have free earlobes
  and one child has attached earlobes. If these
  parents have another child, what is the
  probability that the child will have attached
  earlobes?
• A 25
• B 50
• C 75
• D 100

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Example EOCT question

• In humans, a widows peak is dominant over a
  continuous hairline. Marys father has a widows
  peak, but Mary and her mother have a continuous
  hairline. What is the genotype of Marys father?
• A HH
• B Hh
• C hh
• D cannot be determined

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Incomplete dominance - cross between organisms
with two different phenotypes that produces
offspring with a third phenotype that is a
blending of the parental traits. Ex. Red and
White Pink 
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Incomplete Dominance
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Codominance

• a cross between organisms with two different
  phenotypes produces offspring with a third
  phenotype in which both of the parental traits
  appear together. 
• Ex Yellow and Orange yellow with orange spots

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Codominance

• Both phenotypes are expressed at the same time.
• Example Blood
• Types

Genotype Phenotype
IOIO Type O
IAIO Type A
IAIA Type A
IBIO Type B
IBIB Type B
IAIB Type AB
There are 3 alleles for blood type- multiple
alleles
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CodominanceR allele for red flowers W
allele for white flowers red x white ---gt red
white spotted
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Polygenic traits

• Most traits are controlled by many genes, not
  just one.
• Examples hair color and skin color. There are
  several genes that control them.
• This is the reason that there are so many
  different colors of hair and skin in humans.

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Sex Linked Traits

• Traits associated with particular sexes are
  called sex-linked or X-linked traits.
• These are usually carried on the X chromosome.
• Females XX
• Males XY

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1st 22 are Autosomes, the last pair (XY) are sex
chromosomes)
Karyotype
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Charts that show relationships within a family
Pedigree
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Autosomal-Dominant
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SEX-LINKED
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SEX-LINKED
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Autosomal -Dominant
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Genetic Disorders
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Huntingtons Disease

• Huntington's disease degenerative disease that
  causes certain nerve cells in your brain to waste
  away.
• you may experience uncontrolled movements,
  emotional disturbances and mental deterioration.
• The disorder was documented in 1872 by American
  physician George Huntington.
• Fatal----ages30-60

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Colorblindness

• Sex-linked trait
• Gene for color vision located on the X
  chromosomes.
• Males are more likely to have colorblindness
  because they have only one X chromosome

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What do you see?
What do you see?

• The individual with normal color vision will see
  a 5 revealed in the dot pattern. An individual
  with Red/Green (the most common) color blindness
  will see a 2 revealed in the dots.

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TEST
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Down Syndrome

• Three copies of chromosome 21.
• Symptoms mental retardation and some physical
  deformities

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Downs Syndrome How do you get 3 copies of
chromosome 21?
Nondisjunction failure of chromosomes to
separate properly during cell division
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Cystic Fibrosis

• caused by a recessive allele on chromosome 7.
• Deletion of three bases.
• Affects the body's respiratory and digestive
  systems.

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Hemophilia

• Sex-liked, recessive trait
• Located on the X chromosome
• Missing a protein necessary for blood clotting
• Can bleed to death from minor cuts.

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Queen Victorias Pedigree showing Hemophelia
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Sickle Cell
People who carry the tendency to have sickle cell
anemia are less likely to die from malaria.
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Gene Therapy
The insertion of healthy genes into an
individuals cells or tissues to treat a disease.
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Example EOCT question

• What is nondisjunction?
• A. failure of chromosomes to separate during
  meiosis
• B. failure of the cytoplasm to divide properly
• C. the insertion of a gene into a different
  chromosome
• D. the deletion of a gene from a chromosome

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Which of the following shows how information is
transformed to make a protein? A DNA ?RNA ?
protein B gene ? chromosome protein C cell
respiration ? ATP ? protein D ATP ? amino acid ?
protein
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Information on mRNA is used to make a sequence of
amino acids into a protein by which of the
following processes? A replication B
translation C transcription D transference
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Pea plants have seeds that are either round or
wrinkled. In this cross, what will be
the phenotypic ratio of the offspring?
A 50 RR and 50 Rr B 25 RR, 50 Rr, and 25
rr C 50 round seeds and 50 wrinkled seeds D
100 round seeds
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What is a source of genetic variation? A
mutation B adaptation C replication D
transcription
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In Mendels experiments with a single trait, the
trait that disappeared in the first
generation and reappeared in the next generation
is called the
A homozygous trait B dominant trait C recessive
trait D heterozygous trait
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