Transcript Chapter 8 - Genetics Part 2

Think – Pair - Share
 Selective
Breeding
 People have used selective breeding to
improve crops and domestic animals
 Think of two examples of selective
breeding in domestic animals or crops.
What particular traits may breeders be
looking out for in your examples?
Mendel’s Study of Traits
 Punnett
Squares
 Punnett Squares: predicts the outcome of
a genetic cross be considering all possible
combinations of gametes in the cross
 Assists breeders in predicting how
often a trait will appear when two
organisms are crossed (bred)
Punnett Example 1:
TT x Tt
T
T
Genotypes:
T
TT
TT
t
Tt
Tt
50% TT
50% Tt
Phenotypes
100% Tall
T= Tall
t=Short
Example 2: Complete the Cross
 Brown eyes is dominant. Blue
eyes is recessive. Cross a
homozygous dominant and a
homozygous recessive.
 What percentages of blue-eyed
and brown eyed offspring will you
get?
 Use B for brown and b for blue
Punnett Example:
BB x bb
B
B
b
Bb
Bb
b
Bb
Bb
Genotypes:
100 % Bb
Phenotypes
100% Brown Eyed
B= Brown b=Blue
Example 3: Perform the cross
 Tongue rolling is a
dominant trait. Non tongue
rolling is recessive.
 If the mother is
heterozygous and the
father is heterozygouswhat are their chances of
having a child with the
tongue rolling ability?
 Use R for dominant and r
for recessive
Punnett Example:
Rr x Rr
R
r
R
RR
Rr
r
Rr
rr
Genotypes:
25% RR
50% Rr
25% rr
Phenotypes
75% Tongue Rolling
R= Tongue Rolling
r= Non-tongue Rolling
25% Non-tongue Rolling
Intermediate Traits
 Incomplete
 Incomplete Dominance:
Dominance
 Usually the dominant trait takes
over the recessive
 In some traits, there can be a “mix”
 Ex: Red flowers crossed with white
flowers = Pink flowers
 Ex: Straight hair crossed with curly
= wavy hair
Mendel’s Study of Traits
 Pedigree Chart
 What if you wanted to learn about an
inherited trait present in your family?
 Pedigree Chart: Family history that
shows how a trait is inherited over
generations
 Useful in tracking genetic disorders to see if
an individual is a carrier or may pass it the
disorder to their offspring
Mendel’s Study of Traits
 Carrier
 Carrier: Heterozygous
(ex: Cc) for an inherited
disorder but does not show
symptoms of the disorder
Mendel’s Study of Traits
 Autosomal
Traits
 Occur on chromosomes not related to
gender (body cells)
 Both sexes have same probability of
inheriting
Mendel’s Study of Traits
 Sex-linked
Traits
 Trait whose allele is located on X
chromosome
 Most are recessive
 Males mainly affected because they
only have one X chromosome
 Females usually just carriers (presence
of dominant X to mask recessive one)
 Females would have to be homozygous recessive
to show trait (less likely to inherit)
Examples:
-Colorblindness
-Male Baldness
-Hemophilia
Evaluate the Pedigree
 Answer the questions in your notes using this Pedigree
chart for colorblindness
I
II
III
IV
Assessment Three
 Predict the expected phenotypic and genotypic ratios among the
offspring of two individuals who are heterozygous for freckles (Ff)
by using a punnett square
 Summarize how a test cross can reveal the genotype of a pea
plant with round seeds
 Calculate the probability that an individual heterozygous for a
cleft chin (Cc) and an individual homozygous for a cleft chin (cc)
will produce offspring that are homozygous for a cleft chin
 When analyzing a pedigree, how can you determine if an
individual is a carrier (heterozygous) for a trait being studied?
Complex Patterns of
Heredity
 Polygenic Trait
 When several genes influence a trait (all
on one chromosome or on different)
 Ex: Eye color, height, weight, hair and skin color
 Have degrees of intermediate conditions between
extremes
 Can be complex due to independent assortment
and crossing over during meiosis
Complex Patterns of Heredity
 Intermediat
e Traits
 Incomplete dominance- an
individual displays a trait
that is intermediate
between the two parents
 Ex: white snapdragon x red
snapdragon equals pink snapdragon
 Ex: curly hair x straight hair (both
homoz dom) equals wavy hair
Complex Patterns of
Heredity
 Multiple Alleles
 Genes with three or more alleles
 EX: ABO blood groups
 A and B refer to carbohydrates on
surface of red blood cells, O has none
 A and B dominant over O, but not over
each other (codominant)
 Can only have 2 of the possibilities for
the gene
Possible Blood Type
Possibilities
Possible Blood Type
Possibilities
Complex Patterns of
Heredity
 Codominance
 2 dominant alleles are expressed at the
same time and both forms of the trait
are displayed
 Ex: AB blood group (has both A and B
carbohydrates on the surface of red
blood cells)
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 1: Hydrangea flowers
 Blue (acidic soil) to pink (neutral to basic soil)
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 2: Arctic Fox
 During summer, fox produces enzymes that make
red brown pigments
 In cold, pigment producing genes don’t function
and coat remains white
 Fox blends in with snowy white background
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 3: Siamese Cats
 Genotype results in darker fur color in cooler areas
of the body (ears, nose, paws, tail darker than rest
of body)
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 4: Human Height
 Nutrition and internal environmental conditions
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 5: Human Skin Color
 Exposure to sun
Complex Patterns of
Heredity
 Traits
influenced by
environment
 EXAMPLE 6: Human Personality
 Aggression influenced by environment and genes
Complex Patterns of
Heredity
 Traits
influenced by
environment
 Twins used to study environmental
influences because their genes are
identical, any differences between them
are due to the environment
DO NOW
 Grab a Biology book, turn to page 179
 Take out Notes
 Turn to Page
on genetic disorders
 Think – Which genetic disorder does this picture
represent?
Genetic Disorders
 Genetic
Disorders
 In order for a person to develop and function
normally, proteins encoded in genes must
function precisely
 May have harmful effects produced by inherited
mutations
 Damaged or incorrectly copied genes can result
in the production of faulty proteins
 Mutations are rare, due to efficient correction
systems in cells
 Often carried by recessive alleles in
heterozygous individuals and passed down as
homozygous alleles in offspring
Gallery Walk!
 Genetic
Disorders
 Each group will be assigned a section
 Pages 179 - 182
 Make a poster in 15 minutes on your section that
highlights the IMPORTANT & SIGNIFICANT
details of your section
 Make sure you can answer the questions on
your section – if you can’t – add the info!
 Each group will move around to each section
and will have 5 minutes to answer each question
Genetic Disorders
Genetic Disorders
 Sickle Cell
Anemia
 Caused by mutated allele that produces
defective form of protein hemoglobin
 In rbc’s, Hb binds to and transports oxygen
 Causes sickle shaped red blood cells that
rupture easily, clog blood vessels and can’t
transport oxygen well
 Carriers exposed to malaria can prevent
infection when they have sickle cell. It kills
malaria protozoans and healthy rbc’s can
still transport enough oxygen
Genetic Disorders
 Cystic Fibrosis
 Fatal, recessive trait
 Most common inherited disorder in Caucasians
 1/25 babies are carriers
 1/2500 babies have disease
 No known cure
 Have defective copy of gene needed to pump Cl
in and out of cell
 Lung airways clog with mucus, liver and
pancreas ducts get blocked
Genetic Disorders
 Hemophelia
 Sex linked trait
 Impairs blood’s ability to clot
 Mutation on one of a dozen blood
clotting genes on x chromosome is
hemophelia A
 If male receives defect on x
chromosome from mother, y
chromosome can’t compensate develops disease
Genetic Disorders
 Treating
genetic
disorders
 Most can’t be cured, but can be treated
 Families with histories of genetic
disorders can receive genetic
counseling before having kids to assess
the risk
Genetic Disorders
 Treating
genetic
disorders
 Some genetic disorders can be treated if
diagnosed early on
 Ex: PKU (Phenylketoneuria)- lack enzyme
for converting amino acid phenylalanine to
tyrosine
 Can cause severe mental retardation
 If found immediately right after birth, baby can
be given a diet low in phenylalanine to avoid
the symptoms
 Many states require testing newborns
for PKU (inexpensive)
Genetic Disorders
 Treating
genetic
disorders
 Gene Therapy
 Replace defective gene with healthy one
 Isolate copy of the gene and deliver to
infected cell by attaching it to a virus
 Virus with healthy gene enters cell, starts
producing healthy protein
 “Cures” the genetic disorder
Genetic Disorders
 Gene Therapy
 Tried for cystic fibrosis by using cold
virus
 BUT, most individuals are immune to cold
virus and the lung cells rejected it
 Currently trying with an AAV virus that
produces almost no immune response
Assessment Four
 Differentiate between incomplete dominance and
codominance
 Identify two examples of traits that are influenced by
environmental conditions
 Summarize how a genetic disorder can result from a
mutation
 Describe how males inherit hemophelia
 A nurse states that a person cannot have the blood
type ABO. Do you agree or disagree? Explain
Genetics Websites
 OLogy: The Gene Scene