Chapter 8 Part Two
By:
Brianna Shields

 Punnett
Squares
Mendel’s Study of Traits
 1. Diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross

 Punnett
Squares
Mendel’s Study of Traits
 2. 4 boxes in a large square
 3. One parent’s gametes written across top, other down left side
 4. Fill boxes by combining alleles from top and left sides (creates possible genotypes)

 Punnett
Squares
Mendel’s Study of Traits
 5. Steps:
 A. Set up boxes
 B. Create dominant and recessive key
 C. Write parental gametes across top and down left side
 D. Perform monohybrid cross
 E. Record genotype percentages
 F. Record phenotype percentages

t
T
T T
TT TT
Tt Tt
Genotypes:
50% TT Homozygous
Dominant
50% Tt Heterozygous
Phenotypes
100% Tall
T= Tall t=Short

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?

b b
B B
Genotypes:
100 % Heterozygous
Bb Bb
Bb Bb
Phenotypes
100% Brown Eyed
B= Brown b=Blue

Perform the cross
 A couple is hoping their child will have the tongue rolling ability when it is born.
 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?

R r
R r
RR Rr
Rr rr
R= Tongue Rolling r= Non-tongue Rolling
Genotypes:
25% Homozygous Dominant
50% Heterozygous
25% Homozygous Recessive
Phenotypes
75% Tongue Rolling
25% Non-tongue Rolling

 Punnett
Squares
Mendel’s Study of Traits
 6. Used by horticulturists and animal breeders to predict the crosses that will most likely produce offspring with desirable phenotypes

Mendel’s Study of Traits
 Determining homo and heterozygosi ty
 Test Cross- individual with dominant phenotype but unknown genotype is crossed with a homozygous individual
 Ex: Yellow seeded (Y?) crossed with green seeded (yy)
 If all offspring yellow, their genotype must by
Yy and unknown parent must be YY
 If half are yellow, half are green, unknown parent must’ve been Yy

• Likelihood that a specific event will occur (used to predict genetic crosses)
• Number of one kind of possible outcome divided by total number of all possible outcomes

Mendel’s Study of Traits
 Probability  Ex: Probability of flipping a coin and getting heads is 1/2
 Ex: Probability of a eertain seed color when there are 2 possible alleles for seed color is 1/2

Mendel’s Study of Traits
 Probability  Probability of the outcome of a cross (getting an allele from one parent is separate from getting an allele from the other)
 1/2 x 1/2 equals 1/4 (2 independent events occurring should be multiplied)

 Pedigree
Mendel’s Study of Traits
 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
 Click here to watch a tutorial about pedigrees

Mendel’s Study of Traits
 Autosomal
Traits
 Occur on chromosomes not related to gender
 Appear in both sexes equally

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 trait to mask recessive one)
 Females would have to be homozygous recessive to show trait (less likely to inherit)

 Autosomal
Dominant
Condition
Mendel’s Study of Traits
 Every individual with trait has a parent with the trait

Mendel’s Study of Traits
 Autosomal
Recessive
Condition
 Individual can have one, two or no parents with the condition because trait is recessive

Diagram: Who are the carriers? Who is infected?

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?

 Polygenic
Trait
Complex Patterns of
Heredity
 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

– Ex: white snapdragon x red snapdragon equals pink snapdragon
– Ex: curly hair x straight hair (both homoz dom) equals wavy hair

 Multiple
Alleles
Complex Patterns of
Heredity
 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
 Codominanc e
 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

 Genetic
Disorders
Genetic Disorders
 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

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

 Hemophelia
Genetic Disorders
 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

 Treating genetic disorders
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

 Treating genetic disorders
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)

 Treating genetic disorders
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