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Chapter 8 Part Two. By: Brianna Shields. Punnett Squares. 1. Diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross. Mendel’s Study of Traits. Punnett Squares. 2. 4 boxes in a large square

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Chapter 8 part two

Chapter 8 Part Two


Brianna Shields

Mendel s study of traits

Punnett Squares

1. Diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross

Mendel’s Study of Traits

Mendel s study of traits1

Punnett Squares

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)

Mendel’s Study of Traits

Mendel s study of traits2

Punnett Squares

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

Mendel’s Study of Traits

Punnett example tt x tt
Punnett Example: TT x Tt




50% TT Homozygous Dominant

50% Tt Heterozygous



Tt Tt



100% Tall

T= Tall t=Short

Complete the cross
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?

Punnett example bb x bb
Punnett Example: BB x bb




100 % Heterozygous

Bb Bb


Bb Bb



100% Brown Eyed

B= Brown b=Blue

Perform the cross
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 heterozygous- what are their chances of having a child with the tongue rolling ability?

Punnett example rr x rr
Punnett Example: Rr x Rr




25% Homozygous Dominant

50% Heterozygous

25% Homozygous Recessive



Rr rr



75% Tongue Rolling

25% Non-tongue Rolling

R= Tongue Rolling

r= Non-tongue Rolling

Mendel s study of traits3

Punnett Squares

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

Mendel s study of traits4

Determining homo and heterozygosity

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

Mendel’s Study of Traits

Mendel s study of traits5


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

Mendel s study of traits6


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

Mendel s study of traits7


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)

Mendel’s Study of Traits

Mendel s study of traits8


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

Mendel s study of traits9


Heterozygous for an inherited disorder but does not show symptoms of the disorder

Mendel’s Study of Traits

Mendel s study of traits10

Autosomal Traits

Occur on chromosomes not related to gender

Appear in both sexes equally

Mendel’s Study of Traits

Mendel s study of traits11

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)

Mendel’s Study of Traits

Mendel s study of traits12

Autosomal Dominant Condition

Every individual with trait has a parent with the trait

Mendel’s Study of Traits

Mendel s study of traits13

Autosomal Recessive Condition

Individual can have one, two or no parents with the condition because trait is recessive

Mendel’s Study of Traits

Assessment three
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

Complex patterns of heredity1

Intermediate 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

Complex patterns of heredity2

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

Complex Patterns of Heredity

Complex patterns of heredity3


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

Complex patterns of heredity4

Traits influenced by environment

EXAMPLE 1: Hydrangea flowers

Blue (acidic soil) to pink (neutral to basic soil)

Complex Patterns of Heredity

Complex patterns of heredity5

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

Complex patterns of heredity6

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

Complex patterns of heredity7

Traits influenced by environment

EXAMPLE 4: Human Height

Nutrition and internal environmental conditions

Complex Patterns of Heredity

Complex patterns of heredity8

Traits influenced by environment

EXAMPLE 5: Human Skin Color

Exposure to sun

Complex Patterns of Heredity

Complex patterns of heredity9

Traits influenced by environment

EXAMPLE 6: Human Personality

Aggression influenced by environment and genes

Complex Patterns of Heredity

Complex patterns of heredity10

Traits influenced by environment

Twins used to study environmental influences because their genes are identical, any differences between them are due to the environment

Complex Patterns of Heredity

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 disorders2

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

Genetic disorders3

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

Genetic disorders4


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

Genetic disorders5

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

Genetic disorders6

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

Genetic disorders7

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

Genetic disorders8

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

Genetic Disorders

Assessment four
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
Genetics Websites

  • OLogy: The Gene Scene