Bell Ringer

Which features do you have that match your mother?

Your father?

Which of the following features do you have?

Widow’s Peak?

Ability to roll your tongue?

Attached earlobes?

Simple Genetics

Exploring How Traits are Passed On

Punnett Squares

In order to determine the traits that a person might

inherit, we use a simple diagram called a Punnett Square!

Punnett Squares give us the probability of an offspring having

particular traits

Pieces of the Puzzle

Before completing a square, you must know the components

Allele-An allele is a variant form of a gene

Humans inherit one allele from each parent that determines a trait

For example, alleles might determine if you have curly or straight hair, are tall or short, etc.

Dominant-A dominant allele show their effect even if there is only one copy of the allele (think of them as being strong!)

Dominate alleles are denoted by a capital letter (ex. A)

Recessive- A recessive allele will only show up if no dominant alleles are in place (think of them as being weak!)

Recessive alleles are denoted by a lowercase letter (ex. a)

Dominant and Recessive alleles pair together to determine a trait (ex. AA, Aa, aa)

Homozygous vs. Heterozygous

So…alleles pair together (AA, aa, Aa)

Homozygous-if both letters are identical (both dominant (capital) or both recessive (lowercase)), the alleles are homozygous

“Homo” means “same”

Ex. Let’s say “A” represents the allele for a widow’s peak, and “a” represents the allele for a straight hairline

A person with “AA” would be called homozygous dominant

A person with “aa” would be called homozygous recessive

Heterozygous-if both letters are different (one dominant (capital) and one recessive (lowercase)), the alleles are heterozygous

“Hetero” means “different”

A person with “Aa” would be heterozygous

Would they have a widow’s peak or a straight hairline?

Phenotype and Genotype

All of these allele combinations tell us the phenotype and genotype of a person

Genotype-The genetic, inheritable information of an organism

Example: A person’s genotype is Aa (heterozygous); they can pass on either a dominant allele or a recessive one to their children.

Phenotype-The outward, physical appearance of an organism

Example: A person has a widow’s peak

Let’s Practice

Dominant or Recessive?

A

b

B

Heterozygous or Homozygous?

AA

Bb

cc

Phenotype or Genotype?

She is homozygous recessive (rr)

She has blue eyes

Building a Punnett Square

Consider the following alleles for pea plant color:

AA (Yellow-homozygous dominant)

Aa (Yellow-heterozygous)

aa (Green-homozygous recessive)

Let’s say you had two pea plants, both heterozygous

yellow (Aa), and you wanted to know what color

plants would be produced. How would you find out?

Set up and Punnett Square

Building a Punnett Square

What we know: Both parent plants are Aa

So, cross Aa x Aa will be carried out in the Punnett

Square below: Mother

Father

*Note: It doesn’t

matter where you

set up the

mother/father, the

results will be the

same!

Building a Punnett Square

So, how do you carry out a Punnett Square?

Father’s letters cross to the right

Mother’s alleles cross down, filling in the squares to complete

the allele Mother

Father

AA Aa

Aa aa

*Notice each

potential

combination has

one allele from

mom and one

from dad

Interpreting the Final Square

Once the square is finished, always determine the

genotype and phenotype ratios of the possible offspring

Genotype: 1:2:1

-1 AA, 2 Aa, and 1aa

Phenotype: 3:1

-3 Yellow, 1 Green

Note: These ratios are equally probable for each offspring, meaning each offspring has

the same chance of inheriting the traits!!

Practice

Complete the Cross: Tt x tt

Genotype:

Phenotype:

Practice

What is the probability of producing offspring that have

short whiskers from a cross of two long whiskered seals,

one homozygous dominant and one heterozygous?

Genotype:

Phenotype:

W= long whiskers (dominant)

w=short whiskers (recessive)

A Few Notes on Genetics…

Some traits are controlled by more than one pair of

genes, and so present a wide range of phenotypes

(ex. Skin, hair, eye color)

All traits depend on both genetic and environmental

factors

Heredity determines your traits, but the environment may play

a role in how they act

Bell Ringer

W= long whiskers (dominant)

w=short whiskers (recessive)

What is the probability of producing offspring that have

short whiskers from a cross of two seals, one

homozygous recessive and one heterozygous?

Draw the Punnett Square

Determine the Genotype ratios

Determine the Phenotype ratios

Answer the above question

Bell Ringer

W= long whiskers (dominant)

w=short whiskers (recessive)

What is the probability of producing offspring that have

short whiskers from a cross of two seals, one

homozygous dominant and one heterozygous?

Draw the Punnett Square

Determine the Genotype ratios

Determine the Phenotype ratios

Answer the above question

Genetic Diseases

How Diseases are Carried Through Generations

Dominant and Recessive

If a disease is recessive, both parents have to pass on a

mutated allele to the offspring

Those who are heterozygous (Aa) are carriers, meaning they

have the mutated allele and can pass it on, but are healthy

themselves

If a disease is dominant, only one parent has to pass on

the mutated allele for offspring to have it

Can a person with a dominant disease be a carrier?

Let’s take a look at some specific genetic

diseases…

Cystic Fibrosis (cf)-Recessive

This disease causes a mucus

buildup in the lungs and

digestive system

Those affected have difficulty

breathing and poor growth

Common in those with

European Ancestry

Live expectancy up to 35

years thanks to gene therapy

Sickle Cell Anemia-Recessive

This disease affects a person’s

red blood cells

A mutation causes the cells to be

long and bent (“sickle” shaped)

The odd shape causes the cells

to get stuck in blood vessels

Cuts off blood flow and circulation

Common in those with African

ancestry

Carriers are associated with

malaria resistance-we’ll discuss why

later!

PKU-Recessive

PKU- Phenylketonuria

A condition in which the body is missing the enzyme that breaks down phenylalanine, an amino acid

This means it builds up in the body, which results in mental deterioration

Memory loss/identity loss!

People affected have to keep a low protein diet and have the enzyme injected regularly

This must be done for life!

Genetic Disease Punnett Squares

A woman is concerned that she may develop

Huntington’s Disease because her father has it. What is

the probability that she has Huntington’s?

Note: The mother does not have Huntington’s Disease.

Huntington’s-Dominant

This disease affects the muscles of the body

Those affected will slowly have muscle function decline

Painful, like a muscle cramp that won’t go away

Unfortunately, it often does not show signs until the person reaches mid 30s-can take up to 20 years to kill!

Shows up after the person has already had children, meaning that they have already passed the allele

Affects all people!

Genetic Disease Punnett Squares

A woman who is a carrier for Cystic Fibrosis marries a

man who is also a carrier. What is the probability that

they will have a child with Cystic Fibrosis?

Bellringer-4/23/15

Complete the Genetic Diseases Review Worksheet on

your desk. We will work on this for 30 minutes.

Bellringer-4/24/15

We have a quiz today. You have 10 minutes to study for

your quiz. Be sure to review:

Definitions

How to complete Punnett Squares

Genetic Disease patterns and symptoms

Bellringer-4/27/15

Complete the Punnett Square review sheet on your desk!

Complex Genetics

Codominance, Incomplete Dominance, Sex-Linked Traits, and

Blood Typing

Incomplete Dominance

Sometimes, one allele is not completely dominant over

another allele

In this case, the offspring are blends of both parents!

The heterozygote has a unique phenotype because one gene

does not dominate the other

Example: Red Flower (RR) + White Flower (WW)= Pink

Flowers (RW)

Incomplete Dominance

During incomplete dominance, organisms who are

heterozygous for a trait have the opportunity to pass

either gene to the offspring

Therefore, a cross between two heterozygous organisms

have the following results:

1 RR: 2 Rr: 1 rr

1 Red: 2 Pink: 1 White

Incomplete Dominance Example

A red carnation is crossed with a white carnation and the

resulting offspring are all pink (indicating incomplete

dominance). What would be the result of a cross between

a pink and a white carnation?

Codominance

Sometimes, both alleles are equally dominant

Therefore, both alleles will be expressed in phenotype

In this case, the offspring display the traits of both

parents!

Example: White Cow (WW) + Brown Cow (BB)= White and

Brown Cow (BW)

Case Study: Sickle Cell Anemia

Although we discussed Sickle-Cell Anemia’s recessive

inheritance pattern, the disease does display a certain

codominance

Those homozygous affected (aa) have misshapen cells

Those homozygous unaffected (AA) have normal cells

Those heterozygous (Aa) are unaffected carriers, but can have

some misshapen cells mixed in

This unique feature means heterozygous individuals are resistant to

severe malaria!

Codominance Example

A bird with white and blue feathers mates with another

white and blue bird (BW). What are the phenotypic ratios

of the offspring?

Bellringer-4/28/15

Complete the bellringer sheet

on your desk!

Blood-Typing

Human blood types include a codominance pattern

Humans can have type A, B, AB, or O blood

The alleles involved are two codominant alleles (IA and IB), and

one recessive allele (i)

Genotype Blood Type

IAIA or IAi A

IBIB or IBi B

IAIB AB

ii O

Blood Type Practice Problem

The father is type A homozygous, and the mother is type

O. What are the possible blood types of their children?

Is Parentage Possible?

Ralph has type B blood and his wife Rachel has type A

blood. They are very shocked to hear that their baby has

type O blood, and think that a switch might have been

made at the hospital. Can this baby be theirs? Explain.

Bellringer-4/29/15

Write the possible genotypes for the following blood types:

Type A: __________ or ___________

Type B: __________ or ___________

Type AB: _________

Type O: _________

Solve: There is a mixup between babies at the hospital. The baby has type O blood. On set of parents have the genotypes IAIA and IAi. The other set of parents are a heterozygous Type A mother and a heterozygous Type B father. Make the crosses of both sets of parents. Which set does the baby belong to?

Sex-Linked Traits

Genes located on the sex chromosomes are called

sex-linked genes

Usually found on the X Chromosome

Because of this, males are much more likely to express a

trait than females, because males only have one X

chromosome!

Sex-Linked Traits

Let’s take a look at the possible alleles in a recessive sex-

linked disease:

Female: XAXA, XAXa, XaXa

Notice that the female must inherit 2 recessive copies to display the

trait. It is also possible for females to be carriers of sex-linked traits.

Male: XAY, XaY

Notice the male does not have a second X to help mask the trait. This

means that if he inherits the recessive copy, he will display the trait!

Because of this, males are much more likely to inherit a

sex-linked trait!!!

Common Sex-Linked Traits

Hemophilia-A bleeding disorder that slows the blood clotting process

Color-Blindness-The inability to see color, or perceive color differences

Because of its X-linked inheritance, both of these conditions are more common in men

Sex Linked Problems

Cross a woman carrier for hemophilia to a hemophiliac

man. What percentage of the females could inherit the

trait? Males?

Pedigrees

Inheritance Patterns Through Generations

What is a Pedigree?

A pedigree is the recorded ancestry of a family

Pedigrees allow us to see the genotypes and inheritance

patterns through the generations of a family

What Does a Pedigree Tell Us?

Pedigrees can give us insight into how traits are

passed through families. You can tell a lot through a

pedigree. For example:

The phenotypes and genotypes of individuals

The inheritance pattern.

If more males are affected, it is likely sex linked

If there are no carriers and one of the parents must have

it, the disorder is dominant

If carrier parents produce some affected children, the

disease must be recessive

Pedigree Example Problems

What type of inheritance pattern is shown below?

What would be the genotype of individual I-1?

Pedigree Example Problems

What type of inheritance pattern is shown below?

What would the genotypes be of individuals II-1 and III-5?

Bellringer-4/30/15