Genetics Lesson

Mendelian Genetics

Dominant and Recessive

Gregor Mendel- a monk and mathematician

• known as Father of Genetics

• studied thousands of pea plants and came up with the basic ideas of simple genetics (simple dominance and simple recessive)

• His experiments led him to conclude that each trait was controlled by two factors

Mendel and Modern Genetics

Mendel lived in the 1800s and knew nothing of genetics, yet his findings have been accepted by modern geneticists

Mendel's Pea Plants

• He observed flower colors, seed colors, and seed shapes--- all of which are examples of "traits".

• Traits- characteristics passed on to offspring from parents

Mendel and His Thousands of Pea Plants

• Mendel performed thousands of experiments with the pea plants over many years

• He noticed that certain traits would appear in one generation and then disappear in the next generation

• Then, in later generations of pea plants, the trait that had disappeared would show up again.

Multiple Choice

Which of the following is NOT a trait that Mendel observed in his pea plants?

• seed color

• seed shape

• length of leaves

• flower color

An Example of Disappearing and Reappearing Traits

• Purple versus white flowers

• Generation 1: True-breeding purple crossed with true-breeding purple produced all purple flowers (offspring 1)

• Generation 2: Offspring 1 (all purple flowers) crossed with true-breeding white flowers produced all purple flowers (Offspring 2)

• Generation 3: Offspring 2 self-pollinates (basically reproduces with only itself) and produces mostly purple and some white flowers.

Why did the white flower trait not show up in one generation and then showed up in the next generation?

• Mendel observed this happening over and over and came to the conclusion that the purple was sometimes able to "block" the appearance of the white flowers.

• The purple trait was "dominant" over the white trait.

• The white flower trait was "recessive".

Law of Dominance

• a natural law stating that a dominant allele will always mask a recessive allele

Dominant versus Recessive

• Dominant- a trait that is expressed over another trait

• Recessive- a trait that can be hidden by another trait

• If one trait is dominant and another trait is recessive, and either one appears at different times throughout generations, Mendel concluded that there must be two factors involved in heredity- one factor from each parent.

• Modern genetics calls these factors "alleles".

Multiple Choice

What observation did Mendel make about certain traits that led him to conclude that some traits were dominant to other traits?

• Some traits appeared once every 10 generations.

• Some traits appeared twice every 10 generations.

• Some traits never appeared.

• Some traits appeared in most or all of the generations.

Multiple Choice

Mendel also observed seed color in pea plants. In a study of several generations, yellow seeds appeared more frequently than green seeds. Which of the following is most likely the reason for this observation?

• Green seeds are dominant to yellow seeds.

• Yellow seeds are recessive to green seeds

• Green seeds are recessive to yellow seeds.

Mendelian Genetics in Animals

• There are some traits in animals that follow the pattern of Mendelian genetics.

• Fur color, eye color, length of ears, etc. are all traits that can follow the law of dominance

Modern Mendelian Genetics

• We now know that each trait in an organism is controlled by genes (segments of DNA that code for specific proteins that control specific traits).

• However, a single gene has many different variations within it that provides for diverse options

• Alleles- different variations of the same gene

• There are two alleles for each trait- one from each parent

Possible Alleles

• homozygous (or pure)- having two of the same alleles for a trait 

• heterozygous (or hybrid)- having two different alleles for a trait

• Homozygous dominant- having two dominant alleles for a trait

• Homozygous recessive- having two recessive alleles for a trait

Representing Alleles

• Alphabetic letters represent alleles

• lowercase letters represent "recessive" alleles

• uppercase, or capital, letters represent "dominant" alleles

• 
  

Representing Alleles, continued

• **Recall that there are two alleles for each trait

• two capital letters (ex: TT) are called homozygous dominant alleles

• two lowercase letters (ex: tt) are called homozygous recessive alleles

• an allele pair with one capital letter and one lowercase letter (ex: Tt) are called heterozygous

Multiple Choice

Which of the following is correct?

• Yy is homozygous dominant.

• YY is heterozygous.

• yy is homozygous recessive.

• YY is homozygous recessive.

Multiple Choice

Which of the following represents a heterozygous genotype?

• Aa

• AA

• aa

• Ab

Multiple Choice

A recessive trait would appear in the phenotype of which of these?

• BB

• bb

• Bb

• Bf

Multiple Choice

Which of the following best describes Mendel's law of dominance?

• When an organism has two different alleles of the same gene, both genes will be expressed equally.

• When an organism has two alleles, one of genes will be expressed and the other will be hidden.

• When an organism has two different alleles of the same gene, one will always be dominant.

• The stronger of the two genes will be expressed.

Gregor Mendel's Pea Plants

Give Peas a Chance

Open Ended

Why don't you look like an elephant?

Multiple Choice

True or false: Parents traits blend in their offspring, like mixing paint.

• Always true

• Sometimes true

• Always false

Multiple Choice

True or false: if you look more like your mother, you received more of her genes than your father's genes.

• Always true

• Sometimes true

• Always false

Multiple Choice

All genetic traits are inherited the same way.

• True

• False

Remember:

• Heredity - the passing of traits from parents to offspring

• Genetics - the study of heredity

Gregor Mendel

• before Mendel: people knew traits were passed down, but were unsure how

• Austrian monk and biologist (1822-1884)

• studied pea plants over many generations

• "Father of Genetics"

His Research

• studied over 10,000 pea plants

• chose peas because they pollinate easily

• studied: seed color, seed shape, plant height, pod shape, pod color, flower location, flower color

His Discovery

• Genes come in pairs, one from each parent

• One gene is called an allele

• You have two genes for each trait (eye color, hair color, etc.)

His Discovery

• Genes are inherited separately

• Example: you can inherit your mom's blue eyes gene, but not her black hair gene

His Discovery

• Genes can come in different forms, but the dominant one be expressed

• Example: If you inherit a curly hair gene and a straight hair gene, you will see curly hair (the dominant one)

• Example: You will only see straight hair if you inherited TWO straight hair genes

Late Recognition

• He published his research in 1865, but no one understood its importance.

• After Mendel died, his fellow monks burned most of his work.

• Leftovers were rediscovered in 1900 and finally appreciated!

Multiple Select

Select all that are TRUE about Gregor Mendel.

• He was a lawyer.

• He studied pea plants.

• He was appreciated in his time.

• He discovered 3 main rules about inheritance.

• He was from Austria.

Multiple Select

Select all that are TRUE about inheritance.

• Genes for each trait are inherited separately.

• You get 100% of your mom's genes and 100% of your dad's genes.

• Genes are inherited in groups of 4.

• You can have a gene, but it not be physically seen.

• Dominant genes are those that will be seen, or expressed.

Lesson Overview

The Work of Gregor Mendel

THINK ABOUT IT

What is an inheritance?

It is something we each receive from our parents—a contribution that
determines our blood type, the color of our hair, and so much more.

What kind of inheritance makes a person’s face round or hair curly?

Lesson Overview

The Life of Gregor Mendel

The Life of Gregor Mendel

• Born in 1822 in Austria

• Wanted to be a teacher, but failed the exam (twice).

• Became a monk to have university paid for.

• Used pea plants to conduct his experiments at the monastery.

• Known as the Father of Genetics.

Multiple Choice

Why did Gregor Mendel become a monk?

• They had a good dental plan.

• They served very good food at the monastery.

• He was a deeply religious man.

• They offered to pay for university.

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

Where does an organism get its unique characteristics?

An individual’s characteristics are determined by factors that are passed
from one parental generation to the next.

Multiple Choice

Where does an organism get its unique characteristics?

• An individual’s characteristics are determined by factors that are passed down from the parents.

• An individual’s characteristics are determined by completely random factors.

• An individual’s characteristics are determined by factors that are passed down from the types of plants that are in your house.

• An individual’s characteristics are exactly the same as all other species.

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

Every living thing—plant or animal, microbe or human being—has a
set of characteristics inherited from its parent or parents.

The delivery of characteristics from parent to offspring is called
heredity.

The scientific study of heredity, known as genetics, is the key to
understanding what makes each organism unique.

Multiple Choice

The delivery of characteristics from parent to offspring is called

• exothermic

• Dominoes

• heredity

• trait

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

The modern science of genetics was
founded by an Austrian monk named
Gregor Mendel.

Mendel was in charge of the
monastery garden, where he was
able to do the work that changed
biology forever.

Multiple Choice

Who is Gregor Mendel

• an Austrian Monk from the mid 1800s who contributed to the study of Genetics

• The scientist who discovered the structure of DNA

• a British scientist who discovered penicillin

• The scientist who used X-Ray Crystallography to shed light on the structure of DNA

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

Mendel carried out his work with
ordinary garden peas, mostly because they grow quickly and have a lot of varieties. A single pea plant can
produce hundreds of offspring.

Today we call peas a “model
system.”

Multiple Choice

What did Gregor Mendel study?

• Mold Spores

• Pea Plants

• Sun Flowers

• Rats

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

Scientists use model systems
because they are convenient to study
and may tell us how other organisms,
including humans, actually function.

Lesson Overview

The Work of Gregor Mendel

The Experiments of Gregor Mendel

By using peas, Mendel was able to
carry out, in just one or two growing
seasons, experiments that would
have been impossible to do with
humans and that would have taken
decades—if not centuries—to do
with other large animals.

Multiple Choice

What specifically about Pea Plants did Mendel Study?

• Color of Pea Flower

• Colors of individual Peas

• Texture of Peas

• All of these

Lesson Overview

The Work of Gregor Mendel

The Role of Fertilization

Mendel knew that the male part of each flower makes pollen, which
contains sperm—the plant’s male reproductive cells.

Lesson Overview

The Work of Gregor Mendel

The Role of Fertilization

Similarly, Mendel knew that the female portion of each flower produces
reproductive cells called eggs.

Multiple Choice

What is the name of the female part of the flowering plant?

• plant ear

• little toe

• stigma

• ovule

Multiple Choice

What is the name of the male part of the flowering plant?

• plant ear

• little toe

• stigma

• ovule

Lesson Overview

The Work of Gregor Mendel

Genes and Alleles

From these results, Mendel drew two conclusions. His first conclusion
formed the basis of our current understanding of inheritance.

An individual’s characteristics are determined by factors that are passed
from one parental generation to the next.

Scientists call the factors that are passed from parent to offspring genes.

Multiple Choice

G = green, g = yellow
The genotype for a yellow plant is...

• GG

• Gg

• gg

• all of the choices result in yellow

Lesson Overview

The Work of Gregor Mendel

The Role of Fertilization

To do this, he had to prevent self-pollination. He did so by cutting away the
pollen-bearing male parts of a flower and then dusting the pollen from a
different plant onto the female part of that flower, as shown in the figure.

Lesson Overview

The Work of Gregor Mendel

Genes and Alleles

Each of the traits Mendel studied was controlled by one gene that occurred
in two contrasting varieties.

These gene variations produced different expressions, or forms, of each
trait.

The different forms of a gene are called alleles.

Multiple Choice

Genotype refers to the ...

• physical expression of the genes

• the possible combination of alleles in a gene

• whether an allele is dominant or recessive

• how an organism will appear

Lesson Overview

The Work of Gregor Mendel

Dominant and Recessive Traits

Mendel’s second conclusion is called the principle of dominance. This
principle states that some alleles are dominant and others are recessive.

An organism with at least one dominant allele for a particular form of a trait
will exhibit that form of the trait.

An organism with a recessive allele for a particular form of a trait will exhibit
that form only when the dominant allele for the trait is not present.

Punnett Squares

■

Step 1. State the key by using the capital letter of the dominant trait to
represent the dominant gene and the small letter of the dominant trait to
represent the recessive gene.
Ex: Y is used because Yellow is dominant to green, so a lowercase y is
used to represent green

■

Step 2. Write the cross using Homozygous and Heterozygous based
on information given to show the gametes. Ex: yy x Yy

■

Step 3. Draw the Punnett square and place the letters for the egg
alleles on one side of the square and the letters for the sperm alleles on
the other side of the square.

■

Step 4. Write the results inside each square by intersecting the
parents genes.

Multiple Choice

T - tall and t = short
In the punnett square below, what belongs in the missing square

• tt

• Tt

• Bb

• TT

Multiple Choice

B = brown fur  b = white fur
In the punnett square, what is the probability for white fur? 

• 0%

• 25%

• 50%

• 75%

Try This Punnett Square

In roses, red is dominant over white.

1. What letter represents the red
gene?

2. What letter represents the white
gene?

3. Cross two heterozygous red
roses. Describe the phenotype
of the offspring.

Multiple Choice

In a punnet square where are the parent alleles written?

• Top and inside the boxes

• Only on the left and right side of the boxes. 

• outside of the boxes (top and left side)

• All on the top side of the boxes

Multiple Choice

What is a punnett square?

• graph used to predict the possible genotypes of offspring in a given cross

• a graph used to predict the possible birth rate of offspring.

• a graph used to predict the possible behavioral characteristics an offspring could have

• None of the above

Multiple Choice

Two brown eyed parents (Bb) have a baby. What is the chance the baby is blue eyed?

• 0 %

• 25%

• 50%

• 75%

Multiple Choice

Heterozygous is when...

• the alleles are the same

• the alleles are different

• the alleles are absent

• the alleles are present

Multiple Choice

In a heterozygous genotype, the ___________ allele takes over in the phenotype.

• recessive

• dominant

• lower case letter

• both 

Multiple Choice

Which of the following alleles is homozygous (purebred) recessive?

• Tt

• tt

• TT

• t

Multiple Choice

Dominant alleles are represented by a:

• Male gene

• lowercase letter

• recessive trait

• capital letter

Multiple Choice

Aa, DD, bB, yy are all examples of

• genotypes

• phenotypes

Multiple Choice

In a heterozygous genotype, the ___________ allele takes over in the phenotype.

• recessive

• dominant

• lower case letter

• both 

Multiple Choice

What you see, or the physical appearance.

• Genotype

• Phenotype

• Homozygous

• Heterozygous

Multiple Choice

AA and Aa always show up as

• dominant

• recessive

Multiple Choice

aa always shows up as

• dominant

• recessive

Multiple Choice

Aa is

• homozygous

• heterozygous

Multiple Choice

Which of the following is a phenotype?

• Aa

• red hair

• heterozygous

• DNA

Multiple Choice

What is the dominant trait?

• yellow pea seeds

• green pea seeds

• there is no dominant seed

• Jolly green giant

Sex-linked Traits are found on the Sex Chromosomes

​

​

Sex-Linked Traits

Dropdown

X and Y are ​​

Select answer

chromosomes. Females are ​

Select answer

and males are ​

Select answer

.

​Sex-linked Traits are shown as a Superscript on the X or Y.

Sex-Linked Traits

Multiple Choice

In fruit flies, eye color is a sex-linked trait.  Red (R) is dominant to white (r).

Which genotype shows a female fly with white eyes?

• $$X^{R^{ }}X^r$$

• $$X^RX^R$$

• $$X^rX^r$$

Multiple Choice

Which genotype shows a male with white eyes?

R = Red, r= white

• $$X^rY$$

• $$X^RY$$

Match

Match the following. H= no hemophilia, h = hemophilia

• Male without hemophilia

• Female with hemophilia

• Female Carrier

• Male with hemophilia

• Female who is NOT a carrier

X^HY

X^hX^h

X^H X^h

X^hY

X^HX^H

• X^HY

• X^hX^h

• X^H X^h

• X^hY

• X^HX^H

​ 1. Write out XX or XY

2. Add in trait to the X only

3. Fill out punnett square as normal.

How to show Punnett Square

Multiple Choice

The following punnett square depicts the x-linked cross of a female who carries hemophilia with a man showing no symptoms. Fill in the genootype represented by the blank box in the punnett square.

• X^H X^H

• X^h X^H

• X^H Y

• X^h Y

Draw

Show punnett square for X^rX^r crossed with X^RY

Draw

Hemophilia (h) is recessive. Draw a punnett square for X^hX^h with X^HY

Multiple Choice

What is the likelihood of this cross have a child that is colorblind?

• 100%

• 75%

• 50%

• 25%

Dropdown

​

Select answer

are more likely to have an x-linked trait because males have only ​

Select answer

X chromosome. Females can be ​

Select answer

of an X-linked trait because they can be ​

Select answer

for the trait since they have ​

Select answer

X's.

7.4 Human Genetics and Pedigrees

KEY CONCEPT

A combination of methods is used to study human
genetics.

7.4 Human Genetics and Pedigrees

• Human genetics follows the patterns seen in other

organisms.

• The basic principles of genetics are the same in all sexually

reproducing organisms.
– Inheritance of many human

traits is complex.

– Single-gene traits are

important in understanding
human genetics.

7.4 Human Genetics and Pedigrees

• Females can carry sex-linked genetic disorders.

• Males (XY) express all of their sex linked genes.
• Expression of the disorder depends on which parent carries

the allele and the sex of the child.

X

Y

What is a Pedigree?

• A chart that shows how a trait is inherited

within a family over several
generations.

• Each generation is represented by Roman

numerals and each individual in each
generation is numbered left to right.

• We can use a pedigree chart and key to

determine the genotype and phenotype
of the family members and the genetic
inheritance patterns of traits can be
tracked.

Multiple Choice

What is this?

• Pedigree

• Karyotype

• Venn diagram

• Punnett Square

Symbols Used in Pedigrees

•Circles represent females
•Squares represent male
•Horizontal lines represents mating/marriage
•Vertical lines represents children

• Unshaded represents unaffected individuals

• Fully Shaded represents affected individuals

• Half-shaded represents carriers

Parts of a
Pedigree

Unaffected

Female

Unaffected

Male

Mating

Offspring

Affected
female
offspring

Unaffected

male offspring

Multiple Choice

What does a filled in square represent?

• Not affected Female

• Not affected Male

• Affected Male

• Affected Female

Multiple Choice

How many generations are shown in this pedigree?

• 1

• 2

• 3

• 4

Multiple Choice

What does an open circle represent?

• Not Affected Male

• Not Affected Female

• Affected Male

• Affected Female

Multiple Choice

How many kids did the mother and father from the first generation have?

• 2

• 4

• 5

• 6

7.4 Human Genetics and Pedigrees

• A pedigree is a chart for tracing genes in a family.

• Phenotypes are used to infer genotypes on a pedigree.
• Autosomal genes show different patterns on a pedigree

than sex-linked genes.

7.4 Human Genetics and Pedigrees

• If the phenotype is more common in males, the gene is

likely sex-linked.

Multiple Choice

What is the pattern of inheritance shown in this pedigree?

• autosomal dominant

• autosomal recessive

• sex-linked dominant

• sex-linked recessive

Multiple Choice

Analyze the following pedigree. What type of inheritance pattern is shown?

• autosomal dominant

• autosomal recessive

• sex-linked dominant

• sex-linked recessive

Multiple Choice

For the pedigree below, shaded symbols represent afflicted people. Males are squares; females are circles. If the trait is a sex-linked trait carried on the X chromosome, what is true about the mother represented by circle 1?

• She has the genotype XXY.

• She has two alleles for the disorder.

• She is a carrier for the disorder.

• She has no alleles for the disorder.

Multiple Choice

The trait in pedigree in Figure 14–5 has two alleles: P (dominant) and p (recessive). The black symbols show the dominant phenotype, and the white symbols show the recessive phenotype. What is the genotype of individual number 1?

• Pp

• P

• p

• PP

Multiple Choice

How many generations are shown in the pedigree below?

• 2

• 4

• 6

• 8

7.4 Human Genetics and Pedigrees

• Several methods help map human chromosomes.

• A karyotype is a picture of all chromosomes in a cell.

X Y

7.4 Human Genetics and Pedigrees

• Karyotypes can show changes in chromosomes.

– deletion of part of a chromosome or loss of a

chromosome

– large changes in chromosomes
– extra chromosomes or duplication of part of a

chromosome

Multiple Choice

Examine the pedigree below. Identify the type of inheritance pattern shown in the pedigree.

• Autosomal dominant

• Autosomal recessive

• X-linked recessive

• X-linked dominant

Multiple Choice

Labrador retriever's fur color is an example of epistasis. In this case the E gene controls the expression of the B gene. It a puppy was born with the genotype eeBB its fur color would be ________ and if it was born with the genotype EEbb it would be __________

• yellow, yellow

• yellow, black

• chocolate, black

• yellow, chocolate

Multiple Choice

Term for an interaction where of one allele hides the effects of another allele. It can be seen in the coat color of Labrador retrievers, which can be black, brown, or yellow. Dogs appear yellow because the black/brown dark fur gene is "blocked" by the homozygous recessive yellow fur gene.

• codominance

• dominance

• multiple alleles

• epistasis

Multiple Choice

What type of inheritance is determined by multiple genes located at different loci on different chromosomes and there can be a range of traits?

• Codominance

• Incomplete dominance

• Polygenic traits

Multiple Choice

These type of traits arise from the interaction of multiple pairs of genes. Examples include such traits as skin color, height, and eye color

• epistasis

• polygenic traits

• autosomes

Multiple Choice

Both traits expressed TOGETHER (not blended)

• Codominance

• Incomplete Dominance

• Mendelian trait

• Sex-linked