Mendel, Terms, and How to Show Work on Genetics Problems

Traits and Families

L. Coleman 2013

•

_{We will begin by looking at several families.}

– Each group will look at a different family that has a

specific trait.

– You will look for patterns in the occurrence of that

trait that might help us understand how it might be

passed down in the family.

•

Each group will create a pedigree* of the

family to help uncover any patterns that

might exist.

* A pedigree is just a family tree that shows which

family members have a particular genetic trait.

Pedigree Basics

male

female

affected male

affected female

offspring siblings

parents a mating

Practice

TRAIT = Red Hair

John and Jane Stevens are married. John has red hair but Jane is a brunette. Their first child Susan has red hair, but the second child George is blonde and their youngest, Anne has brown hair. Susan is married to a dark-haired man

named Ted. Their daughter Eva has dark hair.

Make a pedigree for the Stevens family for the red hair trait.

John Jane

Anne George

Susan Ted

Patterns in pedigrees:

DIRECTIONS:

1. Using the information in the family history, create a pedigree of the family on your whiteboard.

2. Identify all family members on the pedigree by first name. 3. Once competed, transfer the pedigree to poster paper.

a. At the top of the paper write: 1) the name of the family.

2) The name of the trait.

3) The # of variations of the trait and what they are. b. At the bottom, write:

1) PATTERNS: list any patterns you noticed in the occurrence of the trait in the family.

2) QUESTIONS: list any questions you have (at LEAST one question required).

Learn about 2 other families.

•

_“A”

_{partners rotate to the next table.}

_“B”

partners stay to teach other groups about your

family.

–

_{“Teachers”:}

• Explain what the trait is and what symptoms it

causes.

• Tell how many variations of the trait are in the

family and what they are.

• Point out any patterns you identified.

–

“Learners”:

feel free to ask questions. Write down

what you learn at each table.

• Check out the posters of the other group (if there is one) that did the same family. Note similarities and differences.

– Tables 1 and 5 MARCUS – Tables 2 and 7 SUMMERS – Tables 3 and 8 McCANN – Tables 4 and 9 MADEIROS – Table 6 REED

1.When done, go back to your own table and take down your poster. 2.If you saw anything at the other group that you’d like to change/add to

What did you observe in

looking at all these families and

their traits?

• Is there just one pattern? Just one way

that traits are passed down in families?

• What are some of the differences you

noticed between the 3 families you

observed?

Model of Inheritance (so far...)

TERMS

gene

trait

allele

RELATIONSHIPS

1. Sexually reproducing organisms

have two genes that determine each trait (inherited characteristic), one from each parent.

a. A parent passes only one of his/her two genes for a trait to each offspring.

b. Random chance determines which of the two genes is passed to each offspring.

2. Genes for a trait can occur in different versions called alleles.

Should already be in your glossary:

ALLELES: different

versions of genes for the same trait (example: for eye color there are blue and brown alleles).

We will start by looking at the most famous genetics data ever gathered...

Gregor Mendel’ s Experiments with Pea Plants

Gregor Mendel was a priest in what is now the

Czech Republic. He was a high school science teacher and keeper of the monastery garden.

Mendel’s monastery today. Mendel’s garden.

His curiosity about heredity led him do numerous experiments on pea plants. His results and conclusions written in 1865 are the foundation of modern genetics.

He chose pea plants because of the structure of their flowers. Male and female reproductive parts are enclosed by petals.

He saw that this would allow him to control the parent plants in a cross.

He meticulously clipped off the stamens of a plant’s flowers to prevent

self-pollination…

He tested more than 70,000 He tested more than 70,000

pea plants!!

pea plants!! _{… then with a small brush moved} pollen from the stamen of the desired parent to the stigma of the first plant.

Pea plants have many traits that Mendel

could have chosen to study.

• Just like the families we studied, he observed many different patterns in the occurrence of the various traits.

• But, he decided the best way to uncover what was going on was to begin with the simplest case.

• So, he decided to focus on traits that occurred in just two distinct variations.

One of those was flower color. Mendel observed

that there were only two colors of flower in his pea

plants: either

white

or

purple

.

Mendel didn’t know about alleles at first but we do. So how many versions (alleles) of the color gene do you think

•Yes, there are two alleles

for color:

purple

purple

and

white

white

.

We will represent the purple

allele with a

1

and the white

allele with a

2

.

1 = purple allele

Mendel began by creating lines of plants that

were

pure-breeding

for purple flowers and

pure-breeding

for white flowers.

A.

Purple: White:

Mendel then crossed (symbolize by “X”) pure-breeding purple pure-breeding purple

flowers

flowers with pure-breeding white flowerspure-breeding white flowers. He called this a “Parental Cross” (“P”) and he called their offspring the “F1”

generation (from Latin “Filia”, meaning daughter).

X

P

P

(parental cross)

(parental cross)

What do you think happened in the F1

generation?

All of the F1 offspring were purple!

F

_F

1

1

(offspring of parental cross)

X

P

P

F

F

1

1

B

.

flowers in the F1 generation have?

C

.

So, when there are two alleles for a

trait (1 & 2 in this case), how many

different combinations of alleles are

possible for individuals to have?

What are they?

Model of Inheritance (so far...)

gene

trait

alleles

1.Sexually reproducing organisms have two genes that determine each trait, one from each parent.

a. A parent passes only one of his/her two genes for a trait to each offspring.

b. Random chance determines which of the two genes is passed to each offspring.

2. Genes for a trait can occur in different forms called alleles.

We can now add to our model:

Add to glossary:

•_PHENOTYPE: the variation of a trait that shows in an individual. Examples: purple flowers, blue eyes

•_GENOTYPE: the combination of alleles that an individual has. Examples: (1,1) (2,2) (1,2)

3.

3. When there are two variations of a trait When there are two variations of a trait

(phenotypes)

(phenotypes) in a population, there are two alleles in a population, there are two alleles (1 & 2) and three possible combinations

(1 & 2) and three possible combinations

(genotypes)

(genotypes) individuals can have: (1,1) or (2,2) or individuals can have: (1,1) or (2,2) or (1,2).

D

There are

3

1,1 and

2,2 and 1,2.

But there are only

2

purple and white.

What do you think might explain this?

PURPLE PARENT PURE-BREEDING WHITE PARENT F1 OFFSPRING

PURPLE

Model of Inheritance (so far...)

1.Sexually reproducing organisms have two genes that determine each trait, one from each parent.

a. A parent passes only one of his/her two genes for a trait to each offspring. b. Random chance determines which of the two genes is passed to each

offspring.

2. Genes for a trait can occur in different forms called alleles. 3. When there are two variations of a trait (phenotypes) in a

population then there are two alleles (1 and 2) and three possible combinations of alleles (genotypes) that individuals can have: (1,1) or (2,2) or (1,2).

a.

a. If (1,1) and (1,2) have one If (1,1) and (1,2) have one

phenotype and (2,2) has the other, phenotype and (2,2) has the other, then 1 is the

then 1 is the dominant dominant allele. It allele. It always shows when present.

always shows when present. b.

b. 2 is the 2 is the recessiverecessive allele. It only allele. It only shows if no dominant allele is

shows if no dominant allele is present. present. recessive recessive phenotype genotype dominant dominant

In further experiments Mendel allowed the F1 purple flowers to

self-pollinate.

F

F

1

1

Both purple and white offspring resulted - but 3 times more purple than white. In other words, the ratio of purple to white was 3:1.

F

F

2

2

(2nd generation

(2nd generation

offspring)

offspring)

What do you think happened?

E. Using the model, predict whether or not it is

F.

Explain why there are three times

more purple offspring than white.

Mendel did the same experiments with several other traits in pea plants. All produced the same result:

One variation of the trait disappeared in the 1st generation

One variation of the trait disappeared in the 1st generation

then reappeared in the 2nd. The ratio was always 3:1.

then reappeared in the 2nd. The ratio was always 3:1.

“Showing your work” in a genetics problem.

Sample problem:

phenotypes of their babies?

1.Show the alleles:

(we will always use “1” for dominant , 2 for recessive)

1= brown

2= white

2. Show the possible genotypes and phenotypes:

1,1 = brown

1,2 = brown

2,2 = white

3. Show the cross with

genotypes and phenotypes:

Pure brown x pure white

1,1 x 2,2

4. Show outcomes (punnett square etc.)

1 1

2 2

1,2 1,2

1,2 1,2 brown brown

Let’s look at a family to see if we can

apply the model and explain the

ALBINISM is a rare genetic trait found in many species. Organisms with albinism are unable to produce pigment

proteins. In animals the protein affected is melanin, in plants it is chlorophyll.

George Arlene

Ann

Sandra Tom Sam Wilma

Alan Daniel

Michael

Christopher Abigail

Add to glossaries

:

• Parental cross: A cross between 2 pure-breeding individuals with opposite traits. Symbolized with a P. Example: 1,1 x 2,2

• F1 generation: The offspring of a parental cross. Genotype is

always 1,2.

• F₂ generation: Offspring of a cross between two F₁ individuals.

• Homozygous: a genotype in which the two alleles are the same. (pure-breeding)

– Examples: (1,1) and (2,2)

• Heterozygous: a genotype in which the two alleles are different.

Mendel figured out 3 REALLY IMPORTANT

things that no one before him had discovered.

He called them “Laws of Inheritance”

1

Law:

We have two genes (he called them

“factors”) for each trait. A parent gives just one of

them to each child - which one is determined by

random chance.

2

Law:

Law of dominance. Some versions of genes

are dominant to others.

3

Law:

Traits are inherited independently of one

another (so each is a separate random chance

Model of Inheritance (so far...)

1.Sexually reproducing organisms have two genes that determine each trait, one from each parent.

a. A parent passes only one of his/her two genes for a trait to each offspring. b. Random chance determines which of the two genes is passed to each

offspring.

2. Genes for a trait can occur in different forms called alleles. 3. When there are two variations of a trait (phenotypes) in a

population then there are two alleles (1 and 2) and three possible combinations of alleles (genotypes) that individuals can have: (1,1) or (2,2) or (1,2).

a.

a. If (1,1) and (1,2) have one phenotype and If (1,1) and (1,2) have one phenotype and (2,2) has the other, then 1 is the

(2,2) has the other, then 1 is the dominant dominant allele. It always shows when present.

allele. It always shows when present.

b.

b. 2 is the 2 is the recessiverecessive allele. It only shows if no allele. It only shows if no dominant allele is present.

dominant allele is present.

recessive recessive phenotype genotype dominant dominant

5. Traits are USUALLY inherited independently of one

5. Traits are USUALLY inherited independently of one

another.

another.

1st _law

2nd law