Intro to Genetics Lesson

Mendelian Genetics

Vocab

• Trait: the physical characteristics of an organism

• Human Traits: Eye color – Skin tone – Hair color – Height

• Heredity: the passing of traits passing from parent to offspring

• Genes: segments of DNA found on chromosomes that control traits

• Phenotype (#10): the physical appearance of a gene

• Allele: the different forms or versions of a gene

• Dominant: an allele that ALWAYS shows up in an organism when its present

• Recessive: an allele that is covered up by the DOMINANT allele

Vocab

• Genotypes: an organism’s genetic make-up, allele combination

• Homozygous: an organism that has two IDENTICAL alleles for a traits

AKA purebred

• Purebred: produces offspring that has two same trait as the parent; has

two identical alleles for a trait

• Heterozygous: an organism that has two different alleles for a trait AKA

hybrid

• Hybrids: carries two different alleles, one dominant & one recessive

Gregor Mendel

“The Father of Genetics”

Gregor Mendel:

The Father of Genetics

- Studied the traits of pea plants to learn

about genetics

- Genetics: the scientific study of heredity

Why did Mendel study peas?

1. Most traits in pea plants have two
distinct forms

2. Pea plants produce large numbers
of offspring

Multiple Select

Which of the following statements are reason's Gregor Mendel used pea plants for his research? Select all that apply.

• They tasted yummy

• Most traits in pea plants have 2 distinct forms

• Pea plants reproduce large number of offspring quickly

• Because pea plants flower

Traits Mendel

Studied

Multiple Select

What are the two distinct forms of flower color in pea plants? (Choose 2)

• purple

• lavender

• pink

• white

Multiple Choice

What does it mean to be a purebred purple flowered pea plant?

• The plant has 1 allele for white color and 1 allele for purple.

• The plant has 2 alleles for purple color.

• The plant has 2 alleles for white color.

• The plant is tall because only tall pea plants are purple.

Multiple Choice

After Mendel crossed a purebred purple flower pea plant and a purebred white flower pea plant, what was the phenotype of all the offspring?

• 75% purple, 25% white

• 75% white, 25% purple

• 100 % white

• 100% purple

Multiple Choice

What was the name of the generation of purebred purple and white flowers?

• P Generation

• F1 Generation

• F2 Generation

• The OGs

Multiple Choice

What was the name of the generation of purple flowers made from a purebred purple plant and a purebred white plant?

• P Generation

• F1 Generation

• F2 Generation

• The OGs

Multiple Choice

The flowers in the F1 generation were...

• purebred

• hybrids

Mendel’s Experiments

STEP 3: Mendel self-pollinated each of
the offspring from the F1 generation

- Result:

75% of the offspring were PURPLE

25% of the offspring were WHITE

RATIO: 3 purple: 1 white

Multiple Choice

When Mendel self-pollinated the flowers in the F1 generation, what were the phenotypes of the offspring?

• 75% purple, 25% white

• 75% white, 25% purple

• 50% purple, 50% white

• 30% purple, 70% white

100% WHITE

Purebred Offspring

100% PUREBRED

PURPLE

Offspring

100% HYBRID

PURPLE
Offspring

3/4 = 75% Purple

1/4 = 25% White

Step

Generation

Description

Flower Colors

(ratio)

P generation

- self-pollinated white and

purple flowers to create
two different purebreds

- Cross-pollinated white
and purple flowers to
create hybrids

100% white
AND 100%
purple

100% purple

Summary of Mendel’s Experiment

1

3

2

F1 generation

F2 generation

-result of the self-
pollinated the F1
generation

3 purple:1 white

Genes & Alleles

• What is a gene?

• Section of chromosome that

codes for a specific protein

• Determines traits (ex. Hair color,

eye color, ear shape, etc)

• Genes are paired on

homologous chromosomes

• Different forms of a gene that

codes for the same trait are called
alleles

• Allele Examples: Blue OR Brown

Eyes – same gene, different
versions

Analogy: These are all the
same brand of shoes
(Nike Jordans) but each
individual is a different
style

Multiple Choice

True OR False: Genes determine an organism's physical traits.

• True

• False

Multiple Choice

Which of the following the an example of a trait?

• hair color

• Ab

• homozygous

• genetic makeup

Multiple Choice

Which of the following is an example of an allele?

• eye color

• brown skin

• height

• skin tone

Genes & Alleles

• Because you get 1 set of chromosomes from your mother and 1set of

chromosomes from your father, you inherit 2 alleles for each gene(your
genotype). Those alleles will determine your phenotype (physical traits).

• What happens when you inherit 2 alleles that each code for a different

version of a trait?

• Inheriting Blue eyes from mother and brown eyes from father

• Dominant vs. Recessive

• Dominant allele: an allele that always shows up in an organism when the allele is

present

• Recessive allele: An allele that is covered up by the dominant allele

Multiple Choice

In HUMANS, brown eyes is dominant to blue eyes. If a baby were to inherit a brown eye allele (B) from his mom and a blue eye allele (b) from his dad. Based on his genotype (Bb) what color eyes will baby have?

• Brown

• Blue

• Green

• Red

Genotype

Phenotype

Homozygous Dominant – two copies of

dominant allele

TT

Tall

Heterozygous – one dominant allele, one

recessive allele

Tt

Tall

Homozygous Recessive – two copies of

recessive allele

tt

Short

Dominant alleles: use the first letter of the dominant trait, CAPTIALIZED
-example: Tall (T)
Recessive alleles: use the first letter of the dominant trait, lowercase
-example: short (t)
Genotypes are written using both alleles from each parent (TT, Tt, or tt)

How to write genotypes

In Mendelian
genetics when

there is 2 different
phenotypes, there

are 3 genotypes

Multiple Select

Select all of the HETEROZYGOUS genotypes below:

• Aa

• TT

• bb

• Cc

• Dd

Multiple Choice

Select the HOMOZYGOUS DOMINANT genotype below:

• Aa

• TT

• bb

• Cc

• Dd

Multiple Choice

Select the HOMOZYGOUS RECESSIVE genotype below:

• Aa

• TT

• bb

• Cc

• Dd

Purebred vs. Hybrid

• Purebred have two copies of the SAME allele

• Homozygous dominant: TT

• Homozygous recessive: tt

• Hybrids have 1 copy of both dominant and recessive allele

• Heterozygous: Tt

Mendel’s 3 Law of Inheritance

1. Law of Dominance: the dominant allele will

always show when it is present, while the
recessive allele will only show trait when two
recessive alleles are present

2. Law of Independent Assortment: genes are

inherited independently of one another as a result
of chromosomes randomly aligning during
metaphase.

3. Law of Segregation: homologous chromosomes

and sister chromatids separate during anaphase
1 & 2 when gametes are being formed

Multiple Choice

A recessive allele is masked (covered up) if a dominant allele is present due to the...

• Law of Independent Assortment

• Law of Segregation

• Law of Dominance