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Genetics Basics Notes

• ________________ are passed on by parents and they determine _______________

• Different forms of the same gene are called ______________

• __________________ are represented with letters

o ___________________ used depends on what you are looking at.

Ex: Color of pea plant (Yellow vs. green) - ____ = _________ and ____ = _________

• The Father of Genetics is ____________________________

Dominant and Recessive

Dominant Trait –

Dominant allele:

Recessive Trait –

Recessive allele:

Genotype and Phenotype

Genotype –

Examples of genotypes for yellow and green peas:

Phenotype –

Examples of phenotypes for yellow and green peas:

Homozygous and Heterozygous

Homozygous = ____________

Homozygous –

Example – Baby with blue eyes

She is _______________ for blue eyes. The only way the trait

will be expressed is if both ______________ genes are

present. Genotype: _____

Heterozygous = _____________

Heterozygous –

Example – Girl with brown eyes

She is ___________ for brown eyes. Her genotype contains

one ___________________ and one _______________ allele.

Genotype: ______

Practice (SpongeBob Genetics Practice Problems)

1. In Squidward’s family, a blue body color (B) is dominant to green (b). Determine the phenotype for each genotype below.

BB _____________ Bb ______________ bb ______________

2. For each genotype, indicate whether it is heterozygous (He) OR homozygous (Ho).

TT _______ Pp ______ kk ______ Ff ______ Tt ______ FF ______

3. For SpongeBob’s family, square body shape is a dominant trait and round body shape is a recessive trait. Using the letter “s”,

write the genotypes for each phenotype below.

Homozygous square shape: _____ Heterozygous square shape: _____ Homozygous round shape: _____

4. SpongeBob is heterozygous for his square shape. If he had children with someone who had a round body, what are the

chances their child would have a square body shape?

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Name ______________________________ Period 1 2 3 4 5 6

Punnett Squares

• Punnett Square –

• How to use a punnett square:

1. ________ a punnett square.

2. Determine ______________ genotypes. Put one parent’s _____________________ at the _____ of the

punnett square and the other parent’s ________________ on the _______ side of the punnett square.

3. Bring letters from _______ and ________ to fill out all _____ boxes.

4. Determine the possible offspring ______________________ and ____________________.

5. Record the chances for each offspring possibility in a ______________________.

Example 1: For eye color, brown eyes (B) are dominant to blue eyes (b). Bob has brown eyes but knows he is

heterozygous for brown eyes. His wife, Susie has blue eyes. If Bob and Susie have a child, what are the possible

genotypes and phenotypes of the child’s eye color?

Parent genotypes:

Bob: _______ Susie: ________

Offspring possibilities:

Genotypes Phenotypes # out of 4 %

Example 2: Cross a person who is purebred for curly hair (CC) with a person who is hybrid for curly hair (Cc). What

are the possible genotypes and phenotypes of the offspring’s hair types?

Parent genotypes:

1: _______ 2: ________

Offspring possibilities:

Genotypes Phenotypes # out of 4 %

 

 

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Punnett Square Practice Problems:

Complete the following problems. List the parent genotypes, draw and fill in a punnett square, and then list the

offspring genotypes and phenotypes.

1. A homozygous dominant brown mouse is crossed with a heterozygous brown mouse (tan is the recessive color).

2. Two heterozygous white rabbits are crossed (brown fur is recessive).

3. A heterozygous white rabbit is crossed with a homozygous brown rabbit (brown fur is recessive).

4. Two heterozygous red flowers are crossed (white flowers are recessive).

5. A homozygous tall plant is crossed with a heterozygous tall plant (short is the recessive size).

Extra credit: Write your own punnett square problem on a sheet of paper. On a separate sheet of paper, write the

solution including parent genotypes, completed punnett square, and offspring genotypes and phenotypes. Staple the

two sheets together and hand in by ____________________________.

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Name ______________________________ Period 1 2 3 4 5 6

Patterns of Inheritance

• Complete Dominance –

Yellow flowers (Y) are dominant to white flowers (y).

How we describe the genotypes Genotype (letter combination) Phenotype (what we see)

Homozygous dominant (Purebred)

Heterozygous (Hybrid)

Homozygous recessive (Purebred)

• Incomplete Dominance –

In flowers, R is dominant for red flowers and W is recessive for white flowers. Hybrids (RW) tend to show a blended trait of pink flowers.

How we describe the genotypes Genotype (letter combination) Phenotype (what we see)

Homozygous dominant (Purebred)

Heterozygous (Hybrid)

Homozygous recessive (Purebred)

• Co-dominance -

Andalusian chickens have one allele for white feathers and one allele for black feathers. Andalusian chickens that are heterozygous appear to have black and white checkered feathers (BW). Where pure chickens are either black (BB) or white (WW).

How we describe the genotypes Genotype (letter combination) Phenotype (what we see)

Homozygous dominant (Purebred)

Heterozygous (Hybrid)

Homozygous recessive (Purebred)

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Patterns of Inheritance Practice Problems

Co-dominance Practice – Consider the Andalusian chickens from p. 4.

1. Cross two Andalusian chickens.

Offspring possibilities:

____% Black Chickens ____% Andalusian Chickens ____% White Chickens

2. Cross a black rooster with an Andalusian hen.

Offspring possibilities:

____% Black Chickens ____% Andalusian Chickens ____% White Chickens

Incomplete Dominance – In shorthorn cattle, color shows incomplete dominance. A red cow has the genotype RR. A white cow has the genotype WW. Heterozygous cattle are called Roan (red and white spotted) RW. 3. Cross a red bull with a roan cow.

Offspring possibilities:

____% Red Cows ____% Roan Cows ____% White Cows

4. Cross a white bull with a red cow.

Offspring possibilities:

____% Red Cows ____% Roan Cows ____% White Cows

 

 

 

 

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Name ______________________________ Period 1 2 3 4 5 6

Incomplete Dominance continued

5. In Gorplex aliens, B is dominant for blue skin and Y is recessive for yellow skin. Hybrids (BY) tend to show an

incomplete dominant trait of green skin. Cross an alien with blue skin and an alien with green skin then answer the questions below.

Offspring possibilities:

____% Blue skin ____% Yellow skin ____% Green skin

If 60 offspring are produced, how many (number) show each of the following:

a) Blue-skinned: ______

b) Yellow-skinned: _______

c) Green-skinned: _______

d) Dominant trait: _______

e) Recessive trait: ______

f) Incomplete dominant trait (hybrid): ______

6. Make your own punnett square problem and have a friend or family member try to solve it.

This problem is: ___ complete dominance ___ incomplete dominance ___ co-dominance

Problem: