Bio I Unit 4: Meiosis & Genetics

1. Inheritance is determined by factors called genes that are passed on from parents to offspring.

* We know that some traits are controlled by more than two genes

2. Some genes are dominant: Represented by a capital letter.

* Genes that "show" or expressed

Some genes are recessive: Represented by a lowercase letter

*Genes that are "hidden" or masked

3. One gene in each pair of genes comes from each parent.

* These genes segregrate from one another during meiosis.

4. Alleles for different genes usually

segregate from each other when gametes are formed

• Passing of traits from parent to offspring

Heredity

• Study of heredity

Genetics

Genetics & Punnett Square Notes

Genetics Introduction & History:

Gregor Mendel:

Mendel’s Guiding

Principles

"Father of Genetics"

Austrian monk

Gardner at the monastery

Used pea plants for his studies

Bio I Unit 4: Meiosis & Genetics

Normal Dominant/Recessive

• One gene dominates over the other and that is the physical trait that is expressed

• Ex: Skin color, hair color

Codominance

• Phenotypes of both alleles are clearly expressed

• Ex: Human blood type

• Feather color in some species of chickens

• Black, white, speckled (erminette)

Incomplete Dominance

• One allele is not completely dominant over another

• Ex: Snapdragon & Four O'Clock plants

Types of Genetic Crosses:

Additional Vocabulary:

• Paired chromosomes in which one set comes from the male and one set comes from the female. Contain genes about the same trait.

Homologous chromosomes

• Having two identical alleles for a particular gene. Ex: AA or aa

Homozygous

• Having two different alleles for a particular gene. Ex. Aa

Heterozygous

• Physical characteristics of an organism. Ex: Blue eyes, Brown hair

Phenotype

• Genetic makeup of an organism, the actual gene combination. Ex: Bb, bb

Genotype

Bio I Unit 4: Meiosis & Genetics

• Diagram that can be used to predict the probabilities of a genetic cross.

Punnett Square

Punnett Squares & Genetics

Examples:

Normal Dominant/Recessive

1. In guinea pigs, black fur (B) is dominant over white fur (b). Cross a male, heterozygous

black furred guinea pig with a female, white furred guinea pig

Genotype: _____________________

Phenotype: _____________________

2. If you cross a homozygous dominant guinea pig for fur color with a homozygous recessive

individual, what is the probability of producing an offspring with a recessive phenotype?

Probability=_______________

Incomplete Dominance

3. Snapdragons are a type of flower that exhibit incomplete dominance for color. The possible

colors for snapdragons are: Red= R, White=W, Pink= RW

Cross a homozygous red snapdragon with a homozygous white snapdragon and show the

Punnett Square. What are the genotype and phenotype ratios of this cross?

Genotype: _____________________

Phenotype: ____________________

Codominance

4. Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red &

white hairs together).

a. Show a Punnett square for a cross between a homozygous white cow and a roan bull.

b. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?