Chapter 11 Study Guide Questions

What is the relationship between characters and traits?

A character is a heritable feature that varies among individuals (like flower color). A trait is the specific variant of that character (like purple or white flowers).

What is a true-breeding plant?

Plants that, over many generations of self-pollination, produce only the same variety as the parent plant (e.g., a purple flower that always produces purple offspring).

What is a hybrid

The offspring of two different true-breeding varieties.

What is a monohybrid

A cross focusing on a single character (e.g., AA x aa).

What is a dihybrid

A cross focusing on two different characters at once (e.g., AABB x aabb).

What is the P generation in Mendel’s experiment?

True-Breeding Parents

• Purple Flowers x White Flowers

What is the F1 generation in Mendel’s experiment?

Hybrid of offspring of P generation

• All plants has purple flowers

What is the F2 generation in Mendel’s experiment?

F1 individuals self-pollinate or cross-pollinate with other F1 hybrids

• 705 Purple Plants, 224 White Plants

Explain a dominant trait

Determines the organism's appearance even if only one copy is present.

• Ex: Purple Flower

Explain a recessive trait

Has no noticeable effect on appearance unless the organism has two copies of that allele.

• White Flower

Define alleles

One of two or more alternative versions of a gene at a specific location (locus) on a chromosome

What are the four concepts that explain the 3:1 inheritance patterns observed in F2 offspring?

1. Alternative versions of genes (alleles) account for variations in inherited characters.

• Purple & White Flowers

2. For each character, an organism inherits two alleles, one from each parent.

3. If two alleles differ, the dominant allele determines the appearance.

4. Law of Segregation

Describe the law of segregation.

The two alleles for a heritable character separate during gamete formation and end up in different gametes

Describe a homozygous individual’s genotype

Organism with 2 identical alleles for character

• PP

• True-Breeding

Describe a heterozygous individual’s genotype

Organism that has 2 different alleles for gene

• Pp

• Not true-breeding

What is a genotype?

Genetic Makeup

• PP, Pp, pp

What is a phenotype?

Physical appearance

• Purple or White

Explain how to do a testcross

Breeding an organism of unknown genotype with a homozygous recessive individual.

What do testcross results show?

• Genotype of that organism

• If any offspring show the recessive trait, the unknown parent must be heterozygous.

Describe the law of independent assortment.

Each pair of alleles segregates independently of each other pair during gamete formation.

When does the law of independent assortment occur?

Meiosis I

How did Mendel identify law of independent assortment?

• Followed 2 characters

• Crossed 2 true-breeding parents differing in 2 characters

  • Produced dihybrids in F1 generation, heterozygous for both characters

When does the law of independent assortment apply to specific genes

Applies only to genes located on different chromosomes or very far apart on the same chromosome.

When does the law of independent assortment NOT apply to specific genes

Homologous genes / "linked" genes close together on the same chromosome.

What is probability?

The mathematical likelihood that a specific event will occur.

• Alleles of 1 gene segregate into gametes independently of another gene’s alleles

Describe the multiplication rule and be able to apply it.

To determine the probability that 2+ independent events happening together (Rr x Rr), multiply their individual probabilities.

Describe the addition rule and be able to apply it.

To determine the probability of any 1 or 2+ mutually exclusive events will occur, add their individual probabilities together.

• Used to figure out the probability that F2 plant from a monohybrid cross will be heterozygous rather than homozygous.

When does a single gene deviate from simple Mendelian patterns?

Patterns deviate when alleles are not completely dominant/recessive, when a gene has more than two alleles, or when a gene produces multiple phenotypes.

Explain complete dominance

Phenotypes of heterozygote and dominant homozygote are identical

Explain incomplete dominance

Phenotype of F1 hyrbids is somewhere between the two parents

Explain co-dominance

2 dominant alleles affect phenotype in separate, distinguishable ways

Explain the difference between complete, incomplete and co-dominance.

Complete: Phenotypes are identical

Incomplete: Phenotype somewhere between two parents

Co-dominance: Both alleles affect phenotype

Explain how genes can have more than 2 allelic forms

Most genes exist in more than two allelic forms in a population

Define pleiotropy and be able to identify pleiotropic genes.

When a single gene has multiple phenotypic effects

• Responsible for multiple symptoms of certain hereditary diseases

• Ex: the gene for sickle-cell disease affects blood cells, organ function, and malaria resistance

Explain how multiple genes could independently affect a single trait.

Occurs through epistasis or polygenic inheritance.

• Gene products may interact

• Multiple genes could independently affect single trait

Define epistasis

Phenotypic expression of a gene at one locus alters phenotypic expression of a gene at a second locus

• Ex: In Labradors, one gene decides hair color, but another gene decides if the color actually shows up in the fur

When does epistasis occurs.

Locus and different loci

What are quantitative characters?

Characters that vary in a population along a continuum (like height or skin color) rather than being "either/or."

What does polygenic inheritance mean?

The additive effect of two or more genes on a single phenotypic character.

How does the environment affect phenotypes?

Phenotype can be influenced by environmental factors (e.g., nutrition affecting height, or soil acidity affecting flower color).

What does it mean for a character to be multifactorial?

A character that is influenced by many factors, both genetic and environmental.

Because it is challenging to do experiments on humans, what other analyses can be used to understand human genetics?

Pedigree Analysis

Define Pedigree Analysis

Family tree with the family’s history for a particular trait.

• Describes traits of parents and children across generations

• Predict future offspring traits

• Use multiplication and addition rules to predict the probability of phenotypes

• Determine the cause of disabling or deadly diseases

What does it mean when a person is a “carrier”?

Heterozygous individuals who carry a recessive allele but don’t show the disorder

Define Cystic Fibrosis

Lethal genetic disease

-Cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes, leading to the build-up of chloride ions outside the cell

Define SIckle-cell Disease

Genetic disease prevalent among African-Americans, 1 of 365 births

• Caused by substitution of single amino acid in hemoglobin protein in red blood cells

Define Huntington’s Disease

Degenerative disease of the nervous system