Chapter 14: Mendel and the Gene Idea

A heritable feature (flower color)

Character

A variant of a character (purple or white)

Trait

Plants that produce offspring identical to themselves when self-pollinated

True-breeding

Crossing two true-breeding parents with different traits

Hybridization

Parental generation

P generation

First filial generation (offspring of P)

F1 generation

Offspring of F1. (self-or cross-pollinated)

F2 generation

What four principles of inheritance did Mendel discover?

1. Alternative versions of genes (alleles) cause variations in traits

2. Each organism inherits two alleles for each gene- one from each parent

3. Dominant and recessive alleles:

   1. Dominant allele determines phenotype 

   2. Recessive allele is masked when dominant is present 

4. Law of segregation

   1. Two alleles for a trait separate during gamete formation

   2. Each gamete receives only one allele

Where was the Law of Independent Assortment discovered from?

Dihybrid crosses (two traits at once)

What is the Law of Independent Assortment?

Each pair of alleles segregates independently of others during gamete formation

When does the Law of Independent Assortment apply?

Applies only to genes on different chromosomes or far apart on the same chromosomes

Two identical alleles (PP or pp)

Homozygous

Two different alleles (Pp)

Heterozygous

Physical appearance

Phenotype

Genetic makeup

Genotype

Cross an unknown dominant (P_) with homozygous recessive (pp) to find genotype

Testcross

What is the Multiplication rule for Punnett squares?

Probability of two events= product of their individual probability

What is the Addition Rule for Punnett Squares?

Probability of any one event= sum of individual probabilities

What is Complete Dominance?

Heterozygote same as homozygous dominant (PP or Pp)

What is incomplete dominance?

Heterozygote is intermediate

What is Codominance?

Both alleles fully expressed

What is Pleiotropy?

One gene affects multiple traits 

What is an example of Pleiotropy?

Cystic fibrosis and sickle-cell disease cause many symptoms due to one gene

What is Epistasis?

One gene masks or modifies another’s effect

What is Polygenic Inheritance?

Multiple genes affect one trait (additive effect)

What is an example of Polygenic Inheritance?

Human skin color, height

What does Polygenic Inheritance produce?

Continuous variation (bell curve pattern)

What are multifactorial traits influenced by?

Genes and environment

What are examples of Multifactorial traits?

Heart disease, diabetes, cancer

What are Pedigrees?

Family trees showing inheritance of traits through generations

What are Pedigrees used to determine?

Dominant vs. recessive inheritance patterns

What are examples of recessive disorders?

• Cystic fibrosis: mucus buildup, lung infections

• Sickle-cell anemia: misshaped RBCs; heterozygotes resistant to malaria

• Albinism: lack of pigment

Why are dominant disorders rare?

because often lethal if homozygous

Sample amniotic fluid; karyotype fetus

Amniocentesis

Sample placental tissue for DNA testing

Chorionic villus sampling (CVS)

Visualize fetus for abnormalities

Ultrasound/Fetoscopy

Test for metabolic/genetic disorders

Newborn screening