Chapter 11 - Gregor Mendel and the Inheritance of Genes

Alelle

Alternative versions of a gene (character)

Genotype

The genetic makeup of an organism, the alleles it carries

Phenotype

The physical traits of an organism, determined by genotype

Homozygous

Having two identical alleles for a particular gene (ex. AA, aa)

Heterozygous

Having two different alleles for a particular gene (ex. Aa)

Dominant Allele

An allele that expresses its phenotypic effect even when heterozygous with a recessive allele (only takes one copy to be expressed)

Recessive Allele

An allele whose phenotypic effect is not expressed in a heterozygote (requires two copies to be expressed, phenotype is masked by presence of dominant allele)

Law of Segregation

Two alleles (on separate chromosomes) for a gene separate (segregate) so that each egg or sperm (gamete) gets only one of the two alleles

Law of Independent Assortment

Copies of different genes (chromosomes) get sorted into gametes independently of one another

However, genes located near each other on the same chromosome tend to be inherited together

When may inheritance patterns deviate from simple Mendelian patterns?

Alleles are not completely dominant or recessive

When a gene has more than two alleles

When a single gene produces multiple phenotypes

Complete Dominance

The heterozygote has the same phenotype as the dominant homozygote

Incomplete Dominance

The heterozygote phenotype is intermediate between the dominant and recessive homozygotes

Codominance

The heterozygote phenotype express both the dominant and recessive phenotypes equally

Are dominant or recessive alleles more common?

They are both equally as common.

What are the blood types in Humans?

A, B, O

A and B are dominant over O
A and B are codominant with each other
O us recessive

Pleitropy

One gene influences multiple traits (phenotypes)

Can cause multiple symptoms in hereditary diseases

Epistasis

One gene controls the expression of another gene (gene interactions)

Polygenic Inheritance

Single phenotypic character results from the additive effects of two or more genes on a single phenotypic character

Quantitative characters (traits) vary along a continuum (not discrete traits)
Skin color and height are two good examples

Pedigree

Family tree that contains a family's history for a particular trait, can help deduce the patterns of inheritance of genetic diseases

Carriers

Heterozygous individuals who carry the recessive allele but are phenotypically normal

Mating between close relatives increases the chance of two carriers producing offspring that are homozygous for a rare recessive disorder

Zygote

The first diploid cell produced by fertilization

Gene

The place in the DNA that encodes information causing a trait

Locus

Location on a chromosome, usually location of a gene

Wildtype Allele

The most common allele in a population

Mutant Allele

A rare allele in a population

Blending Inheritance Hypothesis

The idea that genetic material from the two parents blends together

Particulate Inheritance Hypothesis

The idea that parents pass on discrete heritable units (genes)

Mendel and his pea plants documented this mechanism

What is an example of a human disease that is inherited as a simple recessive trait?

Cystic Fibrosis