Lesson 16: Mendelian Genetics

From powerpoint

What is a gene?

segment of DNA that (often) codes for a protein

What is a trait?

genetically determined characteristic

• Expression of proteins

What are alleles?

alternate forms of a gene

What is a phenotype?

Physical appearance of a trait (what it looks like)

What is a genotype?

genetic make up of a trait (the letters)

What does it mean if an allele is Dominant?

always expressed if present

What does it mean if an allele is Recessive?

only expressed if no dominant allele is present

What is the term for an individual that inherits two of the SAME alleles?

homozygous

ex: BB or bb

What is the term for an individual that inherits two of the DIFFERENT alleles?

heterozygous

ex: Bb

What is P Generation

• true-breeding, parental generation

• homozygous dominant or homozygous recessive for trait

What is F₁ Generation?

• First filial generation

• offspring from the P generation

What is F₂ Generation?

• second filial generation

• offspring from the F₁ generation

What is F_x Generation?

• offspring from the F_x-1 generation

What is the Law of Dominance?

• An organism with a dominant allele will express the dominant trait.

• An organism with a recessive allele will ONLY express that trait if the dominant allele is NOT present.

What is the Law of Segregation?

• each individual has two “factors” (alleles) for each trait

  • one from mom, one from dad

• alleles separate during the formation of gametes

  • alleles are found on homologous chromosomes

• fertilization gives each new individual two alleles for each trait

What is the Law of Independent Assortment?

• each pair of alleles segregates (assorts) independently of other traits in Meiosis

• The inheritance pattern of one trait will NOT affect the inheritance pattern of another.

• For a single human gamete, the possible ways for chromosomes to assort is an astounding 8,388,608 (2²³) possible combinations!

Where do all possible combinations of alleles occur in?

the gamete

What is dihybrid cross?

A genetic cross that considers two traits, each represented by two alleles. It shows how alleles from two different traits assort independently during gamete formation

What do recombinant chromosomes contain?

portions of both the maternal and paternal chromosome

What is a test cross?

used to discover the unknown genotype of a known phenotype (the dominant phenotype)

What are autosomes?

any chromosome that is NOT a sex chromosome (X/Y)

What is a pedigree?

A diagram that shows the occurrence and appearance of phenotypes of a particular gene across generations in a family

Autosomal dominant inheritance =

ALL affected individuals will have a parent who also has the trait

Autosomal recessive inheritance = 

An affected individual can arise from 2 unaffected parents

Characteristics of Multiple Alleles/Codominance:

• some traits have more than two alleles

• more than one allele can act as a dominant allele

  • BOTH dominant alleles show

Characteristics of Incomplete Dominance:

• occurs when one allele is not completely dominant over another

• results in a blending of traits

Characteristics of Incomplete Penetrance:

• alleles have a “true” dominant/ recessive relationship, but dominant doesn’t always determine the pheotype

Characteristics of Pleiotropic Effects:

• a single mutant gene affects two or more distinct and seemingly unrelated traits

Characteristics of Epistasis:

• the action of one gene overrides the actions of another gene

Characteristics of Polygenic Inheritance:

• a phenotype is determined by more than one gene