Lesson 16 - Mendelian Genetics

Gene

segment of DNA (often) codes for a protein

Trait

genetically determined characteristics (expression of proteins)

Alleles

alternate forms of a gene

Phenotype

physical appearance of a trait (what it might look like)

Genotype

genetic makeup of the trait (letters)

An Allele can be either…

dominant or recessive

Dominant

always expressed if present

Recessive

only expressed if no dominant allele is present 

Homozygous

two of the same alleles (BB or bb)

Heterozygous

two different alleles (Bb)

P Generation (true breeding, parental generation)

Homzygous dominant or homozygous recessive for a trait

F1 Generation

first filial generation

offspring from the P Generation

F2 Generation

second filial generation

offspring of F1 generation

Fx Generation

Offspring from the F1-x Generation

Law #1 (Mendel’s Laws)

Law of Dominance: an organism with a dominant allele will present the dominant trait and an organism with a recessive trait will only portray it if no dominant allele is present 

Law #2 (Mendel’s Laws)

Law of Segregation: Each trait has two alleles/factors that determine each trait, expressed in a monohybrid cross/punnett square

Law #3 (Mendel’s Laws)

Law of Independent Assortment: Each pair of alleles separates independently of other traits, all possible combinations are shown in a dihybrid cross

What is a recombination chromosome?

chromosomes that contain portions of both mom and dad

What is a test cross?

used to discover the unknown genotype of a known phenotype

Inheritance can be traced using a ____

Pedigree

In a pedigree, who are circles and who are squares?

Circle = female, Square = male

Autosomal Dominant Inheritance

when one of your parents are affected therefore, the kid is affected too (e,g, Huntington’s Disease)

Autosomal Recessive Inheritance

when neither of the parents are affected but you are (e.g. cystic fibrosis, PKU)

Multiple Alleles/ Codominance

some traits have more than two alleles, they might both show as dominant (e.g. blood type: multiple blood types and then codominance - A and B)

Incomplete Dominance

occurs when one trait isn’t completely dominant over another, they blend (ex. red and white flower=pink flower)

Incomplete Penetrance 

alleles have a dominant/recessive relationship but dominant doesn’t always determine the phenotype (e.g. black and white mouse = white mouse with black spots)

Pleiotropic Effects

A single mutant gene affects two or more distinct and seemingly unrelated traits (sickle cell)

Epistasis

when one gene overrides the actions of another gene

Polygenic Inheritance

a phenotype is determined from more than one gene (e.g. skin color)

X-linked Inheritance

some traits are located on the sex chromosomes (mainly the X chromosome because it’s longer)

How can you tell if it’s an x-linked inheritance based off the pedigree?

mainly males will be affected