MENDELIAN GENETICS

VOCABULARY

Trait- A characteristic Allele – Different form of a traitGene- The chemical factors that determine a trait (actual DNA)

Genotype – The gene make-up of a trait expressed as a set of Capital and lower case letters

Phenotype – The physical presentation of the genetic expression

Dominant – The trait that expresses itself over anotherRecessive – The trait that is masked or hidden by the dominant trait.

Homozygous – Having the same two alleles for a genetic trait.

Heterozygous – Having two different alleles for a genetic trait.

Homozygous Dominant – FF having two dominant alleles Homozygous Recessive – ff having two recessive alleles Heterozygous - Ff having a dominant and recessive allele True breed – Offspring having the same homozygous trait as the parent Hybrid – Offspring having one allele from each homozygous parent Carrier – Offspring having a recessive trait masked by a dominant trait that may express itself in future generations

P – Parent generation – The first generation crossed F – Filial generation – The generations that follow the parent generation. Subscripts show which generation F1; F2; F3

MENDEL’S PRINCIPLES

Law of Segregation- during gamete formation, the alleles for each gene segregate (separate) from each other so that gamete carries only one allele for each gene.

Law of Independent Assortment- Genes fro different traits can segregate independently during the formation of gametes

Law of Dominance- Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele

MONO/ DIHYBRID CROSSES (1&2 TRAIT CROSSES)

Monohybrid cross

A single trait is being looked at

Crossing of the two allele possibilities from both parents (P) to see the possible outcomes of the offspring (F1)

Dihybrid cross

Two traits are being looked at

Crossing of the four allele possibilities from both parents (P) to see what possible outcomes are for the offspring (F1)

POST MENDELIAN CONCEPTS

Incomplete dominance- the heterozygous phenotype lies somewhere between the two homozygous phenotypes

Codominance- the phenotypes produced by both alleles are clearly expressed

Multiple Alleles- a gene with more than two alleles possibilities in the population (blood types)

Polygenic traits- traits controlled by two or more genes (skin color)

INCOMPLETE AND CODOMINANCE

Incomplete Dominance Unlike Complete dominance, there are NO lowercase letters.

NEITHER trait has dominant control

A mixed color or a blending is made. To remember a mixed color is made, think of the

{m} in inco{m}plete.

Dominant red is written as {RR} (a purebred - homozygous)

Dominant white is written as {WW} (a purebred - homozygous)

The mixed color they make is pink {RW} (a hybrid - heterozygous)

Codominance Like Incomplete dominance, there are NO lowercase letters. This time, both traits express themselves in

different locations

The punnet square will be written exactly as in incomplete dominance. One dominant color is written as {RR} (a

purebred - homozygous) The other dominant white is written as

{WW} (a purebred - homozygous) The both colors showing will be written as

{RW} (a hybrid - heterozygous) A cow or horse with both colors (usually brown and

white) showing is called a “roan” horse or cow.

EXTRA

Sometime incomplete and codominance is written with Superscripts (letters above writing) with a common letter representing a trait. In the example {H} stands for horse color. HB stands for a brown horse HW stands for a white color

Again there are NO lower case letters written in the superscript position

Terms for homozygous and heterozygous now refer to the superscripts

Percentages and ratios are done the same way with the different notation

You may see this notation when doing crosses with blood

PEDIGREE

A document to record ancestry, used by genealogists in study of human family lines, and in selective breeding of animals

Used to follow genetic inheritance from generation to generation

KARYOTYPES

Karyotypes describe the number of chromosomes, and what they look like.

Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics