MENDELIAN GENETICS

VOCABULARY  Trait- A characteristic  Allele – Different form of a trait  Gene- 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 another  Recessive – 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 F 1 ; F 2 ; F 3

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 m ixed 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.  H B stands for a brown horse  H W 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