GENETICS, PLANT BREEDING, AND SECTIONS

Genetics, Plant Breeding and Selection Below is a listing which will help you to prepare for the quiz and lab on this material.

CONTENT TO KNOW:

I. Terminology used in Genetics

• KARYOTYPES - a method of viewing chromosomes; o --chromosomes are stained and lined up in pairs;

abnormalities can be seen such as extra or missing homologues.

• Chromosome Number (humans) - 46 total chromosomes, 23 pairs homologous chromosomes - alike in size and type of genes Sex Chromosomes - determine the sex of the fetus XX - 2 X chromosomes = FEMALE Xy - one X, 1 y chromosome = MALE

• GENOTYPE = the genetic make-up of the individual

• PHENOTYPE = the physical manifestation of the genotype; (what the organism shows) --note: letters are used to represent gene pairs

Dominant allele - A gene which can hide or mask the second gene in a pair

Recessive allele - gene which can be masked by the dominant allele

Ex: W - dominant - widow's peak w - recessive - straight hairline

3 possible genotypes: WW, Ww, ww

Genotypes:

WW - homozygous dominant

Ww - heterozygous

ww - homozygous recessive

II. Monohybrid Crosses -

Genotypes of the parents:

When you cross a homozygous dominant (WW) with a homozygous recessive (ww), the results are always:

genotypic ratio - 100% Ww phenotypic ratio - 100% dominant phenotype

(widow's peak)

Cross two parents that are heterozygous for hairline:

III. DIHYBRID CROSSES -

Dihybrid crosses look at possible combinations of two traits:

Key:

A - purple, dominant a - white, recessive B - tall, dominant b - short, recessive

Cross: AABB x aabb - use the "FOIL" method to determine gametes: (First, outer, inner, last) Results: Parental genotypes are in BOLD FACE along the top and sides

AB AB AB AB ab AaBb AaBb AaBb AaBb ab AaBb AaBb AaBb AaBb ab AaBb AaBb AaBb AaBb ab AaBb AaBb AaBb AaBb

Phenotypic ratios: 100% purple, tall Genotypic Ratios: 100% AaBb

Cross: AaBb x AaBb -

Results: Parental genotypes are in BOLD FACE along the top and sides

AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb Phenotypic ratios: 9 out of 16 are purple, tall 3 out of 16 are purple, short 3 out of 16 are white, tall 1 out of 16 is white, short