genes and heredity

heredity

the passing of traits from parents to offspring

genetics

study of the inheritance as hereditary characteristics or traits

why pea plants

• self pollinating and easy to control pollination

• visible characteristics that are expressed in 2 forms (colour: red and white)

law of segregation

during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene

law of independent assortment

shuffling of 2 sets of chromosomes before gamete formation, leading to the alleles of different genes assorting independently from one another.

law of dominance

some alleles are dominant while others are recessive, if one organism has atlest one Dominant allele then it will display as dominant. it can only be recessive if both alleles are recessive

trait

any characteristic that can be passedd from parent to offspring

allele

alternative version of a gene, these produce contrasting effects for a certain trait

dominant

stronger of the 2 genes

recessive

gene that shows up less often

genotype

• the gentic makeup of an individual

• determines the phenotype

phenotype

• the expression of the genes or appearance of an individual

• physical appearance or attiude

pure bred/true breeding

an organism having all homozygous pairs

homozygous

having 2 of the same alleles (purebred)(AA, aa)

heterozygous

having 2 different alleles (Aa)

determining gametes

to predict offspring you must determine the possible gametes (result of meiosis)

monohybrid cross

• mating 2 individuals who have different alleles of one gene (RR x rr)

• results in a ratio of 3:1

genotypic ratio

• homo dom : hetero : homo rec

• AA:Aa:aa

phenotypic ratio

• dom : rec

• ex. 3:1

dihybrid cross

• 2 different pairs of contrasting alleles

• round, wrinkled and yellow, green seeds/peas

• ratio 9:3:3:1

test cross

mating between an individual of unknown genotype and a homozygous recessive individual (only know genotype are recessive rr)

multiple alleles

• when traits are determined by more than 2 alleles

• not just dominant and recessive

• wild type (most dominant and common)

• mutant

• have a hierarchy of dominance

incomplete dominance

• 2 alleles are equally dominant and they interact to make a new phenotyoe

• neither allies are dominant over the other

• blending of phenotypes occur

• ex. red plant and white plant make pink plant

codominance

• both alleles are fully expressed by heterozygous individual at the same time

• expressed in different cells

• red flower and white flower make red and white flower