#inheritance patterns

non-disjunction:

 if non-disjunction takes place in meiosis 1, all four cells will be aneuploids (have abnormal chromosome numbers) * two cells will be monosomic (n-1) and two will be trisomic (n+1) 

if non-disjunction takes place in meiosis 2, 2 cells will be normal (n), 1 cell monosomic, and 1 cell trisomic

polyploidy: having more than 2 chromosome sets (ex: triploid - 3N)

deletion: entire fragment of chromosome is lost

duplication: entire fragment of chromosome is duplicated on the chromosome

inversion: part of chromosome reverses its orientation

translocation: one part of a chromosome is attached to another part of a different chromosome

down syndrome (Trisomy 21): presence of all or part of an extra chromosome 21

XXY: Klinefelter syndrome - phenotypically male but are sterile with reduced testes size and enlarged breasts

XO: Turner syndrome - phenotypically female, but lack of development of secondary female characteristics

RECESSIVE INHERITED DISORDER -  * must receive both non-functional copies from parents * affected individual is homozygous recessive 

 albinism: lack of pigment in skin/eyes/hair; may lead to skin cancers cystic fibrosis: defective/absent chloride channel protein in membranes, causing buildup of mucus in lungs - person is prone to bacterial infections

tay-sachs disease: defective/absent lipase enzyme in brain - predominant in Jewish population

sickle cell disease: defective hemoglobin protein - mainly affects African-American population

DOMINANTLY INHERITED DISORDER -  * absence or malfunction of protein  * must receive at least one non-functional copy from one parent  * affected individual is a heterozygote (Aa) or homozygous dominant (AA) achondroplasia: dwarfism

incomplete dominance: offspring has a phenotype between that of both parents   * NOT a blending hypothesis!!  ex: red x white = pink

codominance: both alleles are expressed at the same time  ex:  MN blood system has three combinations: 

MM - homozygous dominant - only produces M antigen on surface of RBC

MN - heterozygote - produces M and N antigens

NN - homozygous recessive - only produces N antigen on cell surface

multiple alleles: many different alleles can control the expression of a character

pleiotropy: one gene causes multiple different phenotypic effects on an organism ex: the human disease PKU can cause mental retardation, hair loss, and skin pigmentation changes

epistasis: one gene affecting expression of another gene

phenotype ratio usually 9:3:4

polygenic inheritance: two or more genes affecting one phenotype  * leads to a bell curve distribution of phenotypes ex: skin colour 

pedigree analysis: visual depiction of inheritance patterns in multiple family generations  - if two people have an unaffected child, it must be a dominant pedigree  - if two unaffected people have an affected child, it must be a recessive pedigree  - if every affected person  has an affected parent, it is a dominant pedigree (no skipping of generations) - dominant traits never skip generations - squares are male, circles are females - mating is usually indicated by the connection with a line - filled in circles indicate an affected person

the law of multiplication: - independent events are governed by this - for genes that are linked, the law of multiplication cannot be followed  ex: AaBbCc x AabbCC

Aa x Aa -1/2 Aa, 1/4 aa, 1/4 AA //// AabbCC = (1/2)(1/2)(1/2) = 1/8

Bb x bb -1/2 Bb, 1/2 bb //// aabbCc = (1/4)(1/2)(1/2) = 1/16

monohybrid crosses: cross that tracks the inheritance pattern of a single character ex: in pea plants, tall (T) plants are dominant to short (t) plants  * there are 3 allele combinations: TT, Tt, or tt 

test cross: determines whether the dominant parent is homozygous dominant or a heterozygote. * always cross the dominant parent to a homozygous recessive

character: heritable feature   ex: hair colour

trait: variant of a character ex:  blonde hair, red hair

allele: alternative forms of a gene ex: tall plants (T), short plants (t) 

dominant allele: fully expressed

recessive allele: is not expressed if there is a dominant allele present

genotype: genetic makeup of an organism

phenotype: physical appearance of an organism