Gregoe Mendel: 1822-1884 --> Father of Genetics --> pea plants -->

Law of Dominance: only the dominant trait can be seen (expressed) in an organism that is hybrid for a pair of contrasting traits --> pure stable peas (tall, short) P generation --> F1 offsprings: all tall --> dominant trait: tall

Law of Segregation: F2 offsprings: 3 tall, 1 short --> there are two copies (alleles) of a gene for a particular trait --> these alleles separate during the formation of sex cells --> recombine during fertilisation

Generations: P (homozygous: same alleles in 1 gene) --> F1 (heterogeneous: different alleles in 1 gene) --> dominant allele over recessive allele expressed

The Punnet Square: the Punnet Square is a simple representation of the possible allele combinations that can occur when two sex cells or gametes combine --> heterogeneous F1 (T:S) 4:0 dominance --> F2 (T:S) 3:1 segregation --> Assumption: variable independence

Law of Independent Assortment: Genes for different traits must be inherited independently from one another --> peas with two differing traits --> (round/wrinkled) & (yellow/green) --> F1: all R & Y --> F2: 9:3:3:1 => 9+3+3+1=16 --> Punnet Square representation

The Chromosome Theory of Inheritance: Chromosomes carry genes --> alleles are passed on through sex cells (gametes) --> since alleles are contained in genes --> sex cells have only half the number of chromosomes of the body cells --> chromosomes must contain alleles --> hence chromosomes must contain genes --> representing inheritance

Thomas Hunt Morgan: 1st evidence that chromsomes carry genes --> experimented with fruitflies (Drosophilia melanogaster) --> due to its characteristics: 1) easily maintained in large nos. in lab --> 2) rapid reproduction rate --> 3) 4 pairs of chromosomes/cell --> Karyotype: display of all chromosome pairs found in each body cell --> Autosomes: same pairs --> sex chromosomes: female homozygous pair XX; male nonhomozygous pair XY --> Meiosis I: male X,Y & female X,X --> Meiosis II: male X,X,Y,Y & female X,X,X,X --> gametes --> F1: white-eye allele is recessive, red-eye dominant allele --> F2: 3 red-eye females, 1 white-eye MALE --> Gene for white color is missing from the chromosome --> eye colour gene is located on X chromsome -->

Sex-linked trait: a trait controlled by a gene located on a sex chromosome --> traits that can be inherited through the sex chromsome only, not the autosomes

Human Karyotype: 1 human cell: 100,000 genes --> 23 pairs of chromosomes --> each chromosome: thousands of genes

Linked genes: genes located on the same chromosome

Linkage group: all genes on the same chromosome --> 23 chromosomes --> 23 linkage groups

Differing combinations: contrary to independent assortment --> 2 major combinations --> others minority due to crossover of chromosomes during synapsis

Polygenic inheritance: when multiple (two or more) genes reult in a single characteristic

Complete dominance: Mendel's predictions

Incomplete dominance: F1 mixture of traits --> F2: 1:2:1

Codominance: Blood groups A & B dominant over O --> A mix with B => AB group

Human hereditary:

--> curled tongue dominant over uncurled

--> ear lope dominant over non-lope

--> red-green colour blindness gene present only on X sex chromosome --> hence, in males XY chromosomes, Y shorter than X & colour blindness gene lies on X portion extending beyond that of Y --> males only need X chromosome with colour blindness gene to become colour-blind --> females need BOTH defective X chromosomes to be so --> result: more males colour-blind than females

Sex-linked disorders: hemophilia --> blood not clotting due to lack of blood-clotting protein --> recessive gene found on X chromosome beyond Y --> maore males with hemophilia

Autosomal genetic disorder: due to disorder of genes in autosomes --> not sex-related --> sickle-cell anemia --> red blood cells are sickle shape, instead of circular --> they carry less oxygen --> they tend to clump together & clog arteries --> mostly African-Americans

--> Phenylketonuria (PKU) --> no enzyme to break down protein Phenylalanine --> instead, it breaks down into chemicals that damage brain & cause mental retardation

--> Tay-Sachs disease: no enzymes to break down certain lipid in brain --> causes blindness, loss of movement & mental deterioration --> mostly Pennsylvanian Dutch & Ashkenazi Jews

--> Cystic fibrosis: common fatal inherited disorder among white Americans --> recessive allele on chromosome 7 --> mucus collects in lungs --> breathing difficult & lung infections frequent

--> Huntington's disease: caused by dominant allele on chromosome 4 (needs only one allele to get this disease) --> progressive breakdown of nervous system --> ages 30~50

Gene therapy: introduce normal genes into defective body cells to correct genetic disorders --> e.g. CF gene inserted into cold VIRUS --> inhaled by patient in the hope of combining with defective lung cells to correct CF

Chromosomal disorder:

--> Aneuploidy: abnormal no. of chromosomes --> caused by non-disjunction --> chromosome pairs do not separate during meiosis

--> Down's Syndrome: 3 chromosome 21 --> Trisomy --> short, thick tongue, mental retardation --> mostly due to woman >40 years

--> Turner syndrome: only 1 X chromosome (no Y, no X) --> a female without ovaries --> underdeveloped sex characteristics --> occurs 1/2000 births

-->Klinefelter syndrome: XXY chromosome (extra X chromosome) --> a male with female characteristics --> taller than average --> unusually long limbs --> sterile --> mentally retarded

--> XYY males: extra Y chromosome --> fertile --> taller than average