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Genetics
1. Chromosomes
2. Cell Division
3. Inheritance
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1. Chromosomes
Karyotype--the observed characteristics (eg shape, number, type) of the chromosomes.
Homologous chromosomes/ homologues-- 2 chromosomes composing a pair, having the same centromere position, length, and staining patterns.
Sex chromosomes--X and Y chromosomes.
Autosomes-- any chromosomes excluding X and Y.
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2. Cell Division
Sporophyte--The multicellular diploid stage in plants and some algae.
Gametophyte--A spore dividing mitotically, generating a multicellular haploid stage.
Meiosis-- cell division that reduce number of chromosomes sets, from diploid to haploid.
Diploid--having 2 sets of each chromosome.
Haploid--having 1 set of each chromosome.
Synapsis--a process: pairing of homologues, during prophase I. During synapsis, a protein structure: "synaptonemal complex" forms between homologues, holding them tightly together.
Tetrad--a group of 4 chromotids, each having chiasmata, holding the homologues together until anaphase I.
Centrosomes-- consists of 2 centrioles. It forms a spindle in prophase I.
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3. Inheritance
Trait--each variant for a character. eg blue eyes, brown eyes.
Hybridization--crossing of 2 true-breeding varieties.
Law of segregation--consists of 4 laws.
1. Alternative versions of genes account for variations in inherited characteristics.
2. For each characteristic, an organism inherits two alleles, one from each parent.
3. If the two alleles differ, then one, the allele that encodes the dominant trait, is fully expressed in the organism's appearance; the other, the allele encoding the recessive trait, has no noticeable effect on the organism's appearance.
4. The two alleles for each characteristic segregate during gamete production.
Monohybrid--cross of true breeding parents, identically heterozygous at one locus.
Dihybrid--heterozygous for 2 characters.
(c) copyright Susanna Shiu & Queenie Liew, since September 2007