Patterns of inheritance

genetic makeup of an organism

visible characteristics of an organism

the allele of the two which doesn’t express itself (if other allele is dominant)

the allele that’s expressed

• chromosome consists of a single, double-stranded DNA molecule. ( single ‘unit’ before replication but doubles after replication before cell division, so X is now called chromosome) • chromatids are two molecules of double-stranded DNA joined together in the centre by a centromere • chromatin is the complex of DNA and histone protein

one of a pair of chromosomes with the same gene sequence, loci, chromosomal length, and centromere location

duplicated copies of a single chromosome that are attached to each other and are identical

• Centrosome refers to a small region near the nucleus in the cell cytoplasm, containing the centrioles. • centriole - two barrel-shaped organelles that make up the centrosome • Centromere is the central region where the two chromatids are held together.

• when the alleles on both (homologous) chromosomes are different • each allele is a letter = a gene = length of DNA that codes for a polypeptide • before replication one chromosome is composed of one DNA molecule

• when the alleles on both (homologous) chromosomes are the same • each allele is a letter = a gene = length of DNA that codes for a polypeptide • before replication one chromosome is composed of one DNA molecule

when both alleles for a gene in a heterozygous organism equally contribute to the phenotype.

• chemical • physical • biological

• x-rays • gamma rays • UV light

• mustard gas • aromatic amines • benzopyrene ( found in tobacco smoke)

• some viruses • food contaminants • transposons (remnants of viral nuclei that have become incorporated in our genomes)

they can be transmitted through many generations without change

they are not directed by a need on the part of the organism

• deletion • inversion • translocation • duplication • non-disjunction

part of chromosome is lost

when a section of chromosome breaks off, turns 180 degrees and re-joins but can’t be expressed properly as some genes may be too far away from their regulatory nucleotide sequences

piece of chromosome breaks off and attached to another chromosome

a piece of chromosome is duplicated

chromatids fail to separate leaving one gamete with an extra chromosome (trisomy which causes down syndrome)

where there is one extra chromosome or one missing chromosome (may cause trisomy) - in humans, there wouldn’t be 46 chromosomes even if there’s 23 pairs (so 1 left unpaired)