- Homozygous genetic cross results in all offspring being heterozygous
- Heterozygous genetic cross results in mix of homozygous and heterzygous offspring
- Codominance = when both alleles are dominant so both are expressed --> blood types A and B (heterozygous is AB) and snapdragon white and red flowers (heterozygous is pink)
- Multiple genes = when characteristic has more than two alleles (blood type has A, B and O)
- Sex chromosomes --> females have XX but males have XY
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Sex linkage = Y chromosome considerably shorter and don't have all the same genes as X so sometimes whatever allele is on the X is expressed if dominant or recessive <-- characteristic is classed as sex linked
- Colour blindness
- Haemophilia (slow blood clotting due to absence of blood clotting factor) if male gets the recessive gene on the X they won't have the corresponding dominant one so will get haemophilia. Heterozygous females = carriers
- Dihybrid cross is used to show the inheritance of two different genes which may be located on different pairs of homologous chromosomes but control one phenotype --> each gene could have two or more alleles
- Homozygous parents produce all heterozygous offspring
- Heterozygous parents produce 9:3:3:1 offspring (usually)
- Expected ratio different to actual because of random fertilisation and crossing over doesn't always occur
