genetic diagrams to show patterns of inheritance

monogenic, dihybrid, codominance, sex-linkage

genetic cross steps

1. state phenotype of both parents
2. state genotype of both parents (choose letter to represent)
3. state gametes of each parent
4. punnett square
5. ratio of each genotype of offspring
6. ratio of phenotypes

codominance

when two different equally dominant alleles occur for a gene

what is this punnett square an example of?

codominance

example of a gene with multiple alleles

immunoglobulin gene which codes for blood type - Ia, Ib, Io

female chromosomes

XX

male chromosomes

XY

sex linkage

characteristics determined by genes carried on the sex chromosomes

sex-linkage step 1

most genes on sex chromosomes are only carried on X chromosome

sex linkage step 2

men only have one X chromosome so only carry one allele for sex-linked genes

sex linkage step 3

therefore they express the characteristic of the allele even if its recessive so more likely to show recessive characteristics

example of characteristics more likely to be seen in men

colour blindness

dihybrid cross

used to show the inheritance of two different characteristics caused by two different genes

dihybrid cross layout

uses 4 alleles instead of 2

what is this punnett square an example of?

a dihybrid cross