Genetics: Beyond Mendel. IB Biology. Mendelian Genetics. This is the term used to describe the basic principles of inheritance for traits that are not inherited in complicated ways. There are many exceptions to the principles we have learned with basic Mendelian genetics. Incomplete Dominance.
RR x rr = Rr
Crossing a homozygous white horse with a homozygous red horse produces a roan horse with a coat of red AND white hairs.
Normally: B’s and V’s sort independently
Probabilities: ¼ BbVv, ¼ Bbvv, ¼ bbVv, and ¼ bbvv
Linked: B’s and V’s do not sort so if B is on the same chromosome as V, they do not mix with b or v
Probabilities: ½ BbVv, ½ bbvv
Experimental Probabilities: 41/100 BbVv, 41/100 bbvv, 9/100 Bbvv, 9/100 bbVv
(41:41:9:9 ratio) . . . How?
Since genes cross over homologous chromosomes in prophase I of meiosis, in this case, about 18% of the time, we do see some of the unexpected combinations above (9% for each = 18% crossover rate). 82% of the time, normal linked combinations are revealed (41% for each expected result = 82%).
Carrier Female (normal)
Because their Y doesn’t have the colorblindness gene at all, males only need one copy to have the recessive phenotype (disorder); so they are much more likely to inherit sex-linked traits.
In the color slideshow, can you see a number hidden in the circle of dots?