Probability and Heredity

Probability Probability- in the number that describes how likely it is that an even will occur. The laws of probability predict what is likely to occur, not necessarily what will occur. If I flip a coin there is a 50% chance it will land on heads or tails.

Probability and Genetics How is probability related to genetics?  After mendel’s experiment he realized that the probability of crossing a tall plant was 3 in 4. The probability of crossing a short plant was 1 in 4.  Mendel was the first scientist to recognize this.

Punnett Squares Punnett Square- is a chart that shows all the possible combinations of alleles that can result from a genetic cross.

Setting it up Draw the box. Write the male parent’s alleles along the top of the square and the female parents along the left side. M---top-  R r F—side  R r

Punnett Square Bring down the traits R r R r  In a genetic cross, the allele that each parent will pass onto its offspring is based on probability.  RR=1 in 4, Rr= 2 in 4, rr= 1 in4 RR Rr rr

Punnet Square Remember that the Dominant allele will masks the recessive allele.

Phenotype and Genotype Phenotype- is an organisms physical appearance or visible traits. Genotype -is its genetic make up or allele combinations. Homozygous- has two identical alleles for a trait. Heterozygous- has two different alleles for a trait.

Codominance In Mendel’s experiments he always had a dominant allele while the other allele was recessive. This is not always the case. In Codominance, the alleles are neither dominant nor recessive. Because of this, both alleles are expressed in the offspring.