GED Science : Evolution and Genetics
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Example Question #2 : Genetic Inheritance
When two heterozygotes for a given gene come together and mate, what percentage of the offspring will display the recessive phenotype?
Note: assume that the gene is expressed using the mechanism of complete dominance.
a heterozygous organism will have one copy of the dominant allele and one copy of the recessive allele for a given gene. The recessive phenotype is the expression of the recessive allele; this will only occur if the offspring as two copies of the recessive allele.
Since two heterozygotes are mating, each one has a 50% chance of contributing their recessive allele to the offspring. Keeping that in mind, the probability of this happening just becomes 50% multiplied by 50%. This gives us a 25% chance that the offspring will display the recessive phenotype.
In other terms, we can look at all the possible combinations for the offspring. Assume that A represents the dominant allele and a represents the recessive allele.
Each parent will have the genotype Aa. The cross will be Aa x Aa. The possible resulting offspring will be AA, Aa, aA, and aa. Only aa will show the recessive phenotype; therefore, there is a one-fourth chance (25%) that the offspring will show the recessive phenotype.
Example Question #101 : Biology And Life Sciences
What does it mean to say that two genes are linked?
Both genes are on the same chromosome
Both genes are used for the same function in the organism
The genes are directly next to each other
Both genes are always expressed in an organism at the same time
Both genes are on the same chromosome
There are only 23 chromosome pairs in human beings, but there are thousands of genes. This means that many genes will be found on the same chromosome. When two genes are found on the same chromosome, they are said to be linked. Genes that are very close to each other on the chromosome are more likely to travel with each other to the same haploid cell during meiosis, and are frequently inherited together.
An example of linked genes are blue eyes and blond hair. These traits are frequently inherited together because they are found in the same region on the same chromosome.
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