GED Science : Genetic Inheritance
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Example Question #1 : Genetic Inheritance
What does it mean for a gene to be sex-linked?
It is a gene located on the X or Y chromosome
It is found in only one gender: either male or female
It is located on autosomes
It is a gene that only affects the reproductive structures of an organism
It is a gene located on the X or Y chromosome
When a gene is sex-linked, it means that the gene is located on one of the sex chromosomes. These chromosomes are the X and Y chromosomes, with the Y chromosome only being found in males. Sex-linked genes provide the opportunity for the frequency of a phenotype to be seen more often in one gender than the other.
Sex-linked genes can be represented in either sex; if the trait is on the X chromosome, it can be displayed in both males and females but may appear more frequently in males.
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 #3 : Genetic Inheritance
What does it mean to say that two genes are linked?
Both genes are used for the same function in the organism
Both genes are on the same chromosome
Both genes are always expressed in an organism at the same time
The genes are directly next to each other
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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