امتحان الكتروني في الاحياء - الوراثة

Explanation
The probability of having a male child is 1/2, as there is an equal chance of having a male or female child. Since the family already has four daughters, the probability of the fifth child being male is still 1/2. Therefore, the answer 2/1 indicates that there are two possible outcomes, with one of them being a male child.

Explanation
When a girl who carries the gene responsible for color blindness marries a man who is not affected by the disease, the chances of them having a daughter with color blindness is zero. This is because color blindness is a recessive trait, meaning that both parents must carry the gene for it to be expressed in their offspring. In this case, since the father does not have the gene, he cannot pass it on to his daughter, making the probability of having a color blind daughter zero.

Explanation
Turner syndrome is a genetic disorder that occurs due to the presence of only one complete X chromosome or the absence of part of one X chromosome in females. This results in a change in the number of chromosomes in the chromosomal set, specifically a missing or altered sex chromosome. Therefore, the correct answer is "تغير عدد الكروموسومات في المجموعة الكروموسومية" (change in the number of chromosomes in the chromosomal set).

Explanation
The correct answer states that a genetic marker is genes or parts of genes that appear under the influence of fluorescent materials. This suggests that genetic markers are specific sequences of DNA that can be visualized using fluorescent techniques. These markers are often used in genetic research to track the inheritance of certain genes or traits.

Explanation
The correct answer is "والدة الأم". Since the mother is a carrier of the blood clotting disorder, she must have inherited the gene from one of her parents. As her father is not affected by the disease, it can be concluded that the mother inherited the gene from her mother. Therefore, the gene responsible for the disease was passed down from the mother's side of the family.

Explanation
If a person with the genotype Rr (long eyelashes) marries someone with the genotype rr (short eyelashes), they can produce offspring with the genotype Rr or rr. In this case, the couple produced a child with the genotype rr, which means they inherited the recessive trait for short eyelashes from both parents. Therefore, the genotypes of the parents must be Rr and rr.

Explanation
The question is asking which base is adenine in DNA paired with. Adenine always pairs with thymine in DNA through hydrogen bonding. Therefore, the correct answer is thymine.

Explanation
The number of hydrogen bonds between the nitrogen bases C and G is 3. Hydrogen bonds form between complementary base pairs in DNA, with C always pairing with G. Each base pair is connected by three hydrogen bonds, which provide stability to the DNA double helix. Therefore, the correct answer is 3.

Explanation
The correct answer is 1 because a single gene can determine the inheritance of one trait. Each gene carries the instructions for a specific trait, and variations in the gene can result in different versions of the trait. Therefore, one gene can determine the inheritance of one trait.