The birth rate has declined in recent years. It took only a short time from the time a couple can have two children to now that a couple can have three children. In order to encourage childbirth, some places have also introduced a three-child reward policy. For example, families with two and three children in Panzhihua, Sichuan will provide a subsidy of 500 yuan per child per month until the child is three years old. With the implementation of the three-child policy, parents who plan to have children are more concerned about whether their children will look like fathers or mothers in the future. Today we will analyze the genetic principle of single and double eyelids: If the father has single eyelids, will it be passed on to the children?
The first case: the father has single eyelids and the mother has single eyelids, so all children have single eyelids.
Why is it said that when father is a single eyelid and mother is single eyelid, their children must be single eyelid? A single eyelid is a recessive trait and is controlled by a recessive gene. The pair of genes that control a single eyelid can be represented by aa. The genetic diagram is shown in Figure 1. From the genetic diagram, we can see that there are genes aa from the father and mother in the children. The children have single eyelids.
The second case: the father has a single eyelid and the mother has double eyelids (controlled by the heterozygous gene Aa), then half of the children have a single eyelid.
Why is it said that when father has single eyelid and mother has double eyelid, their children may have double eyelid or single eyelid? This happens because the gene that controls the double eyelids in the mother is not homozygous (indicated by Aa), and the genetic diagram is shown in Figure 2. From the genetic diagram, it can be seen that the gene combination that controls the single and double eyelids in the child may be Aa or aa, so the child has a half chance of having a single eyelid.
The third case: father has single eyelid, mother has double eyelid (controlled by homozygous gene AA),Then all the children have double eyelids.
Why do you say that when father has single eyelid and mother has double eyelid, all their children have double eyelid? This is because in the genetic process, the child has gene a from the father and gene A from the mother. When the dominant gene A and the recessive gene a exist at the same time, only dominant gene A is shown. The genetic diagram of the controlled traits is shown in Figure 3. From the genetic diagram, we can see that at this time, there is only one possibility for the gene combination that controls the single and double eyelids in the children: Aa, so all children have double eyelids.
After writing this article, plus the other two articles published before, Mr. Le Lu has analyzed the genetics of single and double eyelids, and Mr. Le Lu will share more with you in the future Biological knowledge.
If you are a student and have any questions about learning, you can leave a message in the comment area below. Teacher Le Lu will answer you for free. If you are a parent and you find a problem in biology or chemistry that you don't understand during the process of tutoring your children, you can also leave a message in the comment area below. Teacher Le Lu will also take the time to provide free assistance to parents.
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