Conception, Heredity, Pregnancy and Sexual Differentiation

In this week’s lesson, we studied conception, heredity, pregnancy and sexual differentiation. We started our lesson with conception. We said that conception is the process when a sperm and ovum unites together and the ovum is fertilized. Then we talked about the male and the female reproductive systems and their parts. Although I knew most of the terms from high school, some were new to me. We also said that a sperm is weaker and smaller whereas an egg is stronger and bigger. In a part of our lesson, we talked about the genetic abnormalities and gave “down syndrome” as an example. We learned that a 45 year old woman getting pregnant has a much higher risk for genetic abnormalities than a 20 year old. This is because a 45 year old woman’s ovum have been exposed to environmental threats like pollution, radiation longer.

Then we compared the cells in our body. Most of the cells in our body have 23 pairs of chromosomes making 46 in total. But sperm and egg have 23 chromosomes. In most cells there is reproduction by mitosis. Within each chromosome we have DNA which contains genetic information. In mitosis the number of chromosomes is duplicated. On the other hand, in sperm and egg, there is meiosis which is reproduction by reduction. At the end we said that a zygote has 23 pairs of chromosomes; 23 from the mother and 23 from the father.

Later, we started the topic “heredity”. In class, we gave the example of Ali Bey and Aslı Hanım having kids which helped me understand the situation better. We assumed that they are both brown haired with the genes Bb (B for brown hair which is dominant and blonde hair which is recessive). We said that they can have four different babies; 3 brown haired with the genes BB, Bb, bB and one blonde with bb. So we understood that when the dominant is paired with a recessive, the dominant shows up. However Aslı Hanım and Ali Bey both have the recessive genes for blonde hair. We say that blonde hair is a recessive trait. I also have friends, brothers and sisters; one with brown hair and brown eyes and the other blonde hair with blue eyes. Although they are related, their colours are very different and this is again due to the dominant and recessive genes of their parents.

We learned that XX represents female and XY represents male. Mother always gives X to the baby but the father can give either X or Y which also means that father determines the sex of the baby. It is interesting to see that in our country, men who want a son leave their wives if the baby born is not a boy although they are the ones who are determining whether the baby is going to be a girl or a boy.

Also we talked about twins. Twins can be two types; dizygotic where 50% of the genes are shared, or monozygotic where 100% is shared. But I still have a question in my mind. I have twin cousins who look exactly the same, act the same, dress the same but although for all this time I thought they were monozygotic in fact they are dizygotic.



Then we talked about pregnancy and said that it had three stages:
1.Germinal Stage:
Formation of blastocyst.
2.Embryonic Stage:
Implantation occurs in the uterus (the implantation outside the uterus is called ectopic pregnancy).
It is the critical developmental period because the lungs and heart are formed. We call growing from head down cephalocaudal and growing from inside out is called proximodistal.
3.Fetal Stage

Lastly, we learned about sexual differentiation. We said that it occurs during the embryonic stage. At first we all have the same sex organs because the male penis and the female clitoris have the same structure. But when developing, if the developing embryo is exposed to androgens, the person becomes a male, if not a female. Probably the most interesting part of this lesson was when we talked about the Androgen Insensitivity Syndrome. We said that it can be either partial (PAIS) or complete (CAIS). In this situation, we have a genetic male whose body is not sensitive to androgens. So the person is a physical female but a biological male and does not have penis.

This is all for this week. Now I will keep on researching for my article.