某研究者用非洲爪蟾性腺为材料进行了下列实验． 请回答下列问题：

（1）对非洲爪蟾的精巢切片进行显微观察，绘制了如图1示意图．

图1中甲、乙、丙、丁细胞含有同源染色体的有____ ；称为初级精母细胞的有____ ．丁细胞中染色体的互换区段内同一位点上的基因____ （填“相同”、“不相同”或“不一定相同”）．

（2）如对卵巢切片进行显微观察，无法看到和乙细胞同时期的细胞，其原因是____ ．

（3）该研究者进行了一系列“诱导早期卵母细胞成熟的物质”的实验，结果如图2：

由实验一可得出推论：____ 含有可以诱导卵母细胞成熟的物质．

由实验二可得出推论：这种诱导早期卵母细胞成熟的“促成熟因子”的化学成分是____；孕酮在实验二中的作用是____ 

    Sam is a four year old boy. He lives in the USA with his father and mother. His father works in a hospital. He goes there by subway. He can read books on it. His mother is a worker in a factory. She often walks to work. They usually do some shopping on Sundays for the next week. But this Sunday they are going to the park to have a picnic because it is Sam's birthday.

    Look, Sam has many birthday gifts(礼物). One of them is a nice drum. He likes music. Of course Sam likes the drum very much. He makes a noise with it all day. His parents don't mind. They are happy. But one of the neighbours(邻居)doesn't like the noise. One day, she brings a knife and says to Sam, “Sam, do you know, there's a very nice gift in your drum. Here's a knife. Open the drum and let's find it. ”“OK!”Sam answers.

子女的性别是由（ ）