Question

Question 1 (7.5 points) Your 35-year-old (female) cousin is growing weary with her nosy aunts and uncles pestering her with advice to get pregnant soon because of her "biological clock". She is annoyed with them for pestering her and for not pestering her twin brother. She is embarrassed to ask you what this whole "biological clock" concern is all about. Having had taken Animal Development, you can now confidently explain this to her. a. What is the most relevant and important difference between gametogenesis in males and in females to explain to her? b. How could you also explain the observed increased incidence of babies born with chromosomal trisomies (an extra chromosome, e.g., Down Syndrome) when mothers are older than 35?

Answer 1

(a) The formation of gametes is called gametogenesis. In males the process is called spermatogeneis and in females it is called oogeneisis. In males spermatogenesis starts after puberty, but in females oogenesis starts during the time of birth. The total number of egg an human female can produce during her lifetime is decided during early growth stages inside womb. During early stage the oocyte division stops at prophase-I of mitosis -I. After puberty the eggs are released every month by both ovaries until a certain age called menopause. After menopause females stop producing eggs unlike males which produce spem throughout the life. Therefore it is very important for a female to marry at a certain healthy age to conveive pregnancy.

(b) When mothers above 35 conceive pregnancy there is fair amount of chance to have genetically abnormal child like Down's syndrome because mainly three  reasons

1. Due to lifestyle disorder, unbablanced diet and environment affecting the hormonal balance.

2. Due to loss of telomers from DNA due to repeated cycles of division the length of telomers get shortened.

3. The proteins namely cohesin and securin which holds the sister chromatid together amount gets reduced with age leading to abnormal cell division causing trisomy.