SAMPLE APA PAPER FOR STUDENTS 2. Abstract. You may not have to include an abstract with your paper; if in doubt, ask your instructor. The. abstract is a single paragraph in block format (without paragraph indentation) and should be. between 150 and 250 words. Be sure to understand the difference between the abstract (a.
In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively. Hormone levels in the male parent affect the sex ratio of sperm in humans.
1 In humans, females have 23 homomorphic pairs and males have 22 homomorphic pairs plus a heteromorphic pair. 2  During meiosis, females produce only one kind of gamete all having one X chromosome. 3  Males produce two kinds of gametes, one with an X and the other with a Y chromosome. XX-XO system in which females have 2 X chromosomes. 2  Males have only 1 X and no additional sex chromosomes. 3  Females have an even number of chromosomes and males have an odd number of chromosomes. 4  This occurs in many species of insects.