Questions and Answers of Biology

Why is it that only one sperm out of the hundreds (or thousands) available enters the oocyte?
What is the function of gastrulation?
Cite two problems with a breech presentation.
What factors are believed to bring about uterine contractions at the termination of pregnancy?
Jenna, a freshman in your dormitory, tells you she just discovered that she is three months pregnant. She recently bragged that since she came to college she has been drinking alcohol heavily and
During Mrs. Li's labor, the obstetrician decided that it was necessary to perform an episiotomy. What is an episiotomy, and why is it done?
A woman in substantial pain called her doctor and explained (between sobs) that she was about to have her baby "right here." The doctor calmed her and asked how she had come to that conclusion. She
Claire is a heavy smoker and has ignored a friend's advice to stop smoking during her pregnancy. On the basis of what you know about the effect of smoking on physiology, describe how Claire's smoking
While Mark was cramming for his anatomy test, he read that some parts of the mesoderm become segmented. He suddenly realized that he could not remember what segmentation is. Define segmentation, and
Assume a sperm has penetrated a polar body and their nuclei fuse. Why would it be unlikely for the resulting cell to develop into a healthy embryo?
Describe the important mechanisms that lead to genetic variations in gametes.
The ability to taste PTC (phenylthiocarbamide) depends on the presence of a dominant gene T; nontasters are homozygous for the recessive gene t. This is a situation of classical dominant-recessive
Most albino children are born to normally pigmented parents. Albinos are homozygous for the recessive gene (aa). What can you conclude about the genotypes of the nonalbino parents?
A woman with blood type A has two children. One has type O blood and the other has type B blood. What is the genotype of the mother? What are the genotype and phenotype of the father? What is the
In skin color inheritance, what will be the relative range of pigmentation in offspring arising from the following parental matches? (a) AABBCC × aabbcc, (b) AABBCC × AaBbCc, (c) Aabbcc × aabbcc.
Compare and contrast amniocentesis and chorionic villus sampling as to the time at which they can be performed and the techniques used to obtain information on the fetus's genetic status.
A color-blind man marries a woman with normal vision. The woman's father was also color-blind. (a) What is the chance that their first child will be a color-blind son? A color-blind daughter? (b) If
Paul is a college student. His genetics assignment is to do a family pedigree for dimples in the cheeks. Absence of dimples is recessive; presence of dimples reflects a dominant allele. Paul has
Mr. and Mrs. Lehman have sought genetic counseling. Mrs. Lehman is concerned because she is unexpectedly pregnant and her husband's brother died of Tay-Sachs disease. She can recall no incidence of
The Browns are both carriers of the recessive allele that causes the metabolic disorder called phenylketonuria. What is the probability of each of the following occurring? (a) All three children will

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