X chromosome inactivation in humans occurs ____

a. after fertilization but before cell division begins
b. just after cleavage begins
c. at implantation
d. gestational week 1
e. just after birth


ANSWER: b

Biology & Microbiology

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Lysosomes function best at a pH of ____

a. 7.4 b. 6.5 c. 3.2 d. 5.0 e. 8.2

Biology & Microbiology

As air moves down the trachea, where does it enter next?

a. esophagus b. larynx c. primary bronchi d. pharynx

Biology & Microbiology

Which organisms lack nuclei?

a. protists b. fungi c. ctenophores d. amoebae e. bacteria

Biology & Microbiology

In humans, hemophilia is caused by a recessive allele on the X chromosome. Suppose a man with hemophilia has children with a healthy woman whose mother had hemophilia. If an ultrasound test shows that their first child is a girl, what is the probability that she has hemophilia? (Enter the probability as a percent. Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5 )  

50 Clarify Question · What is the key concept addressed by the question? · What type of thinking is required? · What key words does the question contain?   Gather Content · What do you already know about X-linked inheritance?   Consider Possibilities · What other information is related to the question? Which information is most useful?   Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?   Reflect on Process · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Biology & Microbiology