Study Guide: Chapter 5 “A Closer Look At Conception”
Read pages 124-129 and answer the questions
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7.
Define the following:
a. Heredity – the passing of characteristics such as physical build, skin color, hair texture and
color, color and shape of eyes, shape and size of ears, hands, and feet, blood type, and some
medical conditions.
b. Chromosomes – tiny threadlike particles in the nucleus of every cell that carry hereditary
characteristics.
c. Genes – the units that determine inherited characteristics.
How many chromosomes does a human baby have at conception? Where do they come from?
At the moment of conception every human baby receives a total of 46 chromosomes. 23 come
from the ovum (mother) and 23 come from the sperm (father).
Explain how dominant and recessive genes work to produce the various characteristics we
inherit from our parents.
For every inherited characteristic, an individual receives two copies of a gene – one from the
mother and one from the father. If both are the same, the child is certain to show that
characteristic. If the child receives two different genes, a gene for brown eyes and a gene for
blue eyes. What color eyes the child has will be determined by the stronger or dominant gene,
even though the child will carry the recessive or weaker, gene.
Why is each individual unique, even though brothers and sisters have the same parent? In
other words, why don’t all of the children of two parents all look the same?
Of the father’s 46 chromosomes, only half go into the sperm cell, one from each pair of
chromosomes. The same is true of the mother. Which of the two genes each possess could go
into the sperm or egg. Thus each egg and sperm contains a different combination of genes on
the chromosomes.
When is the baby’s sex determined? How are sperm different from egg cells when it comes to
chromosomes? Which parent determines the sex of the child? Explain why.
The sex of the child is determined at the moment of conception. Each ovum from the female
contains an X chromosome. Each sperm contains either an X chromosome or a Y chromosome.
The father determines the sex of the cell because the mother can only give an X chromosome
but the father can give either an X or a Y chromosome. If the sperm carries an X , the baby will
be a girl, if the sperm carries a Y, the baby will be a boy.
How are identical twins produced? Why do identical twins have very similar characteristics
(look the same)?
Sometimes the growing mass of cells splits apart soon after fertilization. Each of these two
clumps of cells continues to divide and grow into a separate embryo. This is the process by
which identical twins are produced. Identical twins are always the same sex and will have very
similar characteristics because the two babies have developed from the same zygote.
How are fraternal twins produced? Why don’t fraternal twins necessarily have very similar
characteristics like identical ones?
Fraternal twins develop when two eggs are released at the same time and each is fertilized by a
different sperm. They grow side by side in the uterus.
8.
Define “infertility”. Explain how a doctor would treat an infertile couple.
Infertility is the inability to conceive a child. They make a fertility analysis, a detailed physical
study of both the male and female then prescribe drugs if there is a medication to help the
problem and monitor the results. The doctor will support the couple and make sure they are
aware of all of their options.
9.
Explain each of these options for infertile couples:
a. Adoption – a means of providing a loving home for one or more children who would not
otherwise have one
b. Artificial insemination – the process of injecting sperm into a woman’s uterus with a special
needle. (usually sperm from the husband)
c. In vitro fertilization – A woman whose damaged Fallopian tubes prevent pregnancy may
have the doctor remove a mature egg from her ovary, then it is placed into a special solution
and her husband’s sperm are added. If fertilization takes place, the doctor then inserts the
zygote into the woman’s uterus. If the zygote attaches to the uterus, it will grow into a baby.
d. Ovum Transfer – An egg obtained from a female donor is fertilized by the man’s sperm with
in vitro fertilization and then implanted in the uterus of an infertile woman.
e. Surrogate mother – a woman who carries and delivers a baby for another couple. In some
cases, the surrogate carries a couples’ fertilized egg which has been taken from the
biological mother. Other surrogates are artificially inseminated with sperm from the
husband of an infertile woman.