In higher plant and animals, the cells which make up the body cells of the adult are usually diploid and referred to as somatic cells. The gametes which are produced in the sex organs are always haploid.
Fill in the following chart and place in your notes.
| Terms | Description of terms |
| Somatic Cells | |
| Gametes | |
| Diploid | |
| Haploid |
An individual with a XX chromosome will develop into a female and an individual with a XY chromosome pair will develop into a male.
1. How many autosomes are present in a human male's somatic cell?
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2. How many autosomes are present in a human male's gamete (sperm)?
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3. Which of the following chromosome combinations would be found in a human's female somatic cell?
a) 22 autosomes and 1 X chromosome
d) 44 autosomes and
2 X chromosomes
b) 44 autosomes, 1 X and 1 Y chromosome
e) 22 autosomes and
2 X chromosomes
c) 46 autosomes
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4. Which of the following chromosome combinations would be found in a human's male diploid somatic cell?
a) 22 autosomes and 1 X chromosome
d) 44 autosomes and
2 X chromosomes
b) 44 autosomes, 1 X and 1 Y chromosome
e) 22 autosomes and
2 X chromosomes
c) 46 autosomes
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5. Which of the following chromosome combinations would be found in a female's gamete (egg)?
a) 22 autosomes and 1 X chromosome
d) 44 autosomes and
2 X chromosomes
b) 44 autosomes, 1 X and 1 Y chromosome
e) 22 autosomes and
2 X chromosomes
c) 46 autosomes
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6. Which of the following chromosome combinations would be found in a male's haploid cell (sperm)?
a) 22 autosomes and 1 X chromosome
d) 44 autosomes and
2 X chromosomes
b) 44 autosomes, 1 X and 1 Y chromosome
e) 22 autosomes and
2 X chromosomes
c) 46 autosomes
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During meiosis in females since the somatic cells all contain XX chromosomes, the gametes (eggs) will all contain a single X chromosome. During meiosis in males since the somatic cells all contain XY chromosomes, the gametes (sperm) will contain a single X chromosome and a single Y chromosome.
7. Work the problem showing the segregating of the X and Y chromosomes in humans.
XX x XY
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8. Who determines the sex of the child?
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Remember these are entire chromosomes and not genes that controls the sex of an individual. These chromosomes contain genes which may be passed on to their offspring. These type of problems are called sex-linked problems. Sex linked problems are worked like the monohybrid problems you worked earlier. Keep in mind that when you work six-linked problems the Y chromosome is nonfunctional.
Example: Red/green color blindness is a sex linked trait. Individual who are not red/green color blind (normal) contain a dominant allele (N) for this trait. Individuals who are red/green color blind are homozygous recessive for this trait. Since these genes are located on the X and Y chromosome the genotypes may be written as follows. Note: Alleles are not placed on the Y chromosome because they are nonfunctional. The combination of X and Y determines the sex and the superscript allele represents the gene associated with the sex chromosomes.
XNXN
is a female normal for red/green color blindness (not color blind).
XNXn
is a female normal for red/green color blindness (not color blind);
however, she is a carrier for this allele.
XnXn
is a female who is red/green color blinded.
XNY
is a male normal for red/green color blindness (not color blind).
XnY
is a male who is red/color blinded.
9. Can males be heterozygous for sex linked traits?
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10. In fruit flies (Drosophila) the gene for red or white eyes is located on the sex chromosome. Red (RR or Rr) is dominant to white (rr). State the possible genotypes of both parents when a red-eyed male Drosophila is crossed with a red-eyed female and the resulting offspring include:
19 red-eyed males
11 red-eyed females
10 white-eyed males
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11. In fruit flies (Drosophila) the gene for red or white eyes is located on the sex chromosome. Red (RR or Rr) is dominant to white (rr). State the possible genotypes of both parents when the following F1 offspring were observed:
10 red-eyed males
9 red-eyed females
9 white-eyed males
8 white-eyed females
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12. Normal vision (C) is dominant over color blind (c). This gene
is located on the sex chromosome. A normal vision man and woman produce
three boys, one of which is color blind and the other two with normal vision.
What are the genotypes of the parents.
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13. The disease hemophilia is caused by a recessive allele carried
on the X chromosome. What are the possible genotypes of a father when all
his sons are hemophiliacs?
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14. Consider the following parents:
XHXh x
XhY
What percent of the male's sperm contain the Xh
allele?
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15. Consider the following parents:
XHXh x
XhY
What percent of the female's eggs contain the dominant allele?
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16. Consider the following parents:
XHXh x
XhY
What are the chances for these two parents have a boy with hemophilia?
girl with hemophilia?
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This is the end of lesson five. In the next lesson you will learn
that many genes may be located on the same chromosome. You work the problems
the same way as demonstrated in the lesson involving monohybrid crosses,
however two or more genes will segregate out on the same chromosome.
Click here to go back to the home page and lesson six Linked Genes
and crossing over. click
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Last modified October 22, 1997.