A girl child has which of the following combinations of chromosomes in her cells?
44 autosomes + XX
Understanding Chromosomes in a Girl Child
Human cells contain a specific number of chromosomes which carry our genetic information. These chromosomes are typically found in pairs within the nucleus of most cells.
Chromosome Types in Humans
Humans have a total of 46 chromosomes in most body cells. These 46 chromosomes can be divided into two main types:
- Autosomes: These are chromosomes that carry genetic information for traits other than sex determination. Humans have 22 pairs of autosomes. Since they are in pairs, the total number of autosomes is $22 \times 2 = 44$.
- Sex Chromosomes: These chromosomes determine the biological sex of an individual. Humans have one pair of sex chromosomes. There are two types of sex chromosomes: X and Y.
Sex Chromosome Combinations
The combination of sex chromosomes determines whether a person is biologically male or female:
- A person with two X chromosomes (XX) is typically female.
- A person with one X chromosome and one Y chromosome (XY) is typically male.
So, the total number of chromosomes in a typical human cell is 44 autosomes plus the sex chromosomes.
Chromosome Combination for a Girl Child
A girl child is biologically female. As explained above, the sex chromosome combination for a female is XX. Therefore, the complete chromosomal makeup of a girl child's cell is the standard number of autosomes combined with the female sex chromosomes.
Number of autosomes = 44
Sex chromosomes = XX
Total chromosomes = 44 + XX = 46
Thus, a girl child has 44 autosomes and two X chromosomes.
Analyzing the Options for Girl Child Chromosomes
Let's look at the provided options based on our understanding of chromosome combinations in a girl child:
- Option 1: 44 autosomes + XX - This matches our finding for a girl child, which is 44 autosomes and the XX sex chromosome combination.
- Option 2: 22 autosomes + XX - This is incorrect. Humans have 22 pairs of autosomes, totaling 44 autosomes, not 22 autosomes.
- Option 3: 44 autosomes + XY - This combination (44 autosomes + XY) represents the chromosomal makeup of a typical male, not a girl child.
- Option 4: 22 autosomes + XY - This is incorrect for two reasons: humans have 44 autosomes (not 22), and the XY combination is for a male (not a girl child).
Therefore, the correct combination of chromosomes in a girl child's cells is 44 autosomes + XX.
| Chromosome Type | Number in Humans | In a Girl Child | In a Boy Child |
|---|---|---|---|
| Autosomes | 44 (22 pairs) | 44 | 44 |
| Sex Chromosomes | 2 (1 pair) | XX | XY |
| Total Chromosomes | 46 | 44 + XX = 46 | 44 + XY = 46 |
Revision Table: Human Chromosome Basics
| Term | Explanation |
|---|---|
| Chromosome | Structure in cell nucleus carrying genetic information (DNA). |
| Autosomes | Chromosomes (44 in humans) that are not sex chromosomes. |
| Sex Chromosomes | Chromosomes (XX or XY in humans) that determine sex. |
| Diploid Number ($2n$) | Total number of chromosomes in most body cells (46 in humans). |
| Haploid Number ($n$) | Number of chromosomes in gametes (sperm/egg), which is half the diploid number (23 in humans: 22 autosomes + 1 sex chromosome). |
Additional Information on Chromosomes and Sex Determination
Sex determination in humans is primarily based on the presence or absence of the Y chromosome. The Y chromosome carries a gene called SRY (Sex-determining Region Y) which triggers the development of male characteristics. In the absence of a Y chromosome (as in XX individuals), female development occurs.
Gametes (sperm and egg cells) have half the number of chromosomes found in body cells. This is the haploid number ($n$).
- An egg cell always contains 22 autosomes + one X chromosome.
- A sperm cell contains either 22 autosomes + one X chromosome or 22 autosomes + one Y chromosome.
When an egg (22+X) is fertilized by a sperm (22+X), the resulting zygote is (44+XX), which develops into a girl child. When an egg (22+X) is fertilized by a sperm (22+Y), the resulting zygote is (44+XY), which develops into a boy child.
This process ensures that the offspring inherits the correct number of chromosomes (46) from both parents.
Similar Questions
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Statements:
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