Download Cells and Chromosomes Reading Sheet File

CHROMOSOMES & CELLS READING
Name__________________________________________
Read the following information on cells and chromosomes in cells. Then fill out your note sheet for this lesson
based on what you learned in the article.
 What Is A Chromosome?
o A chromosome is a bundle of your DNA. You get half of your chromosomes from your mother
and you get the other half from your father. All non-sexual cells in the body have the full set of
your chromosomes (which is a full set of your DNA).
o Here are 2 pictures of the structure of a chromosome:
PICTURE 1
PICTURE 2
A single chromosome looks like a single bar or single line. This chromosome is made up of DNA.
A gene is a section of the DNA that provides instruction for a certain trait (for example, there is a
gene for eye color, another for hair color, etc). When a chromosome has copied itself, it has the
two copies next to one another and are bunched together. The copies are bunched together at a
location called the centromere. The two duplicate parts are called sister chromatids.
 How Many Chromosomes Do I Have?
o Each organism has a different number of chromosomes. However, each non-sexual cell in the
human body has 46 chromosomes in it. Of the chromosomes found in these human cells:
 44 of them do NOT determine the sex (or gender) of the individual – these are called
autosomes or autosomal chromosomes
 2 of them do determine the sex (or gender)of the individual – these are called sex
chromosomes
 In humans, the sex chromosomes are the X chromosome and the Y chromosome.
 If you are a male, you have an X chromosome and a Y chromosome (XY)
 If you are a female, you have two X chromosomes (XX)
o You can look at a picture of one’s chromosomes by looking at a karyotype. A karyotype shows all
of the cell’s chromosomes in their pairs. They are arranged from largest pair to the smallest pairs
for the autosomes.
o
Here are two pictures of karyotypes from humans:
PICTURE #1
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PICTURE #2
Notice that each chromosome is paired. This means one chromosome came from mother
and one from father. A pair of common chromosomes that code for the same genes is
called a homologous pair or homologous chromosomes.
The karyotype in picture #1 is of a male human. There are 22 homologous pairs of
autosomes. Then the last homologous pair is the sex chromosomes. One of the
chromosomes is large. This is the X chromosome. The Y chromosome is smaller and
chopped off. Having a sex chromosome pair of different sizes indicates a male.
The karyotype in picture #2 is of a female human. There are 22 homologous pairs of
autosomes. Then the last homologous pair is the sex chromosome. Both chromosomes
are the same size and are large. This means the cell has two X chromosomes. Having a
sex chromosome pair of the same size indicates a female.
 How Are Sperm/Egg Cells Different From Other Cells In The Body?
o Most human cells have 46 chromosomes a piece. However, the sex cells (sperm and eggs) do not.
Sex cells are formally called gametes. Sperm is the male gamete, while the egg is the female
gamete.
o Gametes each have 23 chromosomes in them. This is because when the sperm and egg meet for
fertilization and the creation of a new human baby, there is a total of 46 chromosomes.
o How do biologists refer to cells with different numbers of chromosomes?
 If a cell has the full number of chromosomes it should have (half from mother and half
from father), biologists refer to this cell as having a diploid number. Diploid number is
expressed by the symbol “2n”. 2n indicates that the cell has a pair (2) of each type of
chromosome.
 If a cell has only half of the full number of chromosome it should have, biologists refer to
this cell as having a haploid number. Haploid number is expressed as “n”. n indicates
that the cell has half of its normal chromosome number.
 Here are the details on these numbers for a human:
 The diploid number for humans is:
46
 The haploid number for humans is:
23
 The 2n number for humans is:
46
 The n number for humans is:
23
 The number of chromosomes in an autosomal cell is: 46
 The number of chromosomes in a gamete is:
23