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Cells & Inheritance

Chromosome Theory and Meiosis

Christopher Landry

on 3 January 2015

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Transcript of Cells & Inheritance

Cells & Heredity
- Cells & Inheritance -

What role do chromosomes play in inheritance?
What events occur during meiosis?
What is the relationship
between chromosomes
and genes?
In the early 1900's
scientists were working
to identify the cell structures
that carried Mendel's
herediary factors, or genes.
In 1903, Walter Sutton
observed that sex cells in
grasshoppers had half the
number of chromosomes as
the body cells. Sutton wanted
to understand how sex cells form.
He also noticed that each grasshopper
had exactly the same number of chromosomes
in its body cells as each of the parents.
Sutton reasoned that the
chromosomes in body cells
actually occurred in pairs, with one chromosome in each pair coming from the male and the other coming from the female.
Sutton realized that paired
alleles were carried on paired
chromosomes. From his
observations, Sutton concluded
that genes are located in
Sutton proposed the chromosome theory of inheritance. According to the chromosome theory of inheritance, genes are carried from parents to their offspring on chromosomes.
Walter Sutton
Organisms produce sex
cells during meiosis.
is the process by which the
number of chromosomes
is reduced by half to form sex cells - sperm and eggs.
When they combine,
each sex cell contributes
half the number of chromosomes to produce offspring with the correct number of chromosomes.
During meiosis, the
chromosome pairs separate and
are distributed to two different cells.
The resulting sex cells have only half
as many chromosomes as the other cells
in the organism.
Before Meiosis begins,
every chromosome in the parent cell is copied.
Centromeres hold the two chromotids together.
Chromosomes are made up of many genes joined together like beads on a string. Each chromosome contains a large number of genes, each gene controlling a particular trait.
A Lineup of Genes
However, the alleles for some of
the genes might differ from each other, making the organism heterozygous for some traits.
If the alleles are the same, the organism is homozygous for those traits.
Although you have 23 pairs of chromosomes,
or 46 chromosomes total, your body cells
each contain about 35,000 genes. Each gene
controls a trait.
Meiosis 1
The Chromosome pairs line up in the center of the cell. The pairs seperate and move to opposite ends of the cells.
Two cells form, each with half the number of chromosomes. Each chromosome still has two chromatids.
Meiosis 2
The chromosomes with their two chromatids move to the center of the cell.
The centromeres split, and the chromatids separate.
End of Meiosis
Four sex cells have been produced. Each cell has only half the number of chromosomes that the parent cell had at the beginning of meiosis.
Punnett Squares
Punnett Squares show the results of meiosis.
When chromosome pairs separate, so do the alleles carried on the chromosomes.
One allele from each pair goes to each sex cell.
Full transcript