Download 12.4 * Chromosomes and Inheritance

12.4 – Chromosomes and Inheritance
Essential Questions:
1.
How are chromosomes, genes, and inheritance related?
2.
What happens during meiosis?
3.
How do sexual and asexual reproduction compare?
How are Chromosomes, Genes, and
Inheritance Related?


At the beginning of the
1900’s, Walter Sutton was
studying how egg and
sperm cells form.
He watched the
chromosomes within the
cells and hypothesized
chromosomes are the key
to inheritance.
Chromosomes and Inheritance


Each chromosome exists
as a pair.
Human have 23 pairs of
chromosomes for a total
of 46.

Sex cells have 23
chromosome and when
they meet, there are 46.
Chromosomes and Inheritance


This means that one
allele comes from each
parent on the donated
gene.
According to Sutton’s
chromosome theory of
inheritance, genes pass
from parents to their
offspring on
chromosomes.
A Line-Up of Genes

Humans have 23 pairs of
chromosomes for a total
of 46.

Chromosomes are made of
many genes.

Genes of the same
chromosome are in the same
order.

Genes control traits.
Mitosis Review

During mitosis DNA replicates before a cell
splits into two identical daughter cells.
What Happens During Meiosis

Meiosis is a form of cell division by which the number of
chromosomes is reduced by half as sex cells form.

During meiosis the chromosome pairs separate into two different
cells.

Then these two cells divide again with half the number of chromosomes.
Asexual Reproduction

One parent produces a new organism identical to itself.

An exact copy of the parent’s DNA is passed on.
Sexual Reproduction

Male sperm cell and the female egg cell join together to
form a new organism with traits from both parents.
Comparing Sexual and Asexual
Reproduction
Reproduction Type
Advantages
Disadvantages
Asexual
1. Offspring are produces
quickly.
1. Offspring have the
same DNA as the
parent.
Sexual
1. Offspring have a new
combination of DNA.
1. Requires a mate.
2. Offspring takes longer
to develop.
Sexual and Asexual Reproduction
Type of
Number of
Reproduction Parents
Mitosis or
Meiosis
Offspring
DNA
Offspring
Phenotype
Asexual
1
Mitosis
Exact Copy
Exact Copy
Sexual
2
Meiosis
Mix of the 2
Mix of the 2
Drastic
oversimplification!!!