1. 12.4 – Chromosomes and Inheritance
Essential Questions:
How are chromosomes, genes, and inheritance related?
What happens during meiosis?
How do sexual and asexual reproduction compare?

2. 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.

3. 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.

4. 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.

5. 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.

6. Mitosis Review
During mitosis DNA replicates before a cell splits into two identical daughter cells.

7. 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.

9. Sexual Reproduction
Male sperm cell and the female egg cell join together to form a new organism with traits from both parents.

10. Asexual Reproduction
One parent produces a new organism identical to itself.
An exact copy of the parent’s DNA is passed on.

11. Comparing Sexual and Asexual Reproduction
Reproduction Type
Advantages
Disadvantages
Asexual
Offspring are produces quickly.
Offspring have the same DNA as the parent.
Sexual
Offspring have a new combination of DNA.
Requires a mate.
Offspring takes longer to develop.

12. Sexual and Asexual Reproduction
Type of Reproduction
Number of Parents
Mitosis or Meiosis
Offspring DNA
Offspring Phenotype
Asexual 1
Mitosis
Exact Copy
Sexual 2
Meiosis
Mix of the 2