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.

Sexual Reproduction

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

Asexual Reproduction

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

Comparing Sexual and Asexual Reproduction

Reproduction Type Advantages Disadvantages

Asexual 1. Offspring are produces quickly.

1. Offspring have the same DNA as the parent.

Sexual1. Offspring have a

new combination of DNA.

1. Requires a mate.2. Offspring takes

longer to develop.

Sexual and Asexual Reproduction

Type of Reproduction

Number of 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