sexual and asexual...

Sexual and Asexual Reproduction

Cell Reproduction TEST

Friday, 11/13

What are Chromosomes?How many

chromosomes do humans have?

How many chromosomes came from your mom?

How many chromosomes came from your dad?

What are Chromosomes?

Chromosome – a DNA-containing structure that carries genetic information from one generation to the next.

Chromosomes are inherited from parent cells.

Every species has a specific chromosome number.

What are Chromosomes?

Autosomes – chromosomes with genes that do not determine an individual’s gender

How many autosomes do humans have? 44

What are Chromosomes?

Sex Chromosomes – chromosomes with genes that determine an individual’s gender

Humans X and Y

X chromosome contains many vital genes unrelated to gender

How many sex chromosomes do humans have?

2

What are Chromosomes?

XXXY

Homologous Chromosomes

Homologous chromosomes – chromosomes that are the SAME size and have the SAME genes.

Genes – sections of DNA that code for proteins.

Haploid vs. Diploid

Haploid – describes cells containing half the number of chromosomes

Which cells in our bodies are haploid?

What is the haploid number for humans?

gametes

23

Haploid vs. Diploid

Diploid – describes cells containing 2 of each chromosome

Which cells in our bodies are diploid?

What is the diploid number for humans?

Somatic cells

46

Asexual Reproduction

When a cell reproduces by asexual reproduction,

One parent cell provides all the genetic information.

2 daughter cells are produced

Asexual Reproduction

Daughter cells are genetically identical to the original parent cell and to each other.

No genetic variation exists unless mutations occur.

Genetic variation –differences in the DNA

Mutations – changes in the DNA

When does the cell copy its DNA?

S-phase (interphase)

Why does the cell copy its DNA?

To make identical copies for each daughter cell

Sometimes, there are mistakes mutations

We’ll talk about these more later…

Asexual ReproductionBuilds the bodies of multicellular organisms.

Somatic cells – regular body cells

Created by asexual reproduction (mitosis)

Every cell in your body has the exact same DNA. Cells function differently based on which genes are turned on/off.

Asexual ReproductionSome organisms reproduce by

asexual reproduction to build populations.

Examples:

Prokaryotes – binary fission

Eukaryotes – mitosis

Asexual Reproduction ~ Advantages

Does not require a mate.

Saves time and energy.

Occurs quickly.

Populations grow rapidly.

More offspring can be produced over time.

Asexual Reproduction ~ Disadvantages

No genetic variation among offspring.

Populations are only successful in environments with little stress.

Nutrient availability, space, etc.

No competition which limits adaptations to the environment.

Sexual Reproduction

Requires TWO parent cells

Each parent cell contributes half the genetic information for the offspring.

Gametes – haploid reproductive cells (sperm and egg)

Formed by meiosis in the reproductive organs

Sexual Reproduction

Zygote – the diploid cell that results from the fertilization of the egg by the sperm

Sexual Reproduction ~ Advantages

Produces genetically unique offspring.

Competition among individuals produces a more successful or better adapted population.

Genetic variation allows some organisms to survive when others cannot.

Sexual Reproduction ~ Disadvantages

Requires TWO parent cells, so organisms must find a mate.

Takes time and energy…

Slower process Slower population growth

Sources of Genetic Variation

Crossing over – occurs when homologous chromosomes swap genetic information at the beginning of meiosis (Prophase I)

Sources of Genetic Variation

Law of Independent Assortment – the random distribution of homologous chromosomes during meiosis (Metaphase I)

Sources of Genetic Variation

Law of Independent Assortment – influences the combination of genes in the gametes

Sources of Genetic Variation

Random Fertilization

Only 1 sperm can fertilize each egg.

Just Remember…