sexual and asexual...
TRANSCRIPT
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…