Bold words are essential vocabulary. You should be able to recall each of these terms before the end of the unit.
Italicized words are repeat uses of new vocabulary
Underlined words are supplemental vocabulary that we will use in class. You should recognize these words and understand their meaning.
Italicized words are repeat uses of new vocabulary
Underlined words are supplemental vocabulary that we will use in class. You should recognize these words and understand their meaning.
Introduction
Essential vocabulary:
- Heredity is the way that traits are passed from parents to offspring.
- Genetics is the study of heredity.
- A gene is a specific segment of DNA that codes for a specific trait.
- Generations are the levels in a family line (grandfather, father, son, grandson, etc).
Asexual Reproduction
All organisms reproduce one of two ways; sexually or asexually. Asexual reproduction results in two genetically identical cells/organisms. Asexual organisms are things such as bacteria, fungi, and many protists. Bacteria use a process called binary fission to divide into two identical cells. However, fungi and some bacteria use spores to reproduce asexually. Spores are specialized cells that can survive harsh conditions for a long time and are light enough to get picked up by the wind.
However, some multicellular organisms can be asexual. For example, plants can be easily cloned by breaking a piece off and planting the piece in the ground (such as vegetative propogation in pineapples) or splicing it will a more developed plant (such as grafting in apples). Some animals also reproduce asexually using budding by growing a smaller version on the side that breaks off to become a new organism. Similar to budding, some organisms such as starfish and planarians can reproduce by fragmentation if they are torn or cut apart. In all cases of asexual reproduction, the offspring cells have exactly the same DNA as the parents. Therefore the offspring are clones. |
Sexual Reproduction
Sexual reproduction involves the production of sex cells called gametes. Unlike in asexual reproduction, sexual reproduction produces cells that only have one half of each parent's DNA. The male gametes are called sperm and the female gametes are called eggs. In sexual reproduction the gametes of each parent combine during fertilization. The offspring then is a genetic combination between the two parents.
However, not only is each offspring different from the parents, but there will also be variation among the offspring. Brothers don't look like their sisters even though they both get half their genes from each parent. This is because each gamete produced gets a different combination of genes from each parent. |
Asexual reproduction is advantageous because it allows the organism to reproduce very quickly. This is why bacteria are so good at growing so quickly. E. coli bacteria can reproduce in an hour; therefore within 24 hours a single E. coli bacterium can reproduce to become over 16 million bacteria. However, each bacterium is genetically identical.
This is where sexual organisms have the advantage. Sexual organisms must combine their DNA with another organism in order to produce offspring. However, because of this genetic recombination they offspring and the parents are all unique. This is highly advantageous if a disease happens because it means that some individuals may have resistance. In addition, when those individuals survive they will then be able to spread that gene that provides resistance throughout the population (by reproducing with others).
This is where sexual organisms have the advantage. Sexual organisms must combine their DNA with another organism in order to produce offspring. However, because of this genetic recombination they offspring and the parents are all unique. This is highly advantageous if a disease happens because it means that some individuals may have resistance. In addition, when those individuals survive they will then be able to spread that gene that provides resistance throughout the population (by reproducing with others).
Value |
Happens quickly |
Better survival in changing environment |
Lots of genetic variation |
Doesn't require a partner |
Doesn't Require Complexity |
Asexual Reproduction |
✔ |
X |
X |
✔ |
✔ |
Sexual Reproduction |
X |
✔ |
✔ |
X |
X |
Cell Division
When cells become fully grown, they use two types of cell division to make more cells, depending on what type of cell is needed. These types of cell division are called mitosis and meiosis.
Mitosis
Mitosis (pronounced "my toe sis") is the process used to make more body cells, meaning cells that make up the bulk of the organism's body. This means every eukaryote performs mitosis. In the case of unicellular eukaryotes, mitosis means the cell is simply reproducing asexually. However, multicellular eukayotes also can use mitosis for asexual reproduction, such as budding or fragmentation. When a hydra grows a bud, it is using mitosis to grow the cells that make up the bud. Likewise, when your body is injured, you cells use mitosis to make new cells to repair the damage.
Meiosis
Meiosis (pronounced "my O sis" or "me O sis") is used by only eukaryotic sexual organisms such as most animal and plants. This is because meiosis produces gametes (egg and sperm). Males produce gametes (sperm) in the testis, but females produce gametes (eggs) in the ovaries. These are complex organs that require complex anatomy. This complexity is why unicellular (usually) don't do sexual reproduction.
Differences and Similarities
Mendelian Crosses (Punnet Squares)
Gregor Mendel was an Austrian monk who discovered the principles of heredity by breeding pea plants in the monastery's garden. Mendel was not a trained scientist and did not realize the significance of his work, nor did anyone else until years after his death when his notes were rediscovered and shared with scientists. Despite this, Gregor Mendel is referred to as the father of modern genetics.
Mendel did a number of experiments with different crosses for a wide variety of traits, however his experiments with pea color are most famous. In these crosses, Mendel bred a purebreed yellow pea plant with a purebreed green pea plant. He discovered that the resulting offspring (F1) were all yellow. When he had these plants self-fertilize (using the same plant's pollen to fertilize itself), the resulting offspring (F2) were all yellow, except one green pea. This demonstrated that something was causing the yellow trait to dominate or mask the green trait. Mendel called the yellow trait the dominant trait and the green trait, that was masked, the recessive trait.
Mendel did a number of experiments with different crosses for a wide variety of traits, however his experiments with pea color are most famous. In these crosses, Mendel bred a purebreed yellow pea plant with a purebreed green pea plant. He discovered that the resulting offspring (F1) were all yellow. When he had these plants self-fertilize (using the same plant's pollen to fertilize itself), the resulting offspring (F2) were all yellow, except one green pea. This demonstrated that something was causing the yellow trait to dominate or mask the green trait. Mendel called the yellow trait the dominant trait and the green trait, that was masked, the recessive trait.
What Mendel had observed was a result of sexual reproduction. Sexual organisms have two complete sets of DNA. In sexual reproduction each parent gives one half of their DNA (one complete set). Each set of DNA from each parent contains one copy of each gene. Then when the sperm fertilizes the egg, the offspring will have two copies of each gene.
Each different version of a gene is called an allele. In Mendelian crosses we represent then alleles will a capital or lowercase letter depending on if it the dominant or recessive allele. The dominant allele will be the version that shows up any time an offspring receives it. In the case of Mendel's peas, the yellow peas were the dominant trait. The recessive allele is the one that only shows up if no dominant allele is present.
If the offspring has two of the same alleles, then it is called homozygous from the root word "homo" meaning same (alleles in this case). If the offspring has two different alleles, then it is called heterozygous from the root word "hetero" meaning different (alleles in this case).
Each different version of a gene is called an allele. In Mendelian crosses we represent then alleles will a capital or lowercase letter depending on if it the dominant or recessive allele. The dominant allele will be the version that shows up any time an offspring receives it. In the case of Mendel's peas, the yellow peas were the dominant trait. The recessive allele is the one that only shows up if no dominant allele is present.
If the offspring has two of the same alleles, then it is called homozygous from the root word "homo" meaning same (alleles in this case). If the offspring has two different alleles, then it is called heterozygous from the root word "hetero" meaning different (alleles in this case).