Labs, Videos, and Information For High Schoolers Studying Genetics in Biology

1. Watch this short animation of meiosis. To see the steps in meiosis clearly, watch the movie one step at a time. Then go back and "play" it to see all the steps happen quickly.
2. Read the chapter and answer the review questions.
3. If you'd like, visit this website for a nice chart comparing Meiosis and Mitosis.
Note: I did have another awesome youtube on meiosis here, but it was taken off youtube just last night. I"ll try to get a replacement available as soon as I can.

Observe yeast reproducing until a microscope. (page 151 in our textbook).
Model crossing over (page 147 in our textbook)
Do the meiosis modeling lab in the text book (page 158).

Here's another way to model meiosis. This one uses balls of clay or playdough.

There are two basic ways organisms can reproduce: sexually (with meiosis making gametes that unite to form a zygote), or asexually.

Asexual Reproduction

Asexual reproduction is the process of reproduction that involves only one parent. The offspring is genetically identical to the parent.

clip art of binary fission is by ZabMilenko

Binary fission is one type of asexual reproduction. Many prokaryotes (cells without a nucleus) reproduce by binary fission. They simply copy their own DNA and then divide in the middle by pinching into two (somewhat like squeezing a long skinny balloon in the middle.) Amoebas and e coli bacteria are two examples of organisms that reproduce by binary fission.

Budding is another type of asexual reproduction. A bud forms on the parent organism. It may, or may not, break off of the parent to form an independent organism. Hydra engage in budding. Just like with binary fission, organisms that reproduce by budding are genetically identical to their offspring.

Fragmentation is yet another type of asexual reproduction. In fragmentation, an organism "fragments" into many parts. Some of the pieces later grow into adults by regrowing any missing parts.

Sexual Reproduction
(And Meiosis)

Sexual reproduction involves the joining of two reproductive cells. During meiosis, the parents form reproductive cells (gametes) that contain only 1 set of chromosomes. Because the gametes have only 1 set of chromosomes, they are haploid cells. When the gamete from the male combines with the gamete from the female (their joining is called fertilization), the new zygote that is formed will have 2 sets of chromosomes. Because the zygote has 2 sets of chromosomes, it's a diploid cell. The new zygote will have characteristics in common with both parents, but will not be genetically identical to either. It is this aspect about sexual reproduction - that the offspring are not genetically identical to their parents - that allows for evolution by creating genetic diversity. Genetic diversity means that the genes that are passed on from parent to offspring are not exactly identical.

In humans, each gamete has 23 chromosomes. Each zygote has 46 chromosomes because it received 23 from each of it's parents.

Basically, in meiosis, a diploid cell copies all it's chromosomes, mixes them up some in the crossing over stage, then turns them into 4 haploid cells. Each haploid cell will have half the chromosomes of a normal diploid cell. Although four usable sperm are made during spermatogenesis, only 1 usable egg is made during oogenesis.

Because only diploid cells can repair the own DNA, it is believed that sexual reproduction may have been an advantage to early protists (as they evolved) by allowing them to repair damage to their chromosomes.

Watch the youtube on meiosis again (you can just watch the second half that begins with meiosis) and then tell what happens in each stage as you look at the pictures in the textbook.

Types of Life Cycles

Eukaryotes that reproduce sexually can have one of three types of life cycles: The Haploid Life Cycle, the Diploid Life Cycle, and an Alternating Life Cycle.

Haploid Life Cycle - In this type of life cycle, most of the organism's cells are haploid. Two haploid cells combine to make a diploid zygote, but the zygote them immediately undergoes meiosis in order to create haploid cells again.

Diploid Life Cycle - This is the type of life cycle that humans and most other animals have. Most of the organism's cells are diploid. As with the Haploid Life Cycle, two haploid gamete cells combine to make a diploid zygote, but instead of then using meiosis to create haploid cells (as occurs in the Haploid Life Cycle), the cells use mitosis to create more diploid cells.

Alternating Life Cycle - This type of life cycle alternates between a haploid phase (the gametophyte) and a diploid phase (sporophyte).

Image by: Sporic meiosis

This is the alternating generations life cycle. The Sporophyte (diploid) undergoes meiosis which produces haploid spores. The haploid spores divide repeatedly by mitosis in order to become multicelluar gametophytes. The gametophytes release haploid gametes (sperm and egg cells) which join to create a diploid zygote which divides repeatedly by mitosis to become the next multicellular sporophyte.

In essense, the gametes are made by mitosis, and spores are made by meiosis. Gametes come from the gametophytes, and spores come from the sporophytes.

1. The youtube I had here has been removed from youtube due to copyright issues. I'll get a replacement available asap.
2. Read "Origins of Genetics" in the text.
3. Answer the review questions.

1. The youtube I had here has been removed from youtube due to copyright issues. I'll get a replacement available asap. I apologize for the inconvenience!
2. Read the chapter in the book and answer the review questions.

Genetics Vocabulary Words to Learn:

Alleles - Different forms of a gene. For example, for the gene for flower color, you could have 2 red alleles, 2 white alleles, 1of each, etc.

Dominate - If an allele is dominate, that means it's the one that gets expressed in the individual organism. (It's the one that shows up.) It's usually represented by a capital letter. In Bb, the B would be the dominate allele.

Recessive - If an allele is recessive, it doesn't get expressed in the organism unless the organism receives two of them.
If red flower color = R and white flower color = r, then:
a flower that was RR would be red
a flower that was Rr would be red.
a flower that was rr would be white, because it doesn't have any Rs at all.

Homozygous means the organism received two of the same type of allele.
Example: RR or rr, but not Rr.

Heterozygous means the organism received two different alleles for a particular trait.
Example: Rr, but not RR or rr.

Note: Homo means "same." Hetero means "different."

Genotype is the set of alleles that a particular organism has. For example, BB, Bb, or bb.

Phenotype is the physical appearance of the organism and it's based on the genes that are organism has. The genotype determines the phenotype. (In other words, the genes determine which traits the organism will actually have.)

To remember which is which, look at the beginning of each word. The first syllable in Genotype says, "gene." So genotype is the particular genes (alleles) an organism has. Phenotype starts with a "ph," just like "physical appearance" so phenotype refers to the physical appearance.

Punnett Square - That's the square box that many genetics problems are worked in.

Autosomal traits - These are all the traits that are not sex-linked. These traits appear in males and females equally.

Sex-Linked traits - These are traits which are found on the X chromosome and which shows up more often in males than in females. Color-blindness is an example of a sex linked trait. Since the traits are recessive, in order for a female to actually show the trait, she'd have to receive the trait on BOTH of her X chromosomes. If she has the gene for the trait on one X, but still has one X without the trait, she won't show the trait herself. Females can be carriers of the trait though, meaning they can pass it on along to their children, even without having the trait themselves.

Since males only have one X (and one Y), they are affected with the particular sex-linked trait if they receive it on their one X. The reason for this is because they don't have an X without the trait to "dominate" over the recessive one.

Probability - this refers to the likelihood that something will happen. Flip a coin. What's the probability it will land heads-up? 50%. Roll a regular six sided die. What's the probability you'll roll a 6? 1 in 6.

Mutations - these are changes in the DNA of a gene

Gregor Mendel and His Laws on Heredity

Although Gregor Mendel was not the first person to engage in various breeding experiments, his work stands out because he used a quantitative approach (systemic approach) and also developed laws (rules) that accurately predicted the result of crossing one individual with another.

The Law of Segregation was one of the laws Mendel discovered. The law says that when gametes (reproductive cells) are being formed, the two alleles for a certain gene separate from each other, so that one gamete gets one and another gamete gets the other. (We learned this when studying meiosis. The chromosomes are separated into different cells.)

The Law of Independent Assortment was another of the laws Mendel observed. This law says that traits are not tied or linked together. For example, you can't accurately predict the color of a pea flower just by knowing the height of the same pea plant. Having white flowers does not mean a pea plant is more likely to be short or more likely to be tall. The genes that determine the color of the flower separate during gamete formation from the genes that determine the height of the plant. We now know that there are exceptions to this. If the two types of genes are spaced close together on the same chromosome, they are much less likely to separate during the stage of meiosis called crossing over. Therefore, Mendel's Law of Independent Assortment only applies if the genes are located on different chromosomes or else are located far apart on the same chromosome.

Complex Heredity Patterns

There are some patterns of heredity that work differently.

Polygenic Inheritance - Sometimes multiple genes work together to determine a single trait. For example the height of a person is controlled by several genes. Skin color, eye color, and hair color are other examples of multiple genes working together. That's why there aren't just two or three colors of skin, for example, but many shades in between!

Incomplete dominance - This is where two genes blend together. For example, if you cross a white snapdragon plant with a red snapdragon, you'll get a pink snapdragon.

Codominance - This is where neither allele is dominate. Instead they share dominance, creating a speckled or spotted pattern on the organism.

Multiple Alleles - There are some genes that have three or more alleles, rather than only two. Blood is an example in humans, which is why we have so many different types of blood.

Traits Influenced By The Environment - Some traits are influenced not only by their corresponding genes, but also by the environment.

Genetic Disorders

Although mutations (changes in genetic material) are rare, when they occur and then get passed down to future generations, they are called genetic disorders. Sickle Cell Anemia, Cystic Fibrosis, Hemophilia, and Huntington's Disease are some examples of genetic disorders. Genetic disorders are caused when the proteins (that are encoded by the genes) can't do their job properly because they are mutated.

Visit: How Do Mutations Cause Genetic Disorders? for more information about how mutations cause genetic disorders and the role that proteins play in that.

Treating Genetic Disorders

Some genetic disorders can be treated if caught soon enough. PKU is an example. People with PKU lack the enzyme needed to change phenylalanine into tryrosine. If the phenylalanine can't be converted to tryosine, it builds up in the blood and causes mental retardation. Fortunately, a test is available which can diagnose PKU in newborn babies. Babies found to have the disorder can be placed on a special diet to prevent them from becoming mentally retarded.

Gene Therapy is a treatment that is still in its infancy but looks promising for the future. During gene therapy, a doctor puts a healthy gene into the DNA of a person with the genetic disorder. Viruses are used to transport the healthy gene into the person.

1.The video I had here has been removed from youtube. I'll get a replacement youtube available asap.
2. Read the chapter in the book and answer the review questions.

DNA and DNA Replication - Edible Model

How To Extract DNA From Anything Living (We did this one in our homeschool co-op, and it was pretty amazing!)

A Recipe For Traits

1. Watch: translation.
2. Watch: The Central Dogma: Transcription and Translation .
2. Read the section on Genes to Proteins in your textbook.
3. Watch this short animation of Translation. (I suggest using the step-through version, rather than the verbal narration.)
4. Answer the review questions in the textbook.

Unit 3 of Holt Biology is on The History of Life On Earth, including evolution and the classification of living things.

Homepage: Biology: Information, Videos, and Labs

Unit 1 on Cell Biology
Biology Labs, Activities, Videos, and Study Guides About Cells (Photosynthesis, Mitosis, Cell Organelles, and More)

Unit 2 on Genetics
Labs, Information, And Videos For High School Students Studying Genetics.

Unit 3 on The History of Life on Earth
The History Of Life On Earth.

Unit 4 on Ecology
Ecological Principles / Populations
Ecosystems
Biological Communities - Symbiosis, Niches, and Biomes
Global Changes And The Environment

Unit 5 on Diversity
An Introduction to Taxonomy - The Kingdoms and Domains Of Life
Learning About Viruses And Bacteria
Protists: Paramecium, Amoebas, Algae, Diatoms, Euglena, and Others
The Fungi Kingdom

Unit 6 on All About Plants
The Plant Kingdom

Unit 7 on The Animal Kingdom: Invertebrates
The Animal Kingdom - An Introduction
Sponges are Simple Animals
The Cnidarians: Jellyfish, Sea Anemones, Hydrozoans, and Corals
Earthworms, Christmas Tree Worms, Leeches, and Other Annelids

Check back later for additional biology units!

© 2012 Janiece Tobey. All rights reserved.
Page last updated 6/2/12.