Sexual Reproduction and Genetic Variation

Mutations- beneficial or harmful?

1) Beneficial- skin color differences, can be beneficial to shield from harmful UV rays 2) Harmful- certain types of diseases 3) Neutral

Examples of variation due to environment/lifestyle

1) Hair length 2) Accent 3) Piercings 4) Tattoos 5) Scars

Zygote

A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

Transformation in Prokaryotes

Bacteria have DNA inside. When bacteria die and rupture the cell wall, the DNA may still be intact. Another bacteria can take the DNA and make use of it. This is how traits are passed from one bacteria to another.

Genetic variation

Differences among individuals in the composition of their genes or other DNA segments

Types of genetic variation mechanisms for prokaryotes

Horizontal acquisition -transformation -transduction -conjugation

Where do differences between siblings come from?

Parents. Children get half of their genetic information from mom and half from dad. It depends on which half of their DNA they are giving, which is a big factor that will determine what you will look like. The environment will also shape what you look like. For example, the nutrients you get, the experiences you have, etc... even identical twins will be different based on environmental differences.

Genes and environment work together to make...

Variation in a population (like lions, chimps, aspen trees, ants, etc...)

When does asexual reproduction have an advantage?

When the environment is stable over time (which is rare)

Sister chromatids

X (the left side and right side of the x. The x can represent either the maternal or the paternal chromosome). A sister chromatid refers to the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere.

Many characteristics are due to a combination of both ______ and the _______

genetics and the environment. For example, height. You have a specific height designated by your genetics, but you cannot grow to your height unless you eat a healthy, balanced diet.

5 types of organisms that undergo asexual reproduction

1) Archae and eubacteria (common!) 2) Protista (amoeba) 3) Fungi (yeast, mushrooms) 4) Plantae (strawberries, potatoes, aspen) 5) Animalia (sponges, starfish )

How does sexual reproduction provide for variation?

1) Combining two gametes in random fertilization (both gametes look different from each other) 2) Independent assortment in meiosis (happens during metaphase I) 3) Crossing over (happens during prophase I). Crossing over results in more than 2 to the 23 power gametes.

Examples of variation in humans caused by genes

1) Eye color 2) Blood group [ blood group A means you have alleles for this characteristic]. -You are born with these variations, and nothing can change it.

Where does variation come from?

1) Genes- Your parents. Each parent will give you half of their genetic information. 2) We also get variation from mutations. As DNA is duplicating, it will make mistakes. Some mutations can be helpful. 3) You get variation from your environment-chemicals you are exposed to, your experiences, foods you eat, etc...

What are the two most important things that shape an organism?

1) Genes- traits 2) Environment- Development, appearance, behavior, survival

What are the advantages of asexual reproduction?

1) No need to find a partner 2) Low energy requirements 3) Guaranteed success 4) Genetically identical to parent 5) Ecological "match"

What are examples of errors in meiosis?

1) Nondisjunction- Failure of paired chromosomes to separate during cell division so that both chromosomes go to one daughter cell and none to go the other. Error in chromosome number. Can occur during anaphase when sister chromatids fail to separate when they move to opposite poles of the cell. An example is down syndrome. One chromosome plus or minus, having extra x's and y's. Usually isn't an advantage. 2) Polyploidy- When cells have more than two paired sets of chromosomes. For example, you can have 3 sets of chromosomes [triploid] or 4 sets of chromosomes [tetraploid]. Does seem to provide a benefit in plants (seedless bananas and watermelon are triploid.)

Three things that can have genetic variation

1) Prokaryotes 2) Viruses 3) eukaryotes

Where does genetic variation come from?

1. Crossing over (during meiosis) 2. Independent assortment (during metaphase 1) 3. Random fertilization (during fertilization)

Gametes (egg and sperm cells)

23 chromosomes in sperm, 23 in egg, make a child (46 chromosomes)

How many pairs of chromosomes does one human being have

23 pairs of chromosomes. 23 from mom and 23 from dad.

Diploid

A cell containing two complete sets of chromosomes, one from each parent

Haploid

A cell having a single set of unpaired chromosomes

Haploid

A cell that contains a single set of unpaired chromosomes. Gametes are an example of haploid cells produced as a result of meiosis.

What is asexual reproduction?

A type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from a single cell or from a multicellular organism inherit the genes of that parent. All of the offspring are clones, or are genetically identical to one other. Occurs using mitosis (normal cell division).

Where is genetic variation present?

Between species and in a species (different fur color, some animals have more fluff, different eye color, etc...)

Crossing over in eukaryotes

Crossing over gives us variability. During meiosis 1, you get a chromosome from mom and dad. Sister chromatids have the exact same genes. Crossing over is when homologous chromosomes wrap around each other and share genetic information

Different members of a population and DNA

Different members of a population have different DNA (unless they are identical twins). This means everyone has different versions of genes called alleles, and these alleles give rise to different characteristics. For example, one kitten can have an allele for brown eyes, and another kitten has an allele for blue eyes.

What is the relationship between genetic variation and natural selection?

Due to genetic variation, some individuals are better adapted to their environment than others, allowing natural selection to take place (ex: rats with better eyesight can more effectively avoid being eaten by predators and are more likely to survive and reproduce to pass on their advantage).

What are mutations, and when do mutations occur?

During DNA replication. They are "mistakes" of DNA- sometimes one letter, or big chunks of chromosomes. Mutations are passed down to offspring. Down syndrome is an example of a mutation.

Genetic Variation- helpful or harmful?

Even though some specific variations are beneficial and some are harmful, variation itself is advantageous in that it is built in to the system at many levels

Why do father and son look a lot like one another but are not clones?

Genetic variation. There is variation in rocks, clams, and sunflowers.

Random assortment/independent assortment in eukaryotes

Homologous chromosomes align themselves randomly at the center of the cell. The chromosomes can line up a-b or b-a

Homologous chromosomes

Homologous pair has a similar size, shape, and banding pattern, and contains genetic information for the same traits.

Nature vs. nurture example

Intelligence. Is it due more to genetics (nature) or quality of education (environment/nurture)? Scientists can test this by doing experiments on identical twins who have identical DNA. If the characteristic is the same, it is likely due to genetics. If it is different, it is likely due to the environment. (Ex: Same eye color [genetics] but different personality/talents [environment])

What does inbreeding do to a pedigree?

It makes the pedigree get smaller and smaller at the end instead of getting wider and wider

Random Fertilization in eukaryotes

Males create trillions of sperm during their lifetime. Females have already created all of the eggs they will have. This one egg getting together with this one sperm is very rare, so this also leads to genetic variability.

Sexual reproduction

Produces genetic variation among offspring. Each offspring is genetically unique from each other and from the parent. Provides an evolutionary advantage. If there was a disease based on your genes, everyone in the species would get the disease because they have the same genes.

Transduction in Prokaryotes

Requires a phage. A phage is a virus that infects bacteria. A phage injects its DNA into the bacteria, hijacks the cell so that it makes more copies of the virus. When one of the viruses escapes, it actually carries some of the bacterial genome with it. It'll then inject that genome into another bacteria so that the bacteria can make use of it. The vector is phage.

What type of reproduction is most advantageous, and when is it most advantageous?

Sexual reproduction is most advantageous when the environment is unstable over time

What is sexual reproduction?

Sexual reproduction is the process whereby haploid gametes from two individuals come together (fertilization) to create a new, unique diploid individual. That individual becomes a fetus or a baby.

Homologous pairs of chromosomes-- which ones are inherited by mom, and which ones are inherited by dad?

Sister chromatids of paternal chromosome, sister chromatids of maternal chromosome

Conjugation in Prokaryotes

The closest we have to bacterial "sex." Conjugation is done through the transfer of a plasmid. The plasmid is another bit of auxillary DNA. F Plasmid stands for Fertility plasmid. Bacteria with fertility plasmid will connect to the other bacteria and it will share some of its DNA. Then the recipient gets the fertility plasmid and pilus, and can pass the F plasmid and pilus on. No meiosis, just transferring DNA and plasmid.

Variation

The differences in characteristics within a population. Variation can be due to genetics, the environment, or a combination of both.

Stages of Meiosis I and II

The first meiotic division is a reduction division (diploid → haploid) in which homologous chromosomes are separated. PMAT - Prophase, metaphase, anaphase, telophase S-phase of interphase of meiosis: DNa is replicated, producing two copies of each chromosome called sister chromatids. The paired centrioles in the cytoplasm duplicate and begin extending microtubules that will form the meiotic spindle. Sister chromatids remain attached at the centromere and condense. Prophase-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs Metaphase-I: Bivalents (paired chromosomes) randomly align along the metaphase plate. This alignment is random and adds to genetic diversity. Anaphase-I: Homologous chromosomes separate and move toward opposite poles T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells -------------------------------------------------- Meiosis II The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I) P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before) M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells The final outcome of meiosis is the production of four haploid daughter cells These cells may all be genetically distinct if crossing over occurs in prophase I (causes recombination of sister chromatids)

Why is sexual reproduction more common if there are many advantages to asexual reproduction?

The key is variation. The imperfectness of sexual reproduction is what makes it an advantage to life. Variation means all of the offspring are not identical to each other or to either parent. Variation is beneficial for natural selection to occur (ex: If there was no variation, and every child inherited a particular disease, they would all die and none would survive).

Bacteria

They don't undergo meiosis, but they share genetic material and have mutations. If you wash your hands with an antibiotic wash, you kill of bacteria, but some bacteria remains if they are resistant to antibiotics. The bacteria that are resistant can breed, increasing the number of antibiotic resistant bacteria, so they get stronger over time.

Epigenetics

Things we do can affect our DNA and we can pass this down to our offspring

Horizontal gene transfer

Transfer of genetic material between organisms that are around in the same evolutionary time period

How do alleles contribute to genetic variation?

When two parents have children, there is random mixing of alleles which contributes to extensive genetic variation in a population.

Types of genetic variation mechanisms for eukaryotes

sexual reproduction -crossing over, happens during prophase I -random assortment (independent assortment) happens during metaphase I -random fertilization

Most creatures that reproduce asexually also have ways to reproduce..._________

sexually

Homologous chromosomes

x x (after replication: both different colors representing maternal and paternal). Also l l (before replication: both different colors representing maternal and paternal). "A pair of matching chromosomes [ same length, centromere position, and staining pattern] with one being inherited from each parent. The alleles on homologous chromosomes may be different.