Genetics & Heredity Flashcards
Define Meiosis
A cell division process that produces reproductive cells with half the number of chromosomes.
Define Allele
One of two or more alternate forms of a gene.
Define Gene
The basic unit of heredity. It is a series of nucleotides that encodes for a physical trait.
Define Chromosome
A DNA molecule with part or all of the genetic material of an organism.
Define Homologous Chromosomes
Chromosomes that contain the same genes; each chromosome in the homologous pair may have different alleles.
Define Chromatid
One of two molecules of DNA joined together by a centromere.
What are Mendel’s three laws?
Law of dominance, law of segregation, law of independent assortment
Describe the law of dominance
Mendel’s law of dominance states that in heterozygous (hybrid) offspring, only the dominant trait will be expressed in the phenotype.
Describe the law of segregation
Mendel’s law of segregation states that one of the two gene copies present in an organism is distributed to each gamete, and the allocation of the gene copies is random.
Describe the law of independent assortment
Mendel’s law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. The allele a gamete receives for one gene does not influence the allele received for another gene. The law always holds true for genes that are located on different chromosomes, but not for genes on the same chromosome.
What is the difference between a gene and an allele?
A gene is a portion of DNA (or RNA) that codes for a trait. An allele is a specific variation of a gene.
In what type of organs are the cells that enter meiosis I found?
Sex organs (ovaries and testicles)
What event must take place during interphase before a cell proceeds to division?
DNA replication
What are the key differences between mitosis and meiosis?
Mitosis produces two identical daughter cells, while meiosis produces four unique haploid daughter cells.
Mitosis involves one cell division, while meiosis involves two successive cell divisions.
Mitosis occurs in all organisms except viruses, while meiosis occurs only in sexually reproducing organisms.
Mitosis has no recombination/crossing over in prophase, while meiosis does.
What two structures make up a single replicated chromosome?
Sister chromatids
At which stage in meiosis I do the pairs of homologous chromosomes come together?
Late prophase I
Once the chromosomes have formed a pair, what are they called?
Tetrads
What is the difference between diploid and haploid cells?
Diploid (or 2n) have a full set of chromosomes, while haploid (or n) have half the number of chromosomes.
At which stage(s) of meiosis I are cells diploid?
Prophase, metaphase, anaphase
At which stage(s) of meiosis I are cells haploid?
Telophase after the cell has split.
Describe the relationship between the cells at the end of telophase I and the original cell
The new cells have two copies of half of the genetic information in the original cell.
Will the cells at the end of telophase I be genetically identical to each other?
No, because the homologous pairs separated and the alleles on each homologous pair are not necessarily identical.
During anaphase I, which structures separated?
Homologous chromosomes
During anaphase II, which structures separated?
Sister chromatids
Describe the cells produced at the end of meiosis II
Four daughter cells are produced. They are haploid and each contain one chromosome (sister chromatid) from each homologous pair. Each chromosome contains a complete set of genes.
Describe the relationship between the cells at the end of meiosis II and the original cell
The new cells have one copy of half of the genetic information in the original cell.
What is the name of the cells produced at the end of meiosis I in males?
Secondary spermatocyte
What is the name of the cells produced at the end of meiosis I in females?
Secondary oocyte
What is the name of the cells produced at the end of meiosis II in males, and what do these cells eventually become?
Spermatids, mature sperm
During fertilization, which two cells come together?
Mature sperm and secondary oocyte
During meiosis II, the secondary oocyte divides unevenly. Describe how.
One cell, the ovum, receives half of the chromosomes and nearly all of the cytoplasm and organelles. The other cell, the polar body, is much smaller and eventually degenerates.
Why does the second oocyte divide unevenly?
The ovum will receive more organelles, such as mitochondria for making energy, which will provide the zygote with all of its cytoplasm and organelles (sperm contains only scant cytoplasm, a few mitochondria, and haploid chromosomes). Nuclear division is necessary to produce the correct number of chromosomes in the oocyte.
What is the ploidy of the zygote produced by fertilization?
Diploid
What would the ploidy of the zygote be if egg and sperm were produced by mitosis rather than meiosis? How would this affect the ploidy of each successive generation?
If the egg and sperm were produced by mitosis, each would be diploid, so the zygote would have four sets of chromosomes. Each successive generation would have double the amount of chromosomes as the last.
Explain the origin of the chromosomes found in the zygote
The homologous pairs of chromosomes found in the zygote have come from each parent. One half of each pair is maternal and the other half is paternal.
At which stage of meiosis does crossing over occur?
Prophase I
How does crossover occur?
When the chromosomes come together as homologous pairs, the arms of the sister chromatids may cross over.
What are the crossover points called?
Chiasma
Describe what happens to the chromatids during crossover
Sections of the homologous pair switch places on the chromatids.
What are recombinant chromatids?
The chromatids that are formed after crossing over takes place and the homologous chromosomes separate.
Are the genes on a recombinant chromatid the same as the original chromatid?
Yes, each chromosome in the homologous pair contains the same genes in the same location, so a switch between chromosomes would not affect the genes present.
Are the alleles on a recombinant chromatid the same as the original chromatid?
No, the chromosomes in the homologous pair can have different alleles for each gene, so a switch in a portion of the chromosome would affect the information in that chromatid.
If there were three sets of homologous chromosomes in a cell, how many possible arrangements would there be for the tetrads in late prophase I?
2 x 2 x 2 = 8
Are some tetrad arrangements more likely to occur than others?
No. DNA replication occurs randomly within the nucleus of a cell. When homologous chromosomes come together as tetrads, they are just as likely to line up on one side of a cell as another.
What is a chi square?
A statistical analysis tool used to evaluate the probability of the variation in your observed counts and the predicted counts being because of chance rather than another factor.
How do you calculate a chi square value?
Take the observed number minus the expected number and square it, then divide by the expected number. Do this for each value and then add the values up.
Describe the factors of meiosis and sexual reproduction that lead to variation in genetic makeup
Independent assortment leads to multiple different maternal and paternal gene combinations in the cells at the end of meiosis I. This leads to allele combinations on the chromosomes being shuffled, which further varies the chromosomes that end up in gametes after meiosis II. Random fertilization of eggs and sperm means that when zygotes are formed, the gene combination will be different each time, even if they come from the same two parents.
What does a large chi square value mean?
The observed data is very different from the expected data.
What are degrees of freedom?
Researchers use degrees of freedom to determine if the chi square value is large enough to be significant. This depends on the number of possible outcomes.
How are degrees of freedom calculated?
The degree of freedom is calculated by taking the number of possible outcomes and subtracting one.
How does data analysis change when an experiment has more degrees of freedom?
A larger chi square number is needed for a significant outcome.
What are some examples of environmental effect on phenotype?
Soil acidity affects the color of hydrangea flowers
Temperature affects the fur color of Himalayan rabbits
Gender of clownfish is dependent on need for males/females for reproduction. They are all born male but may become female if necessary
What is incomplete dominance?
When neither form of the gene is able to mask the other, they phenotypically blend together.
What is codominance?
When neither allele is dominant, both show up individually in the phenotype.
Give an example of multiple alleles
Some traits have more than two forms of a gene. An example is in human blood type, which has A, B, AB, or O phenotypes. A and B are dominant to O. A and B are codominant.
Describe the two types of human chromosomes
Autosomes contain genes that code for traits unrelated to the sex of an individual. Somatic cells have 22 pairs.
Sex chromosomes contain genes that code for the sex if the individual as well as other traits. Somatic cells have 1 pair.
Why are sex linked traits more common in males?
Females have two copies of the X chromosome and males only have one. A female would need to inherit two copies of a recessive gene to display the trait, while a male would only need to inherit one. Females cannot have Y linked traits.
What are polygenic traits?
A polygenic trait is a phenotype that is controlled by more than one gene. An example of this is eye color.
What are gene interactions?
Sometimes the expression of one gene can effect the expression of other genes in an organism. Examples of this are epistasis and pleiotrophy.
Define Pleiotropy
Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits.
Define Epistasis
The interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another.
Who was Gregor Mendel?
A scientist who discovered the fundamental laws of inheritance through experiments on pea plants in the 1800s. He is know as the father of modern genetics.
Explain the difference between a genotype and a phenotype
Genotype describes an organism’s genetic makeup. Phenotype describe the physical expression of the gene.
What does the term “true breeding” mean?
Both alleles are the same (dominant or recessive, not heterozygous).
Which stage of meiosis creates the law of segregation?
Metaphase I: homologous chromosomes separate and each allele for a trait is packaged into a different gamete.
Which stage of meiosis creates the law of independent assortment?
Metaphase I: non-homologous chromosomes align independently.
What is the difference between a monohybrid cross and a dihybrid cross?
A monohybrid cross makes predictions for the inheritance of a single trait, while a dihybrid cross makes predictions for the inheritance of two traits.
What does a P value of .7 mean?
There is a 70% chance that the variation is due to random events rather than another factor.
What is meant by a “significant” difference (relating to chi square data)?
In statistics, a “significant” difference means there is less than 5% chance that the variation in data is due to random events. Therefore, the variation is most likely due to an environmental factor.
Meiosis I vs. meiosis II
In meiosis I, homologous chromosomes are separated into two cells so that there is one chromosome (consisting of two chromatids) per chromosome pair in each daughter cell. Produces two haploid daughter cells with double the amount of genetic information. In meiosis II, sister chromatids are separated and four haploid daughter cells are produced.
Prophase I
The nuclear envelope begins to disappear, fibers begin to form, DNA coils into visible duplicate chromosomes made up of sister chromatids, double chromosomes pair up based on size, shape, centromere location, and genetic information. While paired, chromatids exchange genetic information with chromatids from the other chromosome (non sister chromatids exchange genetic information).
Metaphase I
Double chromosomes remain in pairs and are aligned by fibers along the center of the cell.
Anaphase I
Fibers separate the chromosome pairs. Each double chromosome from the pair migrated to opposite sides of the cell.
Telophase I
Nuclear envelope reappears and establishes two separate nuclei. Each nucleus contains only one double chromosome from each pair (half of the total information the parent nucleus contained). Chromosomes will begin to uncoil.
Cytokinesis I
The cell is separated into two daughter cells, each haploid with a double chromosome from each pair.
Prophase II
Nuclear envelope begins to disappear and fibers begin to form.
Metaphase II
Fibers align double chromosomes across the center of the cell.
Anaphase II
Fibers separate sister chromatids, which migrate to opposite sides of the cell.
Telophase II
Nuclear envelope reappears and establishes separate nuclei. Each nucleus contains single chromosomes. Chromosomes begin to uncoil.
Cytokinesis II
The two cells separate into four haploid and genetically unique daughter cells.
Describe how the amount of genetic information changes during meiosis
Genetic information is duplicated during interphase. There are still 46 chromosomes, but each consists of 2 sister chromatids (96 total chromatids). During meiosis I, homologous chromosomes separate into 2 daughter cells. Each daughter cell contains 23 chromosomes but 46 chromatids. During meiosis II, sister chromatids are separated into 4 total daughter cells, each with 23 chromosomes and 23 chromatids (at this stage, chromosome=chromatid). This is half the number of chromosomes as the parent cells, and half the amount of genetic material.
