Bio study: Genetics
What is a zygote?
A zygote is a fertilized egg.
What are some applications of DNA fingerprinting? What part of our DNA is useful for this process?
Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA pattern varies from person to person. DNA fingerprinting analyzes sections of DNA that have little or no known function but vary widely from one individual to another. Can be used in criminal cases or in identifying family relationships. Only identical twins are genetically identical. • DNA samples can be obtained from blood, sperm, and hair strands with tissue at the base. Steps: Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. DNA fragments are separated using gel electrophoresis. Fragments containing repeats are labeled. This produces a series of bands—the DNA fingerprint. Then, compare the bands to fragments of known size to estimate how many base pairs are in each band/fragment, or compare bands to the bands of a relative to see what is shared (or a baby to a potential father to determine paternity, etc)
What does diploid mean? Haploid? Polyploid?
Diploid = 2n = having 2 sets of chromosomes Haploid = n = having 1 set of chromosomes Polyploid = having more than 2 sets of chromosomes
What is incomplete dominance? Be able to explain how it works, and be able to solve Punnett square problems involving incomplete dominance
Dominant trait doesn't totally hide the recessive trait See a "blending" of traits Heterozygous individual has a 3rd phenotype
What is crossing over? What happens during this event? When does it occur? What are chiasmata?
During Prophase I crossing over occurs. During crossing over, segments of non-sister chromatids break and reattach to the other chromatid. The chiasmata (chiasma) are the sites of crossing over
XX = ____ and XY = ____
Female; male (remember: "If there's a Y, it's a guy!"
What are gametes?
Gametes are the "sex" cells and contain only ½ the normal number of chromosomes.... called the haploid number (the symbol is n)..... Sperm cells and ova (eggs) are gametes.
What are genes? Where are they located? What are alleles?
Gene- segment of DNA that codes for a protein (trait) in the order of the nucleotides. Located on chromosomes. Alleles- different forms of a gene.
What is the difference between genotype and phenotype?
Genotype- the alleles an organism has. Written as two letters- PP, Pp, pp. Phenotype- observed trait- purple or white
What is a hybrid plant?
Heterozygous
During which part of meiosis do homologs separate? When do sister chromatids separate?
Homologues- meiosis I; sister chromatids- meiosis II.
What is a synonym for "true-breeding?" What does it mean?
Homozygous; generation after generation, if allowed to self-pollinate, the plant will consistently have the same genotype.
What did Mendel use pea plants to study?
How genetic material is inherited.
Define probability.
How likely an event is to occur
When dealing with blood type problems—how do you express genotypes and phenotypes? Which alleles are dominant? Which is recessive?
In humans, the possible blood types are Type A, B, AB or O- these are PHENOTYPES. We have two alleles that make up this blood type, just like most traits. A and B are both dominant; O is recessive.
What are the 3 principles of Mendelian genetics? ("Mendel's Laws")
Law of Dominance & Recessiveness: some alleles are dominant (visible) and some are recessive (not visible- hidden by the dominant when it is also present). A recessive trait will only be seen if no dominant allele is present. Law of segregation: The re-appearance of the recessive trait would only be possible if recessive alleles can separate themselves from dominant ones during gamete formation. Each gamete must only have a single copy of each gene (1 allele), and offspring get one copy from each parent to give their diploid number. Law of Independent Assortment: genes are inherited independently of one another- for example, just because you are tall does not also mean you will have blue eyes.
How many cell divisions are in meiosis? How many times does DNA replicate?
Meiosis is two cell divisions (called meiosis I and meiosis II), with only one duplication of chromosomes.
Compare and contrast mitosis and meiosis
Mitosis is for Growth and repair while meiosis is for Sexual reproduction
What is co-dominance? Be able to explain how it works, and be able to solve Punnett square problems involving co-dominance
More than 1 dominant allele (there may be more than 2; there may also be a recessive allele present) 2 dominant alleles do not blend or hide each other; they show up side by side "co-existing" Blood types are co-dominant
What is the ultimate source of genetic variation?
Mutations
What is non-disjunction? What is the result?
Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis. Non-disjunction results with the production of zygotes with abnormal chromosome numbers. Remember, an abnormal chromosome number (abnormal amount of DNA) is damaging to the offspring.
What process makes copies of DNA segments? Describe this process. What application does it have? What process that happens naturally in our cells is this process similar to?
PCR= polymerase chain reaction; Polymerase chain reaction (PCR) is a technique that allows biologists to make many copies of genes. Similar to DNA replication in our cells. Small amounts of DNA can be multiplied making it easier to analyze.
What are homologous chromosomes?
Pair of chromosomes (maternal and paternal) that are similar in shape and size. Homologous pairs (tetrads) carry genes controlling the same inherited traits, in the same locations.
. Describe the chromosomes found in the parent cell before and after DNA replication and in the daughter cells of meiosis I.
Parent cell has 23 pairs of single chromosomes (chromosomes with only one chromatid); 46 chromosomes total; diploid. DNA replicates so that they have 23 pairs of double chromosomes (chromosomes with two sister chromatids attached at the centromere); 46 double chromosomes; 92 sister chromatids attached at centromeres to make the 23 pairs of homologous chromosomes; still diploid. After going through meiosis I, each of the 2 daughter cells receives 23 double chromosomes (46 sister chromatids still attached at the centromeres); these daughter cells are haploid.
What does P generation stand for? F1? F2?
Parent, 1st filarial (offspring) and 2nd filarial (2nd generation of offspring)
What does the genotype of an organism look like if it is homozygous dominant? Heterozygous? Homozygous recessive?
RR- homozygous dominant Rr- heterozygous (shows dominant trait) rr- homozygous recessive
What are somatic cells? How many chromosomes do human somatic cells contain?
Somatic Cells are "body" cells and contain the normal number of chromosomes ....called the diploid number (the symbol is 2n). Examples would be ... skin cells, brain cells, etc. Human somatic cells contain 23 pairs = 46 total chromosomes.
Somatic cells are produced by ___ and gametes are produced by ___.
Somatic cells- mitosis; gametes- meiosis.
What is synapsis? What is a tetrad? When does synapsis occur?
Synapsis occurs: homologous chromosomes come together to form a tetrad. Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids This occurs during Prophase 1.
Which chromosomes are autosomes? Which are sex chromosomes?
The autosomes code for most of the offspring's traits. In humans the autosomes are sets 1 - 22 The sex chromosomes code for the sex of the offspring is the 23rd set of chromosomes.
What do the autosomes code for? What do the sex chromosomes code for?
The autosomes code for most of the offspring's traits. The sex chromosomes code for the sex of the offspring
What is a genome?
The complete set of genes for an organism
How many cells, and what type, are produced through meiosis II?
The haploid daughter cells of meiosis 1 contain 23 double chromosomes. During meiosis II, the sister chromatids separate to produce 4 haploid daughter cells (gametes), each with 23 single chromosomes.
What do Punnett squares show you?
When considering genetic crosses, the tool we use to help predict the probability of an outcome (how likely it is for the offspring to have certain traits) is a Punnett square. We can use them to make predictions and show possible gene outcomes in the offspring
What is n? 2n?
n = number of chromosomes in the set. 2n means 2 chromosomes in the set.
Can males be carriers of X-linked genes?
no, they are either affected or unaffected.
How do scientists separate DNA fragments? Describe this process and review diagrams in PPT. Gel electrophoresis separates DNA fragments based on size
• In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel. • The phosphate groups of DNA are negatively charged (DNA moves from negative to positive end of gel with electricity applied). • Steps: First, restriction enzymes cut DNA into fragments. The DNA fragments are poured into wells on a gel. An electric voltage is applied to the gel. The smaller the DNA fragment, the faster and farther it will move across the gel.
Why do sex-linked disorders affect males much more frequently than females?
• Most sex-linked genes that cause a disorder are recessive. • Remember, you must have only recessive alleles to express a recessive phenotype (in this case, having the disease). • Females have 2 X chromosomes- to have an X-linked disease, they have to have two recessive copies of the allele, which is possible, but generally unlikely. • Males only have one X chromosome, so they are affected (have the disorder) by only having one recessive allele- remember, the Y is NOT homologous to the X.
List all possible alleles for each blood type.
• To be type A, you can have 2 alleles: AA or AO. • Type B: BB or BO • Type AB: AB only • Type O: OO only