Genetics Flashcards
Pyrimidines
Cytosine, Thymine, Uracil. These are all cyclic compounds and have Nitrogens and one Oxygen atom.
DNA parts
Deoxyribonucleic acid. Doble stranded helix. Nitrogenous bases (ATGC) sugar phosphate backbone (deoxyribose)
Purines
Adenine and Guanine. Bicyclic compounds with Nitrogens.
What is a nucleotide made of?
Nucleotides contain a sugar [deoxyribose or ribose (RNA)] at the center, a phosphate and a nitrogenous base (CGTAU)
What bonds to T (no T in RNA)
A
What bonds to A
T (U in RNA)
What bonds to C
G
What Bonds to G
C
What is a Gene?
A discrete Unit of inheritance
A sequence of DNA nucleotides that codes for a product (usually protein or RNA)
A specific DNA region on a chromosome.
What is a Chromosome?
Thread-like structures made of protein and a (VERY LONG) single molecule of DNA.
Chromosomes in Eukaryotic Vs Prokaryotic cells.
Eukaryotic: Multiple rod-like Chromosomes in the Nucleus
Prokaryotic: One Circular Chromosome found in the nucleoid region.
What is a Locus?
A locus refers to a specific location on a chromosome. Could be an entire gene sequence down to a single base pair.
What is an Allele?
One or multiple forms of a gene found at a locus.
Phenotype?
An individual’s observable appearance = how the genotype “trait” is expressed or visualized.
Genotype?
Specific alleles an individual possesses at a genetic locus
Homozygote
The same alleles for a trait.
Heterozygote
Different alleles for a trait.
What is the Wild-Type?
The most commonly observed/ standard genotype or phenotype. (Commonly the dominant Allele.)
What are Histone Proteins?
These are proteins used in helping package DNA within chromosomes. They limit accessibility of the DNA to proteins (enzymes) Directing gene Transcription. These help make up Chromatin.
What is Chromatin?
Chromatin makes chromosomes and contains DNA and histone proteins.
How many chromosome copies in a diploid cell
2 copies. EX: humans have 23 pairs of chromosomes; 46 chromosomes.
What are homologs?
Chromosome pairs, these may carry different alleles of the same gene.
How many copies of chromosomes in a haploid?
1 copy.
What is a chromatid?
A chromatid is a half of a chromosome pair and is just one line. During anaphase and after of mitosis cells only have chromatids, which are still considered chromosomes when on their own.
Where are the telomeres on a chromosome?
The telomeres are the ends of the chromosomes
Where is the centromere on a chromosome and how is it related to the kinetochore?
The centromere is the constricted part of a chromosome, it’s where the sister chromatids attach, the kinetochore protein forms here and the spindle microtubules attach.
What is a monohybrid cross?
A type of cross that only studies the outcomes of one loci. this could be eye color, size, texture etc.
What is a test cross?
Breeding the dominant homozygous phenotype with the recessive genotype.
What is a dihybrid cross?
A cross representing two loci. Ex: eye color and size, or Hair color & amount of pigment produced.
What is an autosomal gene?
A gene not located on the sex chromosomes.
What is genic sex determination?
Genes determine the sex, no sex chromosomes- sex becomes an autosomal trait.
in a male with XX-XY sex determination chromosome type. how many gametes will have an X sex chromosome after meiosis?
2 of the four gametes with receive the X chromosome, this is why sex in these situation is 50/50.
Difference between XX-XY and ZZ-ZW?
XX-Male carries the XY sex determining gene trait for male.
ZZ- The female carries the ZW sex determining gene trait for female.
How do sex chromosomes become homologous pairs?
They are not true homolog pairs and have pseudoautosomal regions commonly at the centromeres where they are “homologous”.
The XY do not commonly have any cross over due to this and loci different regions.
What is an SRY gene?
Sex determining region on Y chromosome.
What is Aneuploidy?
Abnormal chromosome number.
Trisomy is more 2n+1
Monosomy is less 2n-1
Better tolerated on sex chromosomes, where as autosomally it is commonly fatal.
What is Hemizygous?
when there is only one allele present for a gene commonly in males on the X chromosome.
How are sex linked genes written?
Usually as a superscript on the X or Y chromosome.
Why are sex chromosome duplicates better tolerated in sex chromosomes than autosomal in Females?
In females one of the X chromosomes remains condensed and inactivated (Barr body)
How many barr bodies in XXX or XXY
2 in XXX and 1 in XXY
What causes mosaicism?
In females (XX) one X chromosome is deactivated into a barr body, this happens randomly early on in each cell. The same barr bodies will remain inactivated through cell division but are not the same in every starter cell.
What is incomplete dominance?
This is when two traits of the same dominance are on the same locus and represent at an intermediate form of the phenotypes. (EX: Red (R) White (W) RW = shows as pink
What is Co-dominance?
This is when two traits of the same dominance are on the same locus and represent both triaits. (EX: A blood type & B blood type= AB blood type- has both antigens.)
How to show ratio when a homozygous trait is lethal?
Get rid of the dead offspring and re-calc ratios.
EX: a cross gives yellow (YY) and gray (yy) fur: YY, Yy, Yy, yy. if YY is lethal the new ratio becomes out of three, not four.
What is penetrance?
The description of how/ if an individual expresses the phenotype of their genotype
EX: if an individual W/ a genetic variant does not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.
What explains the reason that polydactyly is a dominant trait but is not the wild type in the population?
polydactyly has an incomplete penetrance and only 90% of people with the gene actually have polydactyly.
What is epistasis?
The interaction between genes at different loci (still independent.) This can mask the traits of other genes, EX: yellow labs are yellow because the ee gene code over-rides whatever the B/b genotype coded for and will always be a yellow lab.
What happens in cytoplasmic inheritance?
genes from the mitochondria or chloroplasts (plants). This usually only occurs from the mother due to the large egg having more cytoplasm than sperm. (Class Bivalvia will do this but the father also passes mtDNA to the male offsrping. so female- only mother’s mtDNA & Male- Both parents mtDNA.
What is a karyotype?
The general appearance of the complete set of chromosomes. (Sizes, number, shape.)
Why does mosaicism cause patches?
Since the x chromosome that is inactivated into a barr body very early on, the same x chromosome stays inactivated in each cell divided from that cell.