Genetics Flashcards
what is the difference between genes, chromosomes, a genomes?
- genes made of DNA (so is genome), genes contain DNA to code for 1 protein
- genomes is the sum of total DNA
- DNA coils chromosome
what is surprising about the human genomes project?
it only took about 10 years, predicted more genes but found only about 23,000 in humans
what is a gene?
a heritable factor that consists of a length of DNA and influences a specific characteristic
where are genes found?
they occupy a specific position on one type of chromosome
what do you call various forms of genes?
Alleles
how do alleles differ, and how are new ones formed?
differ from each other by one or a few bases only, new alleles formed by mutation
what is a genome and how was it sequenced?
the whole genetic information of an organism, sequenced in Human Genome Project
What causes sickle cell anemia?
- due to a base sequence mutation of the gene that codes for the alpha-globin polypeptide in hemoglobin
- hemoglobin and red blood cells damaged, resulting sickle cells damage tissue by blocking blood flow in capillaries
how does the number of humans genes compare to other species
we have about the same number as a small plant, less than a chimp
whats the difference between prokaryote and eukaryote DNA?
Prokaryote:
- one chromosome consisting of circular DNA molecule
- some have plasmids (eukaryotes do not)
Eukaryote:
- chromosomes are linear DNA molecules associated with histone proteins
- there are different chromosomes that carry different genes
what are homologous chromosomes?
they carry the same sequence of genes but not necessarily the same alleles of these genes
difference between diploid and haploid nuclei? (in terms of chromosomes)
diploid have pairs of homologous chromosomes, haploid have one chromosome of each pair
what is the importance of sex chromosomes?
- the number of sex chromosomes is a characteristics feature of members of a species
- sex is determined by sex chromosomes (autosomes are chromosomes that do not determine sex)
what did Mendel do?
discovered that principles of inheritance with experiments in which large numbers of pea plants were crossed.
what are gametes?
haploids, so contain one allele of each gene
what happens to alleles during meiosis?
two alleles of each gene separate into different haploid daughter nuclei
what does the fusion of gametes create?
results in diploid zygotes with two alleles of each gene that may be the same allele (homozygous) or different alleles (heterozygous)
what do dominant alleles do?
mask the effects of recessive alleles, but co-dominant alleles have joint effects
what causes genetic diseases?
- many due to recessive alleles of autosomal genes
- some are sex-linked
- some due to dominant or co-dominant alleles
why is the pattern of inheritance different with sex linked genes?
their location on sex chromosomes
how common are genetic diseases?
- most are rate
- radiation and methanogenic chemicals increase mutation rate and can cause genetic disease and cancer
describe inheritance in ABO blood groups
- ABO blood is co-dominant, you can have A, B, AB or O
- written in IA IA if homozygous, IAi if heterozygous, or ii if O blood type
describe sex linked inheritance ?
- typically carried on x-chromosomes, typically pass mother to son
- girls can get sex linked-recessive disorders, but have to get allele from both parents
- common in colorblindness and hemophilia
describe the inheritance of cystic fibrosis and Huntington’s disease
- cystic fibrosis autosomal recessive on chromosome 7
- Huntington’s dominant, caused by mutation in one of 2 copies of HTT gene on 4th chromosome
describe consequences of radiation after nuclear bombing and accidents
- studies of Hiroshima and Nagasaki show no evidence of increased birth defects due to bombing
- Chernobyl studies show radiation in wildlife, high rates of thyroid cancer in humans, no evidence for increase of other cancers
how to analyze a pedigree chart?
- women are circles, men are squares, non-binary are diamonds
- dark shape shows person affected by the trait
- people with recessive allele but don’t have trait called “carriers”
- generations labeled with roman numerals, people numbered left to right
- can calculate probability that couple will have child with particular trait
what is the difference between linked and unlinked genes?
- unlinked separate independently due to meiosis
- genes are linked if they are on same chromosome
what can gene variation be?
- discrete or continuous, phenotypes of polygenic characteristics tend to show continuous variation
what do chi-squared tests determine?
- whether the difference between observed and expected frequency distribution is statistically significant
what are dihybrid crosses and how are they analyzed in a Punnett grid?
- occur between organisms that are heterozygous for 2 traits
- set up parent vs parent
- determine 4 possible gametes of each parent and set up Punnett grid
- typical ratio is 9:3:3:1 for simple dominance
describe Morgan’s discovery of non-mendelian rations in fruit flies
- if genes are linked on same chromosome, they will not follow 9:3:3:1 ratio
- using fruit flies, Morgan discovered 1:2:1 and 3:1 ratio with straight linkage, through this does not always happen due to crossing over
what are polygenic traits?
- traits influenced by environment factors, such as human height
- a trait whose phenotype is influences by more than one gene
how to calculate predicted genotypic and phenotypic ratios of dihybrid unlinked crosses?
- multiply the probability of two events to find probability 2 independent events will both occur
how do you identify recombinants in linked gene crosses?
- recombinants are genes that are crossed over
- offspring showing a mixture of parents, or gametes that don’t match either parents are recombinants
how to calculate recombinant frequency?
- # or recombinants / total # of genes x 100%
- usually recombinants are the smaller values
- the closer 2 genes are on a chromosome, less likely to recombine
how to use chi-squared on dihybrid crosses?
- multiply # or phenotypes by correct cross ratio (9:3:3:1), so 9/16 times X
- plug these observed and expected values into formula
- degrees of freedom = # of phenotypes -1
- chi-squared value less than critical = independence, greater chi-squared is assumed linked genes
what is epistasis?
- when a gene at one locus alters the phenotypic expression of a gene at a second locus
explain the genetic causes, symptoms, potential treatment, and 1 interesting fact for sickle cell disease
- cause: HBB gene on chromosome II produced beta-globin protein with an altered shape, causing red blood cells to be rigid and elongated
- follows autosomal recessive inheritance (heterozygus advantage)
- symptoms: some resistance to malaria, pain or damage to organs, spleen, liver, kidney, lungs affected. often leads to anemia
- treatments: antibiotics can prevent infections, folic acid supplements to produce more red blood cells
- blood transfusion and bone marrow transplant in serious conditions
- fact: sickle cells usually line 10-20 days whereas normal red blood cells about 120 days
