7 Genetics & Ecosystems- Genetics Flashcards
What is a gene and its function?
-A section of DNA, located on its locus
-Base sequence of each gene carries genetic info that determines sequence of amino acids in a protein
What are alleles?
-Different variations of a gene; diploid organisms have 2 alleles, 1 on each chromosome
What is a genotype and what does it consist of?
-An organism’s underlying genetic makeup
-consists of both physically visible & non-expressed alleles
What is a phenotype and what is it determined by?
-The observable traits expressed by an organism
-determined by interaction between its genetic constitution & the environment
When are dominant and recessive expressed in the phenotype of an organism?
-Dominant; always expressed
-recessive; only expressed if there’s 2 copies of the allele
What are co-dominant alleles?
Alleles both expressed in the heterozygote
What are homozygotes?
-Organisms w/ 2 copies of same allele
-Can be homozygous dominant/recessive
What are heterozygotes?
Organisms that have different alleles for a gene
What is a monohybrid cross and what does it allow?
-When 2 parents that differ in only 1 characteristic breed
-Allow genotype and phenotype of offspring to be predicted
What is the first step of constructing a monohybrid cross?
identifying the parental genotypes
What are the resulting gamete alleles from a monohybrid cross, what does this represent?
-Gametes= haploid, so only 1 allele from each parent is found in the gametes.
-All possible combinations of parental alleles should be identified; represents meiotic segregation into haploid gametes
What is the F1 offspring and how many offspring combinations does a monohybrid cross produce?
-F1 offspring= first generation of offspring.
-produces 4 different combinations of possible offspring
What is the F2 offspring?
the second generation of offspring
In what 2 ways can a monohybrid cross be drawn?
-Genetic diagrams
-punnett squares
What is a dihybrid cross?
When 2 parents that differ in 2 characteristics breed
What is the law of independent assortment and what does it mean?
-Mendel proved that genes don’t influence each other w/ regard to sorting of alleles into gametes
-means that genes separate independently of each other when gametes are made.
-combination of alleles can be shown in a dihybrid cross
How many gamete allele combinations for each homozygote are possible in a dihybrid cross?
1
What is the F1 offspring result in a dihybrid cross?
-all the F1 offspring have the same genotype
-law of segregation predicts each gamete in F1 generation has equal probability of receiving any allele
-means there are 4 possible combinations of gametes produced by the F1 offspring
What is the F2 offspring result in a dihybrid cross?
-When F1 offspring breed, the 4 possible gametes from 1 individual can combine w/ any of 4 possible gametes from other individual.
-total possible combinations in the F2 generation= 16.
What is the expected ratio for when 2 dihybrid heterozygotes breed?
9:3:3:1
What is codominance and what can it influence?
-where both alleles for same characteristic are simultaneously expressed in heterozygote.
-neither of the alleles are recessive.
-can influence the outcome/phenotypic ratio of monohybrid & dihybrid crosses.
What is an example of co-dominance?
-sickle-cell anaemia, 2 alleles for sickle-cell anaemia;
H^N- normal haemoglobin. (Homozygotes)
H^S- sickle haemoglobin. (Homozygotes)
-people who have 1 H^N allele & H^S allele (heterozygotes) have both normal haemoglobin & sickled haemoglobin.
H^N & H^S= codominant.
What is linkage and what does it show?
-when genes that are close to one another on a chromosome are likely to be inherited together
-shows that some allele combinations aren’t inherited independently of each other
What is Mendel’s law of independence assortment and why is this not always the case?
-states that genes don’t influence sorting of alleles into gametes; isn’t always the case.
-some allele combinations aren’t inherited independently of each other.
-genes located close to each other on same chromosome= more likely to be inherited as a pair (linkage)
What are autosomes and how are they arranged?
-all the chromosomes except the sex chromosomes (X and Y).
-arranged in pairs; homologous chromosomes (1 from the father and 1 from the mother), consist of same genes in same order along chromosome.
-there is some variation if chromosomes have different alleles but genes are the same.
What is recombination and when does it not occur?
-When gametes are produced by meiosis, multiple sections of homologous chromosomes are exchanged
-If 2 genes are located in close proximity on same chromosome, they’re more likely to be exchanged together, not separated in recombination
-genes= more likely to be transmitted to gamete together
How does sex linkage differ from autosomal linkage?
Takes place in sex chromosomes
How do sex chromosomes differ from autosomes?
they are non-homologous; don’t consist of the same genes in the same order along the chromosome.
What is hemizygosity/X-linked genes?
-that there’s no role of dominance & recessiveness.
-if a recessive gene is inherited on the X chromosome, it’ll always be present in the phenotype as it’s the only allele present.
-males only have 1 copy of an allele for X-linked genes.
What is haemophilia and how is it an example of an X-linked disorder?
-a blood disorder that is X-linked
-humans males only need to inherit 1 recessive mutant X allele to be affected by the disorder but females must inherit 2 copies of the recessive allele.
-this means haemophilia= more common in males.
-females can be carriers for the disorder when they’re heterozygous.
What are homologous chromosomes and what do they consist of?
-Chromosomes in diploid organisms
-consist of the same genes in the same order.
-the only variation between homologous chromosomes is in the alleles.
-2 alleles can be present for 1 gene
What are multiple alleles and what do they provide?
-Although only 2 alleles can be present in an organism, there could be multiple different alleles for a single gene.
-have a dominance hierarchy
-provide many different genotype combinations.
-creates large variation at the population level.
What is epistasis and is it dominant or recessive?
-when a gene at one locus inhibits the expression of a gene at another locus.
-can be dominant or recessive.
-alleles that are being masked= hypostatic to epistatic alleles.
-often involves pathway where expression of one gene= dependent on the function of another gene.
What is recessive epistasis?
-where the epistatic allele (the allele that masks another gene) is recessive.
-means two copies of the epistatic allele must be present for expression of the hypostatic allele to be affected.
What is dominant epistasis?
-where the epistatic allele is dominant.
-means only one copy of the epistatic allele must be present for expression of the hypostatic allele to be affected.
What is chi-squared used for in genetics?
-to compare the goodness of fit of observed data with expected data in phenotypic ratios
-tests if the difference between observed and expected values is due to chance.
What are the requirements for chi-squared to be used?
-Variation= discrete not continuous; data are in categories (e.g. Aa and aa).
-Data show absolute numbers (whole), normally frequencies.
What is the null-hypothesis and why is it used in genetics?
-Before using chi-squared, null hypothesis is stated;
‘There is no significant difference between observed and expected data, the difference is due to chance’.
-used to reject or accept the null hypothesis.
What is the Chi-squared equation?
χ=Σ (O−E)²/E
O = observed values.
E = expected values
What are the steps in calculating chi-squared?
-expected values need to be calculated; predicted using genetic diagrams (phenotypic ratios)
-compare expected values w/ observed values & use numbers in equation; calculate chi-squared value
-calculate degrees of freedom = the number of categories (e.g. phenotypes) − 1.
-find critical value that corresponds to degrees of freedom in probability distribution table at 0.05 significance level.
When do you accept or reject the null hypothesis?
-if chi-squared value < critical value= accept null hypothesis, difference between observed & expected data—> due to chance.
-if the chi-squared value > critical value= reject null hypothesis, difference between observed & expected data—> NOT due to chance.
- ^means we would get this chi-squared value <5% of cases (very unlikely)
