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)