Genetics 2 Flashcards
Monohybrid vs dihybrid cross
cross-fertilization to see how a single trait gets inherited (genotypic ratio always 3:1 for D:R) – its purpose is to investigate the pattern of inheritance of two genes (non-linked in most cases)
Two laws of genetics
1| Law of segregation of alleles – two alleles separate into different haploid daughter nuclei during meiosis and then reunite in fertilization
2| The law of independent assortment – the presence of an allele of one of the genes in gametes has no influence over which allele the other gene is present in that gamete (two bivalents orient independently)
Possible relationships between alleles of the same gene
dominant/recessive (dominant has the same effect on the phenotype in both homozygous and heterozygous states and recessive allele influences the phenotype only when in the homozygous state)
codominant (a pair of alleles that both influence the phenotype when in a heterozygous state, both alleles are completely expressed, e.g. erythrocyte blood groups)
incomplete dominance (the alleles combine so the result is an intermediate, blended phenotype)
Carrier
an individual that has a recessive allele of a gene that has no effect on its phenotype (heterozygous) – the allele gets passed on to the next generation but is not expressed in this individual
Test cross
crossing done when the researcher is interested in a genotype of an individual that displays a dominant phenotype – crossing of any genotype with a homologous recessive one always results in a 1:1:1:1 phenotypic ratio
Explain how erythrocyte blood groups are determined
erythrocytes (RBC) can have two different antigens (AG) on their surface, AG A and AG B (I^A,I^B alleles), or they can have no AG at all (i allele). There is also Rh factor (gene D) which has two different alleles: allele D codes for Rh factor (positive) and allele d doesn’t (Rh negative)
How many pairs of linked genes are there in a human cell?
23 because there are 23 homologous pairs of chromosomes
Pedigree chart
a diagram that shows the occurrence and appearance of phenotypes of a particular gene of an organism and its ancestors from one generation to the next
Dihybrid cross ratio
when crossing two purebred genotypes, one dominant and one recessive, their F2 will display a 9:3:3:1 phenotypic ratio which means that there are 6 phenotypic recombinants – all four types of gametes are equally present because the inheritance of alleles of two gametes is separate (unlinked genes)
What happens with the phenotypic ratio when the genes interact, give an example
it is no longer 9:3:3:1, for example one gene that codes for color/albino and the other that codes for agouti/black fur – without the first gene being color the other cannot be expressed (9:3:4 agouti: black: albino)
What is the phenotypic ratio of F2 when a homozygous dominant and homozygous recessive organisms are crossed and gene linkage is involved?
11:1:1:3
Recombinants
individuals with phenotypic traits different from those of parents
What are recombinants result of in linked and what in unlinked genes?
cross-over between linked genes in prophase I
independent assortment of bivalents (unlinked genes) in metaphase I
Describe the process of conducting a chi-squared test
contingency table, degrees of freedom, and the critical value at significance level of 5% determined, chi-squared calculated using the formula, comparing the critical value with chi-squared – if chi is smaller than the critical value, H0 (difference is random) is accepted, and if it is bigger then H1 (another pattern of inheritance is followed) is accepted
What is the probability of conceiving a female child?
Draw the Punnett grid to prove it
50%
…
