y5 bio: cluster 5 (inheritance)

what is an allele?

a specific alternative sequence/form of a gene at a particular chromosomal locus

what is the difference between phenotype and genotype?

genotype is the specific allele combination of an organism, while phenotype is the observable physical or biochemical trait

why is only ONE dominant allele sufficient to produce a dominant phenotype?

a dominant allele codes for a functional enzyme, and just one copy provides enough catalytic activity to produce the dominant phenotype

what is phenotypic plasticity?

capacity of a single genotype to produce various phenotypes. these are normally triggered by environmental changes (like UV, diet, temp) and the phenotype often returns when stimulus is removed

what do SNPs stand for and what are they?

SNPs are single nucleotide polymorphisms, and they refer to positions in a gene where different bases can be present

what pattern of inheritance is demonstrated by ABO blood groups?

codominance between ‘IA’ and ‘IB’ alleles, both being completely dominant over the recessive ‘Ii’ allele

what are codominance and incomplete dominance?

codominance - not a blend, both alleles expressed independently at the same time in the phenotype

incomplete dominance - blended, heterozygous phenotype is ‘middle ground’ between parental phenotypes

who decides zygote’s chromosomal sex and why?

male sperm chromosome, cuz the Y chromosome carries SRY gene that triggers male embryonic development

why do sex-linked recessive traits (like haemopholia) affect males more frequently than females?

males are hemizygous (XY) and need only one copy of the recessive allele on the X chromosome to express the condition - so they cannot be carriers and are either affected or not affected

pedigree charts can indicate if conditions are

autosomal (recessive - skips gen, dominant - does not skip gen) OR sex-linked, no skips in gen (recessive - affected mother affects son, dominant - affected father affects daughter)

what is discontinuous variation

discontinuous refer to qualitative traits controlled by single gene locus (monogenic inheritance), has no intermediate phenotypes between categories (e.g. ABO blood groups)

what is polygenic inheritance and what type of variation does it produce?

a single trait controlled by two or more unlinked additive genes, resulting in continuous variation (e.g., human height or skin color).

what are linked genes?

genes located close together on the same chromosome that do not assort independently during meiosis.

what is the expected Mendealian ratio when 2 double heterozygotes (with UNLINKED genes) are crossed?

9:3:3:1

what is the expected Mendealian ratio when 1 double heterozygote and 1 double homozygous recessive (with UNLIKED genes) are crossed?

1:1:1:1

steps to do chi-square test

1.calculate expected ratios based on either one of the Mendealian ratios

2. sub these values into chi square, x^2, equation (x^2 = sum of (observed - expected)^2/expected for all 4 categories

3. find df value, look at big chi square table to find the column of 0.05, and the row of your df value

4. compare this found value with your x^2 value 5. if x^2 is higher than critical value (from table)

what is the purpose of a chi-squared test in genetics?

to determine whether observed offspring phenotypic counts differ significantly from expected Mendelian inheritance ratios

how do you calculate degrees of freedom (df) for a genetic chi-squared test?

df = n - 1, where n is the total number of phenotypic categories being compared

what does it mean if a calculated x^2 value is greater than the critical value at p = 0.05?

the diff between observed and expected results is statistically insignificant, so diff may be due to chance. this rejects the null hypothesis (suggesting linked genes or selection)