Chapter 3: Mendelian Inheritance

Pagenesis

• Hippocrates proposed that “seeds” produced by all parts of body (organs, etc.), collected and transmitted to offspring at conception 

  • “Nugget” goes into egg/sperm → develop into original organ, tissue, etc.

blending hypothesis

•  factors that control hereditary traits are malleable (can change)

  • Blend together generation after generation

stigma

female part, where pollen ends

ovule

• contains eggs ready to be fertilized (female gamete)

anther

• where pollen (male gamete) is produced and released

pea plant reproduction process

• Often self-fertilize b/c of keel petal: covers anther and stigma (“closed-door”)

• Pollen lands on stigma and grows into ovule, fertilizes egg 

  • Other cells in ovule provide support for embryonic development 

  • sperm cells enter stigma and migrate toward an ovule

  • 1 sperm fertilizes egg, other sperm fertilizes endosperm

True-breeding

•  self-fertilized plants (100% of offspring are identical to original)

• must be homozygous (2 copies of same allele)

height - pea plant trait

tall - dominant

dwarf - recessive

flower color - pea plant trait

purple - dominant

white - recessive

flower position - pea plant trait

axial - dominant

terminal - recessive

seed color - pea plant trait

yellow - dominant

green - recessive

seed shape - pea plant trait

round - dominant

wrinkled - recessive

pod color - pea plant trait

green - dominant

yellow - recessive

pod shape - pea plant trait

smooth - dominant

constricted - recessive

single-factor cross

• looking at only 1 character 

law of segregation

• 2 copies of a gene separate from each other during transmission from parent to offspring (alleles)

• only one copy of each gene is found in a gamete

• occurs during anaphase of meiosis I

two-factor crosses

•  track 2 different characters at the same time

linked inheritance

units of inheritance are linked together in organism, always inherited together (2 different genes)

unlinked inheritance

• can assort independently, do not affect the inheritance of each other 

Non-parental combinations

• offspring characters not seen in parents, suggests unlinked traits 

law of independent assortment

• 2 different genes randomly assort their alleles during the formation of haploid cells  

  • Order in which homologs stack/organize are random during meiosis I

  • Number of possible combinations of chromosomes in the gametes is 2^n

allows new combination of alleles of different genes to occur in future generations of offspring

• occurs during metaphase I

Probability

the chance, likelihood, that the outcome will occur

product rule

• probability that 2 or more independent outcomes will occur is equal to the product of their individual probabilities 

  • Can be used for ordered events

independent outcomes

•  the occurrence of one outcome does not affect the probability of another 

forked-line method

• gives the probability of each phenotype 

• like multiplication of (x+2)(x+3)

binomial expression

• represents all of the possibilities for a given set of unordered events 

chi-squared

statistical method used to determine goodness of fit

goodness of fit

• how close the observed data are to those predicted from a hypothesis 

null hypothesis

there is no real difference between the expected and observed data

p-value

probability that the amount of variation indicated by a given chi-squared value is due to random chance alone

• reject null hypothesis (accept alternative hypothesis) if p-value is less than 0.05