Chapter 3: mendelian Heredity

why are the garden pea, pisum sativum well suited to genetic study?

• annual species

• outcrosser

• each pea is independently fertilized

• small and easy to grow

• lots of varieties available

what is a character?

a category of phenotype

ex: hair, floral color, heigh

trait

the actual version of that character expressed as a phenotype, like brown, purple, short etc.

what are the 7 characters of the pea pods that mendel looked at?

color of seed

shape of seed

color of pod

shape of pod

size of the plant

position of the plant

color of the flower

Gene

heritable unit that encodes or influences a trait. Almost always a protein-coding sequence, often with associated regulatory components

allele

alternative forms of the same gene. May or may not affect the phenotype but usually does

locus

the physical location of genes on chromosomes

genotype

the set of alleles for a trait that an organism has

homozygote

an individual who has identical alleles for a trait

heterozygote

an individual who has different alleles for a trait

phenotype

an observable at least partially heritable characteristics

T/F : phenotypes only occur on one scale?

no

body scale - height, color , pattern

organ scale - functionality, size

molecular scale- A vs. T nucleotide or presence/ absence of band on a gel

monohybrid crosses

crosses that only differed in one character

law of segregation

diploid organisms have two alleles for each gene, one inherited from each parent. When the individual makes games, their alleles segregate individually into gametes at equal proportions

Does independent assortment work with recombination?

yes

law of independent assortment

alleles at different loci segregate independently from each other. This means that alleles at different loci each have a 50/50 chance of being passed on, regardless of what happens at other loci.

what happens when loci are farther apart?

the further away two loci are on the same chromosome the more independent they act

what does the 9:3:3:1 ratio represent?

multiplication of his 3:1 pattern. this means that each character had nothing to do with the other character in the cross, INDEPENDENT

when does the law of independent work?

only when genes are unlinked. they are not close together on the same chromosome

true breeding individuals ?

individuals that have different alleles for two different traits

linked genes

genes on the same chromosome and get inherited as a package deal

unlinked genes

genes are on different chromosomes and display independent assortment

do alleles encoding different traits separate independently?

the allele encoding color separated independently of the allele encoding seed shape, producing 9:3:3:1 ration in f2

what are the different ways for alleles to show different phenotypes for the same genes?

• mutation causing loss of function

• mutation in promoters lowering or raising protein production

• mutation altering but not breaking a gene

what do you know if you have an organism with an unknown genotype?

• test cross

• cross unknown against known homozygous recessive

what is the multiplication rule?

the probability that two or or independent events will occur together is the product of their individual probabilities

Addition rule

• want to know the probability of multiple mutually- exclusive events

• when two events A and B , are mutually exclusive the probability that A or B will occur is the sum of the probabilities for each event

what are branch diagrams?

for each event that happens, draw a branched line for every possible event, and label it with that events probability. at the end of the branch, draw and label the possibilities for the next event and soon.