C3P1 - basic principles of heredity

gene

an inherited factor (encoded in the DNA( that helps determine a characteristic)

locus

the location of a gene (or a significant sequence) on a chromosome

trait

a variation in the physical appearance of a heritable characteristic

phenotype

the expression of a particular trait, for example, skin color, height, behavior, etc., according to the individual’s genetic makeup and environment

genotype

a set of alleles that determines the expression of a particular phenotype

allele

one of two or more alternative forms of a gene (differing in DNA sequence) found at the same locus

homozygous

containing two copies of the same allele for a particular locus

heterozygous

containing two different alleles for a particular locus

t/f; a chromosome can be heterozygous at some loci and homozygous at other loci

true; heterozygosity is allele specific

what was is a summary of the view of heredity before Mendel

people believed that offspring was a blend of characteristics of parents

what is wrong with the view of heredity prior to Mendel

there is no real blend, it is either one gene or the other, this is known as particulate inheritance.

what is continuous variation

the idea that most differences in traits are due to small effects of multiple genes

what are some reasons that the discrete nature of genes and alleles were missed prior to Mendel

• complex organisms have thousands of genes

• most common trait differences are due to differences at multiple genes

• genetics of diploid organisms is challenging

why is the genetics of diploid organisms

• individuals in populations often carry more than one allele of a given gene (heterozygosity)

• populations may carry multiple alleles of a given gene

• large scale breeding and statistical analysis needed

what was Mendel’s organism of study

the garden pea plant

t/f: pea plants reproduce through self-fertilization

true

how does self-fertilization work in plants

• hermaphroditic flowers (male and female), producing pollen and ovules

• pollen from an individual plant fertilizes the ovules from that same plant

what does self-actualization act to do

to rapidly produce pure-breeding populations (a key to mendels success)

what are the five key’s to Mendel’s success

• studying discrete phenotypes (discontinuous variations; looking at big differences)

• using an organism with many such traits already available

• using true-breeding types for experiments

• using an organism that can be bred in high numbers

• using an organism where breeding can be controlled

what are the 7 traits of pea plants studying by mendel

• seed color

• seed shape

• seed coat color

• pod color

• pod shape

• flower position

• stem length

what is the benefit in pea plants being able to be artificially cross-fertilized

• it allows for experimental crossing of any desired strains

• there is almost no risk of confusion from outcrossing

what are the genetic characteristics of outcrossing species

• individuals are often heterozygous at many loci

• different parents often have different heterozygous loci and have them at many loci

• siblings are genetically quite different from one another

• null alleles are rare, heterozygous and different between parents

what are null alleles

non-functioning alleles

what are the genetic characteristics of self-crossing species

• individuals are typically homozygous at most/all loci

• null alleles will also be homozygous

• parental gametes have the same alleles at most/all loci

• offspring will typically be genetically almost identical to themselves and to parents

• “true breeding”

what is the effect of self-crossing species having almost identical genetic makeup

offspring are genotypically and phenotypically uniform

what is true-breeding

a population homozygous at all genes

parental vs filial generations

parents should be from true-breeding populations but the filial generations are results of the crossing of two pure-bred parents and forward

what is a monohybrid cross

cross between true-breeding types of pea plant (monohybrid cross)

what is the F1 generation

offspring of different type parents

if only one parental trait is seen in F1 generation, what is this

dominant inheritance

if dominance inheritance occurs what do we know about the other non-inherited parents alleles

they are recessive

t/f: all seven traits studied by mendel had clear dominant and recessive forms

true

do the F1 offspring of true-bred parents lack the recessive “factor” or do they have it but it is “invisible”

they have it but it is invisible

when does this “invisible factor” become seen again

in the F2 generation

what is the ratio of parental traits seen in the F2 generation from true-breeding parents

3:1

in what other cross does the recessive trait re-emerge from?

reciprocal cross