exam 3 - mendel's experiment and heredity

heredity

process of passing traits from parents to offspring

hereditary

describes traits or conditions passed down

johann gregor mendel

set the framework for genetics long before chromosomes or genes had been identified

mendelian genetics

set of basic principles of inheritance explaining how traits are passed from parents to offspring through discrete units (“genes”)

pea plants

powerful system that was used to study heredity; easy-to-observe, controlled mating, short generation time, large number of offsprings, easy to grow and maintain

monohybrid crosses

crossing of two true-breeding individuals that differ in a single trait

true-breeding individuals

organisms that consistently produce offspring with the same trait as themselves

pair of factors

each trait is determined by these, one inherited from each parent

allele

variant of a gene

dominant traits

expressed when 1+ copy of the dominant allele is present

recessive traits

expressed only when 2 copies of the recessive allele are present

homozygous

individual that has two identical alleles for a gene (TT or tt)

heterozygous

individual that has two different alleles for a gene (Tt)

genotype

genetic makeup of an organism, the alleles it carries (TT, Tt, tt)

phenotype

observable trait or physical expression of those genes (tall, short)

punnett square

diagram used to predict the possible genetic outcomes of a cross between two individuals

law of segregation

each organism has two alleles for a trait, and these alleles separate during gamete formation; each parent passes only one allele to offspring

law of independent assortment

genes for different traits are inherited independently of each other; inheritance of one trait does not affect another

law of dominance

some alleles are dominant and mask others (recessive alleles); dominant allele shows in phenotype while recessive allele only shows if both alleles are recessive

test cross

cross between an individual with an unknown genotype and a homozygous recessive individual to determine the unknown genotype

pedigree analysis

method used to track how traits or genetic conditions are inherited within a family across generations

incomplete dominance

when neither allele is completely dominant over the other, so the heterozygous offspring shows an intermediate trait

codominance

when both alleles are fully and equally expressed in a heterozygous individual

linked genes

genes close together on the same chromosome are inherited together

epistasis

when one gene masks or modifies the expression of another gene at a different locus

sex-linked traits

result in different inheritance patterns in males and females

recessive lethal allele

allele that causes death when an individual has two copies of it (homozygous), but has little or no effect when only one copy is present (heterozygous)

genetics

the study of heredity

P₀,parental

plants used in first-generation crosses

F₁, first filial

offspring of P₀ plants

F₂, second filial

offspring of F₁ plants

1:0

ratio in F₁ generation

3:1

ratio in F₂ generation

incomplete dominance, codominance

exceptions to law of dominance

linked genes, epistasis

exceptions to law of independent assortment

multiple alleles, sex-linked traits, recessive lethal alleles

exceptions to law of segregation

multiple alleles

mendel implied only two alleles can exist per gene, but he was wrong