BIO 201 LECTURE FINAL(Ch. 14)

Gregor Mendel

Gregor Mendel

father of genetics who discovered the basic principles of heredity by breeding garden peas

trait

specific characteristic that varies from one individual to another (ex: purple flower color)

Advantages of pea plants

many variations, mating of the plants can be controlled, and produce many offspring in a short period time

True-breeding

organisms that produce offspring identical to themselves if allowed to self-pollinate (homozygous)

Hybridization

mating or crossing of two, contrasting true-breeding varieties

P generation

true breeding parents

F1 generation

hybrid offspring of the P generation

F2 generation

self pollination of F1 individuals

Alleles

alternate versions of a gene

Dominant allele

allele that determines the organism’s appearance

Recessive allele

allele that has no noticeable effect on the organism’s appearance

Law of segregation

the two alleles for a heritable character separate from each other during gamete formation and end up in different gametes

Four concepts of Mendel’s model

1) alternative versions of genes (alleles) account for variation in inherited characters 2) for each character, an organism inherits two versions of each gene, one from each parent 3) if two alleles at a locus differ, there will be one dominant and one recessive allele 4) law of segregation

punnet square

a chart that shows all the possible combinations of alleles that can result from a genetic cross

homozygote

an organism that has a pair of identical alleles for a gene

heterozygote

an organism that has two different alleles for a gene

phenotype

an organism’s appearance or observable traits

genotype

an organism’s genetic makeup

test cross

breeding an organism of an unknown genotype with a recessive homozygote to reveal its genotype

If you do a test cross and the offspring of an organism with an unknown genotype displays the recessive phenotype, what is the genotype of the unknown parent?

heterozygous

monohybrids

individuals that are heterozygous for one character

monohybrid cross

mating of heterozygotes

complete dominance

occurs when phenotypes of the heterozygote and dominant homozygote are identical (Pp=PP)

incomplete dominance

occurs when neither allele is completely dominant and the hybrids are a blend of their parents

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

what effect does dominant alleles have on recessive alleles?

dominant alleles masks the other effect

tay-sachs disease

human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain, resulting in seizures, blindness, and degeneration of motor and mental performance

polydactyl

condition in which a rare dominant allele causes babies to be born with extra fingers or toes

three possible alleles for ABO blood group in humans

IA, IB, and i

pleiotropy

one gene that effects phenotype in many ways

sickle cell disease

recessive hereditary disease caused by a change in one amino acid in beta hemoglobin which causes the red blood cell to make a crescent shape, and thus the cell cannot carry enough oxygen

quantitative characters

characters that vary in a population along a continuum

polygenic inheritance

an additive effect of two or more genes on a single phenotype (ex: skin color)

multifactorial

many factors, both genetic and environment, collectively influence phenotype

why are humans not good subjects for genetic research?

generation time is too long, produce few offspring, and unethical

pedigree

family tree that describes the interrelationships of parents and children across generations (help make predictions about future offspring)

recessive genetic disorders examples

albinism, cystic fibrosis, and sickle cell disease

recessively inherited disorders

occur only in individuals homozygous for the allele

carriers

heterozygous individuals who carry the recessive allele but are phenotypically normal

cystic fibrosis

a recessive genetic disorder in which the lungs and pancreas are clogged with large quantities of abnormally thick mucus

dominantly inherited disorders

caused by dominant alleles

dominantly inherited disorders examples

Achondroplasia and Huntington’s disease

Achondroplasia

a form of human dwarfism caused by a single dominant allele (the homozygous condition is lethal)

huntington’s disease

genetic disorder that causes degeneration of brain cells, caused by a dominant allele (symptoms do not appear until the age of 30 or so)

aminocentesis

liquid that bathes the fetus is removed by inserting a needle in the amniotic sac to check genetic health and development of a fetus

chronic villus sampling (CVS)

a sample of the placenta is removed and tested to detect fetal abnormalities

gene idea

the model that says parents pass on discrete heritable unit-genes that retain their separate identities in offspring

law of independent assortment

during gamete formation, different pairs of alleles segregate independently of each other

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus