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Chp14: Mendel & the Gene Idea (Scientific approach (Character is a…
Chp14: Mendel & the Gene Idea
Scientific approach
Character is a feature that can vary; trait is the variant of the feature
Peas are used because they have multiple character traits to be affected by breeding
True breeding- self pollination produces same traits after several generations
Hybridization- cross breeding two true breed varieties
True breeds are hybridized to contrast results of offspring(filial generation)
P1 is hybrid breed into F1, F1 self pollinates into F2
F1 only produces dominant traits, while F2 is able to show recessive traits
Alleles- alternative versions of genes that account for variations in inherited characters
each gene is a sequence of nucleotides at a specific place along a particular chromosome
dominant allele, determines the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance
law of segregation- states that the two alleles for a heritable character separate during formation and end up in different gametes.
segregation corresponds to the distribution of copies of the two members of a pair of homologous chromosomes to different gametes in meiosis
Punnett square- diagram predicting allele composition of offspring
a pair of identical alleles for a gene encoding a character is called a homozygote(true breed, PP or pp)
two different alleles for a gene is called a heterozygote
Organisms can have the same phenotype but different genotypes by of dominant traits
Testcrosses Can reveal the genotype of an unknown organism by breeding with a known genotype
A mono hybrid cross is set up by taking true breed organisms to ensure gametes will of a species will have the same phenotype
A dihybrid cross his set up by taking true breed samples that have two related traits and seeing how genotype separates into new gametes
Law of independent assortment- states that several genes assort independently during gamete formation
Probability laws
The multiplication rule- to determine probability, multiply the probability of one event by the probability of another event
When applied this means the probability of two traits occurring together is lower than on their own
Addition rule- probability is calculated by adding the probability of the two traits(used in F2)
Punnett squares can be used to determine the probability of traits
the rules of probability give us the likelihood of various outcomes But doesn’t guarantee results
Inheritance patterns
Alleles can show different degrees of dominance and recessiveness in relation to each othe
Complete dominance refers to filial groups that always share the traits of one parent (pea flowers)
Incomplete dominance is defined as alleles not having complete dominance between phenotypes, forming intermediates(snapdragon color)
Codominance happens when two alleles separately affect the phenotype (human MN blood group)
When a dominant allele coexists with a recessive allele in a heterozygote, they do not actually interact at all
brain cells of a child with Tay-Sachs disease cannot metabolize certain lipids because a crucial enzyme does not work properly(molecularly codominant)
Pleiotropy is the ability of an allele to house multiple phenotypic effects(cystic fibrosis and sickle-cell disease)
Epistasis means a gene in one area of dna affects a gene in another location (Labrador coat color)
Quantitative characters usually define polygenic inheritance where several genes add to affect phenotype(skin color)
Multifactorial- genetic and environmental factors influence phenotype
Human traits
Pedigree refers to tracing a family’s history for genetic traits
Used to predict traits of future generations
Carriers- heterozygotes may transmit the recessive allele to their offspring
Recessive disorders (albinism) only occur in homozygous offspring
Most people who have recessive disorders are born to parents who are carriers of the disorder but have a normal phenotype
genetic disorders are not evenly distributed among all groups of people
Cystic fibrosis- chloride transport channels are defective or absent in the plasma membranes of children who inherit two recessive alleles for cystic fibrosis(rec)
Sickle-cell disease is caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells(rec)
Dominant disorders occur less because recessive traits are more common
Huntington’s disease, is caused by a lethal dominant allele that has no obvious phenotypic effect until the individual is about 35 to 45 years old(don)
Amniocentesis-needle Is inserted into the uterus and extracts about 10 mL of amniotic fluid to test for disorders
chorionic villus sampling- a narrow tube is inserted through the cervix into the uterus and suctions out a tiny sample of tissue from the placenta
