chapter 12 edited
Explain the advantages of Mendel's experimental system
-there were many pure, true-breeding -they were easy to work with, easy to grow & had a short generation time -this allowed Mendel to examine large numbers (hundreds) of offspring over several generations -pollination could be controlled easily by self-fertilization or by cross-fertilization
Summarize Mendel's five-element model
1. parents do not transmit physiological traits directly to their offspring, they transmit discrete information for the traits into factors called genes 2. each individual receives one copy of each gene from each parent 3. not all copies of a gene are identical, the alternative form of a gene is called an allele. when two haploid gametes have the same allele they are called homozygous. when two haploid cells contain different alleles they are called heterozygouos 4.the two alleles remain discrete, they never blend nor alter each other 5. the presence of a particular allele does not ensure that the trait it encodes will be expressed. in heterozygous individuals only the dominant allele is expressed and in other allele is present but unexpressed is the recessive one
Multiple alleles for one gene
Genes may have more than two alleles ex: ABO blood types in humans
Pleiotropy
One gene, an allele which has more than one effect on the phenotype of an organism; a single gene locus has multiple effects, affects more than one trait ex: cystic fibrosis, sickle cell anemia,
monohybrid cross
a cross to study only 2 variations of a single trait
alleles
alternative form of a gene
dominant
an allele, form of a trait that is expressed in the heterozygous individual; an allele that is expressed when present in either the heterozygous or the homozygous individual
recessive
an allele, form of a trait that is not seen in the heterozygous individual; the allele, trait that is only expressed when present in the homozygous condition, but being "hidden" in the heterozygous individual
self-fertilization
both male & female parts enclosed in same flower and fertilization can take place spontaneously
Know how the Punnett square allows symbolic analysis
can be used to predict the genetic outcome of a particular cross
Describe how assumptions in Mendel's model result in oversimplification
each trait is controlled by only one pair of alleles (a single gene), which means the same as each pair of alleles controls one trait; at each gene locus there are two possible alleles, one that is dominant & one that is recessive
dihybrid cross
examination of 2 separate traits in a single cross
Explain Mendel's 2nd Law, the Principle of Independent Assortment
genes located on different chromosomes assort into gametes independently of each other during meiosis, which means the same as each pair of alleles segregates independently of the other allele pairs
environmental factors
genes may be affected by the environment ex: Himalayan rabbits & Siamese cats
Describe the explanations for inheritance prior to Mendel
heredity occurs within species are transmitted directly from parent to offspring This led to the belief that inheritance is a matter of blending of traits within fixed, unchanging species.
Dominance is not always complete
in incomplete dominance the heterozygote is intermediate in codominance no single allele is dominant, and the hetezygote shows some aspect of both homozygotes ex: japanese four o'clocks and human blood groups
Gene interaction
influence the phenotype of the individual.
Evaluate the outcome of a monohybrid cross
it refutes the idea of blending. one trait disappears in the first generation (F1) then reappears in a predictable ratio in the next (F2). The trait observable in the F1 is called dominant and the other is called recessive. in the F2 the ratio of observed dominant offspring to recessive is 3:1 and this represents the ratio of 1 homozygous dominant to 2 heterozygous to 1 homozygous recessive.
Polygenic inheritance
more than one gene can affect a single trait; when multiple genes are involved in controlling the phenotype of a single trait; when a single trait is affected by more than one gene locus ex: human height, hair color, skin color
phenotype
outward appearance/look of an individual; the observable, physical manifestation or expression of the genes present
cross-fertilization
remove male parts of flower before fertilization & introduce pollen from another strain
genotype
the actual genetic make-up of an organism, the total set of alleles of an individual
Know who Gregor Mendel was & know what he did
was an Austrian Monk and laid the foundation for modern genetics by working in the garden of his monastery with a pea plant
Explain Mendel's 1st Law, the Principle of Segregation
when gametes are formed these two alleles at each gene locus separate or segregate from each other during gamete formation in meiosis & remain distinct, each gamete receives only one of the two alleles
