chapter 12

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,

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

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

phenotype

outward appearance/look of an individual; the observable, physical manifestation or expression of the genes present

Know how the Punnett square allows symbolic analysis

can be used to predict the genetic outcome of a particular cross

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

genotype

the actual genetic make-up of an organism, the total set of alleles of an individual

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.

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

alleles

alternative form of a gene

self-fertilization

both male & female parts enclosed in same flower and fertilization can take place spontaneously

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

monohybrid cross

a cross to study only 2 variations of a single trait

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

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

environmental factors

genes may be affected by the environment ex: Himalayan rabbits & Siamese cats

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

cross-fertilization

remove male parts of flower before fertilization & introduce pollen from another strain