Chapter Fourteen: Mendel and the Gene Idea

Q1: why did Mendel use pea?

A1: Short life span, bisexual, many traits known and cross- and self-pollinating.
Q2: how did Mendel work on peas?
A2: he controled other characters but make one variable, by cross-pollination, then record the data.
Q3: why did Mendel record so many data?
A3: for the sake of geting accurate datas



Five Facts:
1. Mendel used the scientific approach to identify two laws of inheritance
2. the laws of probability govern Mendelian inheritance
3. inheritance patterns are often more complex than predicted by simple Mendelian genetics
4. many human traits follow Mendelian patterns of inheritance
5. inheritance is pretty random but follow laws



Figure:


Gnotype A&B are dominate than O.

Summary:
in the 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing that parents pass on to their offspring discrete genes that retain their identity through generations. In a diploid organism, the two allels of a gene segregate(separate)during gamete formation; each sperm or egg carries only one allele of each pair. ratio of F2 3:1. In heterozgotes, the two alleles are different , and the dominant allel phenotypic effect of the recessive allele. Homozygotes have identical allels of a given gene and are ture-breeding. Each pair of alleles segregates into gametes independently of the pair of allels for any other gene. in a cross between dihybrids, the offspring have fou phenotypes in a 9:3:3:1 ratio.
The expresiion of a genotype can be affected by environmental influences. the phenotypic range of a particular genotype is called its norm of reaction. Polygenic characters that are also influenced by the environment are called multifactorial character.

Key Term:

1. allele- Any of the alternative versions of a gene that produce distinguishable phenotypic effects.
2. amniocentesis- A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.
3. codominance-The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.
4. dihybrid-An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.
5. Huntington’s disease-A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.
6. incomplete dominance-The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele
7. monohybrid-An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.
8. pedigree-A diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations.
9. polygenic inheritance-An additive effect of two or more genes on a single phenotypic character.
10. testcross-Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.

Video:

http://www.youtube.com/watch?v=EvR_Sdm1orU

mendel rap