CELLS & HEREDITY  CHAP. 3 SECT. 1       MENDEL’S WORK

heredity- the passing of physical characteristics from parent to offspring

trait- different form of characteristic. ex. height, color, etc.

genetics- scientific study of heredity. Mendel is father of genetics.

fertilization- egg & sperm join.

purebred- offspring of many generations that have same trait.

parent generation- (P generation) organisms first paired.

F₁ generation- offspring from 1^st cross. also called filial generation.

F₂ generation- (2^nd filial generation) ¾ th of offspring had original parental trait, ¼th did not.

in all of Mendel’s crosses, only 1 form of trait appeared in F₁ generation. in the F₂ generation, the lost form of the trait reappeared in 1/4^th of the offspring.

Mendel’s conclusions:

1. sets of genetic information must control inheritance of traits
2. gene that control each trait comes in pairs
3. female contributes 1 gene, male contributes other
4. one gene in pair can hide or mask the other gene

alleles are different forms of a gene. ex. stem height, one that is for tall other that is for short.

organism's traits are controlled by alleles it inherits from its parents. some alleles are dominant, (always shows up) others recessive, (hidden by dominant allele.

hybrid- organism that has 2 different alleles for a trait. ex. 1 dominant & 1 recessive.

symbols for alleles: CAPITAL LETTER FOR DOMINANT; lower case for recessive.

Mendel’s work showed parent’s traits do not just blend in offspring. are determined by individual separate alleles inherited from each parent.

CELLS & HEREDITY  CHAP. 3 SECT. 2     PROBABILITY & HEREDITY

probability- number that describes how likely an event will occur.

1. laws of probability predict what is likely to occur not what will occur. ex. the more trials you do the closer the actual results will be to the results predicted by probability.
2. each event occurs independently of each other. ex. coin toss.
3. principles of probability apply to genetic crosses.

punnett square- chart the shows all the possible combination of alleles that can result from a genetic cross. the boxes represent the possible combinations of alleles that the offspring can inherit. see fig. 7 pg. 86. in a genetic cross, the allele that each parent will pass on to its offspring is based on probability.

phenotype- physical appearance or visible traits

genotype- genetic makeup or allele combination see fig. 9 pg. 88.

1. homozygous- organism that has 2 identical alleles for a trait, ex. SS or ss.
2. heterozygous- 2 different alleles for a trait. ex. Ss (Mendel used term hybrid to describe heterozygous.

codominance- alleles are neither dominant nor recessive. both alleles are expressed in the offspring.  codominant alleles are written with CAPITAL LETTERS with subscripts.

CELLS & HEREDITY  CHAP. 3 SECT. 3 THE CELL & INHERITANCE

Walter Sutton- studied body cells and sex cell of the grasshopper. found sex cells contained exactly ½ of the chromosomes as body cells. when sperm and egg joined during fertilization each donated ½ of the original 24 pairs of chromosomes to the offspring.  created the chromosome theory of inheritance- genes are carried from parent to offspring on chromosomes.

meiosis- process by which the number of chromosomes is reduced by half to form sex cells- egg & sperm.  see fig. 13 pg. 94

during meiosis, the chromosome pairs separate and are distributed to 2 different cells. the sex cells have only ½ as many  chromosomes as the other cells in the organism.

see fig. 14 pg. 95

body cells of humans have 23 pairs of chromosomes. the chromosomes are made up of many genes joined together. each body cell contains about 35,000 genes. each gene controls 1 trait.

CELLS & HEREDITY  CHAP. 3 SECT. 4    THE DNA CONNECTION

function of gene: to control production of proteins in cells. proteins determine traits of organism.

chromosomes are made of DNA. DNA molecule is made up of 4 different nitrogen bases that form “rungs” of DNA ladder:

1. adenine- A
2. thymine-  T
3. guanine-  G
4. cytosine-  C

gene is a section of DNA molecule that contains information to code for 1 specific protein, may contain 1000’s of bases. each gene is located in a specific place on the chromosome.

The order of the bases along a gene forms a genetic code that specifies what type of protein will be produced. 

protein synthesis- the production of proteins. the cell uses information from a gene on a chromosome to produce a specific protein. protein synthesis takes place outside nucleus in cytoplasm, but chromosomes are found inside nucleus.

RNA- is genetic messenger that carries genetic code from DNA to cytoplasm.

                DNA                                         RNA

        2 strands                                          1 strand

        4 nitrogen bases:                             4 nitrogen bases:

adenine, guanine,                             adenine, guanine,

                cytosine, and  thymine                     cytosine, and uracil

types of RNA:

1. messenger- copies the coded message from DNA to ribosome in cytoplasm
2. transfer- carries amino acids to ribosome and adds them to proteins

translating the code:  fig. 17 pg. 100-101   see 4 steps listed on page.

mutations- any change in a gene or chromosome. causes a cell to produce an incorrect protein. the organism’s trait or phenotype, may be different from what it normally would have been.  if mutation occurs in sex cell it is passed onto offspring.

effects of mutations:

1. harmful to organism if reduces the organism’s chance of survival or reproduction.  ex. white animal in green jungle
2. helpful to organism improve chances for survival or reproduction. ex. antibiotic resistance in bacteria.