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Genetics
Chapter 11- pg. 306-329
11.1 pg. 306-312
Every living this inherits characteristics from its parent/parents= heredity.
Genetics: scientific study of heredity, founded by Gregor Mendel.
Fertilization: process in sexual reproduction in which male and female reproductive
cells join to form a new cell.
Trait: specific characteristic of an individual
Hybrids: offspring of crosses between parents with different traits
Mendel’s first conclusion: an individual’s characteristics are determined by factors that
are passed from on parental generation to the next.
Gene: sequence of DNA that codes for a protein and thus determines a trait; factor that is
passed from parent to offspring
Allele: one of a number of different forms of a gene
Principle of dominance: Mendel’s second conclusion, which states that some alleles are
dominant and others are recessive.
Segregation: separation of alleles during gamete formations
Gametes: sex cell

During gamete formation, the alleles for each gene segregate from each other, so
that each gamete carries only one allele for each gene
11.2 pg. 313-318
Probability: likelihood that a particular even will occur- could be used to explain
genetics
Homozygous: having two identical alleles for a particular gene (TT, tt)
Heterozygous: having two different alleles for a particular gene (Tt)
Phenotype: physical characteristics of an organism
Genotype: genetic makeup of an organism

Best way to predict the outcome of a genetic cross is by using a Punnet Square
o Punnett squares use mathematical probability to help predict the genotype
and phenotype combinations in genetic crosses.
Independent Assortment: one of Mendel’s principles that states that genes for different
traits can segregate independently during the formation of gametes
 Accounts for the many genetic variations in plants, animals, etc.
Mendel’s principles of heredity, observed through patterns of inheritance, form the basis
of modern genetics.
Principles:
 The inheritance of biological characteristics is determined by individual units
called genes, which are passed from parents to offspring.
 Where two or more forms (alleles) of the gene for a single trait exist, some alleles
may be dominant and others may be recessive.
 In most sexually reproducing organisms, each adult has two copies of each geneone from each parent. These genes segregate from each other when gametes are
formed.
 Alleles for different genes usually segregate independently of each other.
11.3 pg 319-321

Some alleles are neither dominant or recessive
Incomplete dominance: situation in which one allele is not completely dominant over
another allele
Codominance: situation in which the phenotypes produced by both alleles are
completely expressed

Many genes exist in several different forms and are therefore said to have
multiple alleles.
o Multiple Alleles: a gene that has more that two alleles

Many traits are produced by the interaction of several genes
Polygenic traits: trait controlled by two or more genes

Environmental conditions can affect gene expression and influence genetically
determined traits
11.4 pg 323-329
Homologous: term used to refer to chromosomes in which one set comes from the male
parent and one set comes from the female parent
Diploid: term used to refer to a cell that contains two sets of homologous chromosomes

The diploid cells of most adult organisms contain two complete sets of inherited
chromosomes and two complete sets of genes
Haploid: term used to refer to a cell that contains only a single set of genes
Meiosis: process in which the number of chromosomes per cell is cut in half through the
separation of homologous chromosomes in a diploid cell
 Has 2 distinct divisions
o Meiosis I
o Meiosis II
o By the end of meiosis II, the diploid cell becomes four haploid cells

Meiosis I- just prior the cell replicates its chromosomes
o Prophase I: In this phase, each replicated chromosome pairs with its
corresponding homologous chromosome. This pairing forms:
 Tetrad: structure containing four chromatids that forms during
meiosis
 Crossing-over: process in which homologous chromosomes
exchange portions of their chromatids during meiosis

Metaphase I and Anaphase I: spindle forms attaches to each tetrad
o Metaphase I of meiosis: paired homologous chromosomes line up across
the center of the cell
o As the cell moves to Anaphase I, the pairs of chromosomes separate
o Anaphase I of meiosis: spindle fibers pull each homologous chromosome
pair toward opposite ends of the cell

Telophase I and Cytokinesis: the separated chromosomes cluster at opposite ends
of the cell
o Telophase I: a nuclear membrane forms around each cluster of
chromosomes
o Cytokinesis: forms two new cells

Meiosis I results in two new cells, called daughter cells.


Meiosis II- two cells now enter a second meiotic division
Prophase II: As the cells enter prophase II, their chromosomes- each consisting
of two chromatids- become visible.


Metaphase II, Anaphase II, Telophase II and Cytokinesis
Metaphase II: chromosomes line up in the center of each cell

Anaphase II: the pair chromatids separate

The final four phases of meiosis II are similar to those is meiosis I. However, the
result is four haploid daughter cells.
The haploid cells produced are the gametes that are important to heredity (sperm,
egg).
Zygote: fertilized eggs
Mitosis vs. Meiosis
In mitosis, when the two sets of genetic material separate, each daughter cell receives
one complete set of chromosomes. In meiosis, homologous chromosomes line up and
then move to separate daughter cells.
Mitosis does not normally change the chromosome number of the original cell. This
is not the case for meiosis, which reduces the chromosome number by half.
Mitosis results in the production of two genetically identical diploid cells, whereas
meiosis produces four genetically different haploid cells.