AHSGE Review
J. Pollock
Spring 2007
Cell Reproduction

Compare mitosis and meiosis.
• Mitosis
– cell divides into two nuceli with same number and kind of chromosomes
– 4 stages
• prophase
• metaphase
• anaphase
• telophase
• Meiosis
– cell completes two divisions to create 4 nuclei with 1/2 the original chromosomes
– two unique events
• crossing over
• skipping replication

Mitosis and Meiosis

Compare haploid and diploid cells.
• Haploid
– one set of chromosomes
– egg and sperm cells
– one homologue of each chromosome
• Diploid
– two homologues of each chromosome
– provides double number of chromosomes for organisms
– zygote

Compare sexual and asexual reproduction.
• Sexual
– gametes from opposite sexes combine to form zygote
– meiosis for zygote development
– specialized cells
• Asexual
– no union of gametes
– division of existing cell
– exact copy of existing cell

What is Mendel’s law?
• Gregor Mendel was an Austrian monk who studied the genetic development of pea plants, beginning in 1857.
• He developed a 5-part theory that has now become a law.
• His approach was mathematical.

What is Mendel’s law?
• Parents do not transmit traits directly to their offspring.
They pass on units that are processed within the offspring.
• For each trait, an individual has two factors, one from each parent.
• The physical appearance is determined by the alleles
(genes) that code for traits.
• An individual receives one allele from each parent.
• The presence of an allele does not guarantee that it will be expressed in the offspring.

Compare genotypes and phenotypes.
• Genotype
– genetic makeup of organism based on its set of alleles
– possible appearance, based on genes present
• Phenotype
– observable characteristics of an organism
– actual appearance of organism

Genotype and Phenotype
Both animals are flamingos. The genotypes could make the offspring pink or white. The phenotype shows the actual color.

What are monohybrid and dihybrid crosses?
• A monohybrid cross is a combination of alleles involving one pair of contrasting traits.
• A dihybrid cross is a combination of alleles involving two pairs of contrasting traits.

Monohybrid/Dihybrid Cross

What are homozygous and heterozygous traits?
• Homozygous traits refer to a pair of genes, or an individual with two identical alleles for a trait.
• Heterozygous traits refer to a pair of genes, or an individual with two different alleles for a trait.

Compare dominant and recessive traits.
• Dominant
– expressed when allele homozygous or heterozygous
– expressed in each generation
• Recessive
– not expressed in F1 generation after crossing
– first expressed in F2 generation

What is incomplete dominance?
• Incomplete dominance is a condition in which a trait is intermediate between two parents.
• The offspring demonstrates a combination of the traits from both parents.

What is codominance?
• Codominance is a condition in which both alleles for a gene are expressed when present.
• The cow below is neither white nor brown. It is a combination.

What are alleles?
• Alleles are alternative forms of genes.
• They carry traits from parents to offspring.

How are inheritance patterns determined?
• Medel’s crosses are interpreted according to the rules of probability.
• Monohybrid and dihybrid crosses can be conducted to predict the traits of offspring.
• Environmental factors also have some bearing on phenotypes. For example, some arctic animals have white fur in winter and dark fur in summer.

What is a Punnett square, and how does it work?
• A Punnett square is a diagram used by biologists to predict the possible outcome of a cross.
• The square is a grid where the genotypes of the parents are written on the outside and crossed within the grid to show what phenotypes could be exhibited by the offspring.

Punnett Square

Compare DNA and RNA.
• DNA
– stores hereditary information
– double strand of nucleotides
– contains deoxyribose
– thyamine
• RNA
– participates in expression of genes
– three forms
• mRNA (instructions)
• rRNA (structure)
• tRNA (interpreter)
– single strand of nucleotides
– contains ribose
– uracil

RNA vs. DNA

What are genes and chromosomes?
• Genes are sections of chromosomes that code for proteins or RNA molecules.
• Chromosomes are cellular structures on which genes are located.

Chromosomes and Genes

How do inheritance patterns affect genetic variation?
• Mendel’s model is the basis for inheritance patterns, but it is much more complex.
• Incomplete dominance, codominance, multiple alleles (more than 2), continuous variation, and environmental influences must be factored into the prediction of phenotypes.

How is diversity increased?
• Diversity is considered important to the continuance of populations.
• Mutation and crosses keep the production of variety within species.
• Diversity is important to the theory of evolution and survival of the fittest.

How do genetic disorders and disease relate to inheritance?
• Genetic disorders and disease relate to harmful effects caused by mutations.
• Many mutations that contribute to these problems are carried by recessive genes in heterozygous individuals.
• Phenotypically normal couples can produce children who are homozygous for the recessive gene, if both carry the recessive gene.

Genetic Disorders and Diseases
Cystic Fibrosis
Sickle cell anemia
Mucus clogs lungs, liver, and pancreas
Failure of chloride ion transport mechanism
Poor blood circulation Abnormal hemoglobin molecules
Tay-Sachs disease
Phenyl-ketonuria
Hemophilia
Deterioration of central nervous system in infancy
Failure of brain to develop in infancy
Failure of blood to clot
Huntington’s disease
Gradual deterioration
Muscular dystrophy of brain tissue in middle age
Wasting away of muscles
Defective form of enzyme hexosaminidase A
Defective form of enzyme phelylalanine hydroxylase
Defective form of blood clotting factor
VIII
Production of an inhibitor of brain cell metabolism
Muscle fibers degenerate and atrophy
Recessive
Recessive
Recessive
Recessive
Sex-linked recessive
Dominant
Sex-linked recessive
1 / 2,080 whites
1 / 500 African
Americans
1 / 1,600 Jews
1 / 18,000
1 / 7,000
1 / 10,000
1 / 10,000

How has biotechnology contributed to society?
• Improved treatments for disease
• vaccines
• gene therapy
• insect- and herbicide-resistant crops
• improved livestock
• greater food production