Topic 3 Genetics

3.1 Genes

Understandings

• A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.

Understandings

• A gene occupies a specific position (loci)on one type of chromosome.

Understandings

• The various specific forms of genes are called alleles.

Understandings

• Alleles differ from each other by one or a few bases only.

Understandings

• New alleles are formed by mutation. Mutations are changes in DNA.

Understandings

• The genome is whole of the genetic information of an organism.

Understandings

• The entire base sequence of genes was sequenced in the Human Genome Project.

Applications

• Sickle cell anemia

Applications

• Comparison of the number of genes in humans with other organisms.

Task- Students work in pairs to research humans and four other organisms (plant, bacterium, one w/ more, one w/less). We will create a class continuum.Time-20 minutes

Skills

• Use a database to determine the differences in the base sequence of a gene in two species.

Video Link: https://www.youtube.com/watch?v=OSKwuOccAak

Nature of Science

• Developments in scientific research follow improvements in technology; gene sequencers

3.2 chromosomes

Understandings

• Prokaryotes have one chromosome consisting of a circular DNA molecule.

Understandings

• Some prokaryotes also have plasmids but eukaryotes do not. Plasmids are small extra DNA molecules. Plasmids can be transferred from one cell to another.

Understandings

• Eukaryotic chromosomes are linear DNA molecules associated w/ histone proteins.

Understandings

• In eukaryotic species there are different chromosomes that carry different genes.

Understandings

• Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.

Diploid nuclei have pairs of homologous chromosomes

• Diploid= 2n• Haploid= n• Only gametes (sperm and egg cells) are

haploid.• If an organism has 42 chromosomes in their

haploid cells, how many would be in their diploid?

The number of chromosomes is a characteristic feature of a species

Understandings

• A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.

Understandings

• Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.

Applications

• Cairn’s technique for measuring the length of DNA molecules by autoradiography.

(summary handout)

Applications

• Use of karyotypes to deduce sex and diagnose down syndrome in humans.

Skills

• Use online databases to identify the locus of a human gene and it’s product.

1. Go to: http://www.omim.org/2. Search Gene Map3. Enter the name of a gene (DRD4, CFTR, HBB,

F8, TDF). Record chromosome number and position

3.3 Meiosis

Understandings

• Bozeman Biology Intro

• https://www.youtube.com/watch?v=rB_8dTuh73c

Understandings

• One diploid nucleus divides by meiosis to produce four haploid nuclei.

Understandings

• The halving of the chromosome number allows a sexual life cycle with fusion of gametes.

DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids

Understandings

• The early stages of meiosis involve pairing of homologous chromosomes and crossing over.