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January 5 - 26, 2018

1/4/2018

Housekeeping: We are starting genetics. There are five essential ideas for this unit. They will be posted on the content powerpoint.

Agenda:
1. Have a baby
2. Introduction to Mendelian Genetics

Lesson Objectives: You should be able to...
1. Explain what a gene is and what it does.
2. Define "allele" and describe it in the context of heritable factors.

Content Review:
Links: Genes PowerPoint: Genetics PowerPoint: Chromosomes
Textbook Readings: Chapter 3

Student Missions:
Mission 1: Who's Your Mommy? Now that you have your baby, we can talk about the science behind why your child looks the way s/he does. The lab provided a list of vocabulary that you need to know, and now that you have some experience, you should be able to identify the meanings.

This video from Alex Lee begins with the unpacking of DNA; how chromosomes are formed. We talked about this long ago, and you can read more about it here. Genes are chunks of DNA that contain heritable factors. "Heritable" means that these factors have been passed on to you by your parents. "Factors" is a synonym for genetic traits. Examples of traits include hair color, eye color, lip shape, earlobe structure, etc. It is estimated that humans have 21,000 genes that are organized into chromosomes.

Genes are found at particular places on chromosomes. This place is called a locus (plural-loci). Geneticists have mapped out the loci of each sequence of DNA in order to identify what the gene controls. An exampleis the gene that controls the protein transducin, which enables color vision is found on chromosome 1.

We possess two copies of each gene in our bodies; one from Moms and the other from Pop. Theoretically, you should find the same gene at the same locus on each chromosome.

Alleles are versions of genes. An allele is a specific form of a gene that differs from other alleles by one or more nitrogen bases (C G A T). The example of transducin shows that the "correct" sequence includes a C at position 235, but the mutation has a T in place of the C. This makes an enormous difference, because we know T pairs with A and C pairs with G. This change of base results in the formation of an incorrect protein and thus, a person is literally colorblind. Alleles allow for single traits to have variations.

Read about cystic fibrosis on page 122-123 and ear wax on page 123.

Task #1: What is cystic fibrosis and how does it affect the body? Can it kill a person? Give me a couple of sentences that answers this question.

Task #2: Read about the Human Genome Project on page 147.
.
Mission 2: Chromosomes: Fat DNA.
Mission Objectives. You should be able to...
1. Describe the structure of a chromosome
2. Explain what is meant by the term "homologous" with respect to DNA.
3. Explain the difference between diploid cells and haploid cells.
4. Interpret a karyogram.

This is a short video of Section 3.2 that goes over the general understandings of the section and provides a simplistic explanation of each. It is a good overview of the section. You should write the understandings, pause the video, and try to explain what the video says about the understanding in your own words. I will help you.

When cells are in interphase, DNA is in the form of chromatin, which looks like thread. DNA wraps around histones to form a nucleosome. When DNA is in this form, it is inaccessible to transcription enzymes.

Eukaryotes have multiple pairs of chromosomes, and each chromosome has a different set of instructions. Humans have 46 chromosomes (2n) grouped in 23 pairs. These pairs are called homologous chromosomes, and they are similar in size and shape. There are two of each chromosome because you get one from each parent. The word "diploid" describes a nucleus that has 23 pairs of homologous chromosomes. The word "haploid" contain 23 chromosomes in total. Haploid means "half." Gametes are haploid cells. Autosomes (non-sex chromosomes) are diploid cells.

Chromosomes either look like an "X" or an "H." They're grouped as a pair, but each chromosome has been duplicated as a result of DNA replication during interphase.

Image courtesy of www.passmyexams.co.uk

When an egg is fertilized by a sperm, a zygote is formed and the two haploid nuclei fuse, matching up their chromosomes into pairs. The 23rd pair of chromosomes are called sex chromosomes because they determine the sex of the fetus. Males donate either an X or a Y, and females donate only Xs. Xs are bigger than Ys and contain more genes.

Autosomal traits are located on any of the 22 pairs. Sex-linked traits are associated with the 23rd pair. Below is a karyogram. A karyogram is a "picture" of chromosomes that can provide specific information about a person. To determine sex, look at the 23rd pair. If the chromosomes are the same size, then the person is female. If they are not, the person is a male. Down's Syndrome is the result of there being 47 chromosomes; the 47th is grouped with the 21st pair. As a result, it is also called trisomy-21. See below.

Task #3: Read about bacterial chromosomes and plasmids on pages 149-151.

Mission 3: You Feeling Sexy?
Mission Objectives. You should be able to...
1. Define and describe meiosis and compare it to mitosis.
2. Explain the chromosome reduction process.
3. Explain why meiosis happens in two separate stages.
4. Explain what happens during each phase in each stage.
5. Explain the importance of genetic variation and meiosis' role in it.
6. State the products of meiosis.

Meiosis is the process by which gametes (eggs and sperm) are formed. Cells contain 46 chromosomes, but gametes contain 23. The reason for this is when the gametes fuse during fertilization, there are 46 chromosomes, not 92. In order to do this, a special type of cell division is needed: reduction division.

Here are two short videos I made to try and simplify the process so that you can understand it. But you still need to be able to explain what is happening in each stage in your own words.

Meiosis I
Meiosis II

Mitosis produces diploid nuclei (2n) containing 46 chromosomes organized into 23 pairs. Meiosis produces haploid nuclei (n) that contain 23 chromosomes, each representing half of one pair. Examine the image above. DNA is replicated before meiosis takes place, obviously.

The picture below goes into greater detail. Recall that homologous chromosomes come in pairs, so instead of two (as in mitosis), you have four.

HOMEWORK: Corresponding workbook pages.

Mission 4: Who Are You and Where Did You Get You From??
Mission Objectives. You should be able to...
1. Explain Mendel's contributions to the study of genetics.
2. Predict the genotypes and phenotypes for offspring using Punnett squares.
3. Define and explain the law of segregation and the law of independent assortment.

Before we get into this, we need to talk about Gregor Mendel, the father of genetics.

What you did when you made your babies was choose a set of genes that coded for particular characteristics and that is basically what inheritance (or heredity) is.

Inheritance Addendum.

Mendel's work comes with, like most things, some rules. The law of segregation states that during the production of gametes, alleles segregate (or separate) so that offspring acquire one allele from each parent. The law of independent assortment states that when two or more traits are inherited, independent hereditary factors sort independently in gamete production, giving individual traits an equal opportunity to occur.

We can visualize how genotypes come about with Punnett Squares, as the video mentioned. With this method, you can determine the probability of inheriting certain genotypes and phenotypes when you cross Mom with Dad. We will practice.

Punnett Square 1: Monohybrid Crosses
Punnett Square 2: Dihybrid Crosses

Pedigrees

Pedigree charts are diagrams constructed to show biological relationships. In genetics, they can show how a trait can pass from one generation to the next. It is similar to a family tree. Symbols are used to represent people, shading represents the expression of a trait, and connecting lines denote specific relationships.

Pedigree Practice using the handout I gave you.

HOMEWORK: Complete the Punnett Squares and the pedigrees.

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