347 DNA notes 3

347 DNA Overview

https://education.23andme.com/dna-discovery/#

This lesson is based on the interactive from -

https://education.23andme.com/dna-discovery/#

Most DNA is stored inside a compartment in the cell called the nucleus, similar to an egg yolk inside an egg. There is also some DNA housed outside the nucleus, in structures called mitochondria. All of your DNA together is called your genome.

Checkpoint

Multiple Choice

Almost every cell has DNA. Which of these is NOT a cellular structure inside your body that holds your DNA?

• A. Cell phone

• B. Nucleus

• C. Mitochondria

Most DNA is stored inside a compartment in the cell called the nucleus, similar to an egg yolk inside an egg. There is also some DNA housed outside the nucleus, in structures called mitochondria. All of your DNA together is called your genome.

Multiple Choice

Humans have 23 pairs of chromosomes. Where do they come from?

• A. Both sets from mom

• B. Both sets from dad

• C. One set from dad and one set from mom

How does that work? You inherited one of your mom's two X chromosomes. And you inherited either your dad's X or Y chromosome. If you inherited his X chromosome, then you have XX chromosomes and are genetically female. If you inherited his Y chromosome, then you have XY chromosomes and are genetically male. Sometimes, a person’s genetic sex, the sex assigned at birth, and/or the deeply-held sense of gender are not all the same.

Multiple Choice

Of the 23 pairs of human chromosomes, the 23rd pair (the sex chromosomes) determines your sex. Which combination of sex chromosomes does a person who's genetically female have?

• A. XX

• B. XY

• C. XZ

If all your DNA (your genome) is a cookbook, then your genes are the recipes. Genes are sections of DNA that contain instructions for making proteins and RNAs. Human DNA contains around 20,000 protein-coding genes and likely thousands of RNA genes.

Multiple Choice

_________ are sections of DNA that contain instructions for making proteins and RNAs.

• A. Cells

• B. Amino acids

• C. Genes

The process of building a protein using the DNA code happens in two steps called transcription and translation. During transcription, the cell creates a temporary copy of the gene called messenger RNA. During translation (as shown), the cell follows the gene instructions contained in the messenger RNA to link together a chain of small molecules, called amino acids.

Multiple Choice

Genes are sections of DNA that contain instructions for the cell to make proteins. Which type of molecules does the cell string together to make proteins?

• A. DNA

• B. Genes

• C. Amino acids

Only a small part of your DNA contains the genes that code for proteins.

Some DNA contains regulatory elements, which are stretches of DNA that regulate how and when the cell should "read" different genes.

Some DNA codes for different kinds of RNAs that play a variety of roles in the cell. And some DNA has no known function.

Multiple Choice

All DNA codes for proteins.

• A. True

• B. False

DNA is shaped like a long twisted ladder, or a double helix. Each rung of the ladder is made of two molecules called bases, forming a base pair. There are four types of DNA bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The bases always pair up according to these rules:

A pairs with T C pairs with G

Multiple Choice

DNA follows specific rules when matching up base pairs. Identify the sequence with correctly paired bases below:

• A. A-T, C-G, A-A

• B. T-A, G-A, A-C

• C. A-T, C-G, T-A

It's been estimated that our DNA sequences are about 99.5% identical. But there are parts of our DNA that vary from person to person.

These DNA differences are called genetic variants. Some genetic variants have no effect. Others influence traits and health — like your hair color, weight, and risk of certain diseases.

Multiple Choice

A genetic variant can influence your traits by changing how a protein gets built and how it does its job.

• A. True

• B. False

The most common type of genetic variant is when people have different base pairs (DNA letters) at one particular place in their DNA. For example, at the same place in a gene, one person might have an A (adenine), while another person has a C (cytosine). These differences are called single nucleotide polymorphisms, or SNPs (pronounced “snips”).

Multiple Choice

The most common type of genetic variant is when people have different bases (DNA letters) at one particular place in the genome.

• A. True

• B. False

You inherit genetic variants from your parents, but new variants can also appear in your DNA. They can be the result of damage to DNA, or a side effect of normal cell processes like making new copies of DNA.

Usually new genetic variants are corrected by "DNA repair" proteins in the cell. Most uncorrected DNA segments are not harmful. In fact, they typically have no effect at all.

Occasionally, a new genetic variant can lead to a new trait — for example, by changing the function of the protein that that gene codes for.

Multiple Choice

New genetic variants can appear during normal cell processes, like when cells make new copies of their DNA.

• A. True

• B. False

For example, research suggests that most ancient humans were lactose intolerant, meaning they could not digest the sugar lactose in dairy products like cheese, milk, and yogurt, as they grew older.

But several thousands years ago, in some regions of Europe and Africa, humans started domesticating cows, goats, and sheep and depended on the animals' milk for nutrients. New genetic variants appeared by chance that gave these groups of people the ability to digest dairy into adulthood. This helped them adjust to their new diet, and these genetic variants became more common.

Multiple Choice

If a new genetic variant results in a new trait that helps living things survive and reproduce, that variant and trait will disappear from the population over time.

• A. True

• B. False

For almost all human traits, factors like lifestyle and environment play a role along with genetics. Your height, for example, depends on the effects of many genetic variants as well as environmental and lifestyle factors like your diet.

This means you can have genetic variants that are linked to being tall, but if you have poor nutrition growing up, you may end up being shorter than other people with those same genetic variants.

Checkpoint

Multiple Choice

Which of the following influence your traits?

• A. Only genetics

• B. Only genetics + lifestyle

• C. A combination of genetics + lifestyle + environment