Before+we+start+Genetics

Before we can start to think about factors that cause changes to how populations are shaped by genes, we need to understand what genes do.

Think about what you know:

You know that children look like their parents, on a more basic level you know that one species looks different to another species.

You also know that if you grow a tree in a sheltered part of the garden, or at a windy beach, the same type of tree will grow to a different size.

Individuals are a product of their genes and their environment. The environment can change the end product that the genes started off. The two parts interact to produce the final product.

Genes control the chemical pathways that cause the outward appearance (and the internal chemistry as well! )

The way the genes are expressed in an individual are called the Phenotype. The Phenotype is a description in words. e..g blonde hair or black hair.

The code used to write the words is called a genotype. e.g Bb or bb or BB.

The little letter is a recessive allele, this is one that is hidden or masked by the other letter. The capital letter is a dominant allele, so if you have one dominant and one recessive the one that shows up is the dominant version, Your cells don't express whatever the recessive one controlled in this case.

The only way to express the recessive type is to have two recessive alleles, bb or hh or ll or mm, see the pattern?

If you have two letters both dominant or both recessive they are identical alleles, e.g BB or bb, the description for this is homozygous (homo the same, zygous from zygote which has a full set of chromosomes). HH hh MM mm

if you have two types, one dominant and one recessive the description for this is heterozygous (hetero being different) e.g Bb Hh Ll Mm.

__Key words to use__ Dominant or Recessive Homozygous or heterozygous Phenotype or genotype.

There is information on many different levels about genes, many videos that can help you build a full picture, Khan academy '23 and me' is one set of short clips, https://www.youtube.com/watch?v=ubq4eu_TDFc that you can use. There are many on youtube that go to what ever level of understanding you want to reach.

Go to the Discussion at the bottom of the page, put in your own examples.
What is a species? A species is defined as a group that can interbreed successfully, to have the next generation also able to breed.

All individuals in the same species have a **common set** of genes. You can tell that every one in a species doesn't have the **same set of** genes - if they did they would all be identical. But all individuals have the capacity to mix it up with the full range of genes in the species, depending on what other individuals they breed with. It is this big collection of genes that is important.

Genes are a family of chemicals really. They are constructed out of DNA. They are located along the chromosomes inside the nucleus of cells.

When a sperm and an egg fertilise each other, the type of individual created depends on the combination of genes brought together by the fertilisation. Generally sperm and eggs from different species can't combine together because the codes from their genes don't make successful proteins. so the [|infamous cartoon CAT- DOG] does not exist.

Some genes provide better survival chances than other genes, e.g a camouflaged brown trout hides at the bottom of some rivers but might be really obvious in the bottom of other rocky rivers. So the success of a gene might rely on the environment it is in.

And then sometimes an environment might change, like a desert starts to form, or a mountain range gets pushed up by tectonic plates.

Then the genes that used to be great might not be anymore. So offspring with a different set of genes would be more able to breed and have offspring with their type of genes now. Slowly the genes that are more common have changed, so the population alters.

Not to be confused with the alteration to just the expression of the genes, like having a short stumpy tree because it just can't grow to its potential, the wind or soil limit the growth. If you took the offspring of that tree to another environment, would they grow big? If they would grow big, then the phenotype being expressed was due to the environment's effect on the genotype. If it didn't change, then the phenotype was due to the genotype.

[|What is a gene?] Its not simple, because you have to use the idea of a gene to explain a gene.... try the link to UTAH genetics. Don't forget to come back cos the next video is quite good too.

What is a genome? Try the link to https://unlockinglifescode.org/media/animations/659#660