1. Crossing over Linkages Sex linkages
How to shuffle the genes

2. More Patterns of inheritance
Monohybrid crosses
Simple dominance
Test crosses
Co dominance
Incomplete dominance
Dihybrid crosses
Linked
Crossing over
Sex linked

3. A quick reminder Genes are segments of DNA
They are a series of base pairs
1 gene codes for 1 protein
We need many proteins we use them for enzymes, hormones , structural body parts, pigments, lots of stuff.
Each chromosome has hundreds of genes
Each gene has a special place like beads on a string.

4. The linkage Each chromosme has hundreds of genes on it.
Each gene is found in a certain place or locus
If the two genes we are looking at are on the same chromosome then they are linked.

5. Linked genes and the Law of Independent Assortment
If two genes are on different chromosomes they sort independently and inherited combinations show up in a Phenotypic ratio of 9: 3: 3: 1
If two genes are one the same chromosome they are linked and give a phenotypic ratio of 3:1 just like a monohybrid cross.

8. The tetrad
In Metaphase 1 the two sets of homologous chromosomes line up at the equator of the cell. This is called a tetrad because there are 4 side by side.

9. The chiasma
Sometimes the chromosomes are sticky and the homologous pairs in the middle cross over each other
This is called
A chiasma
The DNA can
Switch chromosomes
And shuffle the genes.

10. Crossing over or Recombination
When there is an equal trade between non- sister chromotids at the chiasma you can get new combinations of genes

11. How we can map chromosomes
The farther apart genes are on a chromosome the more likely they are to cross over.
We count the frequency of crossovers between all the genes on a chromosome and find out their relative positions.

12. Sex chromosomes and Autosomes
You have 23 pairs of chromosomes, one from your mom and one from your Dad. 22 pairs are homologous. These are your autosomes.
The 23rd pair is not homologous. They determine your sex. If you have XX chromosomes you are a girl. XY you are a boy. The Y is very small and doesn’t carry any genes other than sex determination. These are your sex chromosomes.

13. Polygenic Inheritance
So far we’ve only looked at traits that are caused by 1 gene.
Some traits are caused by 2 or more genes.
This is called polygenic inheritance.
Eye colour ,skin colour, and hair colour are all polygenic.