1. How our genes are organized
chromosomes

2. Genes
A gene is an address – a location on the chromosome and in the DNA sequence where info for a specific trait is located.

3. Human Fertilization
ZYGOTE – fertilized egg
Gametes

4. Review of key terms:
Gene
Chromosome
Chromatid
Homologous chromosome

5. What are chromosomes?
All eukaryotic cells store genetic information in chromosomes.
Most eukaryotes have between 10 and 50 chromosomes in their body cells.
Human cells have 46 chromosomes
23 pairs

6. Structure of chromosomes
Complex of DNA and protein called chromatin
Condenses during cell division
DNA exists as a single, long, double-stranded fiber
Organized in coils
DNA is wrapped around proteins called histones

7. Sets of chromosomes
Homologous chromosomes: chromosomes that are similar in size, shape and genetic content
Each homolog (individual
chromosome) in a pair come
from one of the two parents

8. Chromosome replication (S phase)
Each condensed chromosome consists of 2 identical chromatids joined by a centromere.

9. Types of chromosomes
Autosomes: chromosomes that are not directly involved in determining the sex of an individual
Sex chromosomes: pair of chromosomes directly involved in determining the sex of an individual

10. Types of chromosomes In humans: Autosomes: 22 pairs
Sex chromosomes: 1 pair
Referred to as X and Y chromosomes in humans

11. Karyotype: a snapshot of our chromosomes
Arranged by size in
in descending
order
Used to examine
an individual’s
chromosomes

12. Chromosomal mutations
Changes in an organisms chromosome structure are called:
MUTATIONS

13. Four types of chromosomal mutations:
Deletion
Duplication
Inversion
Translocation

14. Deletion mutation A piece of a chromosome breaks off completely:
Consequence after cell division: new cell will lack a certain set of genes

15. Modeling deletion

16. Duplication mutation
A piece of a chromosome breaks off and attaches to its homologous chromosome:
Consequence after cell division: new cell will have an extra set of genes

17. Modeling duplication

18. Translocation mutation
A piece of a chromosome breaks off and re-attaches to a non-homologous chromosome:
Consequence after cell division: new cell will carry genes in the wrong location

19. Inversion mutation
A piece of a chromosome breaks off and re-attaches to its original chromosome in REVERSE order:
Consequence after cell division: new cell will carry genes that are in the wrong order – will code for the WRONG proteins

20. Modeling inversion

21. Wrong order = wrong proteins
Changes in the order of genes on chromosomes has dire effects in the organism
The wrong sequence will code for the wrong protein
In some cases there is little effect, in others the result can be severe or even lethal to the organism.

22. References National Institutes of Health Carolina Biological Supply
Biology Holt (4th Ed.)