Genetics Notes

Genetics Unit Review

1. Cells

1. Why do we need cells?

• To grow 

• To repair/ replace

• To reproduce 

2. What is Cell Theory?

• All cells are made of preexisting cells

• All living things are made of one or more cells

• Cells are the smallest unit of living organisms 

2. Mitosis 

1. The Cell Cycle is made up of 3 parts

• Interphase: Periods of growth in the life of a cell. It consists of two growth stages and a DNA replication stage. 

• G1 or the growth phase is the major period of growth for a cell where it grows in size

• The S or S phase is when DNA replicates and synthesizes 

• G2 or growth 2 is when the cell makes all the proteins necessary for cell division

• Mitosis: The process by which the duplicated contents of a cell nucleus divide into 2 equal parts. AKA division of genetic material. 

• Cytokinesis: Division of the cytoplasm, cytosol, and organelles to create two genetically identical diploid daughter cells. 

2. What are the four stages of mitosis?

3. Miosis 

• It takes place in cells 

• Creates gametes (sex cells)(They are haploid)

• Female gamete = egg (ovaries) & Males gamete = sperm (testes) 

• Genetic Reduction: Meiosis is a form of cell division that produces daughter cells with half the number of chromosomes of the parent cell

• Genetic recombination: The products of meiosis have different combinations of alleles. Genetic recombination gives rise to offspring that are genetically different from one another and their parents. This greatly increases the genetic variation in a population.

1. Begins with interphase

• Cells have to alternate between mitosis and miosis 

• This process is controlled by hormones, which is why we don’t do this before puberty 

2. Prophase I

• Chromosomes have to condense to create Tetrades (Tetrad is when two homologous/same sister chromatids join together)

• When 2 sister chromatids find each other and form a group of 4 (Tetrad)

• Each pair of homologous chromosomes line up side by side. This aligning of homologous chromosomes is called synapsis. They are held together along their lengths 

• During this segments of the chromosomes may be exchanged (this is important for providing genetic diversity)

• The centrosomes move to the piles of the cell and the spindle apparatus forms

3. Metaphase I

• Tetrads line up in the middle instead of sister chromatids

• The spindle fibres attach to the centromere of each homologous chromosome 

4. Anaphase I

• Tetrads are split appart 

• When crossed over tetrads separate chromosomes break and reattach in new combinations crossing over is going to produce variations (Part mom and dad in a single chromosome)

• When they are pulled apart 23 go to the right 23 go to the left 

• They are sister chromatids (replicated copies of each other)

• *The goal is to create Haploids

5. Telophase I 

• The cell is finished pinching 

• Each cell has 23 sister chromatids (2x stranded chromosomes)

• 23 single-stranded chromosomes in cells 

• Crossing over has made sure each cell is unique

• 1 of each chromosome.

6. Miosis II

• The key difference is that the cells that undergo division during Miosis II are haploid instead of diploid  

7. Prophase II - Have 23 sister chromatids 

8. Metaphase II - Haploid number of chromosomes line up at the equator 

9. Anaphase II - Sister chromatids are pulled apart at the centromere by the spindle fibres 

10. Telophase II - the chromosomes reach the poles and the nuclear membrane and nuclei reform

11. Cytokinesis: Results in 4 haploid cells 

*Haploid cells are useless unless they find an egg or sperm 

• Mitosis occurs in ovaries and testicles

• They need more hormones to tell them what to do 

12.  Spermatogenesis: Creation of Sperm 

• The process of spermatogenesis starts with a diploid cell called a spermatogonium. At the beginning of puberty, spermatogonia reproduces by mitosis, and the resulting cells undergo meiosis to form four haploid cells. Following meiosis II, the cells undergo a final set of developmental stages to develop into mature sperm. The nucleus and certain molecules required by the cell are organized into the “head” region. The mid-section holds many mitochondria, which are an energy resource for the cell. Finally, a long tail-like flagellum develops for locomotion.

Diploid Cell 

→ 4 cells each a minor differences

→ will lose all their cytoplasm 

→ Will grow a flagellum 

→ Move mitochondria to the “neck”

- Head = Nucleus  - Neck = Mitochondria 

- Flagella (propellers the sperm cell towards the egg)

13. Oogenesis: Creation of eggs

• Oogenesis starts with a diploid cell called oogonium. Before birth, the oogonia reproduced by mitosis, and they begin meiosis, but stop at prophase I. Meiosis I will continue for one cell each month beginning at puberty. Oogenesis involves an unequal division of cytoplasm. The cell that receives most of the cytoplasm after the first division continue through meiosis I and II to form a viable egg. This cell contains a large quantity of nutrients that will support the zygote after fertilization. The other small cells formed are called polar bodies, they will degenerate. The final stages of meiosis II are not completed unless fertilization by a sperm cell occurs. When meiosis II is completed the mature egg and another polar body are produced. 

• There is an unequal distribution of cytoplasm that creates polar bodies

• The egg cell will be created and it will have all the nutrients it needs to survive

• If fertilization occurs it will become a zygote

• Release 1 egg a month

• 10 - 24 = 35 years of releasing 1 egg a month

4. Mutations and Genetic Disorders 

1. Changes to the chromosome structure:

• Deletion → A section of the DNA disappears

• Duplication → A section of the DNA is copied (with too much information it confuses the cell)

• Inversion → When a section is broken and then flipped (the sequence will not make sense)

• Reciprocal translocation → Changing where information is located 

• Energy changes all these forms of genetic disorders.

2. Changes to chromosome number 

• Non-Disjunction 

• Failure of the chromosomes to separate properly during meiosis 

• Different problems depending on when the non-disjunction occurs 

• This leads to trisomies and monosomies

• Monosomy is the loss of a chromosome as a result of non-disjunction 

• Trisomy is the gain of an extra chromosome as a result of non-disjunction 

• The older you get the harder it is to pull the tetrad and sister chromosomes apart

• 23 tetrads in a human cell

• Having too many or too few can not be good

• Trisomy 21- Down Syndorm 

3. Karyotyping 

• A photograph of pairs of homologous chromosomes in a cell 

• The process used to determine chromosomal abnormalities:

• Uncommon in the larger chromosomes due to the amount of genes

• Aniosyntesis: 

• When you take genes from a growing baby in utero and organize them to find any trisomy or monosomy 

• Today we dye the genes different colours

• Looking for length and lines (bands of genes) to be the same

• The older you get, the more likely it is for non-disfunction to occur

5. Mendel’s Laws 

1. Gregor Medel – Austrian monk – 1800s – Pea Plants

2. Principle of Dominance

• When every individual is composed of 2 traits, if the dominant trait is present the dominant trait will be represented

3. Law of Segregation 

• Every individual has 2 copies of a particular trait. But when producing offspring they will only pass on one. 

• Anaphase I explains the law of segregation 

6. Monohybrid and Test Crosses

1. Order of completion 

• 1. Let statement 

• 2. P1, Parent Generation (with possible gametes)

• 3. F1, Offspring Generation (with percentages) (Bonus: F means Filial)

• 4. P2, cross with possible gametes

• 5. F2 Punnet Square 

• 6. Genotype ratio 

• 7. Phenotype ration 

• 8. Final Statement 

7. Dihybrid Crosses

1. Medals 2nd Law: Law of Independent Assortment 

• The chances of obtaining a particular trait have no effect on the chances of obtaining any other trait. 

• There are no links between genes, chromosomes are independent of each other

8. Exceptions to Mendel’s Rules

1. Incomplete Dominance: Blending of Traits 

• Where the genes can blend to form something new

• Only 3 possible phenotypes

• E.g. Let: R rep Red, W rep white, and RW rep pink 

• P1, RR x WW = R x W (possible gametes)

• F1, RW - 100% of the time (genotype), Pink (Phenotype)

2. Co-dominance: No dominant or recessive as both traits are equally expressed 

• Let: R rep red, W rep white, and RW rep white with red patches) 

• P1, RR x WW - R x W (possible gametes), RW - 100% of the time (roan)

• P2, RW x RW  (R)(W)(R)(W) - possible gametes

3. Multiple Alleles: More than three phenotypes 

• Hierarchical: There is an order of traits from most to least dominant 

4. Blood Types: Co-dominant trait - (Combination)

• 4 Major: Type A, B, AB, O - (O is recessive)(AB is Hetero)

• Antigens - Surface Proteins

• Antibodies - Float through and destroy things that shouldn't be there

• Type A, IAIA, IAi - Have type A Proteins and B Antibodies

• Type B, IBIB, IBi - Have type B Proteins and A Antibodies

• Type AB, IAIB  - Have type AB Proteins No Antibodies (Universal Accepter )

• Type O, ii - Have No Proteins Has A+B antibodies (Universal Donor)

5. Rh factors 

• Rh+ Positive Proteins (Dominant trait)

• RH- No Proteins (Recessive)

• You can only give people who are (-)(+) the same as you 

• O- can give to anyone 

9. Sex-Linked Inheritance 

• Traits found in the x or y chromosome 

• They are absolute traits (will always be passed down)

• X-linked traits affect males more than females and also skip generations 

10. Polygenic Inheritance

• Polygenic inheritance refers to the kind of inheritance in which a trait is produced from the cumulative effects of many genes

• E.g. Human polygenic inheritance includes height, skin colour, eye colour, and weight

11. Heterozygote advantage 

• Heterozygote Advantage 

• E.g. Sickle cell disease

• HbAHbA - normal circular blood cell with a nucleus (has 2 versions of the normal trait)

• HbSHbS - Sickle cell disease, when blood cell is deformed which makes it hard to carry and transport oxygen to your body 

• People cramp much faster

• People with sickle cell disease need new blood on a monthly basis 

• HbAHBS - Sickly cell and normal trait (cell looks like a half moon)

• Out of 2 hemoglobins ½ are damaged

• Increased clots 

• Originated in areas with high malaria, being heterozygous is the best case in areas with high malaria  

12. Lethal Alleles

• Being Homozygous is better in this situation 

• E.g. Achrondorplasial Dwarfism 

• There are only 3 individuals in the phenotypic ratio (specific situations)

13. Pedigrees

1. Human Inheritance 

• Autosomes (Chromosomes #1-22)

• Sex Chromosomes (#23)

• Each gamete produced has 22 autosomes (#1-#22) and 1 sex chromosome (either x or y)

• The zygote has a total of 44 autosomes and 2 sex chromosomes for a total of 46

14. Reproductive Probabilities 

1. Plants - Selective breeding (Mendel)

2. Animals - Artificial insemination and embryo transfer

3. Humans 

• Hormone therapies

• In vitro fertilization

• Surrogates

• Can run genetic tests on embryos before implantation 

4. Cloning 

• Bacteria 

• Involves isolating a desired segment of DNA

• Insert the segment into a new cell 

• Eukaryotic Cloning 

• Therapeutic cloning - cures

• Reproductive cloning - creates a new organism 

5. Stem Cells 

• Embryonic stem cells (from embryos)

• Adult stem cells (certain cells have to ability to become other cells)

• Induced pluripotent stem cells (Adult cells that can be changed back into stem cells)

• Used to create any number of different types of cells and potentially whole organisms 

• Can replace cells damaged by: age, disease, trauma, or genetic defects

6. Transgenic Organisms

• Altered DNA for a particular purpose (GMOs)

• Golden Rice - modified to take up iron and create vitamin A

• Safflower - modified to create affordable insulin

• DNA helps give abilities to organisms that they normally wouldn’t have 

• Ability to develop vitamins and minerals

• Withstand drought

• Withstand parasites

• Withstand temperatures