Genetics + Meiosis

Genes:

- Chromosomes are long, coiled structures; inside the nucleus of human cells, there are 46. DNA forms these structures.
- A gene is a section of DNA that codes for one protein or characteristic.
- Each chromosome has 100s of genes along its length.

- Different species have different numbers of chromosomes; e.g., dog = 78, horse = 64, chimpanzee = 48.
- Chromosomes are in homologous pairs (one from the mother and one from the father). Humans have ≈ 25,000 genes.

- Many genes have different alleles.
→ Alleles still code for the same characteristic but produce a slightly different version, e.g., eye colour.

- Other than the nucleus, the mitochondria also contain some DNA.
- In prokaryotes, DNA is in plasmids and the loops of DNA.

- A genome is the entire genetic material of an organism.
- Organisms pass on their genome (at least in part) when they reproduce.
- There are two main types of reproduction: Sexual and asexual reproduction.

- Male = XY, Female = XX.
- xx (y = transgender) and yy = baby born dead

- The genome and its interactions with the environment influence the development of an organism's phenotype.

Reproduction

- Sexual: Two parents make an offspring, providing variation.
- Asexual: One parent makes an offspring—xefficient and fast.

- Malaria is caused by a protist, Plasmodium; it's transferred to and from humans by a mosquito:
1. The infected mosquito feeds on blood.
2. Your blood receives an injection of parasites.
3. It travels to the liver and reproduces asexually.
4. Some parasites infect red blood cells.
5. More asexual reproduction
6. Some male gametes (sperm/egg cell equivalents).
7. Another mosquito drinks blood with gametes in it.
8. For gametes, sexual reproduction takes place inside the mosquito.

- Advantages of Both Types of Reproduction:

- Asexual reproduction for the parasite in humans is very quick.
- The parasite may start to reproduce sexually when the person's immune system starts to attack so they have more variation.

Fungi:

- Sexual: Fungi produce spores as a result.
- Asexual: Quicker and requires less energy ⇒ TRUE FOR ALL BELOW ASW

Onion Plants:

Sexual: Makes flowers, then reproduces to make seeds. ⇒ SAME FOR STRAWBERRY PLANTS.

- STRAWBERRY PLANTS (said above)

- (Reproducing sexually allows for variation.)

Meiosis

- Meiosis only makes gametes (sperm/egg cells) (plants = pollen).
1.
→ This will only be in ovaries/testes.
→ DNA replication occurs.
2.
→ Chromosomes shorten and thicken.
3.
→ Chromosomes line up in their homologous pairs along the equator.
→ Crossing over occurs (all info has been shuffled up).
4.
→ We pull homologous chromosome pairs apart.
→ These new two cells (diploid) then divide to make haploid cells.

5.

→ These new two cells (diploid) then divide to make haploid cells.
→ Four genetically distinct cells haploids form.
→ Chromosomes line up at a right angle to how they originally did and line up individually (no pairs).

- Meiosis creates haploid gametes; during fertilisation, sperm and eggs fuse and restore the full diploid number of chromosomes.
- Gametes are all genetically unique due to crossover and a random assortment of chromosomes, meaning each gamete gets a random combination of chromosomes from the parental cell.

→ In meiosis, there are 2 divisions, creating 4 unidentical.
→ Zygote: A fertilised egg cell.

Genetic Inheritance

- Dominant: An allele that will always show up in the phenotype, e.g., the brown eye allele dominates over blue.

- Recessive: Alleles that are masked by dominant alleles, e.g., blue eyes.

- Genotype: The alleles a person has inherited (written as two letters).
- Phenotype: What an individual looks like.
- Homozygous: If a genotype has the same 2 letters (2 alleles that are the same), e.g., AA or bb.
- Heterozygous: 2 alleles that are different, e.g., Aa or Bb.
- Punnet Square: A diagram to show a genetic pattern.

e.g., eye colour.

→ Most phenotypic features result from multiple genes rather than single-gene inheritance.

Example:

- Testcross/Backcross: When you can breed an individual with a recessive individual, by looking at babies, you can find out the genotype.

Cystic Fibrosis

- Cystic fibrosis is a genetic disease/inherited disorder.
- It's a recessive condition.
→ A person must inherit 2 recessive alleles to be affected by the disease (ff).

- The gene involved is CFTR and is found on chromosome number 7.
- The protein coded for by the dominant gene is a channel protein that forms part of some cell surface membranes.
- The protein channel controls the movement of water and ions into and out of cells.
- Goblet cells found in the ciliated epithelium lining the airways require these protein channels.

- The recessive allele codes for a faulty protein, which doesn't work.
- People with cystic fibrosis produce mucus that is too thick and sticky. The ciliated cells can't waft it up the airways, and the mucus accumulates, making it difficult to breathe.

- If a person is heterozygous for the CFTR gene, they will not have cystic fibrosis. They use their one dominant allele to make the functioning protein.
- They may pass on the defective allele to their offspring if they are carriers of cystic fibrosis.

Chances for a couple that are both heterozygous for the CFTR gene:

Gregor Mendel

- Gregor Mendel was a monk who worked on genetic theory in the 19th century while studying pea plants.

Why He Chose Pea Plants?

- Clear characteristics, easy to work with.
- Peas were cheap.
- He had a garden and were easy to grow.
- Seeds grew relatively quickly.

- Pure line = homozygous individuals

- Mendel was perplexed by the idea that two purple flowers could produce white and purple flowers. With these observations, his hypothesis was:
→ There are units of inheritance, and every individual has 2 units.
- He tested his hypothesis by experimenting and cross-testing. It's random which one would be passed to each offspring.
- He tested this hypothesis by examining the characteristics of pea plants.
- Mendel's evidence is reproducible, as many scientists repeated his experiment and got the same results.