本期內(nèi)容是孟德爾遺傳學(xué)的基礎(chǔ)理論部分，實(shí)驗(yàn)手冊(cè)與實(shí)驗(yàn)?zāi)M請(qǐng)看后兩期。本部分內(nèi)容來自 University of California, Berkeley - UC Berkeley Extension, 虛擬實(shí)驗(yàn)的內(nèi)容來自 Labster. 本部分內(nèi)容均不會(huì)標(biāo)記為為原創(chuàng)，但由于是UP主購買的課程，因此不接受非授權(quán)的轉(zhuǎn)載，謝謝您的理解。

每一個(gè)生物基礎(chǔ)實(shí)驗(yàn)均會(huì)分為三部分：第一部分為實(shí)驗(yàn)的生物理論；第二部分為實(shí)驗(yàn)的指導(dǎo)手冊(cè)；第三部分為 Labster 的虛擬實(shí)驗(yàn)?zāi)M。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的實(shí)驗(yàn)手冊(cè)來自 Labster, 第三部分的實(shí)驗(yàn)?zāi)M過程均由UP主操作。

Lab 8 - Genetics

熊貓~

Mendel’s Peas

- Gregor Mendel: father of modern genetics;

- He crossed peas and discovered some basic rules of inheritance;

- He tracked only characters that occurred in two forms;

- Mendel used varieties that were ‘true-breeding’ (plants that produce offspring of the same variety when they self-pollinate).

Mendel’s Experiments

- Mendel mated two contrasting, true-breeding varieties = hybridization;

- True-breeding parents = P generation;

- The hybrid offspring of the P generation = F1 generation;

- When F1 individuals breed (F1 X F1), the F2 generation is produced (hybrid cross);

- Example: when he crossed ?and ?flowered pea plants, all of the F1 hybrids were purple.

雜交流程：

Mendel’s Experiments

Mendel observed the same pattern of inheritance in six other characters:

- All offspring showed the dominant trait, and none showed the recessive trait in the F1;

- The F2 generation showed a ratio of 3:1 (dominant: recessive).

Mendel’s Model

- Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring of peas:

1. Genes come in pairs (= alleles);

2. Each parent passes one of the pair to offspring;

3. In hybrids only the ‘dominant’ member of the pair is expressed;

4. The pair separates when gametes are formed.

Mendel’s peas:

- Round: produce an enzyme that converts sugar to starch, which attract water due to osMosis;

- Wrinkled: lack the enzyme (sweet peas).

Law of Dominance

For each character, an organisM inherits two alleles, one from each parent;

- The two alleles may be identical (homozygous);

- The two alleles may differ (heterozygous).

The dominant allele determines the organisM’s appearance, the recessive trait is only seen when the organisM has two recessive alleles (homozygous recessive);

Conventional: dominant allele is designated with a capital letter, recessive allele is designated with a lowercase letter.

Law of Segregation

- The two alleles for a given character separate (= segregate) during gamete formation;

- Segregation of alleles corresponds to the distribution (separation) of homologous chromosomes into different gametes during meiosis;

- The possible combinations (offspring) of sperm and egg can be shown using a Punnett square;

- How to: determine all possible gametes; show possible combinations.

Phenotype vs Genotype:

Test Cross:

Dihybrid Cross

- Cross of true-breeding (homozygous) parents differing in two characters produces dihybrids in the F1 generation (heterozygous at two loci);

- A dihybrid cross = a cross between F1 dihybrids:

????- Are the traits transMitted to offspring as a package?

????- Are the traits inherited independently of each other?

Assortment Hypothesis:

Law of Independent Assortment

- Generally speaking, this law applies only to genes on different chromosomes;

- In peas, seed color gene is on chromosome 1; seed shape gene is on chromosome 7.

Peas:

Meiosis

F2 generation:

Forked Line Method

- Probability method for complex problems;

- What fraction will be homozygous recessive at all loci?

Genotypes & Phenotypes:

Human Genetics

F x f:

- O blood type is recessive, but also the most common;

- Polydactyly is dominant, but not common.

Pedigree:

- Human geneticists construct pedigree from family medical history to study genetic disorders;

- Conventions: square - male; circle - female.

Autosomal Dominant: Huntington’s Disease

- Neurodegenerative disorder caused by a single dominant allele;

- Dominant trait: one copy of the ‘bad’ allele is enough to cause disease.

Autosomal Recessive: Cystic Fibrosis

- Genetic disorder caused by a recessive allele (1/2000 births);

- 1 in 29 Caucasians in the US are carriers (heterozygotes).

Autosomal Recessive:

- Cystic fibrosis: Cl- ions do not pass normally through a cell membrane, resulting in thick mucus in lungs and other places, often causing infections;

- Tay-Sachs disease: lack of the enzyme that breaks down fatty acid proteins in lysosomes results in accumulation;

Sickle Cell Anemia

HbA/HbA (AA): wild type, susceptible to malaria;

HbS/HbS (SS): has sickle cell anemia;

HbA/HbS (AS): carrier, protected from malaria.

Other Inheritance Patterns

- Incomplete dominance: curly, straight, wavy hair;

- Co-dominant alleles: blood type, sickle cell anemia;

- Polygenic inheritance: where multiple genes impact a single trait (Height, Skin color).

sex-Linked Genes

- Traits are controlled by genes on the sex chromosomes;

- X-linked: the allele is carried on the X chromosome;

- Y-linked: the allele is carried on the Y chromosome;

- Most sex-linked traits are X-linked;

- Examples of X-linked traits: Hemophilia - blood clotting disorder; Color blindness; Male pattern baldness.

sex-Linked Genes

- Color blindness;

- If mom is a carrier, and dad is normal;

- 50% of sons will be color blind;

- 50% of daughters will be carriers.

sex-Linked Pedigree

- More males than females show sex-linked traits since males only inherit one copy of the X chromosome;

- Often skips a generation (grandfather to grandson, mom is the carrier).

sex-Linked Genes

- Can a father pass a X-linked gene to his daughter? To his son?

- For a recessive X-linked trait to be expressed (color blindness, hemophilia);

????- A female needs two copies of the allele;

????- A male needs only one copy of the allele.

本期內(nèi)容到此結(jié)束，感謝閱讀！下一期為實(shí)驗(yàn)手冊(cè) & 下下期將進(jìn)行 Labster 實(shí)驗(yàn)！