* Basic genetics (Ch25) Flashcards
Gene
- a short segment of DNA on a chromosome
- controlling the formation of structural / functional protein
Mendel’s breeding experiments
- Mendel carried out many breeding experiments on pea plants. He grew and examined a large number of pea plants to collect a large amount of experimental evidence
- Based on his observation on the large number of offspring with different phenotypes, he worked out a possible explanation for the observation by logical deduction
Reasons to use garden peas
- small and easy to be cultivated
- grows quickly, life cycle is short
- has bisexual flower
Procedures of study
- Remove anthers (prevent self-pollination)
- Cover the flower with plastic bag (prevent further pollination)
Mendel’s First Law (Law of Segregation)
- A particular trait is determined by a pair of hereditary factors (alleles) which will segregate during gamete formation, only one factor will go to each gamate
- When two gamete carrying either one factor of a pair fuse, only the dominant factor will be expressed in the phenotype of offspring
How Mendel designed his experiment so that his findings were valid and reliable?
- Studied one or two traits at a time
- Bred pure line
- A great number of samples to reduce error
- Record quantitative results
- Remove anthers
- Carefully ruled out controlled variables
Monohybrid inheritance (with numbers)
- Number of offspring of each phenotype
- Ratio
- According to Mendel’s First Law
- Both parents must be heterozygous
(5. Dominant character - Phenotype of parents)
Deducing dominant character
父母一樣 子女不同
- Phenotype of parents -> at least one gene for A
- Phenotype of offspring -> at least one gene for B
- Allele of B of offspring must come from either parent
- At least one parent is heterozygous
- Heterozygous condition, only dominant allele is expressed, recessive allele is masked
- Phenotype of both parent -> A must be dominant
Blood transfusion -> blood clumping
- Antigen on red blood cells of donor
- Antibody in plasma of recipient
- Antibody act against antigen
- Blood clumping
Why men can donate blood more frequently than female
- Female has periodic blood loss in menstruation
50% chance of having a baby boy / girl
- Female produce only one type of egg with X chromosome
- Male produce two types of sperm, carrying X or Y chromosome
- There are equal numbers of the two types of sperms
- Random fertilization
Continuous variation
- Variations of certain characteristics that have a wide and continuous range of intermediates between the two extremes
- Normal distribution curve
- Controlled by many genes
- Affected by the environment
Discontinuous variation
- Variations that have distinctive categories with no intermediate categories
- Bar chart
- Not easily affected by the environment
Why sex-linked disorders are more common in males than females
- Female has two X chromosomes, she has the sex-linked disorder only when both her X chromosomes carry the recessive alleles of the disorder
- She will be normal if she is heterozygous because the recessive allele is masked by the dominant allele
- Male has only one X chromosome, he has the sex-linked disorder if the X chromosome carries the recessive allele
Deducing whether a disease is autosomal
Y-linked: 父子（有病 -> 無病）
- All male offspring of a father will be affected individuals
- Son is not affected but father is affected -> not Y-linked
X-linked recessive 父女 / 母子（女有病 -> 男無病）
- An affected female will produce affected male
- Son is not affected but mother is affected -> not X-linked recessive
X-linked dominant 父女 / 母子（男有病 -> 女無病）
- Female offspring of an affected father must be affected (since the father has only one chromosome, he must inherit it to the daughter)
- Daughter is not affected but father is affected -> not X-linked dominant
-> not Y-linked / X-linked recessive / X-linked dominant
