Mendelian genetics Flashcards
Describe the history of genetic modification:
- People have recognized for years that traits are inherited
- Used this to their advantage in “selective breeding”
- Purposely mated individual animals (and plants) to select for certain traits
- Eg. Dog breeds
Who is Thomas Morgan?
- 1933 - discovered the role of genetics on chromosomes in heredity
- Worked with fruit flies
- When crossing flies with red eyes he found some offspring has white eyes
- This caused him to investigate heredity further (up until this point he was doubtful of theories from Darwin and Mendel)
Describe Mendel’s experiments:
- Mendel wanted to test patterns in genetics by observing traits such as flower color
- He let pea plants self-pollinate for several generations to ensure they were pure bred
- Then artificially crossed one type of plant with another to observe results – created hybrids (not purebred)
Define monohybrid cross:
A cross involving only one trait
What are Mendel’s generations?
P - purebred parents generation
F1 - First generation of hybrids
F2 - second generation of hybrids
What happened with the F1 generation?
- Only one trait (of the two possible parent traits) was observed in the offspring
- Mendel decided that the trait observed must be dominant
- The trait not observed was recessive
- In this case one trait showed complete dominance over the other (the recessive trait will not show at all if the dominant gene is present)
What happened with the F2 generation?
- Recessive traits reappeared in some offspring
- About 1 in every 4 offspring showed recessive traits
Describe the law of segregation:
- “All individuals have two copies of each factor. These copies segregate (separate) randomly during gamete formation, and each gamete receives one copy of every factor.”
- Note: we now know Mendel’s “factors” were genes
- Different forms of each gene are now called alleles
- Not all genetic combinations are this simple
Define gene:
A genetic code that designates a specific trait eg. Flower color
Define allele:
Form of a gene eg. Purple vs. white flowers
Define genotype:
Combination of alleles for a trait
Define pheotype:
Physical trait observed (characteristic of an organism)
Define homozygous:
Two identical alleles
Define heterozygous:
Two different alleles (one is likely recessive, but not always)
Define dominant allele:
An allele that has the same effect on an organism whether present in homozygous or heterozygous state
Define recessive allele:
Only has an effect when present in homozygous state
Define carrier:
Has one copy of recessive allele that can cause genetic disease
Describe the relationship between gametes and alleles:
- Gametes are haploid and therefore only have one copy of gene (only one allele)
- When gametes fuse, diploid zygotes end up with two copies of a gene – may be the same allele or different alleles of that gene
How are genotypes symbolized?
- First letter for description of dominant allele is used
- Capital letter represents dominant allele
- Lower case letter (same letter) represents recessive allele
Describe punnett squares:
- Used to analyze/predict genetic crosses
- Used with F1 generation
Describe a test cross:
- Sometimes geneticists will do a test cross to determine the genotype of an individual
- Cross an individual with a dominant phenotype with an individual known to be homozygous recessive
- Used to check to see if dominant phenotype is a result of homo or heterozygous genotype
What is a dihybrid cross?
- Examination of two traits simultaneously
- Four genes (so two genotypes) are observed, instead of two
Describe Mendel’s law of independent assortment:
- The two alleles for one gene segregate (assort) independently of the alleles for other genes during gamete formation
- Translation: one gene does not generally affect the expression of another
How do you analyze a dihybrid cross?
- A punnett square can still be used to predict offspring but sixteen squares rather than four are necessary
- All possible combinations of the two different genes for females are written across the top, those for the male are written down the side