Lecture 1 Genetics Flashcards
What was Gregor Mendel known as & when was he alive?
The father of genetics
1822-1884
What did Gregor Mendel’s work with peas lead to? (3)
- The discovery of dominant and recessive traits
- The concept of the gene (‘heritable factor’)
- The formulation of the basic laws of inheritance
What is a character?
A heritable feature of an individual e.g flower colour
What is a trait?
A variant form of a character (the phenotype)
E.g. purple flower colour
What is Mendel’s first law in The Law of Segregation?
The two forms of a gene (alleles) present in each parent segregate independently
Law formulated by studying results of monohybrid crosses
What is a monohybrid cross?
A cross between two true-breeding individuals differing in only one character
What did Mendel’s model tell us? (5)
- Variations in inherited characteristics are due to the existence of alternative versions of heritable factors (genes) - called alleles
- For each character, an organism inherits 2 alleles, one from each parent
- If the 2 alleles differ, then the dominant allele determines the organism’s appearance (phenotype)
- The alleles do not blend when present in the same individual they remain discrete
- The 2 alleles segregate during gamete formation and end up in different gametes
What is a punnett square ?
A diagrammatic device for predicting the outcomes of crosses between parents of known genotype
How can we distinguish between heterozygote and dominant homozygote?
Testcross - a method for determining the genotype of an individual with the dominant phenotype of a trait
Involves crossing it with a homozygous recessive individual
If GG dominant homozygote 100% offspring dominant
If Gg heterozygote 50:50
What is Mendel’s law of Independent Assortment?
Each pair of alleles (genes) assorts independently of each other pair of alleles (gene) during gamete formation
How did Mendel formulate the Law of independent assortment?
Followed inheritance of 2 characters at the same time
Used dihybrid cross - cross parents differing in 2 characters
What did Walter Sutton find ?
Sutton made the link between the behaviour of chromosomes during meiosis and Mendel’s laws
Homologues
appear alike under the microscope, but they have different versions of genes at some of their corresponding loci
What did Sutton observe? (3)
1.Chromosomes occur in pairs in somatic cells
- Chromosome pairs segregate equally into gametes
- Different chromosome pairs assort independently
What does the Chromosome Theory of Inheritance state? (2)
- Mendel’s ’heritable factors’ (or genes) are located at specific positions (loci) on chromosomes
- It is the chromosomes that undergo segregation and independent assortment
How does chromosome behaviour in meiosis explain Mendel’s Law of segregation? (2)
- The two alleles present in each diploid parent segregate independently (i.e. only one is passed to each progeny)
- because each allele is on a different member of a homologous pair of chromosomes and moves to opposite poles in anaphase I
How does chromosome behaviour in meiosis explain explain Mendel’s law of independent assortment? (2)
- Different pairs of alleles (genes) assorts independently independently to produce different combinations in the progeny
- This is explained by the random way the homologous pairs of chromosomes line up on the metaphase plate during meiosis I
