Lecture 1

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  • Created on: 09-02-16 18:04
Who was the father of Genetics?
Mendel
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Who coined the term genetics?
Bateson
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Who coined the term gene?
Johannsen
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What did Mendel's work with peas lead to?
The discovery of dominant and recessive traits, the concept of the gene (heritable factor), the formulation of the basic laws of inheritance.
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What is a character?
It is a heritable feature of an individual
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What is a trait?
It is a variant form of a character (the phenotype)
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What is Mendel's first law of Segregation?
The two forms of a gene (alleles) present in each parent segregate independently
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How did Mendel formulate the first law?
By studying the results of monohybrid crosses
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What is a monohybrid cross?
A cross between two true breeding individuals differing in only one character.
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What is an example of this?
Inheritance of pod colour
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What were Mendel's observations of Monohybrid Crosses?
All the F1 progeny resembled one of the parents, but both of the original parental traits appeared in the F2 generation. The same pattern of inheritance was seen for all 7 of the characters he studied.
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What did Mendel conclude?
One trait is dominant and the other is recessive. The heritable factor for the recessive trait had not been lost in the F1, just masked by the presence of the factor for the dominant trait.
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What did Mendel's Model state?
That variation in inherited characteristics are due to the existence of alternative versions of heritable factors (genes) called alleles.
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For each character, an organisms inherits how many alleles?
2 - one from each parent
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If the two alleles differ, then which allele determines the organism's appearance?
The dominant
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Do the alleles blend when present in the same individual?
No, they remain discrete
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What happens to the two alleles during gamete formation?
They segregate (separate) and end up in different gametes
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Mendel's law of Segregation:
Two two forms of a gene (alleles) present in each parent segregate independently
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How many alleles does each parent have?
2
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How many alleles do the parents pass on to offspring?
They each pass on one so each offspring receives one allele from one parent and the other allele from the other parent.
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What is a punnet square?
A diagrammatic device for predicting the outcomes of crosses between parents of known genotypes.
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What is the genotype?
It is is the
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What is the phenotype?
It is the
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What is a testcross?
A method for determining the genotype of an individual with the dominant phenotype of a trait
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What is Mendel's Law of Independent Assortment?
Each pair of alleles (gene) assorts independently of each other pair or alleles (gene) during gamete formation.
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What does Mendel's law of independent assortment relate to?
The situation where the inheritance of two or more different pairs of alleles is being studied.
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How did Mendel formulate the Law of independent assortment?
By following the inheritance of two characters at the same time
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What is a cross involving parents differing in two characteristics called?
A Dihybrid cross
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How did Mendel prove his Law of Independent Assortment?
He conducted tests where the parents both had two different alleles, that reproduced to form F2 progeny that had recombinants.
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The chromosome theory of inheritance:
The association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division
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Does Meiosis result in Somatic cells or Gametes?
Gametes
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Does Mitosis result in Somatic cells of Gametes?
Somatic Cells
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Where does meiosis occur?
In the germ line
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Where does mitosis occur?
In somatic cells
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How many cell divisions are there in mitosis?
1
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How many divisions are there in meiosis?
2
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Meiosis produces how many cells?
4 haploid cells
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Mitosis produces how many cells?
2 identical diploid cells
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Is Synapse unique to meiosis or mitosis?
Meiosis
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What is the role of mitosis?
To drive growth and tissue repair
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What is the role of meiosis?
To produce haploid gametes and to introduce genetic variability
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What is a homologous pair?
The two chromosomes of a homologous pair are individual chromosomes that were inherited from different parents
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What is a chromatid?
It is one of the two identical strands of a newly replicated chromosome (not to be confused with the pair of homologous chromosomes)
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What are the sister chromatids?
The two identical chromatids are held together by a common centromere following replication.
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How many stages are there to Meiosis?
2
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What is Meiosis I?
Chromosome replication and recombination, Homologous chromosomes separate, Produces two haploid cells
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What is Meiosis II?
The chromatids separate and produce four haploid gametes
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What is the first stage of Meiosis?
Interphase
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What happens in interphase?
This precedes meiosis, the chromosomes replicate to form pairs of chromatids.
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What happens in prophase?
The parent cell chromosomes condense
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What happens in metaphase?
The chromosomes become arranged on the metaphase plate and attached to the fully formed spindle. The centrosomes are at the opposite poles of the cell.
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What happens in anaphase?
Each sister chromatid of a chromosome has spindle fibers attached to it. The spindle fibers begin to horten and pull the sister chromatids apart at the centromere.
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What happens in telophase?
The chromosomes sets assemble at opposite pole as a nuclear envelope forms around each set.
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What happens in cytokinesis?
The cytoplasm divides and daughter cells form.
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Sutton made the link between the behaviour of chromosomes during Meiosis and Mendel's Laws. He observed that...
Chromosomes occur in pairs in somatic cells, chromosome pairs segregate equally into gametes, different chromosome pairs assort independently
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What does the chromosome theory of inhericance state?
Mendel's heritable factors (or genes) are located at specific positions on chromosomes. It is the chromosomes that undergo segregation and independent assortment.
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Genes determine what?
Traits
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Each gene is located at a particular ... on a chromosome?
Locus
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What are genes that exist in different forms called?
Alleles
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How does chromosome behaviour in meiosis explain Mendel's Law of Segregation?
This occurs because each allele is on a different member of a homologous pair of chromosomes and moves to opposite poles in anaphase I.
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How does chromosome behaviour in meiosis explain Mendel's Law of independent Assortment?
This is explained by the random way that the homologous pair of chromosomes line up on the metaphase plate during meiosis I.
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What does independent assortment of chromosomes mean?
It mean that each of the 4 possible combinations of alleles at the two loci has an equal probability of occurence in the gametes.
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