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Introduction to Genetics

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by

Greg Evans

on 21 January 2014

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Transcript of Introduction to Genetics

11.2 - Probablility and Punnett Squares
11.1 - The Work of Gregor Mendel
11.3 - Exploring Mendelian Genetics
11.4 - Meiosis
11.5 - Linkage and Gene Maps
Introduction to Genetics
Genes and Dominance
Mendel studied seven different pea plant traits
trait - specific characteristic, such as seed color or plant height
hybrid - the offspring of a cross between parents with different traits
genes - chemical factors that determine traits
alleles - different forms of a gene
Segregation
Had the recessive alleles disappeared or were they still present in the F generation?
1
The F Cross
1
When the F plants were crossed with each other 1/4 of the offspring showed the recessive allele.
1
Genetics and Probability
Probability is the likelihood that
a particular event will occur.
Probability can be used to predict
the outcomes of genetic crosses.
Punnett Squares
Punnett squares are diagrams that show the combinations of genes that could result from a genetic cross.
Organisms that have two identical alleles are homozygous.
Organisms that have two different alleles are heterozygous.
The round seeds have the same phenotype but not the same genotype.
Independent Assortment
Two-Factor Cross: F
1
Mendel crossed true breeding green pods with yellow seeds, and produced offspring with green pods and yellow seeds.
Two-Factor Cross: F
1
All the F plants were heterozygous.
How would the alleles segregate?
Would the dominant alleles stay together?
1
*Genes for different traits can segregate
independently during the formation of gametes.
A Summary of Mendel's Principles
Beyond Dominant and Recessive Alleles
Mendel's Principles are only principles and not laws, because many traits are controlled by multiple genes or neither dominant or recessive.
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic Traits
Applying Mendel's Principles
Chromosome Number
Body cells contain two sets of homologous
chromosomes.
Gametes of sexually reproducing organisms have only one set of chromosomes
Haploid = "one set"
Diploid = "two sets"
Homologous = each chromosome that came from the male parent has a corresponding chromosome from the female parent.
Phases of Mitosis
The process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Two Stages:
Meiosis I
Meiosis II
Tetrad = 4 chromotids
shared between two
homologous chromosomes
Crossing-over =
portions of chromotids
are exchanged between
homologous chromosomes
Phases of Mitosis
The cells do not replicate the chromosomes before entering Meiosis II.
Gamete Formation
In males the haploid gametes are called sperm.
plants produce pollen which contain haploid sperm cells
In females the haploid gametes are called eggs.
cell divisions in meiosis I and Meiosis II are uneven and produce 1 egg and 3 polar bodies
Linkage Groups = genes that tend to be inherited together
ie. sex linked traits
Gentic Mapping is a way of assigning DNA fragments to chromosomes.
Full transcript