BIOL 2300 Lecture Notes - Lecture 2: Gamete, Genetic Recombination, Punnett Square
LECTURE 2 EVOLUTION 1
Evolution 1
• Population: a group of individuals of one species living together
o Individual is the reservoir of genetic information.
▪ DNA sequences are passed on to our offspring.
o Populations are where evolutionary change is revealed.
Individual is the Reservoir of Genetic Information
• All cells have DNA composed of 4 nucleotides arranged in an alpha helix.
o Each individual has a unique sequence of nucleotides in their DNA.
• DNA is contained on threadlike structures called chromosomes.
• Chromosomes come in matched pairs, one from each parent.
o We pass on one or the other, but not both.
• DNA is organized into discrete subunits called genes (code for proteins).
o E.g., Cystic fibrosis – a gene codes for a protein that controls the entry
of salts into cells in lungs, digestive tract
• Locus: particular location of a gene on a chromosome
• BUT may have different versions (alleles) of that gene that code for different
versions of that trait.
o E.g., blue eyes and brown eyes
Populations are Where Evolutionary Change Occurs
• Alleles: two or more alternative forms of a gene
o result from slight differences in the DNA sequence of the gene
o cause slight differences in form and function
• Homozygote – an individual that has the same alleles at a particular locus on
the pair of chromosomes (AA, aa)
• Heterozygote – an individual that has different alleles at a particular locus on
the pair of chromosomes (Aa)
2
• If one allele is fully expressed and the other has no noticeable effect
o Dominant allele – fully expressed (A)
▪ E.g., brown eyes
o Recessive allele – unexpressed (a)
▪ E.g., blue eyes
• E.g., Cystic fibrosis – both recessive allele
Genetics Review
• Mendelian Inheritance: breeding of two individuals results in multiple
combinations of alleles
o 1 allele present on each chromosome of a parent
o 1 chromosome (allele) is present in each gamete produced by a
parent
o Punnett square
• Note: AA x AA = all AA and aa x aa = all aa
• 3 genotypes are produced: AA, aa, Aa
• genetic recombination - all possible allele combinations from random mating
of any combination of individuals in a population
• Mendelian Inheritance is how genetic variation is maintained.
AA
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Document Summary
Evolution 1: population: a group of individuals of one species living together, individual is the reservoir of genetic information, dna sequences are passed on to our offspring, populations are where evolutionary change is revealed. If one allele is fully expressed and the other has no noticeable effect: dominant allele fully expressed (a, e. g. , brown eyes, recessive allele unexpressed (a, e. g. , blue eyes, e. g. , cystic fibrosis both recessive allele. Genetics review: mendelian inheritance: breeding of two individuals results in multiple combinations of alleles, 1 allele present on each chromosome of a parent, 1 chromosome (allele) is present in each gamete produced by a parent, punnett square. A aa aa a aa aa a aa aa a aa aa. Individuals with the same genotype may look different under different environmental conditions: e. g. , 1 genotype, 2 phenotypes food abundance influences body size, changes in the expression of genes.