EEB 390 Lecture Notes - Lecture 4: Zygosity, Gamete, Meiosis
9 Oct 2020
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Lecture 4
Sources of variation
• We know there is a lot of natural variation
• We can artificially select for specific traits
In diploid organisms there is the joining of genetic material from two
parents and process of meiosis, crossing over, segregation of homologous
chromosomes
!pea plants
Law of segregation
•Law of segregation: every individual has two gene copies at a locus and these
copies segregate during gamete production so only one goes into a gamete
•Locus: physical location of the gene on the chromosome
•Gametes: sex cells of an organism (think sperm and egg)
• two copies assumes a diploid organism (some are more complicated)
•allele: gene variant (in this case R and r are both alleles)
•homozygote: individual with the same alleles for a locus (rr or RR)
•heterozygote: individual with different alleles for a locus (Rr)
•dominant: an allele is dominant if in a heterozygote has the phenotype of
the allele
•recessive: an allele is recessive if the phenotype is not expressed in a
heterozygote
•R is dominant because Rr show the RR phenotype
•r is recessive (only showing when homozygous)
Dominant/Recessive
• Brown eyes are dominant, green eyes are recessive
• Polydactyly (having more than 5 figures or toes) is dominant—the allele is quite rare, when
people are born like this infant have it surgically removed
• Reactive to poison ivy is recessive.
Law of independent assortment
• Law of independent assortment: the allele passed for one trait is independent of the allele for
another trait at another locus for a gamete
• two traits are randomly passed to offspring (independently) this assumes that genes are not
linked
Linked vs. Unlinked
•Linkage disequilibrium: the presence of statistical association between alleles at different loci
•for genes on the same chromosome, there is the
potential that they tend to be correlated, linked
• when they are physically closer the pattern is stronger
What does this mean for evolution?
• chromosomal crossover and segregation produce
gametes help produce novel allele combinations in
offspring
• beginning a link between genotype and phenotype
• dominant, recessive
Molecular genetics
• Going from genotype to molecular phenotype (DNA to proteins)
Eukaryotic chromosomes
• DNA tightly around in histone
DNA
DNA transcribed into RNA
Transcription: RNA polymerase reads coding sequence of DNA
and produces complementary RNA, messenger RNA (mRNA)
Translation: process where strand of mRNA is decoded by a
ribosome to produce an amino acid
Genetic code
•redundancy: CUU, CUC, CUA,CUG all code for Leucine
•codon: three nucleotides (usually an amino acid)
•stop codons (FYI, start codon is usually AUG)
Gene regions
• RNA polymerase binds to the promoter region that signals where to begin transcription
• introns are not encoded into proteins but can serve important regulatory functions or provide
spacing and secondary structure
•exons are encoded into proteins
Remember there are non coding regions
• Non-coding regions: regulatory elements, pseudogenes, genes encoding functional RNA
molecules (microRNA)
Regulation (how much RNA is produced)
•regulatory elements control rate of transcription of RNA to DNA (and how much
it is being expressed)
•expression: process of gene being transformed into a product
• The more it is expressed the more product
• transcription can be complex and transcription factors are proteins integral to
controlling transcription
• expression and transcription control the phenotype (or the function and form) of the
individual
Alternative splicing
• A particular gene region can be alternatively spliced indifferent regions to
make different proteins
• One gene can make different proteins based what eons are included
• Proteins made from the alpha-tropomyosin gene by alternative splicing.
Orange boxes are introns in the mRNA. The tissues in which these
proteins are found are listed.
Document Summary
Sources of variation: we know there is a lot of natural variation, we can arti cially select for speci c traits. In diploid organisms there is the joining of genetic material from two parents and process of meiosis, crossing over, segregation of homologous chromosomes pea plants. Law of independent assortment: the allele passed for one trait is independent of the allele for another trait at another locus for a gamete two traits are randomly passed to offspring (independently) this assumes that genes are not linked. What does this mean for evolution? chromosomal crossover and segregation produce gametes help produce novel allele combinations in offspring: beginning a link between genotype and phenotype, dominant, recessive. Molecular genetics: going from genotype to molecular phenotype (dna to proteins) Eukaryotic chromosomes: dna tightly around in histone. Transcription: rna polymerase reads coding sequence of dna and produces complementary rna, messenger rna (mrna)
