Genetics amazonaws com
Genetics You are on a research expedition to China and discover a previously unknown organism bearing closest resemblance to amspecies of deer known as the Indian muntjac. 3 chromosome pairs Indian muntja
23 Chromosome pairs Your organism
You tentatively think you have identified a close relative to the Indian muntjac. However, when you karyotype each organism, you find the Indian muntjac has 3 chromosme pairs and your organism has 23 pairs. You conclude: A. Your organism is likely to have more genes B. Your organism is likely to have more complex phenotypes C. All of the above D. None of the above
3 chromosome pairs Indian muntjac
23 chromosome pairs Your organism
You can make no firm predictions about gene content of the genomes from the karyotype Does a larger genome mean more genes? - no: human genome has 3.4 billion base pairs - worm: 100 million base pairs - BUT number of genes in human and worm: both ~20thousand genes Does a more “complex” organism have more genes? - more complex than worm, still have about same genes - drosphila fly: only has 14 thousand genes vs worm w/ 20thousand genes - would think fly more complex but has less genes - however one gene in drosophila that can be alternatively spliced into 35 thousand different
Mitosis in diploid cell
Mitosis in haploid cell
Meiosis: makes haploid cells, don't need to do meiosis in haploid (can't reduce 1N)
Meiosis
What is going on at the molecular level during the formation of sister chromatids?
DNA molecules replicate to form identical chromatids
Null: no gene function
Can we track single gene inheritance at the DNA level? • Saves time • A morphological phenotype not necessarily needed • Can distinguish heterozygous from homozygous states Restriction Enzymes can cut DNA in a sequence specific way
Palindrome!
Single-gene inheritance tracked at the DNA level
What is the evidence for the chromosomal theory of inheritance? How do we know genes reside on chromosomes? Thomas Hunt Morgan 1910-1911 experiments w/ model organism Drosophila melanogaster
Human sex chromosomes
Red-eyed and White-eyed Drosophila • mutant gene: white gene → needed for eye pigmentation • white-eyed gene encodes a transporter protein that trasnsports protein to eye • pigments being made in mutant, but no pigments being deposited in eye
← Male Drosophila have only one X
An example of X-linked inheritance • all F1 red eyes • red eyes dominant over white Second cross • 3:1 → red: white • but all white eyed fliew were male! • Maybe the white eyed females are dead? Third cross • F1 female x white male (back cross)s • half males red, half white • half females red, half white
Third cross
model: the white mutation was on the x chromosome Test of the model: Reciprocal crosses yielded different F1 results
• • •
first observation of a gene trait (white eyes) that segregated with gender. best evidence that genes reside on chromosomes Morgan’s experiments in 1910 with the white eye fly was the birth of modern day genetics
Human Pedigree Analysis • •
breeding experiments cannot be applied to humans but careful analysis of family pedigrees can help determine the genetic basis of a particular condition
Person under study
23 Chromosome pairs Your organism
You tentatively think you have identified a close relative to the Indian muntjac. However, when you karyotype each organism, you find the Indian muntjac has 3 chromosme pairs and your organism has 23 pairs. You conclude: A. Your organism is likely to have more genes B. Your organism is likely to have more complex phenotypes C. All of the above D. None of the above
3 chromosome pairs Indian muntjac
23 chromosome pairs Your organism
You can make no firm predictions about gene content of the genomes from the karyotype Does a larger genome mean more genes? - no: human genome has 3.4 billion base pairs - worm: 100 million base pairs - BUT number of genes in human and worm: both ~20thousand genes Does a more “complex” organism have more genes? - more complex than worm, still have about same genes - drosphila fly: only has 14 thousand genes vs worm w/ 20thousand genes - would think fly more complex but has less genes - however one gene in drosophila that can be alternatively spliced into 35 thousand different
Mitosis in diploid cell
Mitosis in haploid cell
Meiosis: makes haploid cells, don't need to do meiosis in haploid (can't reduce 1N)
Meiosis
What is going on at the molecular level during the formation of sister chromatids?
DNA molecules replicate to form identical chromatids
Null: no gene function
Can we track single gene inheritance at the DNA level? • Saves time • A morphological phenotype not necessarily needed • Can distinguish heterozygous from homozygous states Restriction Enzymes can cut DNA in a sequence specific way
Palindrome!
Single-gene inheritance tracked at the DNA level
What is the evidence for the chromosomal theory of inheritance? How do we know genes reside on chromosomes? Thomas Hunt Morgan 1910-1911 experiments w/ model organism Drosophila melanogaster
Human sex chromosomes
Red-eyed and White-eyed Drosophila • mutant gene: white gene → needed for eye pigmentation • white-eyed gene encodes a transporter protein that trasnsports protein to eye • pigments being made in mutant, but no pigments being deposited in eye
← Male Drosophila have only one X
An example of X-linked inheritance • all F1 red eyes • red eyes dominant over white Second cross • 3:1 → red: white • but all white eyed fliew were male! • Maybe the white eyed females are dead? Third cross • F1 female x white male (back cross)s • half males red, half white • half females red, half white
Third cross
model: the white mutation was on the x chromosome Test of the model: Reciprocal crosses yielded different F1 results
• • •
first observation of a gene trait (white eyes) that segregated with gender. best evidence that genes reside on chromosomes Morgan’s experiments in 1910 with the white eye fly was the birth of modern day genetics
Human Pedigree Analysis • •
breeding experiments cannot be applied to humans but careful analysis of family pedigrees can help determine the genetic basis of a particular condition
Person under study
