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Biology Unit Four D– Human Genetics and Pedigrees Mrs. Pearson’s First Semester Biology *For those watching by recording, watch for questions on the slides throughout the presentation. Email me the answers to the questions within two days of the lesson being presented in order to receive credit for watching the recording. AND THE WINNER IS… • Food Spoilage!! – Because I won’t know what foods I can use until I get there, I will do it in reverse and run the Costa Rica piece first and the Wisconsin piece second. – Because the amount of “critters” in Costa Rica, I will use a container with a thin fabric screen and will not leave it outside. Let’s have a hand for… • • • • • • • • • • • • Caitlyn Abbott Kristen Barstow Sabrina Haug Leeanna Heinrichs Melissa Hunt Christopher King Kayla Morris Chyenne Nechkash Emily Patik Courtney Pigeon Dana Radtke Stephanie Spatz The Prize • 50 extra credit points OR • 100% on one lab not yet completed (be sure to tell me which one) • Email Mrs. P today with your choice! 7.3 Gene Linkage and Mapping KEY CONCEPT Genes can be mapped to specific locations on chromosomes. 7.3 Gene Linkage and Mapping Lesson Objectives • Discuss gene linkage and mapping • Discuss expression of sex-linked traits • Understand pedigrees and karyotypes 7.3 Gene Linkage and Mapping Gene linkage was explained through fruit flies. • Morgan found that linked traits are on the same chromosome Wild type Mutant 7.3 Gene Linkage and Mapping Chromosomes, not genes, assort independently during meiosis • Remember that meiosis is the making of sperm and egg cells • Remember that during meiosis the cell divides in such a way that only half of the genetic material will be passed on • So what does it mean when we say that the chromosomes assort independently? 7.3 Gene Linkage and Mapping Chromosomes, not genes, assort independently during meiosis • Maybe they will separate like this… 4 4 4 4 7 7 7 7 7.3 Gene Linkage and Mapping Chromosomes, not genes, assort independently during meiosis • BUT maybe they will separate like this… 4 4 4 4 7 7 7 7 7.3 Gene Linkage and Mapping Chromosomes, not genes, assort independently during meiosis • They are independent – don’t have to separate the same 4 4 4 4 7 7 7 7 7.3 Gene Linkage and Mapping • Linked genes are not inherited together every time. • Chromosomes exchange homologous genes during meiosis – what do we call this process? 7.3 Gene Linkage and Mapping Linkage maps estimate distances between genes. • The closer together two genes are, the more likely they will be inherited together. • Cross-over frequencies are related to distances between genes. • Linkage maps show the relative locations of genes. 7.3 Gene Linkage and Mapping • When crossing over happens here, genes A and B stay together. A B A B A B A B 7.3 Gene Linkage and Mapping • But, when crossing over happens here, genes A and B get separated. • When genes are close to each other on the chromosome, it’s more likely that they will be inherited together. A B A B A B A B 7.3 Gene Linkage and Mapping • Cross-over frequencies can be converted into map units. – gene A and gene B cross over 6.0 percent of the time – gene B and gene C cross over 12.5 percent of the time – gene A and gene C cross over 18.5 percent of the time **Those watching by recording, include in your email why genes A and B would be more likely to be linked than A and C. 7.4 Human Genetics and Pedigrees KEY CONCEPT A combination of methods is used to study human genetics. 7.4 Human Genetics and Pedigrees Human genetics follows the patterns seen in other organisms. • The basic principles of genetics are the same in all sexually reproducing organisms. – Inheritance of many human traits is complex. – Single-gene traits are important in understanding human genetics – why? **Those watching by recording, include in your email why single-gene traits are important in understanding human genetics. 7.4 Human Genetics and Pedigrees Females can carry sex-linked genetic disorders. • Males (XY) express all of their sex linked genes – why? • Expression of the disorder depends on which parent carries the allele and the sex of the child – why? Y X 7.4 Human Genetics and Pedigrees What chromosome will the mom give to the baby? The X or the Y chromosome? Why? • She will always give the baby an X chromosome because that is all she has. • So… if mom is a carrier of a sex-linked disease, will her daughters have the disease? • Her daughters will only have the disease if they receive mom’s X chromosome that has the disease gene Y on it AND X they receive an X chromosome from dad with the disease gene on it. • They might be a carrier. • They might not be a carrier • Will her sons have the disease? 7.4 Human Genetics and Pedigrees What chromosome will the mom give to the baby? The X or the Y chromosome? Why? • Will her sons have the disease? • Her sons will only have the disease if they receive mom’s X chromosome that has the disease gene on it. Y X 7.4 Human Genetics and Pedigrees What chromosome will the dad give to the baby? The X or the Y chromosome? • The dad’s sons will receive the Y chromosome from their dad. • The dad’s daughters will receive the X chromosome from their dad. • If the dad has a sex-linked disease gene on his X chromosome, will his daughters have the disease? Y X • They will ONLY have the disease if they also receive an X chromosome from their mom that ALSO has the disease gene on it. • If they do not have the disease, will the daughters be carriers? • Yes – they will for certain have the disease gene from the X chromosome from their dad. 7.4 Human Genetics and Pedigrees What chromosome will the dad give to the baby? The X or the Y chromosome? • If the dad has a sex-linked disease on the Y chromosome, will his sons have the disease? • Yes – they can only receive the Y chromosome from their dad so they will have the disease. Y X 7.4 Human Genetics and Pedigrees A pedigree is a chart for tracing genes in a family. • Phenotypes are used to infer genotypes on a pedigree – which phenotype would help the most in determining unknown genotypes? • Autosomal genes show different patterns on a pedigree than sex-linked genes. 7.4 Human Genetics and Pedigrees • If the phenotype is more common in males, the gene is likely sex-linked – why? 7.4 Human Genetics and Pedigrees Several methods help map human chromosomes. • A karyotype is a picture of all chromosomes in a cell. ** Those watching by recording, include in your email whether the person this karyotype came from was male or female. XY 7.4 Human Genetics and Pedigrees • Karyotypes can show changes in chromosomes. – deletion of part of a chromosome or loss of a chromosome – large changes in chromosomes – extra chromosomes or duplication of part of a chromosome 7.4 Human Genetics and Pedigrees Review • Linkage maps estimate distances between genes • Human genetics follows the patterns seen in other organisms • Females can carry sex-linked genetic disorders • A pedigree is a chart for tracing genes in a family • If the phenotype is more common in males, the gene is likely sex-linked • A karyotype is a picture of all chromosomes in a cell 7.4 Human Genetics and Pedigrees Questions?