Human Genetics Chapter 7

1. Human GeneticsChapter 7

2. 23 23 The Role of Chromosomes A. Chromosome number 1. Each human sperm/egg has 23 chromosomes 2. Each human body cell has 23 pairsof chromosomes 3. Each type of organism has a different number of chromosomes. Humans - 46 chromosomes Fly – 8 chromosomes Cat – 38 chromosomes 23 PAIRS

3. Chromosome number - The last pair of chromosomes, or the 23rd pair are called the sex chromosomes. - Males have an X and a Y chromosome (XY) - Females have two X chromosomes (XX) - Autosomes do not determine a person’s gender. They are body chromosomes. They determine ones characteristics! - Chromosome #1-22 The Role of Chromosomes

4. X & Y Chromosomes& Traits • X chromosome much larger than the Y

5. A way to tell chromosome number Karyotype Amniocentesis, a sampling of the fetal fluidwhich then can help determine if there are any geneticdisordersof the developing fetus. Geneticist will look at the chromosomes of the fetus.

6. Human Traits A. Incomplete dominance, neither allele/gene is completely dominant nor completely recessive. - Heterozygous phenotype is in betweenthe two homozygous phenotypes - individual is a blend Snap dragons (flowers) RR= Red WW= White If a red snap dragon were crossed with white snapdragon, the heterozygous plant would be PINK! RR x WW Offspring = RW = pink

7. Codominance - Codominant alleles/genes are both fully and separatelyexpressed. - Both phenotypes are shown in the Heterozygousindividual. - Black hamster crossed with a white hamster - BB X WW - The heterozygous individual BW, would be both black and white in color. B B W BW BW W BW BW

8. More Codominance Normal Red Blood Cell Sickled Red Blood Cell • African American Population • Resistance to Malaria

9. Sickle Cell • NN= Normal Blood Cells • SS=Sickled Blood Cells • NS = Both Normal and Sickled Cells • Cross a heterozygous mom with a heterozygous dad for blood cells. Parent genotypes: Genotypes: Phenotypes:

10. Co-dominance and Multiple Alleles in Blood Types Example: Blood Types The four blood types are Type A, Type B, Type AB, Type O

11. Codominant alleles are neither dominant nor recessive. • The ABO blood types result from codominant alleles. • Codominant alleles will both be completely expressed. • The 3 multiple alleles are A, B, and O • Aand B are always dominantto O (i). • IAi = _____ type blood IAIA = _____ type blood • IBIB = _____ type blood IBi = ____ type blood

12. A and B are NOT dominantto each other, they are Codominant • AB genotype would look like this… IAIB So remember… There are 3 alleles(A, B, O), however there are 4 blood types. (A, B, AB, O)

13. IAIA IAi IBi IAIB IA i IA GenesBlood type ii O type IAIBAB type IAIA or IAi A type IBIB or IBi B type Cross a woman Heterozygous for A-blood and a man with AB-blood • Parent genotypes: • Genotypes: • Phenotypes: IB IAi x IAIB 1IAIA:1IAIB:1IAi:1IBi 1: AB type 2: A-type 1: B-type

14. NOW YOU TRY: Bb x Bb as Complete, Incomplete, & Co- Dominance 1:BB 2:BW 1:WW 1:BB 2:Bb 1:bb 1:BB 2:BW 1:WW 1:Black 2:Black & White 1:White 3:Black 1:White 1:Black 2:Grey 1:White

15. Polygenic Traits • Polygenic traitsare produced by two or more genes. • This occurs when many genes interact to produce one trait. • Order of dominance: brown > green > blue. • Example: Eye Color, skin color, height

16. X Y X X C. Sex-linked traits - Genes on the X chromosome 1. Only the X Chromosome carriesgenes so if a gene is on the X chromosome, the female would have TWO of those genes and the male would have only ONE. Female that has the disorder Female carrier for a disorder Male that has the disorder

17. Sex-linked traits • A genetic disorder that is found or linked to the X chromosomeONLY • Females can carry a sex-linked genetic disorder and not have the disorder. • This is known as being a carrier of the disorder. • In order for the female to have the disorder both Xchromosomes must have the gene for the disorder • Males (XY) express all of their sex linked genes because they only have one X chromosome. • If the X chromosome has the gene, the male has the disorder. • Males can not be carriers because they only have one X chromosome • Examples: HemophiliaandColorblindness

18. Y X X X 1. Colorblindness a sex-linked recessivetrait. (C- normal vision; c- colorblindness) • In order for a female to be color blind, she would have to have two colorblind genes. • A maleneeds to only have one colorblind gene.

19. Colorblindness - is a sex-linked recessive trait. (C- normal vision; c- colorblindness) • In order for a female to be color blind, she would have to have this many colorblind genes. _______ • A male needs to have this many _______ • It is more likely to have a colorblind male than a colorblind female because ______________________________________ 2 1 The male only needs one gene

20. What do you see?

21. X N Xn Xn Y A woman is heterozygous for Normal vision. She marries a man who is colorblind. What is the predicted colorblindness outcome for their children? LET … N = normal vision and n = color blind Parent genotypes: XN XnxXnY Mom Dad FIND THE: Genotypic Ratio: Phenotypic Ratio:

22. X N Xn Xn Y Answer: LET … N = normal vision and n = color blind MOM = heterozygous normal vision. XN Xn DAD = colorblind.XnY Genotypic Ratio 1XNXn : 1XnXn : 1 XNY : 1 XnY Phenotypic Ratio1 normal female carrier : 1 colorblind female : 1 Normal male : 1 colorblind male XNXn XnXn XnY XNY

23. X Chromosome Inactivation • Males and females can differ in sex linked traits. • The expression of genes on the sex chromosomes differs from the expression of autosomal genes. • Genes located on the sex chromosomes are called sex- linked genes or X-linked genes. • Males express all of the alleles on both sex chromosomes. • In females one of the two X chromosomes is randomly turned off by a process called X chromosome inactivation.

24. Environment + Genes • Your phenotype is not just dependent on your genes, but also the environment • Examples • Sea turtles gender –determined by the temp of sand • Gender of alligators – determined by temp. • Height of people- influenced by nutrition

25. A pedigree is a chart for tracing genes in a family. • Phenotypes are used to infer genotypes on a pedigree. • Autosomal genes show different patterns on a pedigree than sex-linked genes.