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Two copies of each autosomal gene affect phenotype (physical). • Mendel studied autosomal gene traits, like hair texture. Autosome – chromosome with genes not related to sex of organism (body cells) Compared to: Sex Chromosomes: control the development of sexual characteristics – Carrier – has an allele for a trait or disease that is not expressed. – Carrier does not have disease symptoms but can pass it on to offspring. Does not have disorder Dominant allele disorders are rare. Huntington’s disease is an example of a disease caused by a dominant allele. Has disorder (dominant) • Genes on sex chromosomes are called sex-linked genes. . – Y chromosome - male characteristics . – X chromosome - genes affects many traits. Males can pass on X or Y Females only pass on X Who determines the sex of the offspring? FATHER Father – he can provide an X or Y chromosome Egg X X XX XX X X Body Cell X XX XX XY XY X XY Body Cell Y Y Sperm 1female:1male How are sex-linked genes expressed differently in phenotypes of males & females? • Males have an XY genotype; therefore... – All of a male’s sex-linked genes are expressed. – Males have no second copies of sex-linked genes to mask the effects of another allele. Therefore, you will see sex linked genetic disorders more often in males than females. – Y chromosome is much smaller • Females have an XX genotype. X chromosome inactivation -randomly “turns off” one X chromosome. Why are males more likely than females to have sex-linked genetic disorders? All sex-linked genes are expressed in males, even recessive. Females have a backup X chromosome which can mask genetic disorders. Page 203 Can you explain what is going on in this picture? Why is there a color variation between the female & male calico cats? The female calico cats have two chromosomes with different alleles for fur color. Both alleles are expressed in a random pattern. The male cat has only one X chromosome, and it’s allele for fur color is expressed across the entire body. Xº = Orange fur Xº = Black fur allele • Color blindness is a problem in which red or green look like shades of gray or other colors. • The gene is carried on the X chromosome and is a recessive trait. XC XC Y XCXC = normal female Xc XCXC XCXc XCY XcY XCXc = female, normal vision (carrier) XCY = normal vision male XcY = color blind male Neither female are colorblind – 1 female is a carrier however 1 male born normal & 1 male born colorblind • Some traits are neither totally dominant nor totally recessive. • Incomplete dominance - when neither gene/allele is completely dominant nor completely recessive to the other - Heterozygous phenotype is intermediate between the two homozygous phenotypes – Example: White flowers and red flowers produce pink flowers Codominance When both alleles of a gene are expressed- neither is dominant or recessive Disease in which the body makes sickleshaped red blood cells. Sickle-shaped cells don’t move easily through your blood vessels. They’re stiff and sticky and tend to form clumps and get stuck in the blood vessels . • Sickle Cell Anemia • R = Round blood cells • R’ = Sickle Cells R R R’ RR RR’ RR’ R’R’ RR = normal blood RR’ = some sickle cells, some normal cells R’R’ = has sickle cell anemia R’ • Codominant - alleles will both be completely expressed. – Codominant alleles are neither dominant nor recessive. – The ABO blood types result from codominant alleles. Example – red and white flower produce a flower with BOTH colors • Many genes have more than two alleles. • Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue. • Epistatic gene - can interfere with the expression of all other genes. Mice have 5 genes that control fur color. 2 genes for general color 1 for shading 1 for spots 1 epistatic gene for color that overrules all other genes • Phenotype is a combination of genotype and environment. • The sex of sea turtles depends on both genes and the environment. Warm eggs develop into females • Height is an example of a phenotype strongly affected by the environmental factors such as early nutrition and health care. Gene linkage was explained through fruit flies. (b/c could quickly and cheaply grow new generations) • Morgan found that linked traits are on the same chromosome. Traits can be inherited as a group. • Chromosomes, not genes, assort independently during meiosis. Mutant Wild type Common phenotype Different phenotype Famous Scientist Mendel said: Genes assort independently of one another. Punnett & Bateson said: (invented the punnett square) Suggested some genes are linked together Morgan said: Chromosomes, not genes assort independently. Sturtevant (Morgan’s student) said: frequency of crossovers was related to the distance bw genes. • Linked genes are not inherited together every time. • • Gene linkage: the tendency: for genes located close together on a chromosome to be inherited together. Chromosomes exchange homologous genes during meiosis. Genes Close together Linkage maps – map of location of genes on a chromosome. • The closer together two genes are, the more likely they will be inherited together. • Cross-over frequencies are related to distances between genes. How frequently a cross over will occur is related to the distance bw the genes! • 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 Study Guide worksheet page 44 Linkage Map 7.3 Cross-Over Frequencies: A-B 20% B-C 5% A D B C 0 7 20 25 A-C 25% A-D 7% D-B 13% 20-7=13 D-C 18% 25-7=18 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. Females can carry sex-linked genetic disorders. • Males (XY) express all of their sex linked genes. • Expression of the disorder depends on which parent carries the allele and the sex of the child. X chromosome carries about 1100 genes while the Y carries about 250 Pedigree - chart used 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. How can you tell if a chromosome is a autosome or a sex chromosome? If the same # of male & female have the phenotype then the gene is most likely autosome. Widow’s peak: W = widow’s peak w = non widow’s peak • If the phenotype is more common in males, the gene is likely sex-linked. Colorblindness: M = normal vision m = colorblindness Several methods help map human chromosomes. • Karyotype - a picture of all chromosomes in a cell. Shows changes in chromosomes. Ex: if you have an extra chromosome Two methods used to study human chromosomes: 1.Pedigrees 2. Karyotypes XY • 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