* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Survey
Document related concepts
Behavioural genetics wikipedia , lookup
Medical genetics wikipedia , lookup
Gene expression programming wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Sexual dimorphism wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genomic imprinting wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Genome (book) wikipedia , lookup
Microevolution wikipedia , lookup
Designer baby wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Y chromosome wikipedia , lookup
Neocentromere wikipedia , lookup
Transcript
Genetics Notes Part II Sex Determination O Each cell in your body (somatic cells), except for gametes, contains 46 chromosomes, or 23 pairs of chromosomes. O One pair of these chromosomes, the sex chromosomes, determines an individual's gender. O The other 22 pairs of chromosomes are called autosomes. The Sex Chromosomes O There are two types of sex chromosomes—X and Y. O X chromosome is larger than the Y chromosome. O X chromosome carries a variety of genes that are necessary for the development of both females and males. O Y chromosome mainly has genes that relate to the development of male characteristics. O XX - Females – have 44 autosomes (22 pair) plus 2 X chromosomes (44 + XX) – The only possibility that a female can offer is “X” O XY - Males – have 44 autosomes (22 pair) plus 1 X and 1 Y chromosome (44 + 1 X + 1 Y) O The offspring's gender is determined by the combination of sex chromosomes in the egg and sperm cell O When gametes (sex cells) are formed, the number of chromosomes reduces by ½ (haploid) O (22 + X) = gamete of female (egg or ovum) O (22 + X) or (22 + Y) = gamete of male (sperm) Only sex chromosomes are shown. We can use a Punnett Square to determine the possible sex of the offspring. Alleles: XX = female XY = male Cross a male and a female = XY x XX •Father (sperm) determines the sex of the offspring. Twins O There are two types of twins: O Fraternal twins – these individuals arise from and develop from separate eggs fertilized by separate sperm. They are not necessarily alike O Identical twins – These individuals started as a single egg fertilized by one sperm. After the first division of the egg, the 2 cells separate and start dividing all over again. It may result in identical twins, triplets, etc…. *Will have the same genetic code Sex Linked Traits O Traits controlled by genes located on the X chromosome are called sex-linked traits, or X-linked traits. O The sex-linked trait is represented by writing the allele on the X chromosome. Common Sex Linked Traits O Red-green color blindness recessive X-linked trait. About 8 percent of males in the United States have red-green color blindness. red-green color blindness is very rare in females. People who are colorblind See shades of grey instead of red or green Why is this trait so rare in females? O Because males have only one X chromosome, they are affected by recessive X-linked traits more often than are females. O Females are less likely to express a recessive X-linked trait because the other X chromosome may mask the effect of the trait. O In genetics, a carrier is an individual who has the gene but not the disease. For X-linked traits, the carrier will be a female. O The possible outcomes of a sex linked characteristic are as follows: Females: Normal, Normal Carriers, Inflicted (have the condition) Males: Normal or inflicted Ex. Cross a colorblind male with a female who is normal, but is a carrier. Ex. Cross a colorblind male with a female who is normal, but is a carrier. Hemophilia O Hemophilia, another recessive sex-linked disorder, is characterized by delayed clotting of the blood. O Hemophilia is sometimes called “free bleeding.” O more common in males than in females Ex. Cross a normal female with a male who is a hemophiliac. Ex. Cross a normal female with a male who is a hemophiliac. Multiple Alleles Not all traits are determined by two alleles. Some forms of inheritance are determined by more than two alleles referred to as multiple alleles. An example of such a trait is human blood group. Blood groups in humans The ABO blood group has three forms of alleles O IA is blood type A; IB is blood type B; and i is blood type O. Type O is the absence of AB O Each individual can only have two of the alleles O Note that allele i is recessive to IA and IB. O However, IA and IB are codominant; blood type AB results from both IA and IB alleles. O the ABO blood group is an example of both multiple alleles and codominance. Blood Allele Combinations X A A B O B O Blood Allele Combinations X A A B O B O Blood Types A B AB O Possible Genotypes AA or AO BB or BO AB OO O Blood typing is not connected in any way with the sex chromosomes O Blood type is genetically determined by the presence or absence of a specific complex carbohydrate found on the surface of red blood cells Rh Factors O The Rh blood group includes Rh factors, inherited O O O O O from each parent. Rh is another important antigen found on the surface of red blood cells Rh factors are either positive or negative (Rh+ or Rh-); People who have this protein are said to be Rh+ 85% of humans have the Rh+ Rh+ is dominant. The Rh factor is a blood protein named after the rhesus monkey because studies of the rhesus monkey led to discovery of the blood protein. Rh- mothers must be careful! O If both parents are positive or if both are negative O O O O everything is ok. If the father is Rh- and the mother is Rh+ everything is ok BUT if the mother is Rh- and the father is Rh+ problems can arise – a condition known as Erthroblastosis When an Rh- mother gives birth to an Rh+ infant, the Rhmother begins to make anti-Rh antibodies which can be fatal for future pregnancies. The treatment is typically “RhoGAM” a blood product that can suppress the ability to respond to Rh+ red blood cells More Multiple Alleles O Multiple alleles can demonstrate a hierarchy of dominance. O In rabbits, four alleles code for coat color: C, cch, ch, and c. O the hierarchy of dominance can be written as C > cch > ch> c. O Full color is dominant over chinchilla, which is dominant over Himalayan, which is dominant over albino. In humans…. O Eye color and skin tone are both examples of traits that have multiple alleles Importance of Multiple Alleles O The presence of multiple alleles increases the possible number of genotypes and phenotypes. GENETIC DIVERSITY! Visible traits can be influenced by more than the genotype. Hormones and Chemicals O Genes are present in both male and females, but show up only in one sex due to the presence of sex hormones. The examples of this are a man’s beard, development of breasts and the plumage in birds. These occur because of the hormone testosterone (in males) and estrogen (in women). Genes – Protein - Hormones O Hormones are like messengers in your body that give orders to your cells to do particular things. O Chemicals that are manufactured by glands and released into the bloodstream, sort of holding a sign up with a type of cell's name on it (like a limo driver at the airport waiting to pick up a client.) O Most cells ignore the hormone, but when it comes across the right one its chemical "message" is read and the cell starts to do what it has been told. O The X and Y chromosomes code for different hormones. Environmental Influences The environment also has an effect on phenotype. O For example, the tendency to develop heart disease can be inherited. However, environmental factors such as diet and exercise also can contribute to the occurrence and seriousness of the disease. O Sunlight, water, and temperature are environmental influences that commonly affect an organism's phenotype. O The cat's tail, feet, ears, and nose are dark. These areas of the cat's body are cooler than the rest. The gene that codes for production of the color pigment in the Siamese cat's body functions only under cooler conditions. Therefore, the cooler regions are darker; and the warmer regions, where pigment production is inhibited by temperature, are lighter. Polygenic Traits O You have examined traits determined by a pair of genes. O Many phenotypic traits, however, arise from the interaction of multiple pairs of genes. Such traits are called polygenic traits. Traits such as skin color, height, eye color, and fingerprint pattern are polygenic traits. O Human skin color is thought to be controlled by 12 genes! END DAY 1 More Genetics Karyotype Studies O The study of genetic material does not involve the study of genes alone. O Scientists also study whole chromosomes by using images of chromosomes stained during metaphase. O The staining bands identify or mark identical places on homologous chromosomes. Karyotype O During metaphase of mitosis, each chromosome has condensed greatly and consists of two sister chromatids. O The pairs of homologous chromosomes are arranged in decreasing size to produce a micrograph called a karyotype Karyotype O Karyotypes of a human male and a human female, each with 23 pairs of chromosomes Notice that the 22 autosomes are matched together with one pair of nonmatching sex chromosomes. Karyotype Nondisjunction During cell division, the chromosomes separate, with one of each of the sister chromatids going to opposite poles of the cell. Therefore, each new cell has the correct number of chromosomes. If sister chromatids fail to separate properly in cell division nondisjunction occurs Nondisjunction O If nondisjunction occurs during meiosis I or meiosis II, the resulting gametes will not have the correct number of chromosomes. O When one of these gametes fertilizes another gamete, the resulting offspring will not have the correct number of chromosomes. Nondisjunction O Notice that nondisjunction can result in extra copies of a certain chromosome or only one copy of a particular chromosome in the offspring. O Trisomy set of three chromosomes of one kind O Monosomy only one of a particular type of chromosome Nondisjunction O Nondisjunction can occur in any organism in which gametes are produced through meiosis. O In humans, alterations of chromosome numbers are associated with serious human disorders, which can be fatal. Down Syndrome O One of the earliest known human chromosomal disorders is Down syndrome. It is the result of an extra chromosome 21. O one out of 800 O The frequency of Down syndrome increases with the age of the mother. Studies have shown that the risk of having a child with Down syndrome is about six percent in mothers who are 45 and older. Sex Chromosomes O Nondisjunction occurs in both autosomes and sex chromosomes. Some of the results of nondisjunction in human sex chromosomes are: O Turner’s syndrome and Klienfelter’s syndrome O Note that an individual with Turner's syndrome has only one sex chromosome. This condition results from fertilization with a gamete that had no sex chromosome. Pedigree O a scientist studies a family history using a pedigree, a diagram that traces the inheritance of a particular trait through several generations. O A pedigree uses symbols to illustrate inheritance of the trait. Males are represented by squares, and females are represented by circles Pedigree O Pedigrees help genetic counselors determine whether inheritance patterns are dominant or recessive. Once the inheritance pattern is determined, the genotypes of the individuals can largely be resolved through pedigree analysis. Analyzing a Pedigree O One who expresses the trait being studied is represented by a dark, or filled, square or circle O One who does not express the trait is represented by an unfilled square or circle O A horizontal line between two symbols shows that these individuals are the parents of the offspring listed below them. O Offspring are listed in descending birth order from left to right and are connected to each other and their parents. O A pedigree uses a numbering system in which Roman numerals represent generations, and individuals are numbered by birth order using Arabic numbers. O This pedigree shows the inheritance of the dominant genetic disorder polydactyly. People with this disorder have extra fingers and toes. O Recall that with dominant inheritance the trait is expressed when at least one dominant allele is present. An individual with an unaffected parent and a parent with polydactyly could be either heterozygous or homozygous recessive for the trait. Each unaffected person would be homozygous recessive for the trait. O individual I2 has polydactyly, indicated by the dark circle. Because she shows the trait, she is either homozygous dominant or heterozygous. It can be inferred that she is heterozygous—having one dominant gene and one recessive gene—because offspring II3 and II4 do not have the disorder. O Notice that II6 and II7, two unaffected parents, have an unaffected offspring—III2. What can be inferred about II2, based on the phenotype of her parents and her offspring?