Genetics Notes

Transcription

1 Genetics Notes Day 1: History of Genetics, Monohybrid Crosses & Genes Vocabulary Terms Genetics is the study of. Heredity: the passing of traits from to their. Gregor Mendel ( ) Austrian monk who cultivated in the monastery garden. First person to study. Considered the because he crossed pea plants & studied the outcomes. Mendel s Experiment Step 1-Cross a tall plant with a short plant P generation: tall x short The P generation is the that are crossed. Step 2- Outcome of Crossing Parents F 1 generation= The F 1 (first filial) generation is the of the P generation. Step 3- The outcome of crossing the F 1 offspring F 2 generation= Mendel s Discoveries 1.One trait in the F 1 generation & reappeared in the F 2 generation. 2.Each organism has factors for its traits. 3.These factors are segments of DNA on chromosomes called. 4.Genes exist in alternative forms called. Dominant & Recessive Traits A trait (T) can be observed and will mask other traits. A trait (t) is one that can disappear. Example: The allele for tall plants ( ) is dominant to the allele for short plants ( ). Example of a recessive trait: Plants that have two alleles for tallness (TT) appear, plants that have two alleles for shortness appear (tt). Plants that have one allele for tall and one allele for short (Tt) appear because the allele for tallness (T) is to the allele for shortness (t).

2 Out of Mendel's work came two "Laws" of inheritance: 1) The states that the effect of a recessive allele is not observed when a dominant allele is present. 2) The formulated by Mendel Two alleles for a trait must separate when gametes are formed. (gametes are sex cells created by meiosis) Therefore, a parent passes only one allele for each trait to an offspring. (one gene from mom, one from dad) Phenotypes & Genotypes the way an organism looks and behaves. Example: a tall plant looks tall regardless of the genes it contains the gene combination an organism contains. Example: A genotype for a tall plant could be TT or Tt. A genotype for a short plant would be tt. Homozygous & Heterozygous Homozygous an organism is homozygous for a trait if its two alleles for the trait are the (TT is considered homozygous dominant and tt is considered homozygous recessive). Heterozygous an organism is heterozygous for a trait if its two alleles for the trait are (Tt) Monohybrid Crosses Monohybrid crosses only involve or characteristic. Example: G=green seed, g=yellow seed P generation= Heterozygous green x pure recessive seed Punnett Square Practice ff x FF

3 In dogs, wire hair (S) is dominant to smooth (s). In a cross of a homozygous wire-haired dog with a smooth-haired dog, what will be the phenotype of the F 1 generation? Three things I learned from the review video: Genes are segments of DNA on. (humans = 46 chromosomes) Genes come in pairs (humans = pair) Gene pairs are found on paired chromosomes called chromosomes (like ones) Homologous chromosomes carry genes for the same Gene Location Example: The gene location for is 3 q 21 The first number stands for the number of the. p= half (above the centomere) =lower half (below the centromere) 3 q 21 would be on the half of the pair of chromosomes Day 2: Incomplete & Co-Dominance Incomplete Dominance Incomplete dominance means that one allele is NOT fully dominant over the other in a individual. In incomplete dominance, the new phenotype is an intermediate between the two homozygotes. An example of incomplete dominance would be when flowering plants crossed to flowering plants yield flowering plants. Example 1 In cattle, longhorns are incompletely dominant to shorthorns. A heterozygous individual would have medium horns. Cross a longhorn bull & a shorthorn cow. Give the genotypes & phenotypes (with ratios) of the offspring. LL=longhorn, SS=shorthorn, LS=medium horn

4 Example 2 The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants? Co-Dominance means that one allele is NOT fully dominant over the other in a heterozygous individual. In such cases, the heterozygous phenotype does not look like either homozygous phenotype. Instead, the two contrasting alleles produce a new phenotype. Both alleles are in the heterozygous individual. An example of co-dominance would be when a red-flowered plant is crossed to a white-flowered plant yielding a peppermint flowered offspring (showing both red & white colors). Practice #1 RR=red RW=roan WW=white Cross a roan bull with a red cow. Is it possible to obtain white offspring? Practice #2 In Tupelo chicken, the alleles for feather color are black (B) and white (W). These 2 alleles are co-dominant. When both alleles are present, the resulting birds have both black feathers & white feathers, giving it a checked appearance. Cross a checked rooster with a checked hen. Give the genotypes & phenotype along with the ratios. Day 3: Dihybrid Crosses Dihybrid Crosses Dihybrid crosses are those where we consider the inheritance of characteristics at the same time. Mendel s Peas (again!) Mendel had observed that the seeds of his pea plants varied in several ways among them, whether the peas were round or wrinkled and whether they were green or yellow.

5 He did crosses on both characteristics, but then decided to look at how they were inherited together. There are four possible combinations of the two characteristics. Peas can be: 1) 2) 3) 4) From his monohybrid trials, Mendel had discovered that the allele for yellow colour was to that for green. He had also found that the allele for round peas was dominant to the allele for peas. Starting with individuals that were homozygous, either for both dominant characteristics or both recessive characteristics, he set off breeding again Phenotype: round, yellow wrinkled, green Genotype: Gametes: all RY all ry F1: all RrYy All of the F1 generation would be heterozygous for both characteristics, meaning that they would all be round and yellow. As with monohybrid crosses, he then crossed two of the F1 generation together Phenotype: round, yellow round, yellow Genotype: RrYy RrYy Gametes: RY, Ry, ry, ry RY, Ry, ry, ry F2: We really need a punnet square for this RY Ry ry ry F2 generation: RY Ry ry ry *This is the typical ratio expected in a dihybrid cross.

6 Day 4: Blood Groups & Multiple Alleles Blood Types There are types of blood due to the surface molecules present. These surface molecules are called. The four types are: Importance Why do we need to know our blood type? --Incompatible blood types could clump together and result in death. Cases of disputed Donating & Receiving Blood A B AB O Type: Can give to: Can receive from: Universals Universal Donor: Type Can donate blood to any blood type Universal Recipient: Type Can receive blood from any blood type What does the + and mean? The Rh factor genetic information is also inherited from our parents, but it is inherited independently of the ABO blood type alleles. There are 2 different alleles for the Rh factor known as Rh+ and Rh-. Someone who is "Rh positive" has at least one Rh+ allele, but could have two. Their genotype could be either Rh+/Rh+ or Rh+/Rh-. Someone who Rh- has a genotype of Rh-/Rh-. Inheriting Blood Type Inherited from your mother & father. Caused by multiple. (In other words, more than two alleles exist for a trait.) Due to the or of certain molecules on the surface of red blood cells.

7 Blood Genetics The gene for blood type is. There are three different alleles: I A and I B are and i is recessive. This means that neither A or B will block out the other. Genotypes & Phenotypes Phenotype Genotype(s) Disputed Parentage A lady has a baby but is unsure of who the father is. The child has AB blood and the mother has type A. We know a man with Type blood could not be the father. The father would have to have type blood. Remember: Blood tests alone cannot prove a definite father, indicates only that he could be. Practice Mom is heterozygous for type B blood. Dad is heterozygous for type A blood. What are the possible blood types for their children? Day 5: Meiosis Meiosis is the type of cell division by which cells (eggs and sperm) are produced. Meiosis involves a in the amount of genetic material. Meiosis is divided into two steps:. Meiosis I includes Prophase I, Metaphase I, Anaphase I and Telophase I. Meiosis II ( ) includes Prophase II, Metaphase II, anaphase II and telophase II. Each of these phases are similar, but not identical to the corresponding mitosis phases. Difference between mitosis and meiosis Meiosis is different than mitosis in terms of the cell division number. During mitosis, chromosomes are duplicated, and cell divides, therefore each daughter cell has chromosome number in daughter cells ( ).

8 During meiosis, chromosomes are also duplicated, cell division occurs consecutively, leading to of the chromosome number in daughter cells. This process is used for generating the gametes. When gametes from male and female parents meet, they form normal diploid chromosome number again. Vocabulary: ( ) - Normal amount of genetic material ( ) - 1/2 the genetic material. haploid sex cell Day 6: Sex-linked Inheritance Chromosomes There are pairs of human chromosomes (total 46) The first 22 chromosomes are called and carry genes for all the physical traits. o Autosomes chromosomes not associated with sex The pair are called sex chromosomes and determine the sex of the human (male or female). o Sex chromosomes last pair (determine sex) female male Sex Determination When a male and a female have a child, there is always a % chance the child will be female and a % chance the child will be male. Crossing a Male (XY) with a female (XX) Sex-linked Traits Trait whose gene is carried only on the chromosome Alleles for sex linked traits are written as super scripts on the X chromosome. (The Y chromosome will not carry the allele) In humans, sex linked disorders are usually passed on from to by a defective gene on the chromosome. Examples of sex-linked traits Duchenne Muscular Dystrophy

9 Color Blindness Test Color Blindness Practice Problem = not colorblind =colorblind Parent Genotypes: Male= X B Y Female=X B X b Hemophilia Hemophilia is a rare, inherited bleeding disorder in which your blood doesn t normally. If you have hemophilia, you may bleed for a longer time than others after an injury. Sometimes people with hemophilia need injections of a clotting factor or factors to stop bleeding. About people in the United States have hemophilia. Each year, about babies are born with the disorder. Hemophilia Practice Problem Cross a normal carrier woman with a normal male. What are the possible genotypes & phenotypes or their children? Day 7: Karyotypes & Pedigrees The Human Karyotype In humans, the normal diploid number of chromosomes is. Females have 22 pairs of autosomes & 2 chromosomes. Males have 22 pairs of autosomes, 1 chromosome, & 1 chromosome. The chromosomes of an individual can be photographed and examined in a procedure called. Making a Karyotype Cells such as blood cells or skin cells are cultured in the growth medium for a few days and then treated with chemicals which block them in of mitosis. These cells have condensed that can be stained with special stains, then observed and photographed under a microscope. Next, the chromosomes are cut out and paired with one another. Finally, they are arranged according to their, banding pattern, & position of the centromeres.

10 This pictorial presentation of the chromosomes is called a. What do Karyotypes Tell Us? of individual Chromosomal aberrations (deviation from normal) chromosomes chromosomes chromosomes What Happens If the Chromosomes Are Abnormal? About % of all pregnancies involve an embryo with chromosome defects. Most offspring with chromosomal aberrations are severely defective. Many fail to develop to term and are usually early in pregnancy. About % of all spontaneous miscarriages involve embryos with major chromosomal defects. What happens if these babies aren t miscarried? About 1 in infants are born with chromosome defects of some sort. Usually, these are severely defective individuals. Most die shortly after birth or in early childhood. What are some examples? There are viable chromosomal disorders you need to know: syndrome (Trisomy 21) syndrome syndrome Down s syndrome (Trisomy 21) One of the most common chromosome defects. Occurs in approximately 1 out of every births. These individuals have chromosomes with 3 copies of chromosome. Individuals are mentally retarded, & have round faces, short/stocky bodies, thick tongues, & heavy-lidded. Turner s syndrome (XO) Occurs only in. They have chromosomes instead of 46 because they are missing their second chromosome. Occurs in 1 out of every births. Lack functional ovaries, thus. Sex organs remain undeveloped.

11 Don t menstruate. Less than 5 feet tall. Normal intelligence. Often have webbing of the skin between &. Klinefelter s syndrome (XXY) Occurs only in. They have 47 chromosomes with 2 copies of the chromosome & 1 Y chromosome. Occurs in 1 of every male births. Mental retardation, small, & partial development common. Sterile- do not produce. What is a human pedigree? A simplified diagram of a family s that shows the family members relationships to each other and how a particular trait or has been inherited. What is the purpose of a pedigree? Classical cross-fertilization breeding experiments as performed by Mendel are not allowed in humans! Human geneticists are not allowed to selectively breed for the traits they wish to study, so they rely on observations made while working with individual families. One of the most useful tools in human genetic studies is analysis. Pedigree symbols

12 Example 1 How many males are in the pedigree? How many deceased people are in the pedigree? How many females are affected in this pedigree? Example 2 How many females are in the pedigree? How many males have hypercholesterolemia? Does person III-4 have hypercholesterolemia? How are II-3 and II-4 related? How are III-3 and III-5 related? How many children did I-1 and I-2 have?