-Genetics- Guided Notes

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1 -Genetics- Guided Notes Chromosome Number The Chromosomal Theory of Inheritance genes are located in specific on chromosomes. Homologous Chromosomes chromosomes come in, one from the male parent and one from the female. Diploid a cell that contains sets of homologous chromosomes. (2N) Diploid cells contain two complete sets of chromosomes and two complete sets of genes ( set from each parent). Haploid a cell only containing set of chromosomes. (N) Meiosis Meiosis a process of reduction division in which the number of chromosomes is cut in through separation of homologous chromosomes in a diploid cell. o Meiosis takes place in two distinct divisions: Meiosis I and Meiosis II. Meiosis I Interphase cells undergo DNA, forming duplicate chromosomes during the S phase. Prophase I each chromosome pairs with its corresponding homologous chromosome to form a tetrad. over occurs in prophase I. Metaphase I chromosomes line up in the of the cell and attach to spindle fibers. Anaphase I spindle fibers pull toward opposite ends of the cell. Telophase I and Cytokinesis nuclear membrane and the cell divides into two cells. Crossing Over in prophase I, homologous chromosomes portions of their chromatids. This produces new combination of alleles and allows for more genetic.

2 Meiosis II Prophase II meiosis I resulted in two haploid daughter cells with the number of chromosomes as the original cell. Metaphase II the chromosomes line up in the of the cell. Anaphase II chromatids are separated and move toward opposite ends of the cell. Telophase II and Cytokinesis nuclear membranes form and meiosis II results in haploid daughter cells. Gamete Formation In male animals, meiosis results in four equal- sized gametes called. In many female animals, only one results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. Comparing Mitosis and Meiosis Mitosis results in the production of two genetically diploid cells, whereas meiosis produces four genetically haploid cells. The physical processes that occur during is identical to the physical processes that occur during. Gregor Mendel Gregor Mendel is known as the father of. In 1866, he published his findings on the method and mathematics of inheritance in garden plants. Pea plants reproduce by self- fertilization. Self- fertilization occurs when a male gamete within a flower combines with a female gamete in the flower. Mendel discovered that pea plants could be easily - pollinated. As Mendel bred his pea plants, he analyzed his results using to form hypotheses concerning how traits were.

3 Genetics The passing of traits from one generation to the next is called inheritance, or. is the study of heredity. The Inheritance of Traits Mendel noticed that certain varieties of garden pea plants produced specific forms of a, generation after generation (like yellow and green seeds). To begin to understand how the traits were inherited, he used - pollination: o Transferring male gametes from a true- breeding - seed pea plant to the female organ of a flower from a true- breeding - seed pea plant. He called this parent generation, the generation. The offspring of the P cross, called the F1 generation, all had seeds o Why didn t any of have green seeds if one of the parents had green seeds??? Mendel allowed the F1 generation to self- fertilize and the offspring of the F2 generation had mostly yellow seeds, but some seeds too o How did the green seeds reappear in the F2 generation??? Conclusions From The Experiment There must be forms of the seed- color trait in the pea plants (yellow and green) These are called, or difference forms of a single gene/trait o The gene/trait: seed color o Alleles: green or yellow Based on his observations, he decided that some alleles must be over others. We called the allele that gets masked.

4 Representing Alleles Alleles that are dominant are represented with letters. Alleles that are recessive are represented by the letter as the dominant allele for the trait, just - case. For example: If yellow seeds are dominant over green seeds. o The dominant allele, yellow seeds: Y o The recessive allele, green seeds: y You try In pea plants, if round seeds are dominant over wrinkled seeds o The dominant allele, round seeds: o The recessive allele, wrinkled seeds: In pea plants, if tall stems are dominant over short stems o The dominant allele, tall stems: o The recessive allele, short stems: Homozygous and Heterozygous Remember that each offspring has an for each trait from both parents. If both alleles are the same, we say that the offspring is for that trait. o YY (homozygous dominant) o yy (homozygous recessive) If the two alleles are different, we say that the offspring is for that trait. o Yy Genotype and Phenotype The organisms allele pairs (YY, Yy, or yy) is called its. The observed characteristic or outward expression (yellow or green) of an allele pair is called the. The Laws During Mendel s study of heredity in pea plants, he was able to develop two laws: o Law of o Law of Assortment Law of Segregation The law of segregation states that two alleles for each trait separate during the formation of (meiosis). o During, two alleles for that trait unite. Monohybrid Cross A cross that involves for a single trait is called a monohybrid cross.

5 This occurred during the - fertilization of Mendel s F1 generation. Yy x Yy Dihybrid Cross The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross. Dihybrids are heterozygous for both traits YyRr x YyRr Law of Independent Assortment The law of independent assortment states that a random distribution of alleles occurs during metaphase I of meiosis as chromosomes down the center of the cell. Therefore, the genes of one trait do influence the genes of another trait. Dr. Reginald Punnett In the early 1900 s, he developed what is known as the Punnett square to the possible offspring of a cross between two known genotypes. Punnett squares can be used to determine possible and of the cross. These can be represented as ratios: o Genotypic ratio o Phenotypic ratio Using a Punnett square 1. Create a box with 4 squares. 2. Identify the alleles for the trait/gene (T and t). 3. Identify the genotypes of the individuals being crossed. 4. Place the alleles for the genotypes in the appropriate places around the box. 5. Fill in the box by carrying the letter across and down.

6 Single Factor Cross Two Factor Cross Complex Inheritance Patterns Some alleles are dominant nor recessive, and many traits are controlled by alleles or genes. These types of inheritance patterns are called complex inheritance patters Incomplete Dominance Incomplete Dominance one allele is completely dominant over another. o In incomplete dominance, the phenotype is somewhere in- between the two homozygous phenotypes. Codominance Codominance both alleles to the phenotype. o Example: AB blood type

7 Multiple Alleles Multiple Alleles genes having more than alleles. o This does mean that an individual can have more than two alleles, but it means that more than two possible alleles in a population for a given trait. o Example: human blood type/groups (A, B, AB, O) Human Blood Groups o The ABO blood group has three alleles I A, I B, and i. o Alleles I A and I B are. These alleles produce molecules known as antigens on the surface of red blood cells. o The i allele is to both I A and I B and produces no antigen. Polygenic Traits Polygenic Traits controlled by or more genes. o Example: skin color of humans controlled by more than 4 different genes Applying Mendel s Principles Mendel s principles don t apply only to plants, but other organisms and too. In the early 1900s, Thomas Hunt Morgan found a model organism to advance the study of genetics: the common fruit. Fruit flies were an ideal organism for several reasons: o They reproduce and have many. Morgan and other biologists learned that Mendel s principles applied not to just pea plants, but all since is universal and contains genetic information.

8 Genetics and the Environment The characteristics or phenotypes of any organisms are not determined solely by the it inherits, but by the interaction between genes and the. o Example: Genes may affect a sunflowers height and the color of its flowers, but these same characteristics are also influenced by climate, soil conditions, and availability of water. Karyotype Studies The study of genetic material doesn t involve alone. Scientists also study whole by using images of chromosomes taken during mitosis. A stain is used to identify or mark identical places on chromosomes. The pairs of homologous chromosomes are arranged in size to produce a diagram called a. Karyotype (male or female?) Pedigree Charts A is a diagram that traces the inheritance of a particular trait through several generations. A pedigree uses symbols to illustrate the inheritance: o Males are represented by o Females are represented by o One who expresses a trait is dark or o One who doesn t express the trait in o One who is a carrier is shaded (heterozygous) only done in recessive disorders A line between two symbols shows that these individuals are the parents of the offspring listed below them. Offspring are listed below them, oldest on the to youngest on the right.

9 A numbering system is used in which numerals represent generations and numbers are used to describe birth order. Pedigree Analyzing Pedigrees A pedigree shows an individual s You can analyze a pedigree to genotypes and whether the trait that is being inherited is a recessive or dominant genetic disorder Pedigrees are useful if good records have been kept within families. It allows genetic disorders in future offspring to be. Dominant or Recessive Disorder? View the pedigree below. Is this disorder dominant or recessive?

10 Genetic Disorders: Recessive Disorders Many disorders seen in humans are caused by. A recessive disorder is expressed when the individual is recessive for the trait. An individual that is for a recessive disorder, and therefore doesn t express it, is called a. Genetic Disorders: Dominant Disorders Not all disorders are caused by recessive inheritance. Some are cause by alleles. Dominant disorders are not present in individuals that are recessive for the trait.

11 Meiosis and Nondisjuction Recall, that meiosis is the process used to form (Diploid cell! haploid cells) During meiosis I, homologous are separated. During meiosis II, chromatids are separated. If homologous chromosomes or sister chromatids don t separate during meiosis, this is known as. Nondisjunction Down s Syndrome 21 Characteristics of the disorder: o Distinctive facial features o Short stature o Heart defects o Mental disability Sex Determination Your gender is inherited based on your 23 rd pair of chromosomes, called. 2 types: X and Y XX = XY = The other 22 pairs of chromosomes are called.

12 Sex-Linked Inheritance Sex- Linked Genes genes located on the sex are said to be sex- linked. Males have just one X chromosome, thus all X- linked alleles are expressed in males, even if they are.