Pre-AP Biology Unit 7 Genetics Review Outline

Transcription

1 Unit 7 Genetics Review Outline Pre-AP Biology LT 1 - I can explain the relationships among alleles, genes, chromosomes, genotypes, and phenotypes. This target covers application of the vocabulary words above. Study your completed vocabulary list assignment and refer to the diagrams below.

2 LT 2 - I can summarize the work of Gregor Mendel and the genetic principles that arose from that work. Gregor Mendel was a monk that studied pea plant breeding in the 1800 s o First person to have correct ideas about inheritance o Experiments took eight years ( ) and results were published in Used pea plants as his model organism because they grew quickly and were easy to study because of their variety of traits (round v wrinkled, yellow v green, tall v short) o He grew over 10,000 pea plants, keeping track of progeny number and type. o Mendel figured out that genes come in pairs and are inherited as one from each parent. o Tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. Mendel conducted crosses of true-breeding (homozygous) parents to produce a heterozygous F1 generation, which were then crossed back to themselves (F1 x F1) to produce an F2 generation that showed a genotypic ration of 1:2:1. Mendel's Laws of Heredity: 1) The Law of Segregation: Each trait is inherited by a gene pair. Parental genes are randomly separated so that sex cells contain only one gene of the pair (meiosis). Offspring therefore inherit one genetic allele from each parent when sex cells fertilize. 2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not necessarily dependent on the inheritance of another. 3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

3 LT 3 I can complete Mendelian genetics Punnett square questions Mendelian Punnett Squares follow the Law of Dominance one allele is dominant and the other is recessive. The recessive phenotype is only displayed by an organism with a homozygous recessive genotype. o EXAMPLE: o Dominant Phenotype can be AA or Aa for genotype o Recessive Phenotype can only be aa Monohybrid crosses show the possible offspring in a cross of one trait. Genotype probability can be 0 out of 4 (0%), 1 out of 4 (25%), 2 out of 4 (50%), or 4 out of 4 (100%) Phenotype probability can also be any of the above, or expressed as a ratio. Dihybrid crosses show the probability of offspring in a cross of two traits. Probability is now out of a total of 16. WATCH THE AMOEBA SISTERS VIDEO IF YOU STILL ARE STRUGGLE TO SET UP THESE PROBLEMS!

4 LT 4 I can complete Non-Mendelian Punnett Square questions. Non-Mendelian inheritance refers to traits that do not follow standard dominant-recessive patterns. This includes: o Incomplete Dominance: Truebreeding phenotypes are homozygous; heterozygous genotype produces new phenotype that is an intermediate, or mixture, of the two. Example: a red flower is represented by RR, a white flower is represented by WW, and the heterozygous RW appears as pink.

5 o Codominance: Some alleles can be equally expressed when both present, for example in how the A protein and B protein are codominant in blood type such that a Type AB individual expresses both proteins. Another example could be the flower color scenario, where red is RR, white is WW, and RW is red-and-white splotches.

6 o Epistatis: The expression of some traits is determined by genes that can turn on and turn off the phenotype, this is called epistatis. For example, alpacas can be black or tan in terms of wool color, but there is another gene that controls whether or not pigment in the wool appears at all. o Sex-Linked: Some traits are located on the X or Y sex-chromosomes and therefore are considered sex-linked. The gender of the individual determines how many copies of the allele an individual inherits. Remember females are XX and males are XY.

7 o Polygenic: Some traits, such as eye color or height in humans, are influenced by many genes working in conjunction. This produces a wide array of possible phenotypes (i.e. there are many different shades of brown eyes). LT 5 - I can summarize how genetic abnormalities can cause disorders in an organism, such as nondisjunction. Genetic disorders are caused by mutations within the DNA sequences (substitution or frameshift mutations) or by a chromosomal abnormality (nondisjunction) o Point/Substitution Mutation Examples: Tay-Sachs Disease, Hemophilia, Sickle-Cell Anemia o Chromosomal Abnormality Examples: Down Syndrome (Trisomy 21), Turner Syndrome (Monosomy x), Klinefelter Syndrome (Trisomy XXY) Nondisjunction is the failure of chromosomes to properly separate during gamete formation in meiosis. This results in gametes with the improper number of chromosomes (usually having one extra or one missing, n+1 or n-1). o This can result in Trisomy (3 chromosomes instead of 2 at a specific location) or Monosomy (1 chromosome instead of 2 at a specific location). o It is possible to have more than 3 chromosomes at a location, but this is uncommon.

8 Chromsomal abnormalities can be assessed using a karyotype, which is a picture of all chromosomes arranged by largest to smallest and numbered, with the sex-chromsomes appearing last. Humans have 23 pairs 1 through 22 are autosomal (not sex-related) and the last pair are the sex chromosomes (XX or XY in a normal individual).

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10 LT 6 I can analyze a pedigree chart to determine mode of inheritance for a given trait. A human pedigree shows the pattern of inheritance of a trait/gene across generations Males are represented by squares and females are represented by circles Individuals with the trait/gene are colored in and those that do not have it are left blank For recessive traits, known carriers would be half shaded Genes are located on different chromosomes: o Autosomal Inheritance: gene/trait is unrelated to gender, NOT on a sex-chromosome (effects males and females equally) o Sex-Linked Inheritance: gene/trait is inherited from either the X or the Y sex chromosome (effects either males or females more) Many patterns of inheritance, but for this class you should know: Pa#ern 1: Autosomal Dominant Only one copy of a disease allele is necessary for an individual to express the phenotype. Males and females affected equally. All affected individuals will have at least one parent who carries the disease allele. Pa#ern 2: Autosomal Recessive Two copies of a disease allele is necessary for an individual to express the phenotype. Males and females affected equally. The parents of an affected individual may not affected but are gene carriers. Pa#ern 3: X-Linked Dominant Only one copy of a disease allele on the X chromosome is necessary for an individual to express the phenotype. Males and females affected equally. When a female is affected, there is a 50% chance for the offspring to inherit the disease allele. When a male is affected, all his daughters will be affected, but none of his sons will be affected. Pa#ern 4: X-Linked Recessive Two copies of a disease allele on the X chromosome is necessary for a female to express the phenotype, but only one copy for a male since the alternate Y chromosome does not influence X-linked traits. Males affected more frequently than females. Affected males transmit the disease allele to all of their daughters, who are then carriers, but to none of their sons. Women are affected when they have two copies of the disease allele. All of their sons will be affected, and all of their daughters will be unaffected carriers.

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