A. Incorrect! Cells contain the units of genetic they are not the unit of heredity.

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1 MCAT Biology Problem Drill PS07: Mendelian Genetics Question No. 1 of 10 Question 1. The smallest unit of heredity is. Question #01 (A) Cell (B) Gene (C) Chromosome (D) Allele Cells contain the units of genetic they are not the unit of heredity. B. Correct! Genes are made up of nucleotides in a specific sequence that code for a protein. Chromosomes are made up of genes. These are not therefore the smallest unit of heredity. Alleles are different forms of a gene. For instance brown eyes, blue eyes. Genes are the smallest unit of genetic information. They contain the information. Alleles are different forms of genes. Chromosomes are made up of many genes. Cells contain all the chromosomes of organisms. Somatic cells have a diploid or 2N of each gene, germ cells have 1N or a single copy of each gene or allele.

2 Question No. 2 of 10 Question 2. Variations of a gene are referred to as and are a result of a process called? Question #02 (A) Mutants, mutation (B) Recessive, dominant (C) alleles, mutation (D) chromosomes, mitosis Mutants and mutations describe changes in the gene. B. Incorrect! Recessive and dominant refer to the effect that a given gene has on the phenotype. C. Correct! Alleles are other forms of a gene such as eye color. Alleles can be created through the process of mutation and selection. Chromosomes are carriers of genes. Alleles are different forms of the same gene and variations can be introduced by the process of mutation. Following the mutation natural selection, or evolution, will determine if the mutation will become a part of the gene pool.

3 Question No. 3 of 10 Question 3. If parents have three normal children but are both known carriers of a recessive disorder what is the probability that their fourth child will inherit the disorder? Question #03 (A) 0 (B) 1/4 (C) 1/2 (D) 3/4 Because of Independent assortment a chance exists for inheriting the disorder. B. Correct! There is a ½ chance that the child will be a carrier of the gene i.e. heterozygous, but since it is recessive the child will have to be homozygous for the gene to have the characteristic. There is a ½ chance that their off spring will be heterozygous for the gene. However since it is recessive the disorder will not be seen in the phenotype. The gene is recessive. This answer would be possible only if the gene was dominant. From the question we see that the parents are both carriers of the gene in questions. From this we know that they must be heterozygotes. From Mendelian genetics we know that in a cross between two heterozygotes the chance of having: A a A AA Aa a Aa aa Also from the question we see that 3 of the kids are normal which implies that the heterozygotes are normal. Therefore only the recessive homozygote recessive displays the trait.

4 Question No. 4 of 10 Question 4. A gene can have many alleles. Why is it that a person only carriers two copies of each alleles possible? Question #04 (A) This is a function of co-dominance, or incomplete dominance. (B) Chromosomes loose the extra alleles during cross over or recombination. (C) Having more then one allele results in cell death. (D) During fertilization a gamete only contributes one allele from each parent. Co-dominance or incomplete dominance is a description of gene expressivity not inheritability. B. Incorrect! Recombination affects which chromosomes carry a specific allele not segregation or assortment of the chromosome. Having more then one allele may result in problems with a cells ability to survive but does not effect assortment or segregation of alleles. D. Correct! Each gamete is haploid 1N only carrying one copy of a gene or one allele. When an egg and sperm fertilize the resultant cell is 2N or diploid. The process of fertilization brings two 1 N or haploid gametes together. Each gamete has a single copy of an allele. After fertilization therefore the new cell has 2N or two copies of the gene.

5 Question No. 5 of 10 Question 5 The expression of a gene is called while the allele combinations of genes are referred to as. Question #05 (A) karyotype, phenotype (B) phenotype, genotype (C) meiosis, mitosis (D) phenotype, autosome Karyotype is a cells entire genetic composition. B. Correct! The expression or what you see is refereed to as the phenotype. The complete set of genes giving rise to the phenotype is called the genotype. Meiosis is the process of gamete formation reducing the number of copies of genes in half. Phenotype referrers to the physical expression of a gene. Autosome is a chromosome other than the X or Y sex chromosomes. Karyotype: a cells entire genetic composition, how many and what types of chromosomes are present. You would see the cerotype in a chromosome smear or panel. Phenotype: the visible expression of the genotype Meiosis: the reduction in chromosome and gene copy number, production of germ cells Autosome: non germ cells Mitosis: the production of identical daughter cells. From the definitions of each it is clear that answer B is the best fit.

6 Question No. 6 of 10 Question 6. Genetic diseases are unlike other diseases in that. Question #06 (A) They are inherited. (B) There is a predictable pattern of inheritance. (C) Different populations will show different frequencies of these diseases. (D) All of the above. Genetic diseases are inherited but this answer is incomplete. B. Incorrect! There is a predictable pattern of inheritance in genetic disorders, but this answer is incomplete. Different populations will show different frequencies of genetic diseases. An example of this would be sickle cell anemia. However, this answer alone is incomplete. D. Correct! Genetic diseases typically are associated with given populations. An example of this is Tay-Sachs diseases. This disease is particularly high among people from Eastern European descent as well as Askhenazi Jewish descent. Genetic disease: A disease that is genetic in origin not a result of injury or infection. Genetic diseases can arise spontaneously or through DNA mutation. Typical of genetic diseases are: a predictable pattern of inheritance, different frequencies between populations or subgroups, and they are inherited.

7 Question No. 7 of 10 Question 7. The two long strands of identical chromosomes are called. Question #07 (A) centromeres (B) genes (C) telomeres (D) chromatids Centromeres are the portion of a chromosome that spindle fibers bind to in order to pull the chromosome during cell division. B. Incorrect! Many genes together make up a chromosome. Telomeres are found at the ends of chromosomes. They are made up of nucleotide repeats that do not code for a specific protein product. They are typically lost or shortened during replication. D. Correct! A chromatid is each of two daughter strands of a replicated chromosome that is connected at the centromere during mitosis and meiosis. Telomere Chromatid Centromere Telomere

8 Question No. 8 of 10 Question 8. Egg and sperm are. Question #08 (A) monoploid (B) haploid (C) diploid (D) multiploid Monoploid is usually a mutation of a cell normally containing a diploid set of chromosomes. Monoploid is not the same as haploid in that these are aberrant cells having a single set of chromosomes that should have a 2N or diploid set. B. Correct! Egg and sperm are produced as a function of meiosis and have a haploid set of chromosomes. These differ from monoploids in that these are germ cells and should have a single set of chromosomes. Diploid chromosome number is found in non germ cells. Multipoid means that a cell has more chromosomes then it should. This is typically an aberrant situation. Sperm and egg cells are formed during meiosis. Meiosis is the process where two consecutive cell divisions results in the diploid progenitor cells reduce their chromosome (and gene) number by half, hence haploid.

9 Question No. 9 of 10 Question 9. This human pedigree crosses an unaffected female (circle O) with an affected male (dark square ). The phenotype shows what type of inheritance genetics? Question #09 (A) Autosomal dominant (B) Y Linked (C) X Linked Recessive (D) X Linked Dominant Pedigree indicates that this is a sex-linked gene. Therefore it is not autosomal. B. Incorrect! If it were Y linked the male off spring would inherit. If the gene were recessive the contribution of a normal gene from the mother should have resulted in unaffected female off spring. D. Correct! Only the females express the disease indicating it is an X linked gene. Since all of the female off spring have the disease it indicates it is dominant. This pedigree demonstrates a common sex linked phenotype. This is indicated by the fact that only one gender is affected. The male parent can only contribute an X chromosome to his daughters, which must be affected since the father has the trait. The mother contributes another X chromosome yet the daughters show the phenotype indicating that the paternal gene is dominant. The sons do not inherit the gene because the father only contributes the Y to the sons. The mother contributes the normal X to the son.

10 Question No. 10 of 10 Question 10. A diploid cell contains 16 chromosomes and undergoes gametogenesis. How many chromosomes are in the cells formed? Question #10 (A) 4 (B) 8 (C) 16 (D) 2 A cell that under goes Gametogenesis or meiosis would result in 4 daughter cells with half the chromosome number. B. Correct! When a diploid cell undergoes gametogenesis or meiosis the number is reduced by half. A cell that under goes gametogenesis or meiosis would result in 4 daughter cells with half the chromosome number. A cell that under goes gametogenesis or meiosis would result in 4 daughter cells with half the chromosome number. Gametogenesis is the formation of germ cells (sperm and egg). This process involves meiosis, which means that the diploid genotype is reduced by half to haploid or 8.