Homework#6 Genetics

.docx

School

Everett Community College *

*We aren’t endorsed by this school

Course

211

Subject

Biology

Date

Dec 6, 2023

Type

docx

Pages

Uploaded by BrigadierField12131

Biology 211 Homework#6 Genetics What are genes, and what are different versions of genes? How are they inherited and when are they expressed? Genetics is the study of the outcome of sexual reproduction. Sexual reproduction (the outcome of Meiosis and fertilization), generates diversity in a population. Diversity is generated as a consequence of several important aspects of sexual reproduction, some of which you learned about when we studied the difference between Mitosis (somatic cell division) and Meiosis (generation of eggs and sperm). Because homologous chromosomes segregate from each other during Meiosis randomly, each egg or sperm is essentially unique. This is the big picture of Meiosis, at the chromosome level. While homologous chromosomes are similar in size, and genetic content (the order of the genes in the DNA), they are also different from each other with respect to the exact structure and function of each gene. Some genes may be identical on both chromosomes, if they code for something that all cells have in common (housekeeping genes for example; genes that regulate DNA replication, the cell cycle, essential functions for all cells). But the diploid genome (sum of all genes and DNA) contains two copies of all genes, which combine to result in the phenotype of each organism. Obviously, humans around the world are quite different in appearance from each other, despite the fact that they have many genes in common. Different versions of genes are called “alleles”. A simple example is the one of hair color. There are different alleles for proteins that code for blond hair, brown hair, black hair, and red hair etc. When different alleles combine (like when a blond haired woman has kids with a black haired man), the result may vary depending on the genetics involved. Traits are the outcome of this protein expression. Blond hair is a trait (phenotype), and black hair is a trait. The alleles of genes that combine to create the outcome, or trait, are deKined as their genotype. Alleles are found in the same location on different homologous chromosomes. Fertilization results in the mixing of alleles, and some alleles are stronger than others when proteins are being expressed. This is really what genetics is all about. Stronger genes are what we call “dominant”, and weaker genes are what we call “recessive”. When we study genetics, we use capital letters to describe the dominant genes, and lower case letters to deKine the recessive genes. It can get a little tricky solving problems in genetics, because sometimes different traits start with the same letter. For example if black hair alleles are dominant over brown hair alleles we would use “B” for the black hair allele, and “b” for brown. Same if blond is recessive to black, we would use “b” for blond also. Not because “b” stands for brown or blond, but because they are both recessive to black, which gets the capital “B”. If red hair is recessive to black hair, we would also call it “b”.

Be sure you understand what the terms homozygous and heterozygous mean. If one is homozygous for a particular gene, it means that the alleles are the same on both homologous chromosomes. Heterozygous means there are two different alleles on each chromosome for that particular gene. Ex 1: A woman who is heterozygous for eye color mates with a man who is homozygous for blue eyes, which are recessive to brown eyes. What would be the expected genotypes and phenotypes of the offspring? (This is an example of a monohybrid cross because only one trait, eye color, is being studied). In order to answer this question, perform the following steps: 1) Chose letter symbols to represent all the alleles involved. ● Use one letter to represent each trait . For example, to represent the eye color trait, one might chose the letter “B”. ● Use the capital version of the letter to represent the dominant form of the trait. For example, to represent the brown eye allele , one should choose the letter B. ● Use the lower-case version of the letter to represent the recessive form of the trait. For example, to represent the blue eye allele , one should choose the letter b. 2) Use your chosen letters to write down the cross being performed. In this problem it’d be: Bb x bb (woman) (man) 3) List the possible genotypes that each parents’ gametes could have. In this problem, it’d be: This woman’s eggs could have 2 possible genotypes, either B or b. This man’s sperm could only have 1 possible genotype, which is b. Each gamete should only have one version of each gene. Explain why. On a piece of scratch paper, draw a Punnett square to help you with your calculations. Each gamete should only have one version of each gene because in meiosis homologous chromosomes separate which equals haploid cells containing one allele for each gene.

Ex 2: A woman who is heterozygous for eye color and heterozygous for hair color mates with a man who is homozygous for blue eyes and homozygous for dark hair color. What would be the expected genotypes and phenotypes of the offspring? (This is an example of a dihybrid cross because only two traits, eye color and hair color, are being studied). 1) Chose letter symbols to represent all the alleles involved. ● Use one letter to represent each trait . For example, to represent the eye color trait, one might chose the letter “E” (You can choose any letter for any trait, just be sure you write down what you mean so you can keep track of what you are doing). To represent the hair color trait, one might choose the letter “H”. ● Use the capital version of the letter to represent the dominant form of the trait. For example, to represent the brown eye allele , one should choose the letter E. To represent the dark hair allele , one should choose the letter H. ● Use the lower-case version of the letter to represent the recessive form of the trait. For example, to represent the blue eye allele , one should choose the letter e. To represent the blond hair allele , one should choose the letter h. 2) Use your chosen letters to write down the cross being performed. In this problem it’d be: EeHh x eheh (woman) (man) Each parent should have two copies of each gene. Explain why. One from mother one from father 3) List the possible genotypes that each parents’ gametes could have. In this problem, it’d be: Woman: EH or Eh or eH or eh Man: eh or eh or eh or eh Each gamete should only have exactly one version of each gene. Explain why. On a piece of scratch paper, draw a Punnett square to help you with your calculations. Each parent passes one copy of each gene, man can only produce eh because alleles are recessive. EX#3: Martian goat frogs have traits with the following inheritance patterns:

Body color: Green is dominant over white Eye color: Red is dominant over black a) What letters would you use to designate each of these four alleles? green-G white-g red-R black -r b) Write all the possible genotypes that may be possessed by a green-bodied, red-eyed Martian goat frog. GGRR,GrRg, GGRr,GgRR c) Chose two of the genotypes you listed in part b , and mate them. What are all of the possible genotypes for the offspring of your cross? On a piece of scratch paper, draw a Punnett square to help you with your calculations. GGRR vs GGRr EX#4: 1) Suppose that there’s a gene that produces a protein that causes hair to have a dark color. One allele of this gene produces the functional “hair darkening” protein. The other allele of this gene produces a non-colored version of the protein. If an individual is heterozygous for this gene, he has fully dark hair. In other words, the heterozygote’s hair is just as dark as the hair of someone who’s homozygous for the “dark hair” allele. Based on this information, you can deduce that the allele that produces the functional “hair darkening” protein is… ( BOLD the correct answer) a. recessive to the allele that produces the non-colored protein. b. dominant over the allele that produces the non-colored protein. c. incompletely dominant over the allele that produces the non-colored protein. d. co-dominant with the allele that produces the non-colored protein. 2) Explain your answer to the previous question. No mixture of phenotype

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version