Log in to StudySoup
Get Full Access to Towson - Biol 120 - Study Guide - Midterm
Join StudySoup
Get Full Access to Towson - Biol 120 - Study Guide - Midterm

Already have an account? Login here
Reset your password

TOWSON / Biology / BIOL 120 / What is when an individual inherits the same alleles for a particular

What is when an individual inherits the same alleles for a particular

What is when an individual inherits the same alleles for a particular


School: Towson University
Department: Biology
Course: Principles of Biology
Professor: Jennifer wenzel
Term: Fall 2016
Tags: Biology
Cost: 50
Name: BIOL120 Exam Two Study Guides
Description: These notes cover the material from lectures 6-9. The notes are in fill-in-the-blank format, so take a guess, highlight the underlined section, and see if you're right! (:
Uploaded: 10/18/2016
27 Pages 262 Views 1 Unlocks


What is when an individual inherits the same alleles for a particular gene from both parents?

1.DNA is an information molecule with a double helix. This means that two complementary strands are wound together. These strands are  held together with hydrogen bonds.

2.DNA is made of nucleotides¸ each of which is  made of a phosphate, sugar, and a base. The  sugar and the phosphate make up the sugar phosphate backbone of DNA. These bases  make up genetic instructions.

3.The bases of DNA are complementary¸  meaning that one base always pairs with the  same strand. The C ( Cytosine), G ( Guanine), A   ( Adenine) and T ( Thymine)—in RNA, this base is U ( Uracil).  

What is when an individual inherits two different alleles for a particular gene?

4.All living things contain these four bases! The   amount / number of bases in organisms make  the DNA different. More pairs do not mean a  ‘ better’ or more sophisticated organism.

5.The order of the bases also many DNA  different. The bases code for amino acids,  which make up specific proteins that make a  unique individual.

6.In the Prokaryotic Cell, the DNA is floating in  the cytoplasm inside of the nucleoid. In the  Eukaryotic Cell, the DNA is housed inside of a  solid nucleus in the cytoplasm.

What is the connection between generations (egg and sperm)?

We also discuss several other topics like How do you check resistance with a multimeter?

7.DNA is neatly packaged in the nucleus. The  base pair makes itself into the helix, then more tightly around the histones (like pearls on a  string). The histones get super close and coil  up into nucleosomes, and then chromosomes.

8.Humans have 23 pairs of chromosomes, 46 total. These pairs are called homologous. One  is donated by the father, sperm, the other is  donated by the mother, via egg.  

9.When all of the chromosomal pairs are laid out  in a row, it is called a karyotype. Each  chromosome is made out of genes. 

10. Genes are the basic unit of heredity (or the  passing of traits from parent to offspring).  Genes are sets of instructions to produce these traits (like eye color). Genes are the portion of  DNA that codes for a trait. Proteins are the  biological correlate of traits (like blue eyes are  a trait. That eye color pigment is made of a  certain protein). If you want to learn more check out Who said disease and famine kept population numbers down?

11. In order for the cells to produce these  traits, they need to read their genes, follow the

instructions, and make proteins; this making of  proteins is called gene expression. This has two phases, transcription and translation.

12. In the first phase (transcription), DNA for a  certain gene is unwound and a complementary mRNA strand is produced. This takes place in  the nucleus. Bases of the ribo-sugar backbone  are bonded via hydrogen bonds. Bonds open so that the cell can make mRNA (messenger RNA) to form a complementary strand (ACGU). DNA  is unwound and mRNA strand is formed  because DNA can never leave the nucleus.  

13. In the second phase (translation), the RNA  strand leaves the nucleus, meets up with a  ribosome and instructs the cell how to build the protein for that gene. This takes place in the  cytoplasm. mRNA leaves the nucleus to tell  the ribosome how to build the protein for that  gene.

14. Chromosomes carry genes. The locus is the specific place on a chromosome where a  specific gene is found.  We also discuss several other topics like What is the definition of organic organizations?

15. All members of a species have the same  genes on the same chromosomes at the same  loci. The reason why all humans don’t have the same diseases is because we all have different

alleles. Everyone has two alleles for every  gene, one from their mom and one from their  dad. They may be the same allele or they may  be different alleles of the gene. Some alleles are more susceptible to diseases than others,  so we don’t all have the same diseases (or  chances for opportunities) to get diseases. Don't forget about the age old question of What is the meaning of transponders in satellites?


1.The cell cycle is a repeating series of event  that include:

a. Growth of the cell

b. DNA synthesis

c.Cell division 

2. Interphase is cell growth and preparation for  division 

3.The mitotic phase is the act of cell division

4.Interphase can be subdivided into the following three phases:

a.Growth phase 1 ( G1; Gap Phase 1): i. Cell grows rapidly, makes proteins 

needed for DNA replication, copies  

some of its organelles

ii. A cell typically spends most of its life in this phase

b. Synthesis Phase (S):

i. Cell’s DNA is copied in the process of  DNA replication 

c.Growth Phase 2 (G2; Gap Phase 2): i. The cell makes final preparations to  divide 

5.After cells grow to their maximum size, they  divide into two new cells. One parent cell ends  up as being two identical daughter cells. Each  daughter cell is diploid, which means it We also discuss several other topics like What does meteorology mean?

contains 23 pairs of chromosomes. We also discuss several other topics like What is the eustachian tube?

6.If the cell needs to divide, first it needs to make more DNA. This is DNA replication. The DNA  opens, the enzymes copy both sides, and  complementary bases are added. DNA  replication is semiconservative, which means  that each new strand is half old and half new.

7.After replication is complete, both double  helixes (sister chromatids) stay connected for a while. They are still considered one  

chromosome (a replicated chromosome). The  part of the chromosome that links sister  chromatids is called the centriole. Each copy  contains exactly the same information.

8.The four stages of mitosis are prophase,  metaphase, anaphase, and telophase. a. Prophase: from the parent cell, chromatin  condenses into chromosomes and the  nuclear membrane breaks down. Centrioles move to opposite poles of the cell and  spindles start to form between them.

b. Metaphase: the sister chromatids line up at the equator of the cell. Spindles attach to  centromere.

c. Anaphase: the sister chromatids are pulled  apart to opposite ends of the cell by the  shortening of the spindle fibers.

d. Telophase: chromosomes uncoil and form  chromatin. The spindle also breaks down,  and new nuclear membranes form. This  process creates two daughter cells.

9. Cytokinesis is the final stage of cell division  where the cytoplasm splits in two and the cell  divides.

10. Cell division:

a.Sometimes a cell never divides:

i. the heart muscle

ii. the liver

iii. the kidneys

iv. mature brain cells

b.the cell might need to divide for:

 i. growth 

 ii. repairing damage 

 iii. replace dead cells 

11. There are checkpoints in cell division. If a  cell doesn’t pass a checkpoint, it initiates  apoptosis, which is programmed cell death. a. The checkpoints are:

i. Metaphase  anaphase (are all of the  chromosomes aligned at the equator?) ii. G1  S (is the DNA intact?)

iii. G2  M (has the DNA been completely  replicated?)

12. The two types of cell division are mitosis (how body (somatic) cells divide) and meiosis (how sex cells (gametes, like sperm or eggs)  divide

13. Sexual reproduction requires sex cells  (gametes). The male gamete is sperm (spermatozoa), and the female gamete is the  egg (ovum). The gametes are haploid cells,  which means that they only carry half of the  number of chromosomes of other cells. The  mother give 22 pairs of chromosomes and an  XX pair, and the father gives 22 pairs of  chromosomes and an XY pair, equaling 46 pairs of chromosomes in the zygote.

14. There are two types of twins, identical and  fraternal.  

15. Monozygotic (MZ) twins, single ovulated  egg fertilized by one sperm. The embryo splits  into two—monozygotic twins (100% genetic  identity).  

16. Fraternal (dizygotic (DZ)) twins, two  ovulated eggs fertilized by different sperm— decrease in genetic dissimilarity relative to  unrelated individuals  

a. 25% decrease in genotypic dissimilarity b. 50% decrease in allelic dissimilarity.

17. A parent can only give what they have, so  a mother is only able to give an X 

chromosome, while a father is able to give an X or a Y.

18. From fertilization, zygotes are either XY (genetically male) or XX (genetically female).  For the first month, XX and XY fetuses appear  identical, which means that they have  undifferentiated genitalia. If the fetus has Y  chromosome (male), the gene on the Y  chromosome (the SRY gene) causes testes to  develop, which secrete testosterone to  masculinize genitalia. Hormones secreted by  testes (like testosterone) masculinizes the body and brain—this occurs in utero as well as  throughout life. If the fetus has no Y  

chromosome (female) there is no SRY gene,  and the genitalia is feminized. In puberty,  ovaries secrete hormones (like estrogen and  progesterone) that feminize the body and  brain.

19. Meiosis is cell division of gamete (or sex)  cells—in males, these are sperm; in females,  these are eggs. Gametes come from germ cells in testes or ovaries. Two cell divisions occur  during meiosis, and a total of four haploid  daughter cells are produced (Meiosis I and

Meiosis II, which has similar steps as mitosis,  but in two back-to-back cycles).

20. Chromosomal crossover (or crossing over)  is the exchange of genetic material between  homologous chromosomes that results in  recombinant chromosomes. Chromosomes  replicate prior to meiosis, then like  

chromosomes pair up and swap sections of  DNA, creating a mix of new genetic material in  the offspring’s cell. The nucleus divides twice  into daughter nuclei and the daughter nuclei  have single chromosomes and a new mix of  genetic material. In Meiosis I, homologous  chromosomes line up and exchange alleles,  which add genetic diversity to daughter cells.

21. Without crossing over, each couple has the  potential to produce around 750 genetically  unique offspring. Each human couple actually  has the potential to produce more than 64  trillion genetically unique children.


1. Genetics are the study of genes, heredity, and  genetic variation in living organisms.

2. Homozygous is when an individual inherits the  same alleles for a particular gene from both  parents.  

3. Heterozygous is when an individual inherits two different alleles for a particular gene.

4.A dominant allele is one that produces the  phenotype (represented by upper case letters).

5.A recessive allele is one that only expresses its  phenotype if there is no dominant allele  (represented by lower case letters).

6.A genotype is the genes that an organism has.

7.A phenotype is the trait that the organism  expresses.

8. Gametes are the connection between  generations (egg and sperm). Gametes are  haploid, so they have 1 allele for every gene.

9. Gregor Mendel is the “Father of Genetics.” He  was a monk that raised pea plants. He made  careful observations of the traits of pea plants  that grew during each season. Mendelian Inheritance = simple dominant/recessive.

10. The Law of Segregation says that each  organism has two hereditary units for each trait (two of each gene) and during gamete  formation, these units separate from each  other and pass into different gametes  (meiosis).

11. The Law of Independent Assortment says  that in the formation of gametes, the  distribution of hereditary units for one trait is  independent of the distribution of hereditary  units for the other trait.

12. The Punnett square is a diagram that is  used to predict an outcome of a particular  cross or breeding experiment.

13. Holstein cattle have a spotted coat due to  a recessive allele while a solid colored coat is  dominant. The genotypes are spotted x  spotted, the parent genotypes are hh x hh.  Because the only thing that the parents can  give is the spotted trait, the only possibility for  the offspring is to be spotted.  

14. In mice, black fur (B) is dominant to brown  fur (b). a cross between a brown and a black  mouse produces all black mice. The parent  genotypes are BB x bb, so all of the offspring  are going to be dark-brown/black-furred.

15. Incomplete Dominance says that a  ‘dominant’ allele doesn’t fully cover up a  ‘recessive’ allele.

a.A = straight hair

b.a = curly hair

i. Aa = wavy hair

1.R = red

2.W = white

3.RR = red flowers

4.WW = white flowers

5.RW = pink flowers

16. Gene is on a sex chromosome, either on  the X or Y chromosome. Males have XY,  females do not have Y. females have XX, males only have X. more X-linked than Y-linked traits

in humans (because the X chromosome is  bigger).  


1.Condition is recessive (like  


a.Father is unaffected

b.Mother is carrier 

c.All daughters are unaffected

d. ½ of daughters are carriers

e. ½ of sons are affected

2.Dominant condition (rare)

a.On the X chromosome

b.Father has condition

c.Father gives Y to every son

 i. With unaffected mother, all 

sons are unaffected 

d.Father gives X to every  


 i. all daughters are affected,  

regardless of mother 

3.Dominant condition (rare)

a.Mother is heterozygous—


b.Since mother gives an X to  

every child, there is a 50%  

probability that any child from  

this mother will be affected 

17. Females and X-linked traits

a.Every cell in our body contains all our DNA b.Every cell in a female’s body contains XX  chromosomes

c.Each X chromosome has the exact same  genes on it, only different (maybe!) alleles  of that gene

i. In cells that express an X-linked gene,  which X chromosomes is it expressed  on?


 b. One or the other! 

 i. The inactive X chromosome 

coils up so tightly that it  

can’t be read (Barr body) 

18. Example: Calico Cats

a.Fur color is on the X chromosome

b.One X has allele for brown fur

c.One X has allele for black fur

d.Some cells can’t express pigment  


e.Male calico cats are so rare, 1/ 3000 chance!

19. Codominance:

a.Neither allele covers up the other

b.Both are dominant, both are expressed

20. Multiple alleles:

a.More than two options

b.Each person will only have to alleles for the gene

21. There are three possible alleles

i. IA 

ii. IB 

iii. I

b.You only get two

c.Six possible genotypes

i. IAIA 

ii. IAi

iii. IBIB 

iv. IBi

v. IAIB 

vi. ii

d.Four possible phenotypes

i. A

ii. B

iii. AB

iv. O

22. Environmental effects:

a.Even though DNA says one thing, the  phenotype can be altered by  

environmental factors 

i. Siamese cats have a heat-sensitive  pigment protein

ii. This protein is expressed more in areas  of their bodies that are cooler

a.In warmer temperatures, the  

fur becomes lighter

b.In cooler temperatures, the fur  

becomes darker

23. Lethal alleles:

a.In crossing a yellow (AY) (mutated) mouse  with an agouti (A) (brown, natural) mouse,  the offspring turns out as brown. In  

crossing two yellow mice (AYAY), the  

offspring is not even born, but dies as an  embryo.

24. Continuous variation:

a.Several genes work together to produce  one phenotype

b.Many different possible phenotypes, such  as human skin color

25. One gene, multiple effects:

a.A single gene can cause many effects b.Example: gene for albinism

i. Lack pigment in hair and skin

ii. Also have higher rate of crossed eyes  (because gene also controls how eves  connect to brain)


1.Chromosomes are composed of chromatin,  which is DNA wound around proteins called  “histones,” which are a protein associated with  DNA.

2. Methylation of DNA and histones causes  nucleosomes to pack tightly together.  

Transcription factors cannot bind the DNA, and  genes are not expressed.  

a.Transcription factors = proteins that  

facilitate gene transcription. Nucleosome = small portion of DNA wrapped around a  histone.

3.Histone acetylation results in loose packing of  nucleosomes.  

a.Transcription factors can bind the DNA and  genes are expressed.

4. Methyl groups and acetyl groups are  responsible for regulating which genes are  expressed. This means that these chemicals  control gene activity and their presence or  absence within a cell or at a specific gene  dictates what that cell does—this influences  “who” we are.

5.Our experiences shape our genes—not which  genes we have, but where, when. And how  they are being expressed

6. Epigenetics is the study of phenotypic trait  variations caused by external/environmental  factors that switch genes on and off and affect  how cells read genes. These are NOT caused by changed in the DNA sequence.

7.How are changes in gene expression due to  external factors involved in:




d.Psychological disorders

e.Changes in our offspring


1.Chromosomal abnormality—a missing, extra, or irregular portion of chromosomal DNA a.Problems in number of chromosomes – too  many or too few of a chromosome

b.Missing pieces of chromosomes – some  pieces of a chromosome may be lost or  rearranged

c.Translocations on chromosomes – a piece  of a chromosome breaks off and reattaches d.Single gene mutations


a.The number and appearance of  

chromosomes in the nucleus of a  

eukaryotic cell. We can compare an  

individual’s karyotype to the normal  karyotype to determine the existence of a  chromosomal abnormality.  

b.Pair of homologous chromosomes:

i. One from mom and one from dad 

ii. Have the same genes arranged in the  same order

iii. Slightly different DNA sequences

3.Chromosomal Abnormalities:

a.Chromosomal abnormalities result in  various symptoms based upon the  

chromosome affected and how

b.Problems in number of chromosomes: i. Nondisjunction



3.Kleinfelter Syndrome

4.Turner Syndrome


ii. Problems in structure of chromosomes 1.Deletion




iii. Single gene mutations

4.Problems in number: nondisjunction

a.Each species has a specific number of  chromosomes

b.If homologous chromosomes don’t  

separate properly during cell division (this  is called nondisjunction), you get cells with  incorrect numbers of chromosomes

c. Aneuploidy: an abnormal number of  chromosomes

i. Monosomy = when an individual is  missing a chromosome from a pair

ii. When an individual has more than two  chromosomes of a pair = trisomy,  

tetrasomy, etc

5.Trisomy21: Down Syndrome 

a.Occurs when individual has three copies of  chromosome 21 

b.Physical symptoms:

i. spots on the eye, flattened facial  

profile, poor muscle tone, short stature, etc

c.cognitive symptoms:

i. speech delay, intellectual disability,  impulsivity, etc

d.1/700 births

e.Older women have increased risk because  the eggs are older and have a greater risk  of improper chromosome division 

6.Trisomy13: Patau Syndrome

a.Most lethal trisomy with median survival is  3 days – many are miscarried


i. Severe mental deficiency, facial  

clefting, neurological and heart defects c. 1/9500 births

d.Increased risk with mother’s age

7.XXY: Klinefelter Syndrome:

a.Genotype is male 

b.Phenotype can be male, female, or intersex – usually make

c. 1/500 – 1/1000 male births

d.Extra X could come from mother or father e.Symptoms:

i. Sterility, less testosterone production  leading to slightly feminized  

appearance in adolescence (less  

muscle tone, less body hair,  


ii. May have cognitive and physical delays

8.XO: Turner Syndrome:

a.Genotype and phenotype female 

b.Only 45 chromosomes

c. 1/2500 girl births

d.Missing chromosome from mother or father e.Symptoms:

i. Short stature, webbed neck, broad  chest, etc

f. some have difficulty with imagining objects in relation to each other, nonverbal  

memory and attention, sense of direction,  manual dexterity, nonverbal learning and  social skills

9.XYY: XYY Syndrome:

a.1/1000 boy births

b.Usually no huge impact, most don’t even  know

c.Boys with XYY karyotype have an increased growth velocity from early childhood, with  an average final height approximately 7 cm (3”) above expected final height

10. Problems in structure

a.Typically occur due to errors in crossover  i. Deletion 

a.Part of a chromosome is  


 ii. Duplication 

a.Production of one or more  

copies of any piece of DNA

 iii. Inversion 

a.Segment of a chromosome is  

reversed end to end

 iv. Translocation 

a.Rearrangement of parts  

between non-homologous


11. Deletion

a.Cri du chat, “cat’s cry” syndrome

b.Deletion on chromosome 5 

c.Extent of deletion varies

d.Symptoms = intellectual disability and  delayed development, small head size  (microcephaly), low birth weight, and weak  muscle tone

e.1/20000 – 1/50000 births

f. From mother or father 

12. Duplication

a.1q21.1 microduplication

b.Genetic information at the q21.1 position of chromosome 1 is duplicated at least once c.May represent a number of symptoms  including:

 i. Autism 

ii. Large head

iii. Learning disability

 iv. Heart defects 

v. Seizures, etc

d.Prevalence is unknown, but 1/700 people  tested for 1q21.1 have it

13. Inversion: inv(9)p12q13

a.Inversion of chromosome 9 – inv(9)p12q13 b.Most common inversion

i. Occurs in 2% of population

c.Likely harmless

d.Some controversial reports suggest it  contributes to male infertility

14. Translocation

a.Philadelphia Chromosome

b.Translocation of chromosome 9&22 c.Contributes to chronic myelogenous  leukemia (CML)

15. Single Gene Mutations

a. Alteration in the DNA sequences forming a  single gene

b.May be inherited or acquired through  environmental exposure

c.A mutated gene will not be able to produce the correct amino sequence, which may  lead to problems

i. E.g., Huntington’s Disease

a.Brain disorder affecting ability  

to think, talk, and move 

b.Mutation in a gene on  

chromosome 4, which codes for

the huntingtin protein

c.Normally, this gene’s DNA  

sequence contains “CAG”  

repeated again and again  

(usually 10-20 times)

d.People with Huntington’s  

Disease have an abnormally

high number of these CAG  

triplets (around 40+)

e.The brain cells of Huntington’s  

Disease patients accumulate  

clumps of protein that become  

toxic, resulting in cell death

f. Some patients lose more than  

25% of their brain cells before  

they die

16. You need the correct number of  chromosomes 

a.You need the chromosomes to have all of  the genes 

b. You need the genes to have the correct  order of bases

Page Expired
It looks like your free minutes have expired! Lucky for you we have all the content you need, just sign up here