Name: __________________________

REVIEW 5: GENETICS

1. Chromosomes: a. Humans have _______ chromosomes, or ________ homologous pairs.

• homologous: ________________________________________________________________

b. Chromosome pairs carry genes for the same traits. Most organisms have two copies of the ! gene for each trait - one from each parent.

c. Sex chromosomes - in humans, females are XX and males are __________.• The Y chromosome is much _________________ than the X, so it is missing many genes.

This means many genes on the X chromosome do not have a “partner”.

d. Common mistakes: “Humans have 23 chromosomes (or 46 pairs of chromosomes, or some ! other incorrect number).” These numbers are often confused, learn them correctly - the right ! numbers are 46 chromosomes and 23 homologous pairs.

2. Chromosomes and Genes: a. Humans have over 25,000 genes!

b. Each chromosome has hundreds or thousands of genes.

c. Each gene codes for a particular protein.

• common mistake: “Genes/DNA are made of protein.”

! ! Genes carry the instructions to make protein.

! ! The genes themselves are made of nucleotides.

d. Genes determine our traits, but the environment can affect the expression of genes.

3. DNA a. DNA is the chemical that makes up our genes and chromosomes.

• Analogy: All the DNA in the nucleus of one of your cells - all 46 of your chromosomes together

make a cookbook. Each individual chromosome is a chapter in that book and each gene is a

single recipe in that chapter. Ribosomes serve as the chefs of your cells, using the DNA

recipes to produce proteins.

b. The shape of the DNA molecule is a double _____________, which resembles a twisted ladder.

c. The shape of DNA allows it to ___________________________, or

! copy itself exactly. DNA replication is semi-conservative, meaning

! each molecule has one original and one newly copied strand.

d. DNA is made of 4 bases: _______, ______, ______, ______

• Paring of bases: Adenine (A) pairs with ______________ (___)

• Cytosine (C) pairs with _______________ (___)

• in RNA the base pairs are _____ : _____ and _____ : _____

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A

C

DNA Replication

4: Protein Synthesis: This is how your genes control your body.

a. There are two processes involved in protein production.

• The process of copying DNA into messenger (mRNA) is called _________________________

and takes place in the nucleus. The copying is performed by the enzyme RNA polymerase.

• The mRNA is then transported to ribosomes which perform the process of _______________.

b. A codon is a sequence of ______ bases.

• Each codon represents a specific amino acid.

• As ribosomes read the codons on the

mRNA, ________ molecules bring the

correct amino acid to the ribosome. The

ribosome then bonds the two amino acids

together. (dehydration synthesis)

• Amino acids are bonded together to

make a ______________________.

• The order of the amino acids - Which is

determined by the DNA sequence - then

determines the __________________ of

the protein.

• The shape of protein then determines its

________________________.

• Therefore: The sequence of bases DNA will determine the ________________ of all the

proteins in the body.

• These proteins - coded for by DNA - build and run the body.

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structure process

transcription

translationtRNA

The Universal Genetic Code

5. Mutations: ________________________________________ a. Can only be passed on to offspring if they occur in

! reproductive cells (eggs/sperm)

b. Gene mutations: may cause a change in a gene

! which can change the __________________ of the protein

! produced from that gene. This will have an effect on how

! the protein functions. (If it still functions at all)

• Gene mutations are caused when DNA bases are changed. (added, deleted, substituted)

c. Mutagenic agent: ________________________________________________________________

• common mutagenic agents include: _______________________________________________

d. Chromosome mutations: often caused when a person inherits too many or too few chromosomes.

• Chromosome mutations affect many genes at once.

• Down’s Syndrome: non-lethal mutation caused by inheritance of

an extra copy of chromosome 21 due to nondisjunction in meiosis.

• Can include deletions, duplications, inversions and translocations.

6. Genetic Technology a. Selective breeding intentional breeding of plants (food crops, such

! as corn and wheat) and animals (livestock, such as cows) for

! agriculture as well as the breeding of animal as pets (dogs/cats)

b. Genetic engineering ____________________________________________________________

• Restriction ___________________ are used to cut and paste DNA segments together.

• Organisms that receive the gene will produce the ________________ coded for by that gene.

• The new protein will be exactly the ____________ as the one produced by the original

organism.

• ___________________ are often used because they

are simple and reproduce quickly.

• Bacteria have been engineered to produce

________________ for diabetics.

• Bacteria have also been engineered to produce

human ________________ hormone.

• These engineered hormones are safe because

they are identical to normal human hormones.

c. New technologies (karyotyping and DNA fingerprinting) are

making it easier to diagnose and treat genetic disease, though

we can not yet cure them.

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• Karyotype: A photograph of an organism’s chromosomes

• Can determine if a person has a chromosome disorder such as Down’s

Syndrome.

• DNA Fingerprinting or gel electrophoresis allows us to compare DNA. It

creates banded patterns of DNA based on a persons DNA sequence.

• Is possible due to negative charge of the DNA phosphate group

• When exposed to current, DNA migrates to _______ end of the gel.

• ________________ fragments move further than larger fragments.

• Each fingerprint is unique, so it can be used to identify people.

• Fingerprints of relatives are similar to each other, so can be used to

determine genetic relationships between two people or even groups of

organisms for the purpose of evolutionary classification.

d. Genetic research has posed many ethical problems (i.e. right and wrong) that

science alone can not answer.

• You may one day be expected to vote on these issues in bioethics.

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matching samples

human insulin

A karyotype shows all 23 pairs of human chromosomes arranged by size. Note the last pair identifies this individual as a female. Also note trisomy in pair 21 resulting in Down’s Syndrome.

7. Inheritance: There are 7 terms you MUST understand to be able to interpret problems involving genetic inheritance. ! a. Allele - different versions of the same gene

• Diploid organisms have two alleles for each gene.

b. Homozygous - If organisms have two of the same allele they ! are referred to has homozygous (homo = same and zygous = ! zygote)

• Homozygous can also be called true-breeding.

c. Heterozygous - If organisms have two different alleles they are ! referred to has heterozygous (different zygote).

• Heterozygous can also be called hybrid.

d. Dominant - the allele that is expressed, or translated into the ! protein product that we see.

e. Recessive - the allele that is masked by the dominant allele• recessive alleles are not weak or out-competed by the dominant

allele. They are genes with mutations that typically do not make a functional protein.

• example: In Mendel’s pea plants, purple is dominant to white. White is recessive and the allele for white has a mutation preventing production of purple pigment.

! f. Genotype - the gene combination of the organism• examples: BB (homozygous dominant) Bb (heterozygous) and bb

(homozygous recessive)

g. Phenotype - the appearance of the organism• examples: BB and Bb would both have brown eyes and bb would

have blue eyes.

8. Patterns of Inheritance: a. Patterns of inheritance can be shown and predicted using ___________________________.

b. Complete dominance - Pattern of inheritance observed by Mendel ! where the dominant allele completely masks the recessive, such ! that both homozygous dominant and heterozygous have the ! dominant phenotype. Example: PP and Pp are both Purple

c. Incomplete dominance - Pattern of inheritance where the ! heterozygous appears as an intermediate between the two ! homozygous phenotypes. Ex. RR = red & rr = white, but Rr = PINK ! (having one dominant allele produces some pigment but not enough ! to be red)

d. Codominance - Pattern of inheritance where multiple alleles can ! be equally dominant.

• In human blood type, both the A and B alleles are equally dominant. So an individual with AB blood type is codominant.

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Complete Dominance

Incomplete Dominance

Punnett Square

e. Sex-linked - Pattern of inheritance that is often expressed differently in males than females due to the gene being located (linked) on the X ! chromosome.

• Since males only have one X chromosome they will have the disorder if their only copy of the gene is dysfunctional.

• Females have two X chromosomes. Therefore, they would need two recessive copies to express the disorder.

9. Pedigree analysis - aid in tracking genetic traits through families and predicting the odds of passing on a genetic disorder.

• Individuals with the trait being evaluated are shaded.

• Males are represented with squares.

• Female are represented with circles.

• Heterozygous individuals who have a copy of the mutation but don’t express it are referred to as___________________ because they carry a copy that could be passed on to their offspring.

SAMPLE EXAM QUESTIONS

1. Plants inherit genes that enable them to produce chlorophyll, but this

pigment is not produced unless the plants are exposed to light . This

is an example of how the environment can.

a. cause mutations to occur

b. influence the expression of a genetic trait

c. result in the appearance of a new species

! d. affect one plant species, but not another.

2. One variety of strawberry is resistant to a damaging fungus, but

produces small fruit. Another strawberry variety produces large fruit,

but is not resistant to the same fungus. The two desirable qualities may be combined in a new variety

of strawberry plant using the process of

a. cloning! ! ! c. direct harvesting

! b. asexual reproduction ! ! d. selective breeding

3. A product of genetic engineering technology is represented to the right. Which substance was needed

to join the human insulin gene to the bacterial plasmid DNA as shown?

a. a specific carbohydrate c. hormones

! b. a specific enzyme! ! d. antibiotics

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aa

A?

Aa

aa

carriers

autosomal recessive pedigree

Aa Aa

A?

Aa

4. The diagram below represents a common laboratory technique in molecular genetics. One common

use of this technology is.

! a. production of a human embryo to aid women who are unable

! to have children

! b. change of single-celled organisms to multi-cellular organisms.

! c. introduction of a toxic substance to kill bacterial cells.

! d. production of hormones or enzymes to replace missing human

! body chemicals

Questions 6-7. The four wells represented in the diagram to the right were

each injected with fragments that were prepared from DNA samples using identical techniques.

5. The laboratory procedure is known as.

a. use of a dichotomous key

b. gel electrophoresis

c. cloning

d. chromatography

6. The arrow represents the direction of the movement of the DNA

fragments. What is responsible for the movement of the DNA in this

process?

____________________________________________________________________________________

____________________________________________________________________________________

7. The four samples of DNA were taken from four different individuals. Explain how this is evident from

the results shown in the diagram.

____________________________________________________________________________________

____________________________________________________________________________________

8. An alteration of genetic information is shown: A-G-T-A-C-C-G-A-T → A-G-T-A-C-C-T-A-T

This type of alteration of genetic information is an example of

a. deletion! ! ! ! c. substitution

b. insertion ! ! ! ! d. recombination

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9. In DNA, a sequence of three bases is a code

for the placement of a certain amino acid in a

protein chain. The table to the right shows some

amino acids with their abbreviations and DNA

codes. Which amino acid chain would be

produced by the DNA base sequence below?

10. Identify one environmental factor that could cause a base sequence in DNA to be changed to a

different base sequence.

____________________________________________________________________________________

____________________________________________________________________________________

11. The Punnett square below shows a pea plant with green pods (GG) and a pea plant with yellow pods

(gg). All of the offspring have green pods (Gg).

Explain why the offspring with Gg genes for pod color look the same as the pea plants with GG genes for pod color.

____________________________________________________________________________________

____________________________________________________________________________________

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Questions 12-14. Base your answers on the information and the pedigree chart below.

Inheritance of Color Blindness

! Gender in humans is determined by a pair of sex chromosomes. A female has two X

chromosomes and a male has one X and one Y chromosomes. A recessive gene that causes color

blindness is located on the X chromosomes. When a male inherits this gene, he will be color-blind

because the Y chromosome does not contain a gene for color blindness.

! In order for a female to be color-blind, she must inherit the recessive gene on both X

chromosomes. If she has the gene on only one chromosome, she is not colorblind. She is called a

carrier because she can pass this gene along to her offspring. The pedigree chart shows the children and

grandchildren of a female carrier and a male who is not color-blind.

12. What is the total number of children and grandchildren who are color-blind in this family? _________

13. What is the probability a carrier female will pass on the color-blind gene to her child? ____________

14. What was the genotype of the original parents: female ___________ male ___________ (hint: you

will need to include the XX and the XY)

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