Download Unit A: Biodiversity Section 3 Study Guide

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Unit A: Biodiversity
Section 3 Study Guide
Sections out of the Text Book
Section 2.1
Section 3.1
Section 3.2
Section 3.3
1. What is the material responsible for variation? (1 Mark)
DNA, deoxyribonucleic acid
2. Heritable characteristics are passed from generation to generation. What are the two main
types of characteristics? Describe them, and provide an example. (6 Marks)
Discrete variation: has an either or form (you have it or you don’t)
i.e. eyecolor, hair color, attached earlobes, hitch hikers thumb etc…
Continous Variation: falls within a range
i.e. height, hair texture, skin pigmentation, body shape, weight etc..
3. Compare the three types of Cell division? What cells do they occur in? How are they similar?
How are they different? (12 Marks)
Binary Fission: Unicellular Organisms,
produce two identical daughter cells with a complete set of DNA,
But results in a new organism
Mitosis: Occurs in the somatic cells of the body of Multicellular organisms.
Produces two identical daughter cells
Are designed for growth and repair of existing cells of the body
Meiosis: Occurs in multicellular organisms
Involves two cell divisions, that result in 4 sex gamete cells that only contain ½ the
chromosomes needed
The male sperm gamete, and female ova gamete will come together in fertilization to
produce a zygote, the first cell of a new organism in sexual reproduction
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4. If all humans contain the same amount of DNA, explain why we are all different? What is
responsible for these differences? (2 Marks)
Although we contain the same amount of DNA, the sequence of bases making up our genes are
quite different
Also through sexual reproduction, there is an exchanging of genetic material, and genes from
both the mother and father are combined to produce the new offspring, adding to the amount
of variation
5. How are chromosomes formed? And where are they located? (2 Marks)
Chromosomes are located in the nucleus of the cell
They are formed by the DNA molecule tightly winding around a protein known as Histones, until
they form a compact structure
6. What would happen if you were missing any of your 46 chromosomes?
Since each chromosome is like a piece of a puzzle, you would be unable to finish the puzzle
So essentially the blueprint for your body would be incomplete, and your body would be missing
key information about what it needs to do
So essentially you would be unable to live
7. What are sex chromosomes? Are they different for boys and girls? Explain…
(2 Marks)
Is a pair of chromosomes that determine whether an individual is a male or female
Boys contain an X Y pair of chromosomes
Girls contain two X X chromosomes
8. What is an Allele? Why would a human have these? (2 Marks)
Most genes in most species exist in an array of possible forms that differ as to their exact DNA
sequence, these different possible forms are known as Alleles
Humans will have these due to the variation of receiving chromosomes from both parents
9. What does the shape of DNA look like? What are the main structures of the molecule?
(3 marks)
DNA molecule resembles a “twisted ladder” it is referred to as a double helix
The main structures are the SUGAR PHOSPHATE backbone that make up the outsides of the
ladder (fruit roll up part in our lab)
And also the “rungs” of the ladder, the nitrogenous bases, adenine, guanine, thymine, cytosine
that pair together
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10. Explain how there can potentially be so many different genes if they are only made up of the
Nitrogenous bases (4 chemicals)? (2 Marks)
The arrangement of the four chemical bases (A, T, G, C) form the genetic code, and just like our
alphabet can be rearranged to form millions of letters, so can the chemical bases in the
sequences we call genes
11. Why is it important for sex gamete cells produced in Meiosis to only contain ½ the DNA required
by an organism?
Because otherwise when they combined in sexual reproduction you would have more
chromosomes than your body would need
12. How is an organism known as a Hybrid created? (2 Marks)
So when you take two parent Purebreds that display differing traits (so in the case of the cats in
your textbook Black fur (BB) dominant, and White Fur (bb) recessive and have them produce
offspring the result will be Hybrids (Bb) for all four potential outcomes of offspring. Therefore
they will all have Black fur, but also carry a recessive white fur gene
13. Explain Dominant traits, and Recessive Traits in your own words? (2 Marks)
Dominant trait is an allele (form of a gene) that when present will always display itself on an
organism
Recessive trait is an allele (form of a gene) that will only display itself in the absence of a
Dominant allele
14. Explain Incomplete Dominance? (2 Marks)
The dominant/recessive pattern of inheritance does not always prevail. Sometimes neither
form of allele will prevail over the other, so this will result in a blending of the two.
I.e. so if white (normally recessive) flowers breed with red (normally dominant) flowers, and
incomplete dominance occurs, this will result in pink colored flowers
15. Explain how environment can alter hereditary characteristics? Give two examples (3 Marks)
Genes can be greatly altered by the environment in which an offspring develops
i.e. plants not receiving enough sunlight will fail to grow to their full potential
-similarly children who do not receive enough nutrition will fail to grow as tall or or
strong as their genes would normally allow
-Also babies developing the womb, can have their development altered by alcohol or
drugs consumed by the parent while they are in the womb
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16. Using Punnett squares explain Mendel’s pea plant experiment, and how a short hybrid can
appear in the second generation after originally breeding a Tall Pea Plant (TT) with a short Pea
Plant (tt)… (7 Marks)
First Generation
t
t
T
This will result in four potential offspring containing the alleles
T
Tt,
Tt,
Tt,
Tt
All of these offspring display the “Tall” dominant trait and will grow tall, but contain the second
recessive short allele
Second Generation
T
t
T
This will result in four potential offspring containing the alleles
T
TT,
Tt,
Tt,
tt
Three of the possibilities will result in Tall plants since they have the dominate tall allele
Where as one will contain two recessive “short” alleles, and will be a short pea plant