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Genetics Study Guide
1. Describe DNA – What is it? Where is it found? Why is it important?
Deoxyribnucleic acid is a complex chemical found in the nucleus of most cells and near the
center of cells without a nucleus (bacteria). DNA is important because it provides the
instructional code for the structure and function of all living things.
2. Define genes. List three traits that genes are responsible for in organisms.
DNA is found in long stringy strands called chromosomes. Genes are sections of chromosomes
that control specific traits.
3. What is the study of heredity called? Genetics
4. What do scientists mean when they say a trait like eye color is hereditary?
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Parents pass traits to offspring through DNA.
5. The theories of Gregor Mendel can be summed up in 3 statements: traits are controlled by
_genes_ on the chromosomes; genes have different forms that are called _allele_; an allele
may be _dominant_ or _recessive_ in form; and when a pair of chromosomes separates
during _meiosis_, the different alleles for a trait move into separate sex cells.
6. Explain the difference between genotype and phenotype.
Genotype is the exact make up of a gene (the letters in a Punnett square).
Phenotype is the results, the appearance caused by the genotype.
7. Hairline shape is an inherited trait in humans. A widow’s peak is dominant over the recessive
straight trait. Use a Punnett square to infer how parents with widow’s peaks could have a
child with a straight hairline.
8. When making predictions, we should always remember that
_probability_ may be changed by _chance_, _luck_, or _fate_.
9. List the 3 possible alleles for blood type. A, B, O
10. Blood type is an example of inheritance by _multiple_ _alleles_.
11. Each of the 10 fingerprints on an individual may be different because fingerprints are the
result of _polygenic_ _inheritance_.
12. Why are males affected more often than females by sex-linked genetic disorders?
The X chromosome is dominant over the Y chromosome.
13. Use a Punnett square to explain how a woman who is a carrier for color blindness can have a
daughter who is color-blind.
The 23rd pair of chromosomes is the pair that determines the gender. Each one contains 1,000s
of genes including the gene that codes for color eyesight. The Punnett square looks like the
following and shows a normal female carrying colorblindness (XXc) crossed with a normal male.
One possible female offspring XX is normal. One possible female offspring XXc is normal
carrier. One possible male is normal XY. One possible male is colorblind XcY because the Xc is
dominant over the Y.
Extra Credit:
14. A _pedigree_ is a tool for tracing the occurrence of a trait in a family. Males are
represented by _squares_ and females by _circles_. A circle or square that is completely
shaded shows that the person has the condition. A half colored circle or square indicates
_carrier_ of the condition.
15. A chart that shows the location of individual genes on a chromosome is called a _genome_.
16. What are the advantages of having a complete map of the human genome?
Identifying the genes that cause diseases and disorders.