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Unit 7: Continuity of Life/Genetics
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Essential Understandings for Bio 4 and 5:
Many organisms are capable of combining genetic information from two parents to produce offspring.
Sex cells are produced through meiosis. This allows sexually reproducing organisms to produce
genetically differing offspring, and maintain their number of chromosomes. Meiosis occurs in sexual
reproduction when a diploid germ cell produces four haploid daughter cells that can mature to become
gametes (sperm or egg).
Genetically diverse populations are more likely to survive changing environments.
Recombination and mutation provide for genetic diversity. Some new gene combinations have
little effect, some can produce organisms that are better suited to their environments, and others can be
deleterious.
Mitosis and meiosis refer to division of the nuclear material.
Cytokinesis is the division of the cytoplasm and organelles.
The many body cells of an individual organism can be specialized to perform different functions, even
though they are all descended from a single cell and contain essentially the same genetic information.
Mendel’s laws of heredity are based on his mathematical analysis of observations of patterns of
inheritance of traits. Geneticists apply mathematical principles of probability to Mendel’s laws of
heredity in order to predict the results of simple genetic crosses. The laws of probability govern simple
genetic recombinations.
Genotype describes the genetic make-up of an organism and phenotype describes the organism’s
appearance based on its genes. Homozygous individuals have two identical alleles for a particular trait,
while heterozygous individuals have contrasting alleles. When one allele masks the effect of another,
that allele is called dominant and the other recessive. When an intermediate phenotype occurs and no
allele dominates, incomplete dominance results. Many other patterns of inheritance exist including
multiple alleles, polygenic inheritance, and sex-linked inheritance.
Inserting, deleting, or substituting DNA bases can alter genes. An altered gene may be passed on to
every cell that develops from it, causing an altered phenotype. An altered phenotype may be neutral,
beneficial or detrimental. Sometimes entire chromosomes can be added or deleted, resulting in a
genetic disorder. These abnormalities may be diagnosed using a Karyotype.
DNA technologies allow scientists to identify, study, and modify genes.
Forensic identification is an example of the application of DNA technology.
Genetic engineering techniques are used in a variety of industries, in agriculture, in basic research,
and in medicine. There is great benefit in terms of useful products derived through genetic engineering
(e.g., human growth hormone, insulin, and pest- and disease-resistant fruits and vegetables).
Eugenics, a pseudo-science of selective procreation, was a movement throughout the twentieth
century, worldwide as well as in Virginia, that demonstrated a misuse of the principles of heredity.
The Human Genome Project is a collaborative effort to map the entire gene sequence of organisms. This
information may be useful in detection, prevention, and treatment of many genetic diseases. The
potential for identifying and altering genomes raises practical and ethical questions.
Cloning is the production of genetically identical cells and/or organisms.
Genetic predisposition towards diseases impacts human health. Awareness of genetic predisposition
allows individuals to make lifestyle changes that can enhance quality of life.
GLOSSARY
1. allele – one of a number of different forms (versions) of the same gene for a specific trait; usually
represented by alphabet letters
2. altered gene – change in a gene caused by addition, deletion or substitution of DNA bases
3. cloning – process of making genetically identical cells or organisms
4. deletion – type of chromosome mutation that occurs when a piece of a chromosome is lost
5. dihybrid – the crossing of two different factors
6. diploid – a nucleus having 2 sets of chromosomes, 2N
7. dominant allele – allele that masks another allele’s expression
8. gametes – sex cells (egg and sperm)
9. gene – segment of a chromosome that controls traits; contains the code for making a single protein
10. genetic cross – an actual or possible breeding between two sexually-reproducing organisms of the
same species, resulting in various genotypes and phenotypes in the offspring
11. genetic disorder – an inherited disease caused by an abnormal gene
12. genetic engineering – techniques used to deliberately alter an organism’s DNA includes human
growth hormone, insulin, and resistant fruits and vegetables
13. genetic recombination – new DNA molecule formed from the combination of portions of two
different DNA molecules
14. genotype – the genetic makeup of an organism
15. genome – the entire set of an organism’s genes; genomics is the study of entire genomes
16. haploid – describes a nucleus that has only one set of unpaired chromosomes (N)
17. heterozygous – having two different alleles of the same gene
18. homozygous – having two identical alleles of the same gene
19. Human Genome Project – collaborative effort to map the entire human genetic sequence
20. incomplete dominance – when an intermediate phenotype occurs, no dominant trait
21. inheritance – the process of passing traits from parents to offspring
22. insertion – type of chromosomal mutation that occurs when a piece of a chromosome reattaches to
the original chromosome but in a reverse direction
23. karyotype – a display or picture of all the chromosomes in a cell’s nucleus
24. meiosis – a process in which the number of chromosomes in a cell is reduced in half; produces
haploid sperm and egg
25. monohybrid – the crossing of one type of trait or factor
26. mutation – a change or mistake in the DNA sequence
27. pedigree chart – diagram that shows the occurrence of a genetic trait over several generations
28. phenotype – the physical characteristics of an organism
29. probability – mathematical way to predict the results of simple genetic crosses
30. Punnett square – a chart used to show genetic crossing and probabilities
31. recessive allele – the allele that is masked by another
32. sex-chromosomes – chromosomes that are different in males and females; X and Y
33. trait – a genetically determined characteristic
34. translocation – type of chromosomal mutation that occurs when a chromosome piece ends up on a
completely different nonhomologous chromosome
35. trisomy – chromosomal mutation that occurs when chromosomes fail to separate during meiosis,
Trisomy of chromosome 21 results in Down Syndrome causing mental retardation
36. autosomes-chromosomes that are identical in males and females