Chapters 9 biology
Terms in this set (82)
Particles called pangenes travel from each part of an organisms body to the eggs or sperm and then are passed onto the next generation. In addition changes that occur in the body during an organisms life are passed on in the same way.
The idea that the hereditary materials contributed by the male and female parents mix in forming the offspring similar to the way that blue and yellow paints blend to make green.
Why was the pangenesis theory reject?
Because we now know that reproductive cells are not composed of particles from somatic or body cells and the changes in somatic cells do not influence eggs and sperm.
Why was the blending hypothesis rejected?
The blending hypothesis was rejected because it does not explain how traits that disappear in one generation can reappear in later ones
Traits passed from one generation to the next
The scientific study of heredity. Modern genetics began with the work of Gregor Mendel in the 19th century.
A heritable feature that varies among individuals with in a population, such as flower color in P plants or eye color in humans
A variation of a character found within a population such as purple or white flowers in P plants or brown or green eyes in humans.
A form of reproduction that involves the fusion of sperm and egg produced by the same individual organism.
Refers to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents.
The fusion of sperm and egg derived from two different individuals.
The offspring of parents of two different species or of two different varieties of one species.
The mating of two sexually reproducing individuals. Cross-fertilization itself is referred to as hybridization or simply a genetic cross.
The parent individuals from which offspring are derived; P stands for parental.
The offspring of two parental (P generation) individuals; F1 stands for first filial.
The offspring of the F1 generation; F2 stand for second filial
Explain why Mendel's decision to work with peas was a good choice
Good choice because they had short generation times, produced large numbers of offspring from each mating, and came in many readily distinguishable varieties. Most importantly Mendel could could strictly controlled the meetings of people.
Why was the development of true breeding varieties critical to the success of Mendels experiments?
True breeding varieties allowed Mendel to predict the outcome of specific crosses and thus to run controlled experiments.
An experimental meeting of individuals different in only a single character.
what were the pea plant characters that Mendel studied?
Flower color, flower position, seed color, seed shape, pod shape, pod color, and stem length
What were Mendels 4 hypotheses?
1) there alternative versions of genes that account for variations in inherited characters.
2) For each character, an organism inherits two alleles, one from each parent
3) if the two alleles of an inherited pair differ, then one determines the organisms appearance and is called the dominant allele. The other has no noticeable effect on the organisms appearance and is called the recessive allele.
4) a sperm or egg carries only one allele for each inherited character because allele pairs separate from each other during the production of gametes.
Alternative versions of a gene are called alleles. For example the gene for flower color in P plants exists in two versions one for purple and the other for white.
having two identical alleles for a given gene
Having two different alleles for a given gene
The allele that determine the phenotype of the gene when the individual is heterozygous for that gene
In allele that has no noticeable effect on the phenotype of a gene when the individual is heterozygous for that gene
Law of segregation
A general rule in inheritance that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, each resulting gamete ending up with only one allele of each gene; also known as Mendels first law of inheritance
A diagram used in the study to show the results of random fertilization.
The expressed traits of an organism
The genetic makeup of an organism
How can two plants with different genotypes inherited character be identical in phenotype?
One could be homozygous for the dominant allele and the other heterozygous.
A specific location of a gene along the chromosomes
Describe the genetic relationships between homologous chromosomes
Homologous chromosomes have genes for the same characters located at the same positions along their lengths. However, to homologous chromosomes may bear either the same alleles or 2 different ones. This is the connection between Mendels laws and homologous chromosomes: alleles of a gene reside at the same locus on homologous chromosomes.
An experimental mating of individuals different in two characters, such as seed shape and seed color.
Law of independent assortment
A general rule in inheritance that individuals have two alleles for each gene and that when gametes form during meiosis each pair of alleles for a particular characteristic segregate independently of other pairs. In other words, the inheritance of one character has no effect on the inheritance of another character. this is known as Mendel's second law of friction inheritance.
The meeting between an individual of unknown genotype for a particular characteristic and an individual that is homozygous recessive for that same characteristic.the testcost can be used to determine the unknown genotype (homologous dominant versus heterozygous parentheses).
Rule of multiplication
A rule stating that the probability of a compound event is the product of the separate probabilities of the independent events.
Rule of addition
A rule stating that the probability that an event can occur in two or more alternate ways is the sum of the separate probabilities of the different ways.
Why was Mendel wise to use large sample sizes in his studies?
Mendel knew that he needed to obtain large samples before he could begin to interpret inheritance patterns.
The version of a character that most commonly occurs in nature
A family genetic tree representing the occurrence of heritable traits in parents and offspring across a number of generations. Used to determine genotypes of matings that have already occurred.
Explain how family pedigrees can help determine the inheritance of many human traits.
Pedigrees show how characteristics are passed from one generation to the next. They are used in studying human genetics because it is not possible to carry out controlled breeding experiments with humans, as we can with other animals or with plants. Instead we have to use the natural 'experiments' carried out when people have children, and see which characteristics tend to run in a family
And individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder but who may pass on the recessive allele to offspring.
The most common life-threatening genetic disease in the US. In people with two copies of a certain recessive allele. It is characterized by an excessive see creation of mucus and vulnerability to infection. It is fatal if untreated.
Mating blood relatives
A form of human dwarfism caused by a single dominant allele. The homozygous condition is lethal.
A human genetic disease caused by a single dominant allele. It is characterized by uncontrollable body movements and D generation of the nervous system. It usually sets in in middle age and is fatal 10 to 20 years after the onset of symptoms.
Explain how recessive and dominant disorders are inherited provide examples of each.
Most people who have recessive disorders are born to normal parents who are both heterozygous. That is parents who are carriers of the recessive allele for the disorder, but our phenotypically normal. Each child of two carriers has a one quarter chance of inheriting two recessive alleles. An example of a recessive disorder is cystic fibrosis.
Dominant disorders are rare and typically arise by mutations (changes to the DNA) in cells that produces sperm/eggs. They sometimes causes the death of offspring, making it imposssible for the allele to be passed from generation to generation and making dominant disorders less common than recessive disorders. Examples include achondroplasia and Huntington's disease.
A technique for diagnosing genetic defects while a fetus is in the uterus a sample of amniotic fluid, obtained by needle inserted into the uterus, is analyzed for defective fetal cells.
Chorionic villus sample
A technique for diagnosing genetic defects while the fetus is in an early development stage within the uterus. A small sample of the fetal portion of the placenta is removed.
A technique for examining a fetus in the uterus. high-frequency sound waves echoing off the fetus are used to produce an image of the fetus. Usually happens about 20 weeks into the pregnancy.
Describe the ethical dilemmas created by advances in biotechnology.
The information obtained through genetic testing can give people with family histories of genetic disorders information to make informed decisions about having children, but these new screening methods have problems too. For example, if confidentiality is breached, will carriers of recessive allele's be stigmatized? Will they be denied health or life insurance even though they themselves are healthy? Will people equate carrier with disease?
Another ethical issue is what is to be done if fetal tests reveal a serious disorder. The parents must choose between terminating the pregnancy and preparing themselves for a baby with severe problems.
A type of inheritance in which the phenotype of a heterozygote is intermediate between the phenotypes of the two types of homozygotes. An example of incomplete dominance are red and white snapdragons which when crossed all the F1 hybrids will have pink flowers. An example in humans is hypercholesterolemia, dangerously high cholesterol levels.
A type of inheritance in which the phenotypes of the heterozygotes and dominant homozygotes are indistinguishable. An example of complete dominance are Mendel's pea crosses because the S1 offspring always looked like one of the two parental varieties.
ABO blood group
Genetically determined classes of human blood that are based on the presence or absence of carbohydrate A and carbohydrate B on the surface of the red blood cells. The ABO blood group phenotypes,also called blood types, are a, B, AB and O.
Any of a set of three or more alleles, or alternative states of a gene, only two of which can be present in a diploid organism. This is different from Gregor Mendel's studies which involveed characteristics having only two allele types. An example of multiple alleles is the ABO blood group in humans. There are three alleles for the ABO blood type: A, B and O. These alleles can produce four phenotypes: A, B, AB or O.
Inheritance pattern in which a heterozygote expresses the distinct traits of both alleles. An example of codominance would be the blood type AB.
The control of more than one phenotypic characteristic by a single gene. An example of pleiotropy is sickle cell disease in humans.
The additive effects of two or more genes on a single phenotypic characteristic. Skin color is an example of Polygenic inheritance. It occurs on a continuum of light to dark.
What is the difference between pleiotropy and Polygenic inheritance?
In pleiotropy a single gene may effect many phenotypic characters. In Polygenic inheritance multiple genes effect a single phenotypic character.
What other factor can affect many characteristics?
What are some examples of environmental factors that influence phenotypic characters?
In humans, nutrition can influence heights; exercise can influence build; suntanning can influence skin color; and practice can improve performance on IQ tests. In trees, the leaves of the tree may all have the same genotype, but they may vary greatly in phenotypes such a size shape and color, depending on exposure to wind and sun and the trees nutritional state.
Are all characters influenced by both genes and by the environment?
No. For some characters, such as the ABO blood group, a specific genotype determines a very specific phenotype, and the environment plays no role at all. For other characters the environment can play a very influential role, not just the genes.
If most characters result from a combination of environment and genes, why was Mendel able to ignore environmental influences on his pea plants?
The characters Mendel chose to study were all entirely genetically determined. They were not influenced by the environment at all.
Chromosome theory of inheritance
A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis to accounts for inheritance patterns
Law of segregation
A general rule in inheritance that individuals have two alleles for each gene and that when gametes formed by meiosis the two alleles separate, each resulting gametes ending up with only one allele of each gene.
Law of independent assortment
A general rule in inheritance that when gametes form during meiosis, each pair of alleles for a particular characteristic segregate independently of other pairs.
Genes located near each other on the same chromosome tend to be inherited together.
How are linked genes inherited differently from non-linked genes?
Linked genes tend to be inherited together and do not follow Mendels law of independent assortment. Non-linked genes do follow Mendels law of independent assortment.
Describe T H Morgan's studies of crossing over in fruit flies.
In one of Morgan's experiments he crossed a wild type fruit fly, a fly that has a grey body and long wings, and a fly with a black body and undeveloped wings. He knew the genotypes of these flies from previous studies. If the genes were not linked, then independent assortment should produce offspring in a phenotypic ratio of one to one to one to one. But because the genes are linked, Morgan obtained different results. Most of the offspring have parental phenotypes, but 17% of the offspring flies were recombinants. When Morgan first obtained these results he didn't understand crossing over. To explain the results, he is hypothesized that the genes were linked at that some mechanism occasionally broke the linkage.
Explai how crossing over produces new combinations of alleles.
Over between homologous chromosomes produces new combinations of alleles in gametes. Crossing over is the mechanism that breaks linkages between genes.
Explain how Sturtevant created linkage maps.
Sturtevant predicted that the further apart two genes are, then the higher the probability that a crossover will take place. Then he constructed genetic maps based on recombination frequencies.
With respect to two genes, the number of recombinant offspring from a meeting divided by the total number of offspring.The percentage of recombinants.
A listing of the relative locations of genes along a chromosome, as determined by recombination frequency
Explain how sex is genetically determined in humans.
If an egg is fertilized by sperm bearing in X-chromosome a female will be produced. If it is fertilized by sperm with a Y chromosome a mail is produced.
Purpose of the SRY gene
One gene on the Y chromosome plays a huge role in sex determination in humans. This gene is called SRY and triggers testes developments. In the absence of SRY and individual develops ovaries rather than testes
Nation system in humans to those in fruit flies grasshoppers birds and bees.
Fruit flies: sex is determined by the ratio between the number of X-chromosome's and the number of autosomes sex, although the Y chromosome is essential for sperm formation.
Grasshoppers: grasshoppers do not use an X-Y system. They have an X-O system, in which O stands for the absence of a sex chromosome. Females have 2 X chromosomes; males have only one X chromosome. Females are XX; males are XO, where a O represents the absence of a sex chromosome. Males produce two classes of sperm, X bearing and lacking any sex chromosomes, and sperm cells determine the sex of the offspring at fertilization.
Birds: birds do not have an X-Y or X-O system. The sex chromosomes in birds are designated Z and W. Males are ZZ; females are ZW. In birds sex is determined by whether the egg carries a Z or a W.
Bees: In B's sex is determined by chromosome number rather than by sex chromosomes. Females develop from fertilized eggs and are diploid; males develop from unfertilized eggs and are haploid.
In some organisms environment can even determine sex. For example, green sea turtle hatchlings that incubate above 30°C will be male. Temperature dependent sex determination is an extreme example of the environment affecting the phenotype of an individual.
A gene located on a sex chromosome. In humans, the majority of sex linked genes are located on the X chromosome.
A human genetic disease caused by a sex linked recessive allele. The disease is characterized by excessive leading following injury. Hemophiliacs lack one or more of the proteins required for blood clotting.
A category of common, sex linked human disorders involving several genes on the X chromosome. It is characterized by a malfunction light sensitive cells in the eyes and effects mostly males but also homozygous females.
Duchenne muscular dystrophy
A human genetic disease caused by a sex linked recessive allele. It is characterized by progressive weakening and a loss of muscle tissue by age 12 most end up in a wheelchair and affected individuals rarely live there early 20s
Describe patterns of sex linked inheritance noting examples include examples in fruit flies and humans.
When the female parent is a dominant homozygote and the male parent is recessive, all the offspring exhibit the dominant allele, but the female offspring are all carriers of the recessive allele. An example in fruit flys is red vs. white eye color, red is dominate.
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