chapter 11 Flashcards
disease that develops when a person has received 2 copies of a gene (one from each parent) that codes for altered subunit of hemoglobin
sickle cell disease
blending theory of inheritance
was believed up until 1900s : suggested that hereditary traits blend evenly in off- spring through mixing of the parents’ blood, much like the effect of mixing coffee and cream
variation in ‘‘character’’ according to Mendel is called a ____
trait
Mendel observed parental traits appear unchanged in offspring, whereas others disappear in one generation to
reappear in next; what did he observe?
segregation of chromosomes to gametes in meiosis
f1 generation
the first generation of offspring from the cross
masking a gene
dominance
dihybrid
a zygote produced from a cross that involves 2 characters
what is the principle of segregation?
The pairs of alleles that control a character segregate (separate) as gametes are formed; half the gametes carry one allele, and the other half carry the other allele.
homozygote
Both alleles (traits) are the same
heterozygote
Alleles (traits) for a given gene (character) are different
locus
The location on a chromosome of a particular gene
phenotype
The appearance of an organism
genotype
The genetic constitution of an organism
testcross
A cross between an individual with the dominant phenotype and a homozygous recessive individual
Define the principle of independent assortment
This refers to the fact that during gamete formation, the alleles for two different traits segregate independently from each other
What is a testcross, and why is it used?
A test cross is a cross between an individual with the dominant phenotype and a homozygous recessive individual. It
is performed to determine if a phenotype is the product of a homozygous genotype or a heterozygous dominant genotype
Describe the chromosome theory of inheritance
Genes and their alleles are carried on chromosomes; discovered by Sutton
Suttons conclusions:
- Chromosomes occur in pairs in sexually reproducing, diploid organisms, as do the alleles of each gene.
- The chromosomes of each pair are separated and delivered singly to gametes, as are the alleles of a gene.
- The separation of any pair of chromosomes in meiosis and gamete formation is independent of the separation of other pairs, as in the independent assortment of the alleles of different genes in Mendel’s dihybrid crosses.
- Finally, one member of each chromosome pair is derived in fertilization from the male parent, and the other member is derived from the female parent, in an exact parallel with the two alleles of a gene.
Compare and contrast pleiotropic and polygenic characters.
In the case of a pleiotropic character, a single gene would give rise to multiple traits whereas in polygenic inheritance and single character (e.g. the height of a human adult) is determined by the combined effects of multiple genes.
Codominance
occurs when alleles have approximately equal effects in individuals, making the alleles equally detectable in heterozygotes.
Incomplete dominance
occurs when the effects of recessive alleles can be detected to some extent in heterozygotes. Ex: Flower colour in snapdragons If true-breeding, red-flowered and white-flowered snapdragon plants are crossed, all the F1 offspring have pink flowers. It may seem as if the colors have blended until you cross the F1 offspring and you will get the 1 red : 2 pink : 1 white. This outcome can be explained by incomplete dominance between a CR allele for red colour and a CW allele for white colour.
multiple alleles
although alleles do indeed occur in pairs in individuals, multiple alleles (more than two different alleles of a gene) may be present if all the individuals of a population are taken into account. Multiple alleles present no real difficulty in genetic analysis because each diploid individual still has only two of the alleles, allowing gametes to be predicted and traced through crosses by the usual methods. Ex: ABO Blood types; The four blood types—A, B, AB, and O—are produced by different combinations of multiple (three) alleles of a single gene
Epistasis
Genes interact, with one or more alleles of a gene at one locus inhibiting or masking the effects of one or more alleles of a gene at a different locus ex: dog fur appears black or brown depending of the melanin gene. in a different locus there is an inhibitor gene to the melanin and if the gene is inhibiting the black or brown fur the dog will have yellow fur. so the dog fur depends firstly on the inhibitor gene then the fur color gene and the inhibitor gene is said to be epistatic
Define pleiotropy
Single genes affect more than one character of an organism. For example, sickle cell disease (see earlier discussion) is caused by a recessive allele of a single gene that affects hemoglobin structure and function.
cross-pollination
Mendel prevented self-fertilization simply by cutting off the anthers. Pollen to fertilize these flowers must then come from a different plant. This technique is called cross-pollination, or more simply, a cross. This technique allowed Mendel to test the effects of mating pea plants of different parental types.
self-fertilization
in the case of plants (and mendels experiments) he chose self-fertilizing pea plants, meaning sperm nuclei in pollen produced by the anthers fertilize egg cells housed in the carpel of the same flower
true-breeding
when self fertilized (or selfed), they passed traits without change from one generation to the next
polygenic inheritance
several different genes each contribute to the phenotype. In addition, alterations in a single gene sometimes affect more than one phenotype in an organism; this phenomenon is called pleiotropy. .
why did Mendel choose garden peas for his research?
- could be grown easily in monastery garden without elaborate equipment
- as in other plants, the gametes are produced in the structures of the flowers
What was the significance of mendels experiments in regard to dominance, segregation, and independent assortment
-Mendel’s experiments in regards of dominance: breeding 2 true breeding pea plants (one with purple flowers & one with white flowers) would result in a 3:1 for purple flowers. This was because the dominant gene in pea plants is the purple flower and with the punnett square we can now predict the outcome for certain traits.
what were mendels 3 hypothesis?
1) the adult plants carry a pair of factors that govern the inheritance of each character.
2) if an individual’s pair of genes consists of different alleles, one allele is dominant over the other.
(his hypothesis assumes that one allele is dominant and the other allele is recessive. When a dominant allele for a trait is paired with a recessive allele for the same trait, the dominant allele is expressed. By contrast, a recessive allele is expressed only when two copies of the allele are present. For example, for flower colour in Mendel’s experiments, the allele for purple flowers was dominant and the allele for white flowers was recessive)
3) The pairs of alleles that control a character segregate (separate) as gametes are formed; half the gametes carry one allele, and the other half carry the other allele (now known as principle of segregation)
significance of mendels experiments
- Mendel’s methods illustrate, perhaps as well as any experiments in the history of science, how rigorous scientific work is conducted: through observation, making hypotheses, and testing the hypotheses with experiments.
- Mendel’s hypotheses explain how individuals may differ genetically but still look the same
- Mendel could predict both classes and proportions of offspring from his hypotheses
significance of mendels principle of segregation
the principle of segregation the it states that during fertilization, fusion of the haploid maternal and paternal gametes produces a diploid nucleus called the zygote nucleus. The zygote nucleus receives one allele for the character from the male gamete and one allele for the same character from the female gamete, reuniting the pairs. This shows us where some genetic traits come from and the probability of certain genes appearing in offspring.
