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42 Cards in this Set

  • Front
  • Back
Unit of heredity that encodes info for the form of a particular characteristics
The location of a gene on a chromosome
Homologous chromosomes
Carry the same kinds of genes for the same characteristics
-Genes for the same characteristic are found at the same loci on both homologous chromosomes
-Alternate versions or forms of genes found at the same gene locus
-Each carries two alleles per characteristic, one on each of the two homologous chromosomes
Both homologous chromosomes carry the same allele (gene form) at a given gene locus
Heterozygous (hybrid)
Two homologous chromosomes carry different alleles at a given locus
Gregor Mendel
-Czech Republic monk in late 1800s
-Botonist and mathematician
-Pea plant inheritance experiments (cross-fertilization, observing one trait at a time)
Pea plants specifics
-If homozygous for a particular characteristic, always produce the same physical forms
--Plants homozygous for a characteristic are True-Breeding
Genetic cross
The mating of pollen and eggs (from same or different parents)
Notation for Parental Generation:
First Filial Generation:
Second Filial Generation:
Plant experiments specs
1. Mendel crossed a true-breeding pruple flower plant with a true-breeding white-flower plant (P)
2. F1 generation consisted of all purple-flowered plants
3. Let F1 self fertilize: F2 had 1/4 white flowers
-Particular combination of the 2 alleles carried by an individual
-3 possibilities (PP, Pp, pp) (homo, hetero, homo)
Physical expression of the genotype (e.g. purple flowers)
How Meiosis Separates Genes
-Homologous chromosomes separate in meiosis anaphase I
-Each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic
Mendel’s Law of Segregation
Separation of alleles in meiosis
How to bookkeep
1. Add fractions of any genotypes of the same kind (1/4Pp + 1/4pP= 1/2Pp total)
2. From the sums of all the different kinds of offspring genotypes, create a genotypic ratio
1/4 PP, ½ Pp, ¼ pp is in the ratio 1PP: 2Pp: 1pp
Test cross
Used to deduce the actual genotype of an organism with a dominant phenotype (i.e., is the organism PP or Pp?)
"Linked gene characteristics"
-Different gene loci located on the same chromosome tend to be inherited together
-Characteristics whose genes tend to assort together are "linked"
-Messes up ratio in independent assortment; recombination increases variability also
General thoughts on Mendel system
Great for very simple situations, however doesn't work as things get more complicated (see
Not sex chromosomes
Genes carried on one chromosome are...
-X is so much larger than Y chromosome; less in men to mask a bad recessive trait in Y
X and U have very few genes in common, thus...
-Females (XX) can be homozygous or heterozygous for a characteristic
-Males (XY) have only one copy of the genes on the X and Y
Sex-linked (specifically X-linked) recessive alleles display their phenotype ___ often in males
Assumptions drawn from Mendel's Rules
–All genes are governed by alleles found at a single locus on a pair of homologous chromosomes
–There are two alleles (gene forms) for each characteristic or gene type
–One allele is dominant over the other, which is recessive
Incomplete dominance inheritance pattern
-When the heterozygous phenotype is intermediate between the two homozygous phenotypes
Multiple Allelism
-Thousands of alleles for eye color in fruit flies, producing white, yellow, orange, pink, brown, or red eyes
–Human blood group genes producing blood types A, B, AB, and O
--Three alleles in this system: A, B, and O
-Some alleles are always expressed even in combination with other alleles
--Heterozygotes display phenotypes of both the homozygote phenotypes
Polygenic inheritance
-Genes governed by the interaction of more than two genes at multiple loci
-Human skin color is controlled by at least 3 genes, each with pairs of incompletely dominant alleles
-Alleles of a characteristic may create multiple phenotypic effects
-Cascading effect
-Careful analysis of the diagram of records of gene expression over several generations of a family
-Reveals inheritance pattern of a trait
Heterozygous individuals are _____ of a recessive genetic trait (but otherwise have a normal phenotype)
enzyme that produces melanin
Sickle-cell Anemia
-A mutant hemoglobin gene causes hemoglobin molecules in blood cells to clump together
-Homozygous carriers face great difficulties
-Heterozygous carriers have great resistance to malaria, however
Dominant Genetic Disorders
-Affects heterozygous carriers as well, 50% in kids
How dominant disease alleles disrupt normal cell functions:
-Produce an abnormal protein that interferes with the function of the normal one
-Encode toxic proteins
-Encode a protein that is overactive or active at inappropriate times and places
Sex-linked disorders
appear more frequently in males and often skip generations
Incorrect separation of chromosomes or chromatids in meiosis
Turner Syndrome
(XO): an underdeveloped, infertile woman with only one X chromosome
Trisomy X
(XXX): a fertile, “normal” woman with an extra X chromosome
Kleinfelter Syndrome
(XXY): an infertile man with an extra X chromosome, having partial breast development and small testes
XYY Male
a tall man with an extra Y that produces high levels of testosterone and may score lower on IQ tests
Trisomy 21
(Down Syndrome) is an example of an abnormal autosomal number
-Down syndrome individuals have three copies of chromosome 21