14 Mendel and the gene idea Flashcards
What is a character? Give an example.
It’s a heritable feature that varies among indivduals. Example would be flower colour
What is a trait? Give an example.
A trait is a variant of a character, such as purple or white colour for flowers. they are characterisitcs defined by genes
What is the haploid reproductive unit of plants?
Spores
How do pollen plants self-fertilize?
Pollen grains from the stamen fall on the carpel of the same flower and the sperm released from the pollen grains fertilize the egg in the carpel.
What are the reproductive organs of a flowering plant?
They’re in the flower itself. The pollen-producing organs are called stamens. The egg-bearing organs are called carpels
How did Mendel cross (mate) pea plants?
He removed the immature stamen from a purple flower, and transferred sperm-bearing pollen from stamens of a white flower to carpel of purple. The pollinated carpel turned into a pod, whose seeds Mendel planted.
What is a true-breeding plant?
they are a variety that over many generations of self-pollination have produced only the same variety as the parent plant.
What is hybridization?
It is the crossing of two true-breeding varieties.
List the three generations involved in true-breeding and their names
The P generation are the true breeding parents
The F1 geenration are the first filial generation (filia means son in latin). They are the hybrid offspring of P-gen
The F2 generation are the second filial generation, produced by allowing F1 to self-pollinate or cross-pollinating them with other F1 hybrids
Explain Mendel’s experiment to find what traits appear in F2 gen when F1 hybrids cross or self pollinate, and his conclusion
Mendel crossed two true-breeding vareities (purple and white flowers) and the F1 gen were all purple flowers. After the F1 gen self or cross pollinated, the F2 offspring had a ratio of 3:1 purple to white results.
what is an allele? What causes their existence?
It is an alternative version of a gene. It is caused by the fact that each somatic cell has two copies of each chromosomes and therefore two copies of each gene which may be identical or different alleles.
What accounts for variation in inherited characters?
Alternative versions of genes, or alleles
How many copies of each gene does an organism inherit ?
For each character, an organism inherits two copies, one from each parent
Which allele determines the organism’s character if two alleles at a locus differ? In Mendel’s experiment, which one would this be?
the dominant allele, the purple colour
What is a recessive allele?
It is the vairation that does not appear in a phenotype if a dominant allele is present
What is the law of segregation?
Two alleles for a heritable character segregate during gamete formation and end up in different gametes.
What is meant by segregate?
Seperate from each other
Explain the variation in alleles of the gametes if an orgnaism is true-breeding for a character; if it is an F1 hybrid
If it is true-breeding, then the same allele for that character is present in all of its gametes
If it is a hybrid, 50% of gametes receive dmoinant allele, 50% receive recessive
What is a Punnett square?
a device that predicts the allele composition of offspring. A capital letter is sued for dominant alleles and small letters for recessive
What is meant when a character is homozygous?
The organism has identical alleles for that character
What is meant when a character is heterozygous?
the organism has different alleles for that character
What is a phenotype? What is a genotype? Give an example of each?
A phenotype is an organism’s appearance or observable traits. In F2 generation, the phenotype would appear to have the 3:1 ratio (purple to white)
A genotype is an organism’s genetic makeup. In F2 generation, the genotype would appear to have the 1:2:1 ratio (dominant homozygous to heterozygous to recessive homozygous)
What is a testcross; explain how it is performed
It is a test to find the genotype of a mystery organism by breeding it with a recessive homozygote
What are monohybrids?
A hybrid that is heterozygous for the one aprticular character that is followed in the testcross
Monohybrid cross
A cross between two monohybrids
What is a dihybrid
A hybrid that is heterozygouys for the two characters being followed in the cross
Dihybrid cross
Cross between two dihybrids
State the law of independent assortment
Each pair of alleles segregate independently during gamete formation
Explain the dihybrid cross Mendel performed, and the phenotypic ratio of the offspring of the F2 gen. Why is this the ratio instead of the 3:1 just as in a monohybrid cross?
He crossed YR, Yr, yR, and yr sperms with eggs of the same alleles. The phenotypic ratio he got every time was 9:3:3:1 (YYRR to
State the multiplication rule
To determine a probability of two events happening simultanetously, multiply the probability of one event by the probability of the other
What is the only condition needed for the law of independent assortment to apply?
The genes or allele pairs need to be located on different chroms
Give an example of the multiplication rule in genetics
Each hetrozygous plant has 1/2 chance of carrying the dominant allele (non-wrinkled) and 1/2 chance of recessive allele (wrinkled). The probability of zygote to have both dominant (RR) is 1/2 * 1/2 or 1/4
What is the addition rule?
The probability that one of two independent events will occur is calculated by adding their individual probabilities.
What is complete dominance?
Form of dominance where the dominant allele is seen in phenotype while recessive allele isn’t
What is incomplete dominance?
Form of intermediate dominance in which resulting phenotype is a combination of phenotypes of both parental alleles
What is codominance?
When both alleles affect phenotype in separate distinguishable ways
What does the observed dominant/recessive relationship of alleles depend on for any character?
On the level that we examine the phenotype: organismal, biochemical, etc
Define pleiotropy
The property of having multiple phenotypic effects
Why does Mendelian inheritance not portray how genes really affect phenotypes?
Because most genes have the pleiotropy property
What is epistatis? Explain how it is applied to Labrador dogs
when the phenotypic expression of a gene at one locus alters that of a gene at a different locus
What are quantitative characters? What does this variation indicate?
They are characters that vary in the population in gradiations. An example would be human skin. This variation indicate phenoytpic inheritance, the effect of two or more genes on a single character
What do scientists mean when they refer to certain characters as multifactorial?
They mean that many factors including genetic and environmental, influence the phenotype
