Week 13 Flashcards
What does the study of molecular genetics deal with?
deals with genes as molecules and investigates their interactions, patterns of inheritance, and functions.
What terms are used to describe molecular genetics?
Genotype & Phenotype Dominant & Recessive Wild type & Mutant Genes & Alleles F1 & F2 generations
What is commonly used to investigate genetics?
Arabidopsis seedlings
How are the roots observed from a number of different Arabidopsis seedlings?
compound microscope
How do you prevent contamination of the seedlings?
The seedlings have been grown on sterile petri dishes containing agarose plant growth medium, and it is necessary to prevent contamination of these plates.
Define- 1- Character 2-trait 3-Phenotype 4-Gene 5-Allele 6-Dominant allele 7-Recessive allele 8-Dominant phenotype or trait 9-Recessive phenotype or trait 10-Genotype
1-Character - A heritable feature of an organism, such as flower colour.
2-Trait - The trait is each alternative form of a character determined by a gene or set of genes, e.g. red or blue flowers. Some traits are present and heritable but may not be observable.
3-Phenotype - The phenotype is a trait which is visible or detectable, e.g. we can observe different flower colours.
4-Gene - A genetic sequence coding for a particular character or trait.
5-Allele - A single copy of alternative forms of a gene. Pairs of alleles are found at the same locus on pairs of homologous chromosomes.
6-Dominant allele - If inherited by offspring, its effect will be seen in the phenotype. Often represented by upper case letters, e.g. A or B or CEN1.
7-Recessive allele - If inherited by offspring, its effect will not be seen in the phenotype in the presence of a dominant allele. Two copies of recessive alleles are needed for the effect to be shown. Often represented by lower case letters e.g. a or b or cen1
8-Dominant phenotype or trait - Determined by the dominant allele and will be observable if one dominant allele is inherited by the offspring.
9-Recessive phenotype or trait - Determined by the recessive alleles and will only be obervable if both copies of the ercessive allele are inherited by the offpsring.
10- Genotype - The alleles of particular genes which determine the phenotype e.g. A a or A A or a a or CEN1 cen1. Less commonly, it can also refer to an organism’s general genetic make-up.
Define- 1-Homozygous 2-Heterozygous 3-Locus 4- F1,F2 Generations
1-Homozygous - A genotype which has the same alleles for a single gene, e.g. a a or B B or CEN1 CEN1.
2-Heterozygous - Having different alleles for a single gene, e.g. A a orB b or CEN1 cen1.
3-Locus - The position of an allele on a chromosome.
4-F1, F2 generations - The parental generation, also known as the F0 or P generation, produces offspring in the F1 generation. Crossing offspring from the F1 generation produces the F2 generation.
How are alleles and genotypes written/formatted?
When writing genotypes and alleles you should use the same letter for each allele and use upper case to define dominant allele and lower case for recessive and written in italics. Therefore, heterozygous genotypes would be written Yy or Gg. If there are two genes being crossed then each gene would have a different letter, e.g. YyGg, and three genes could look like this, e.g. YyGgSs.
How are genes and mutants written/formatted?
n this practical you will come across the names of genes and the proteins which the code for. Genes are written in italics and are often shortened versions of the full gene name. Example:
The gene centipede1 is written as CEN1 with the number referring to the fact there may be more than one gene with the same name.
The wildtype is written in upper case letters (see above) and the mutant of that gene is written in lower case letters cen1 .
To refer to alleles of a single gene a hyphen can be used folllowed by a number. For example, the shrivel1 gene, shortened to SHV1 for the wildtype may have two alleles SHV1-1 and SHV1-2.
Wildtype: CEN1
Mutant: cen1
Gene name: centipede1
How are proteins written/formatted?
Naming proteins uses the same shortened code as the gene name but is not italicized and is often in upper case, e.g. the CEN1 gene codes for the CEN1 protein.
Protein: CEN1
What is a punnett square and what does it show?
A Punnett square is a diagram used for working out the predicted offspring of a cross between two parents. It appears as a grid with the alleles of the parents along the top and to the left, and the boxes of the grid containing the potential genotypes of the offspring.
The most basic Punnett square involves a single gene or locus with two alleles per gene per parent. This is known as a single locus or monohybrid cross. In terms of inheritance by offspring from each parent there are only 2 possibilities: allele 1 or allele 2. Therefore a 2 x 2 grid is used. Each box within the grid should have a 25% or 1 in 4 chance of appearing within the offspring.
If the number of loci is increased to 2 in a double locus or dihybrid cross, then the number of combinations which can be inherited by offspring from each parent increases to 4. Therefore a 4 x 4 grid is needed and each box within the grid has a 1 in 16 or 6.25% chance of appearing within the offspring.
What is a ratio and what is it used to show?
A ratio shows the number of one group relative to another group or groups. For example if there are 3 apples and 1 banana the ratio is apples:bananas = 3:1. The ratio would also be 3:1 if there were 6 apples to 2 bananas, or 300 apples to 100 bananas. If there was 2 oranges, 4 apples and 2 bananas the ratio would be oranges:apples:bananas = 2:4:2 = 1:2:1. The ratio would still be 1:2:1 if there were 50 oranges, 100 apples, and 50 bananas.
Ratios can also be written for percentages and vice versa. For a 3:1 ratio the percentage would be 75% to 25% (because 3 x 25% =75%), and a 1:2:1 ratio would be 25% to 50% to 25%.
Understanding ratios and percentages is important when using Punnett squares. Each box of the grid represents a possible genotype for the offpsring and each has a 25% chance of appearing. This means that all potential genotypes and phenotypes can be converted into ratios and percentages to predict the number of each type in the offpsring. Bare this is mind when using Punnett squares to predict the outcome of crosses.
What is the difference between- 1-Offspring phenotype 2-offspring genotype 3-Maternal genotype 4-Paternal genotype
1- The phenotype is the visible characteristic determined by the combination of alleles inherited from each parent. The phenotype for each box within the grid is determined by the genotype.
2- This is the combination of alleles, one inherited from each parent. The genotype determines the visible phenotype. Each box within the grid will contain a potential genotype.
3- This is the split into the separate alleles so that eacch one is placed alongsite a row of the grid.
4-This is separated into single alleles with one placed above each column of the grid. Alleles would be separated during meiosis when gametes are produced.
A single allele has alternative versions called genes. True or false?
False
Which of these statements about Mendel’s first law is TRUE?
Pairs of alleles are segregated at meiosis with one allele per gamete.
A cross is set up between two plants with blue flowers.
Most of the offspring produce blue flowers, about 75%, and the the rest produce white flowers.
Assuming that the flower colour is determined by a single gene, what can you tell from this about the parents’ genotypes?
They are both heterozygous for the flower colour gene.
A cross between two heterozygous parents for a single gene produce a phenotypic ratio of 3:1 in the offpsring.
Assuming that one allele is dominant and the other recessive, what percentage of the offspring are predicted to have the same phenotype as both parents?
75%
A true breeding wildtype flower with blue flowers, is crossed with a mutant with white flowers.
The first generation (F1) produces all blue flowers. Assuming the mutation affects only a single gene, which of these statements is TRUE?
The wildtype is homozygous
When the interaction of genes alters genetic ratios, this is called
epistasis
Thomas Hunt Morgan was one of the major contributers to the chromosomal theory of inheritance. Which of the following did Morgan study?
Eye color in fruit flies
The ______chromosomes are a pair of chromosomes that are different in males and females.
sex
In Drosophila melanogaster, which of the following sex chromosomes are found in a female?
XX
A human female will normally have \_\_\_\_\_\_ autosome(s), \_\_\_\_\_\_ X chromosome(s), and \_\_\_\_\_Y chromosome(s).
Blank 1: 44 or forty-four
Blank 2: 2 or two
Blank 3: 0, zero, or no
In a certain plant, fruit color is affected by an epistatic interaction between two genes. The fruit is red in the presence of at least one dominant allele of either or both gene A or gene B, and white when there are no dominant alleles present. What proportion of the offspring of a cross of AaBb x AaBb plants is expected to be red?
15/16
What researcher discovered that inheritance of eye color in fruit flies is sex-linked?
Morgan
What is an autosome?
Any chromosome that is not a sex chromosome
The term sex chromosomes refer to a distinctive pair of chromosomes that vary between ____and _____
individuals.
Blank 1: male or XY
Blank 2: female or XX
True or false: In humans, the Y chromosome contains many genes which have to be continuously expressed.
False
Match each organism with the correct description of its sex determination system. 1-Humans 2-Birds 3-Grasshoppers 4-Honeybees
Humans: Females are XX, and males are XY.
Birds: Females are ZW, and males are ZZ.
Grasshoppers: Females are XX, and males are XO
Honeybees: Females are diploid, and males are haploid
A trait that causes a disease, will occur more frequently in males than females if the trait is which of the following?
Recessive and X-linked
What chromosomes are normally found in a human male?
22 pairs of autosomes, one X chromosome, and one Y chromosome
What ensures that females do not produce twice as much of the proteins encoded by genes on the X chromosome as males produce?
Dosage compensation
Females may be genetic mosaics due to which of the following?
Inactivation of the X chromosome
_____ is the term for any chromosome that is not a sex chromosome.
autosome
Crossing over occurs during which phase of meiosis?
Prophase I
In humans, which of the following estimates represents the number of genes on the Y chromosome that are expressed?
Few
Recessive X-linked alleles affect which of the following?
Males more than females.
What is the purpose of dosage compensation?
It ensures that males and females express X-linked traits (proteins) at equal levels.
Females may be genetic mosaics due to inactivation of one of the two ____ chromosomes.
X
If two loci are on the same chromosome, a recombinant combination of alleles will occur in which of the following circumstances?
Only if a crossover occurs
When does crossing over occur?
During meiosis I
The study of the arrangement of genes in a species’ genome is known as which of the following?
Genetic mapping
If two crossovers occur between two loci, the gametes will receive which of the following?
The parental combination of alleles
What is the purpose of a three-point cross?
To order genes that are far apart from one another
For two genes on the same chromosome, a recombinant gamete will be produced only if a(n) _______ occurs between the two genes.
Blank 1: crossover, recombination, or crossing-over
Select all that apply
If one homologue carries alleles A and B and the other homologue carries alleles a and b and two crossovers occur between these loci, what allele combinations will be found in the gametes?
AB
ab
