Lab 5 & 6 Flashcards
Define Gene
A factor of inheritance for a particular trait or characteristic.
- Passed on from your parents to you
What is a gene composed of?
A specific nucleotide sequence in the DNA
- which acts as a template for RNA synthesis and ultimately the formation of a specific protein in a cell
A gene can come in different forms called ______
alleles
What is the difference between a gene and alleles?
Gene -seed color
Allele - green, yellow
Define Dominant allele
One whose phenotypic effect is the same in both the heterozygous and homozygous conditions
Define Recessive allele
One that is not expressed phenotypically in the heterozygous condition
Define Heterozygous
If it has two different alleles for the gene
Define Homozygous
If it has two identical alleles for the gene
Define Genotype
The genetic makeup of an organism
- always use letters
- Rr or GgHH
Define Phenotype
Expressed traits of an organism
- use descriptive words (physical appearance)
- purple seeds
Define Frequency
The proportion of one type of thing to the total population.
- range between 0 and 1
Give an example of a genotypic and phenotypic frequency
Genotypic frequencies - .5 Dd, .25 DD, .25 dd
Phenotypic frequencies - .75 green seeds, .25 white seeds
Define Ratio
The proportion of one type of thing to another
Give an example of a genotypic and phenotypic ratio
Genotypic ratio - 1 DD: 2 Dd: 1 dd
Phenotypic ration - 3 green seeds: 1 white seed
What is a Punnett square used for?
To stimulate the combinations of male and female gametes to form diploid zygotes (offspring)
Define a monohybrid cross
A cross between two organisms that differ with respect to one characteristic
- ex plant height
What is the principle of dominance ? (according to Mendel)
When parents differ in one characteristic, their hybrid offspring resemble only one of the parents, and are not a blend of the two parent phenotypes.
What is the principle of segregation? (according to Mendel)
Producing two kinds of reproductive cells
- half passing on the dominant character of one parent, and the other half passing on the recessive character of the other parent
What is Mendel’s first law?
Alleles of one gene segregate from one another during the formation of gametes
- monohybrid cross
Define Homologous
Chromosomes that carry the same genes at the same locations although the particular forms may be different.
The behavior of chromosomes during ______ account for Mendel’s 1st law ______
meiosis
The principle of segregation
The Mechanism of Segregation of Alleles during Gamete Formation
For a chromosome, in Prophase I with the genotype Tt:
- How many chromosomes would you need to draw for this stage?
- Are these chromosomes single of duplicated?
- 2
- duplicated
TTtt
Define a dihybrid cross
A cross between two organisms that differ with respect to two characteristics
- EX. plant height & plant color
Monohybrid cross between T&t:
- P1 tall plant genotype =
- P2 dwarf plant genotype =
- Genotype of P1 gametes =
- Genotype of P2 gametes =
- F1 generation genotype =
- Genotypes of F1 gametes =
- TT
- tt
- T
- t
- Tt
- T & t
Dihybrid cross: A plant that was homozygous for tall height and green color was crossed with a plant that was homozygous for dwarf size and albino color Use T for height & G for color - P1 tall & green plant genotype = - P2 dwarf & albino plant genotype = - Genotype of P1 gametes = - Genotype of P2 gametes = - F1 generation genotype = - Genotypes of F1 gametes =
- TTGG
- ttgg
- TG
- tg
- TtGg
- TG, Tg, tG, tg
What are the predicted phenotypic frequencies for the F2 generation of this cross?
0.5625 tall & green, 0.1875 tall & albino, 0.1875 dwarf & green, 0.0625 dwarf & albino
What is Mendel’s 2nd law?
Alleles of different genes assort independently of one another during gamete formation
- dihybrid cross
The Mechanism of Independent Assortment of Alleles of Different Genes during Gamete Formation
For a chromosome in Prophase I with the genotype of F1 TtGg:
- How many chromosomes will you need to draw for this stage?
- Are these single or duplicated?
- 4
- Duplicated
Define a Test Cross
Between a heterozygous individual and homozygous recessive individual (AaBb x aabb) to determine if genes are linked or not
Which type of cross is used to determine if the genes are on the same or different chomosomes (gene linkage)?
Test cross
Use the symbols A = seed color, B = texture:
- Heterozygous (red & smooth) =
- Genotype of gametes =
- Homozygous recessive (yellow & wrinkled) =
- Genotype of gametes =
Draw the test cross
- AaBb
- AB, Ab, aB, ab
- aabb
- ab
Based on the previous test cross:
- What is the predicted genotypic ratio?
- What is the predicted phenotypic ratio?
1 AB: 1 Ab: 1 aB: 1 ab
.25 AB, .25 Ab, .25 aB, .25 ab
Define Gene Linkage
How many gametes are formed?
Gene linkage is when the genes are linked together on the same chromosome
- only 2 gametes
Define Chiasma formation
Chromosome breakage and reunion occurs at this stage
Define crossing over
When genes are linked, the middle chromatids cross is late Prophase I and exchange 1 gene
Define Recombinant type gametes
Ex. Ab or aB
Result due to the crossing over with gene linkage
Define Sex chromosome
The morphology indicates whether an individual is male or female
Define Autosomes
The remaining non-sex chromosomes in the nucleus
What type of chromosomes do females have? Where are they located?
Females have two X chromosomes in the nucleus of every diploid cell
What type of chromosomes do males have? Where are they located?
Males have one X and one Y chromosome in the nuclei of their diploid cells
- What will the gametes produced through meiosis in females contain?
- What will the gametes produced by males contain?
- They will contain a single X chromosome along with 22 autosomes
- They will have either an X or Y chromosome plus the 22 autosomes
The gender of any new offspring resulting from sexual reproduction is determined by what?
By the type of male gamete (X or Y) that fertilizes the female gamete (always X)
Define Karyotype
The photographic representation of the chromosomes of an actively dividing cell, showing the number, shape and size of the chromosomes
How is the karyotype for Turner Syndrome different from a normal female karyotype?
What are some phenotypic abnormalities?
It occurs when one of the two X chromosomes in WOMEN is missing
- short stature, non-functioning ovaries (infertility)
- also webbed neck
How is the karyotype for Down Syndrome different from a normal karyotype?
What are some phenotypic abnormalities?
It is caused by an extra autosomal chromosome (#21)
- mild/moderate mental deficiency, almond shaped eyes, protruding tongue, poor muscle tone, shorter limbs + back
How is the karyotype for Klinefelter Syndrome different from a normal male karyotype?
What are some phenotypic abnormalities?
It occurs when MEN have an extra X chromosome
- sterile with small testes, low levels of testosterone in their blood
Define Mendelian fashion
Characteristics that appear to be inherited as dominant or recessive alleles of SINGLE genes
Are the dominant phenotypic characteristics always the most common ones in the class?
No, most of the traits are in majority recessive, except for the tasting trait
Genes located on the X chromosome are said to be _______
Sex-linked or X-linked genes
What are some examples of phenotypes determined by sex-linked recessive genes?
Red-green color blindness
Total color blindness
Hemophilia
Define Hemophilia
A genetic disease which is characterized by excessive bleeding (blood does not clot) following injury and is caused by a sex-linked recessive allele.
Who is more likely to exhibit a sex-linked recessive trait? Why?
Males; because they only carry a single X chromosome… whereas women have two
Would a Heterozygous female exhibit a sex-linked recessive trait?
A Heterozygous female would NOT exhibit a sex-linked recessive trait, but are ‘carriers’ of the trait
Define Red-green color-blindness
General term for a spectrum of relatively common sex-linked recessive disorders
What is a Protan deficiency?
Occurs is 2% of males and 0.04% of females
- Caused by reduced amounts or complete absence of red photoreceptors in the eye
- Results in reduced visibility of reds, along with darkening of reds
What is a Deutan deficiency?
Occurs is 6% of males and 0.4% of females
- Cause by reduced amounts of complete absence of green photoreceptors in the eye
- Results in reduced visibility of greens
What can result in a person having difficulty differentiating reds and greens? or distinguishing red and green shades?
Both Protan and Deutan deficiency
Problems involving sex linkage:
- A hemophiliac woman marries a normal man. (use H and h)
- draw a Punnett square and predict the offsprings of this couple
All their sons would be hemophiliac
None of their daughters would have the condition, though they would be carries of it
LAB 6 - P.7
Define Pedigree charts
The analysis of how phenotypic traits or genetic diseases are passed on from parents to offsprings
- sex-linked or autosomal traits(not sex-linked)
What is the genotype of Queen Victoria of England?
What is the genotype of Alexis, son of the Tsar of Russia?
- XHXH (normal female)
- XhY (affected male)
How can you determine whether a trait is sex-linked or autosomal?
Sex-linked = uses chromosomes XX and XY Autosomal = uses letters
In a pedigree chart, How can you determine if the allele is dominant or recessive?
Count
Black vs. white
Ex. More black diseased = disease is dominant
Albinism is cause by what type of allele?
An autosomal recessive allele ‘a’
The crossover frequency between two linked genes is proportional to what?
To the distance between them
When is there a higher chance of crossover occurring?
If the two genes are farther apart, there is an increased probability of a crossover occurring during meiosis.. And therefore a higher proportion of recombinant gametes expected
If recombinant types make up 18% of the test cross off springs, the two genes are considered to be ___ map units apart on the chromosome
18 map units apart
What are recombinant gametes? And how can we identify them?
Recombinant gametes result from crossovers
We can identify them easily because they are produced in lower numbers than parental gametes in meiosis
How can we calculate the percentage recombination?
It can be calculated by dividing the number of recombinants by the total number of offspring, and then multiplying by 100
Polygenic traits
EX?
Show a continuous range of phenotypes in a population that approximates a normal distribution
EX. human height, skin pigmentation, IQ, production level of milk in cattle
The effects of multiple alleles are ______
Additive
EX. skin pigmentation - a greater # of dominant alleles results in a darker skin pigment
Dermatoglyphics
The pattern and number of epidermal ridges on the fingers (fingerprints)
- A polygenic trait
What are the 3 types of epidermal ridges?
Arch, loop, whorl
