Chapter 14: Mendel and the Gene Flashcards
Examples of epistasis
Lab coat color - lab will be yellow if pigment deposit gene is homozygous recessive regardless of coat color gene (pigment deposit gene is epistatic to coat color gene)
Gene for widows peak hidden by gene for baldness (baldness gene is epistatic)
Why was hemophilia common among the royal families of Europe?
Inbreeding. Small gene pool so a higher chance of members carrying the gene
White dogs and deafness/blindness pleiotropy example
White pigmentation gene suppresses melanocytes which leads to the degeneration of cochlear blood supply which leads to deafness
What does gene distance on chromosome predict?
The farther they are, the more likely a crossover event will occur
When is the addition rule used?
OR. The probability of two or more mutually exclusive events occurring
This determines the phenotype. If this is present, the organism will express the associated phenotype
Dominant allele
What causes Huntingtons disease?
Expansion of a tri-nucleotide repeat on chromosome 4. Repeats get larger as it is passed down
What are quantitative traits and when are they seen?
Traits that vary along a continuum. They are seen in polygenic inheritance
Phenotypic ratio of crossing true breeding parents of different phenotypes
3:1 (1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive)
What are multiple alleles?
Genes that have more than 2 alleles resulting in more possible combinations (like eye color and ABO blood groups)
Different versions of the same gene
Alleles
What are linked genes?
Genes close together on the same chromosome that are unlikely to sort independently. Expected to stay together during gamete production
Is polydactyly dominant or recessive?
Dominant. Extra digits is actually dominant
Most common lethal genetic disease in US
cyclic fibrosis
Why do we know now that the principle of independent assortment can be broken?
If the alleles of different traits are on the same chromosome, they could travel together. The closer they are on a chromosome, the less likely they are to travel apart
What is PKU recessive disorder?
Lack enzyme to break down phenylalanine, buildup interferes with development and results in severe mental retardation, outcome can be prevented in phenylalanine is removed form diet
Is gender more complex than sex development?
Yes, far more complicated
Huntington’s disease death rate and onset
Death usually 15-20 years after onset (pneumonia, heart disease, suicide). Late onset around 35-45
What can happen with recessively inherited disorders?
Occurrence can skip a generation
Pedigree circle
female
Heterozygotes have an intermediate phenotype (in between dominant and recessive)
Incomplete dominance
Pedigree half colored in shape
carrier
An organism that has two different alleles for a gene
Heterozygous
Incomplete dominance vs codominance
Incomplete shows fur that would be a blend of the two colors. Codominance is both colors expressed together; individual hairs are one color or the other
Pedigree square
male
What did the white fly mutants uncover?
Sex linked characteristics
Pedigree dot in center of shape
carrier (X linked)
An affected father will pass it on to all of his daughter and an affected mother will pass it on to 50% of offspring
X linked dominant pedigrees
An organism that has two identical alleles for a gene
Homozygous
How was the pivotal role of SRY discovered?
Injecting SRY DNA into an XX embryo and the mouse develops as a phenotypic male
What are recombinants?
Offspring that have phenotypes that do not match either parent
How can XY be phenotypically female?
Loss of SRY gene or other mutations in other critical genes (like androgen receptors. If cant respond to androgen, then phenotypic female)
Examples of X-linked disorders
Color blindness, Duchene muscular dystrophy, hemophilia
What is a transcription factor?
Proteins capable of interacting with DNA
Determines the organisms appearance
Dominant allele
How many genes are on the Y chromosome and what does it lead to?
78 genes that encode 25 proteins. Leads to very few disorders being passed from father to son
Examples of polygenic inheritance
Skin color (controlled by at least 3 different genes) and may diseases/disorders (diabetes, cancer, autism)
Phenotypic ratio of crossing F1 generation from parents that were homozygous dominant and homozygous recessive for 2 traits
9:3:3:1
What does the principle of segregation state?
The two alleles for a gene separate from each other during gamete formation and end up in different gametes (separation of homologous chromosomes in meiosis)
When is the multiplication rule used?
AND. The probability of two or more events occurring in a specific combination
How we collect info about a family’s history for a particular character. Info is assembled into a family tree called this
Pedigree
What is the chromosomal theory of inheritance?
Mendelian genes have specific loci along chromosomes. It is the chromosome (not individual genes) that undergo segregation and independent assortment
Examples fo dominantly inherited disorders
Achondroplasia, osteogenesis imperfecta, Liebenberg syndrome, and Huntingtons disease
What causes genetic recombination?
Crossing over allows for the recombination of linked genes
How is a dihybrid produced?
Crossing true breeding plants that differ in both traits
What type of dominance is shown by ABO blood groups?
Codominance
Heterozygous for 2 traits
Dihybrid
How many genes are on the X chromosome and what does this tell us?
About 1100 genes. Tells us most sex linked genes are linked to X
Look for an unequal number of males affected and if there is a pattern of mother to son transmission
X linked recessive pedigrees
What accounts for Mendels observations?
Meiosis
Huntington’s disease symptoms
Involuntary movement, behavioral disturbances, dementia
How is a test cross performed?
Cross the unknown (test) individual with an individual with a known genotype (homozygous recessive)
How can XX be phenotypically male?
Translocation of SRY gene
How do number of repeats determine Huntingtons?
More repeats = earlier onset and higher chance of having Huntingtons
What is pleiotropy?
Genes with multiple phenotypic effects (most genes). Single genes affect multiple traits/systems in the body
What does the SRY gene do?
Codes for a transcription factor and causes gonads to develop into testes
Has no noticeable effect (recedes/masked)
Recessive allele
Why cant dominantly inherited disorders skip generations?
Cant be a carrier. You either have it and express it or you dont
What are pure lines (true breeding plants)
Plants which only produce same variety as parent when self pollinated
Are traits transmitted together or inherited independently? (Will GY and gy always stay together?)
Independently. They will not always stay together
When do gonads begin to develop as either male or female? What determines which gonads will develop?
After 2 months. Depends on the presence of Y chromosome
Pedigree colored in shape
affected
Appearance or observable trait
Phenotype
What is the F2 generation?
The generation that results from the cross of the F1 generation. The recessive traits can reappear
Why is the allele in Huntingtons disease maintained in the population?
Late onset means most have already had children and passed it on
2 or more genes have an additive effect on a single phenotypic character (quantitative traits)
Polygenetic inheritance
Examples of recessively inherited disorders
PKU, Tay-Sachs, sickle cell anemia
What is osteogenesis imperfecta?
Mutation in type 1 collagen that causes “brittle bone disease”. No cure. Dominantly inherited disorder
When the phenotypic expression of one gene alters that of a different gene
Epistasis
What can we do with knowledge from pedigrees?
Genetic testing and counseling. Raises ethical issues on abortion, health insurance, and jobs
Examples of pleiotropy
Multiple symptoms associated with most hereditary diseases (PKU - mental retardation, reduced pigmentation and eczema, Marfan syndrome - tall long limbs with abnormally shaped chest and heart problems, white dogs and deafness/blindness)
What is achondroplasia?
Point mutation (G to A) in fibroblast growth factor receptor gene. Spontaneously inherited mutations exclusively from father. Homozygous = lethal. Dominantly inherited disorder
Neither allele is dominant and both are expressed with no blending (two sets of capital letters)
Codominance
What often happens in cystic fibrosis?
Bacteria get into the mucus and are hard to get rid of which causes bad infections that lead to more issues. Avg lifespan is only 37 years
Actual genetic makeup (the letters)
Genotype
How can environment impact phenotype?
Many traits of a phenotype can be altered/influenced by the environment. Like PKU if phenylalanine is eliminated from diet, development would be normal as long as caught early
What did Mendel not account for?
Linked genes, not all alleles are completely dominant or recessive, some genes have more than 2 possible alleles, some genes produce multiple phenotypes, some phenotypes determined by multiple genes
Why are X-linked recessive disorders far more common in males than females?
Females have 2 copies of the X chromosome so both must contain the defective allele. Males only have 1 X chromosome so if they inherit a bad copy from their mother, they will express it
What does the principle of independent assortment state?
Each pair of alleles separates independently of every other pair of alleles during gamete formation
What causes cystic fibrosis?
Missing/defective channels cause a buildup of mucus. Normal allele codes for a membrane protein that transports chloride ions
What causes different alleles?
Differences in nucleotide sequences
Used to determine genotype when an organism expresses a dominant phenotype (heterozygous or homozygous?)
Test cross
What is particulate inheritance?
Mendels proposed model of inheritance that said there are discrete, unchanging particles (genes) that are passed to offspring
Heterozygous for the one trait being followed that is produced by crossing true breeding plants (P)
Monohybrid
What is the F1 generation?
The generation that results when cross pollinating two contrasting pure lines
Pedigree diamond
sex unspecified
What happens when a X bearing sperm fertilizes an egg? A Y bearing one?
X = female Y = male
What did Medels numbers show?
Almost perfect results. Less than 1% statistical chance to obtain the results but he had to know the right numbers without any proof if he did fudge them
What causes gonads to develop into testes?
SRY gene (sex determining region of Y)
