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29 Cards in this Set

  • Front
  • Back
What is a genotype?
Refers to the genetic makeup (alleles) of an individual
What are genotype and phenotype ratios for various crosses?
TT - Homozygous

Tt - Heterozygous

tt - Homozygous recessive
What is a phenotype?
Refers to the physical appearance of the individual
What is dominance?
Trait is visible and masks the recessive trait capital letter.
What does it mean to be recessive?
Trait is NOT visible (hidden), lower case letter.
What is incomplete dominance?
Phenotype of offspring = blend of 2 parental phenotypes

Red & white --> pink petals

Curly & straight hair --> wavy hair

Pitch of male voice
Lowest = PP
Baritone = Pp
Highest = pp

Incomplete dominance = when an intermediate phenotype is expressed
Flower color in the carnation
Sickle cell
What is codominance?
Codominance = alleles are equally expressed

Codominance = More than 1 allele is fully expressed
ABO blood type = multiple allelic traits
What is a multiple allele system?
Multiple Allelic Trait = controlled by multiple alleles (several forms)

ABO blood type = multiple allelic traits
Are there always only two alleles for every trait?
No, but any individual has at most two different alleles, most genes exist in a large number of allelic forms in the population as a whole. In some cases, the alleles have different effects on the phenotype, and their dominance interactions with each other can be described as a series.
What is Mendels law of segregation?
Mendel's first law, stating that the two alleles in a pair of segregate (separate) into two different gametes during gamete process.

Each individual has 2 factors (alleles) for each trait

Alleles segregate (separate) during gamete formation

Each gamete contains only 1 allele from each pair

Fertilization gives each new individual 2 factors for each trait

Reshuffling of genes leads to genetic variation
What is mendels law of independent assortment?
Mendell's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes.

Each pair of genes separates independently of the other pairs

All possible combinations of genes can occur in the gametes
How was Mendel lucky with the law of independent assortment?
Mendel was lucky in choosing the characteristics he worked with, since the were not linked and found on separate chromosomes.

Genes that are found on the same chromosome will not follow the law unless it happens in meiosis - prophase I chromosomes.
What does it mean to say genes are linked?
X-linked (sex-linked) = genes carried on X chromosome
Y chromosome = missing these alleles
Y chromosome cannot offset the inheritance of an X-linked recessive allele

any pair of genes that tend to be transmitted together
How do autosomal dominant disorders that are lethal to their owner persist in populations?
Recessive genes, Imbreeding, low variations of chromosomes,
**Autosomal Dominant Disorder that affects 1:20,000 (Age 35-45)

So the reason these genes are capable of lasting is because they do not activate until after the breeding process.
What are the ways in which recessive disorders persist in populations? Think tay sachs and sickle cell.
These disorders are not necessarily life threatening and can then be passed recessively.

Intuitively, natural selection should eliminate these lethal genetic disorders from the population.....However, natural selection does not act on the genotype of an individual, but on the phenotype. Many of these lethal genetic disorders are the product of two "recessive alleles" that were masked in the parents with a "dominant allele."
What is epistasis?
A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

When 1 gene affects the expression of another gene
Black coat color is dominant to brown in mice (B,b)
Another gene determines whether or not pigment is deposited in the hair C,c
Individuals with cc as their genotype will be albino regardless of the genotype at the coat color gene.

Epistasis = A gene at 1 locus interferes with the expression of a gene at a different locus (albinos)
Human skin color = polygenic inheritance
What is polygenic inheritance?
Human skin color = polygenic inheritance

Occurs when 1 trait is governed by 2 or more sets of alleles

Each dominant allele has a quantitative (additive) effect on phenotype

Result = continuous range of phenotypes
skin color (genes code for pigment)

Polygenic Disorders:
Cleft lip
3 copies of chromosome 21
nondisjunction during egg & sperm formation

Sperm has extra chromosome 21 (23% of cases)

Translocation between chromosome 21 & 14 (5% of cases)

Gart gene causes mental retardation

Detected by: amniocentesis, chorionic-villi sampling, & karyotyping

Mothers 40+ years = at higher risk
Trisomy - Down Syndrome
Autosomal dominant disorder that affects 1:20,000 (age 35-45)

Causes progressive brain damage

Mutation in gene on chromosome 4
Abnormal huntington protein forms clumps in neurons

severe muscle spasms
personality disorders
death within 10-15 years of onset
Huntingtons Disease
1:400 African Americans

RBC = sickle-shaped
Defect in hemoglobin
Clog vessels
Poor circulation & anemia
Resistance to malaria (1:10 = heterozygous)

blood disorder

Red blood cells = sickle-shaped due to defect in hemoglobin
Clog vessels
Poor circulation
Resistance to malaria (heterozygous)
Sickle Cell

Broad chest

Skin folds on neck

Nonfunctional ovaries

Do NOT undergo puberty
Turner (XO)
Affects 1:2000

Undeveloped testes

Some breast development

Possible retardation

Barr body present
Klinefelter (XXY)
Autosomal recessive disorder that affects 1:3000 newborns

1:20 caucasians = carriers
Carriers = resistant to cholera

Mutation in gene on chromosome 7
Lack of water release leads to thick mucus

Thick mucus clogs lungs & pancreatic ducts

Life expectancy = 35 years
Cystic Fibrosis
Skeletal & connective tissue
Extra fingers or toes
Lysosome storage disorder
Affects 1:3,600 Jewish people (Ashkenazi)
Lack enzyme needed to digest glycosphingolipids
Blindness, seizures & paralysis
Death by age 3 or 4
Carriers (Tt) = more resistant to Tuberculosis
Tay-Sachs Disease
How does environment influence phenotype?
One of the examples includes:

If height were affected by balanced diet then that would indicate enviroment.

Himalayan rabbits & Siamese cats:
Enzyme coding for black fur = active at low temperatures
Black fur only occurs on extremities (ears, nose, feet, tail)
How does environment influence phenotype contribute to the patterns of inheritance we see in natural populations?
Himalayan rabbits & Siamese cats:
Enzyme coding for black fur = active at low temperatures
Black fur only occurs on extremities (ears, nose, feet, tail)
What are some of the chromosomal level changes we can see?
End of chromosome breaks off

2 simultaneous breaks lead to loss of internal segment

Chromosome segment moves from 1 chromosome to another (nonhomologous) chromosome

Down Syndrome: occurs between chromosome 21 & 14

Chromosomal segment occurs more than once in the same chromosome

Caused by:
Unequal crossing over

Inversion = when segment that has become separated is turned 180 Degrees and reinserted