Biology 1 Chapter 14 (Lecture) Flashcards
Gene
A heritable unit that determines a character; can exist in different forms.
Allele
An alternative version of a gene
Character
A heritable feature that varies among individuals
Trait
A variant for a character
Dominant Allele
Determines phenotype in a heterozygote
Recessive Allele
Has no effect on phenotype in a heterozygote
Genotype
The genetic makeup of an individual
Phenotype
An organism’s appearance or observable traits
Homozygous
Having two identical alleles for a gene
Heterozygous
Having two different alleles for a gene
Testcross
A cross between an idividual with an unknown genotype and a homozygous recessive individual
Monohybrid Cross
A cross between individuals heterozygous for a single character
Complete Dominance
Phenotypes of heterozygote and dominant homozygote are indistinguishable
Incomplete Dominance
Phenotypes of heterozygotes is intermediate between the two phenotypes of both homozygotes
Codominance
Two alleles each affect the phenotype in separate distinguishable ways
Wild Type
Phenotype most commonly observed in the natural population
Sex-Linked Gene
A gene located on sex chromosomes (x or y); usually occurs on x chromosome; fathers transmit this and other x-linked alleles to all daughters but not to sons. Any male who inherits such an allele from his mother will express the trait. (Thus, more males than females have x-linked recessive disorders)
Genetic Recombination
Production of offspring with combination of traits that differ from those found in either parent
Crossing Over
Reciprocal exchange of genetic material between nonsister chromatids during prophase I of Meiosis
Nondisjunction
An error in meiosis or mitosis in which memebers of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.
Cystic Fibrosis
- Most common lethal genetic disease in US
- Normal allele for this gene codes for chloride transport channels
- C. f. allele is recessive
- If homozygous for cf allele then high concentration of extracellular chloride which causes mucus buildup in organs
- If untreated most die before 5th birthday; in US half with cf survive to 20’ or 30’s
Sickle-Cell Disease
- Most common inherited disorder among people of African descent
- Caused by substitution of single amino acid in hemoglobin protein
- Person homozygous all RBC are sickel shaped: can cause cells to clump and block blood vessels
- Regular blood transfusion and new drugs can help or prevent other problems it causes, but no cure
- Codominant at molecular level
- Sickle Cell Disease: both alleles are sickel cell alleles
- Sickel Cell Trait: One allele normal; one sickle cell
- Heterozygous advantage
Huntington’s Disease
- Degenerative disease of the nervous system
- Irreversible & inevitably fatal
- Lethal dominant allele no obvious phenotypic effect until individual is 35 to 45 years old
- Child born to parent with Huntington’s Disease allel has 50% chance of inheriting the allel and the disorder
- Can do genetic testing to see if an individual has huntington’s allele in genome.
Muscular Dystrophy
- Affects 1/3500 males born in US
- Progressive weakening of the muscles and loss of coordination
- Rarely live past early 20s
- X-linked disorder
Hemophilia
- X-linked recessive disorder
- Absence of one or more of proteins required for blood clotting
- Treatment with IV injections of the protein that is missing
Down’s Syndrome
- Usually result of extra chromsome 21- each body cell has total of 47 chromosomes
- Also called trisomy 21
- Characteristic facial features, short stature, developmental delays
- Increases chance of developing many diseases
- Have life span shorter than normal
- Frequency increases with age of mother
- Most cases result from nondisjunction during meiosis I
Klinefelter Syndrome
- XXY
- Males- testes small and man is sterile
- Some breast enlargement and other female body characteristics are common
- May have subnormal intelligence
XYY
- Males- undergo normal sexual development
- Tend to be somewhat taller than average
Trisomy X (XXX)
- Females; Healthy
- No unusual physical features other than being slightly taller than average
- At risk for learning disabilities
- Fertile
Turner Syndrome
- Monosomy X (xo)
- Only known viable monosomy in humans
- Female; sterile because sex organs do not mature
- When provided with estrogen replacement therapy, do develop secondary sex charateristics
- Most have normal intelligence
“Cri du chat”
- Cry of the Cat
- Results from specific deletion in chromosome 5
- Severely intellectually disabled
- Small head with unusal facial features
- Cry that sounds like meowing of a distressed cat
- Usually die in infancy or early childhood
CML (Chronic Myelogenous Leukemia)
- Occurs when recriprocal translocation happens during mitosis of cells that will become WBC
- Exchange of large portion of chromosome 22 with small fragment from a tip of chromosome 9 produces a much shortened chromosome 22 (Philadelphia Chromosome)
- Causes cancer by activating a gene that leads to uncontrolled cell cycle progression
A cross between homozygous purple flowered and homozygous white flowered pea plants results in offspring with purple flowers. This demonstartes…
Dominance
Which of the following is (are) true for alleles?
A) They can be dominant or recessive
B) Thay can represent alternative forms of a gene
C) They can be identical or different for any given gene in a somatic cell
D) Only A and B
E) A, B, And C
E
P-purple, pp-white. The offspring of a cross between two heterozygous purple flowering plants (PpxPp) results in
Purple flowered plants and white flowered plants
In snapdragons, heterozygotes have pink flowers, whereas homozygotes have red or white flowers. When plants with red flowers are crossed with plants with white flowers, what proportion of the offspring will have pink flowers?
100%
Tallness (T) is dominant to dwarfness (t), while red (R) flower color is dominant to white (r). The heterozygous condition results in pink (Rr) flower color. A dwarf, red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the F1 individuals?
TtRr- tall and pink
A woman who has blood type A, has a daughter who is type O positive and a son who is type B negative. Rh positive is a simple dominant trait over Rh negative.
What is a possible genotype for the son?
BO
A woman who has blood type A, has a daughter who is type O positive and a son who is type B negative. Rh positive is a simple dominant trait over Rh negative.
What is a possible geneotype for the mother?
AO
A woman who has blood type A, has a daughter who is type O positive and a son who is type B negative. Rh positive is a simple dominant trait over Rh negative.
What is a possible genotype for the father?
B
A woman and her spouse both show the normal phenotype for pigmentation, but both had one parent who was an albino. Albinism is an autosomal recessive trait.
What is the probablity that their first child will be an albino?
1/4
A woman and her spouse both show the normal phenotype for pigmentation, but both had one parent who was an albino. Albinism is an autosomal recessive trait.
If their first two children have normal pigmementation, what is the probability that their thrid child will be albino?
1/4
Huntington’s Disease is caused by a dominant allele. If one of your parents has the disease, what is the probablility taht you, too, will have the disease?
1/2
A woman has six sons. The chance that her next child will be a daughter is
1/2
Substitution of the “wrong” amino acid in the hemoglobin protein results in this disorder.
Sickle-Cell Disease
Individuals with this disorder are unable to metabolize certian lipids, affecting proper brain development. Affected individuals die in early childhood.
Tay-Sachs Disease
This is caused by a dominant single gene defect and generally does not appear until the individual is 35-45 years of age.
Huntington’s Disease
