14 15 Flashcards
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects
Allele
A discreet unit of hereditary information consisting of a specific nucleotide sequence in DNA
Gene
An observable heritable feature that may vary among individuals
Character
One of two or more detectable variants in a genetic character
Trait
An allele that is fully expressed in the phenotype of a heterozygote
Dominant allele
An allele whose phenotypic effect is not observed in a heterozygote
Recessive allele
The genetic makeup or set of alleles of an organism
Genotype
The observable physical and physiological traits of an organism which are determined by its genetic makeup
Phenotype
Having two identical alleles for a given gene
Homozygous
Having two different alleles for a given gene
Heterozygous
A cross between two organisms that are heterozygous for the character being followed
Monohybrid cross
Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype
Test cross
Phenotypes if heterozygote and dominant homozygote are indistinguishable
Complete dominance
Phenotypes of heterozygote a is intermediate between the two phenotypes of both homozygotes
Incomplete dominance
Two alleles each affect the phenotype in separate distinguishable ways
Codominance
Phenotype most commonly observed in the natural population
Wild type
A gene located on sex chromosomes; usually occurs on X chromosome; fathers transmit this and other x-linked alleles to all daughters but to no sons. Any male who inherits such an allele from his mother will express the trait
Sex-linked gene
Production of offspring with combination of traits that differ from those found in either parent
Genetic recombination
Reciprocal exchange of genetic material between no sister chromatids during prophase 1 of meiosis
Crossing over
An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other
Nondisjunction
- Most common lethal genetic disease in US
- Normal allele for this gene codes for chloride transport channels
- Allele is recessive
- if homozygous for this allele then high concentration of extra cellular chloride which causes mucus buildup organs
- if untreated most die before 5th birthday; in US half with this survive to 20s or 30s
Cystic fibrosis
- most common inherited disorder among people of African descent
- caused by substitution of a single amino acid in hemoglobin protein
- person homozygous all rbc are sickle shaped: can cause cells to clump as block blood vessels
- regular blood transfusion and new drugs can help or prevent other problems it causes, but no cure
- codominant at molecular level
- disease: both alleles are sickle cell alleles
- trait: one allele normal; one sickle cell
- heterozygous advantage
Sickle cell disease
- Degenerative disease of the nervous system
- irreversible and inevitably fatal
- lethal dominant allele no obvious phenotypic effect until individual is 35-45 years old
- Child born to parent with this allele has 50% chance of inheriting the allele and the disorder
- can do genetic testing to see if an individual has this allele in genome
Huntington’s disease
- affects 1/3500 males born in US
- progressive weakening of the muscles and loss if coordination
- rarely live past early 20s
- x-linked disorder
Muscular distrophy
- x-linked recessive disorder
- absence of one or more of proteins required for blood clotting
- treat with Iv injections of the protein that is missing
Hemophilia
- usually result if extra chromosome 21- each body cell has total of 47 chromosomes
- also called trisomy 21
- characteristic facial features, short stature, developmental delays
- increased chance if developing many diseases
- have life span shorter than normal
- frequency increases with age of the mother
- most cases result from nondisjunction during meiosis 1
Down’s syndrome
- XXY
- males- testes small and man is sterile
- some breast enlargement and other female body characteristics are common
- may have subnormal intelligence
Klinefelter syndrome
- males- undergo normal sexual development
- tend to be somewhat taller than average
XYY
- females; unhealthy
- no unusual physical features other than being slightly taller than average
- at risk for learning disabilities
- fertile
Trisomy X (XXX)
- 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 characteristic
- most have normal intelligence
Turner syndrome
- results from specific deletion in chromosome 5
- severely intellectually disabled
- small head with unusual facial features
- cry that sounds like mewing of a distressed cat
- usually die in infancy or early childhood
“Cri du chat” cry of the cat
- occurs when reciprocal translocation happens during mitosis of cells that will become WBC
- exchange of a large portion of chr 22 with small fragment from a tip of chr 9 produces a much shortened chr 22
- causes cancer by activating a gene that leads to uncontrolled cell cycle progression
CML chronic myelogenous leukemia
The inactive X in each cell of a female condenses into a compact object called a _____. Most of these genes are not expressed. Females are a mosaic of two types of cells: those with the active X derived from the father and those with the active X derived from the mother
Barr body
Genes located on the same chromosome that tend to be inherited together in genetic crosses are said to be _____ genes
Linked
Offspring that inherit a phenotype that is different from either parent are said to be ____
Recombinants
The reason that linked genes are inherited together is that
They are located on the same chromosome
What is the mechanism for the production of genetic Recombinants
Crossing over and independent assortment
Males are more often affected by sex linked traits than females because
Males are hemizygous for the X chromosome
A man who carries an x linked allele will pass it on to
All of his daughters
Which syndrome afflicts mostly males
Duchenne muscular dystrophy
If a chromosome lacks certain genes, what has most likely occurred?
Deletion
The human trisomy that generally has the most severe impact on the health of the individual is
Trisomy 21
What do all human males inherit from their mother?
An X chromosome and mitochondrial DNA
False about Down syndrome
It is a sex linked disorder
Not true of turners syndrome
They are genetically XXX
What results in male sex organs but may have some female body characteristics present?
XXY
Not sex linked disorder
Sickle cell anemia
What kind of chemical bond is found between paired bases of the DNA double helix
Hydrogen
An analysis of the nucleotide composition of DNA
A+C=G+T and G+A=T+C
The strands that make up DNA are anti parallel this means:
The 5 to 3 direction of one strand runs counter to the 5 to 3 direction of the other strand
What is the function of DNA polymerase
To add nucleotides to the end of a growing DNA strand
A cross between homozygous purple flowered and homozygous white flowered pea plants results in offspring with purple flowers. This demonstrates
Dominance
Can be dominant or recessive, can represent alternative forms of a gene, can be identical or different for any given gene in a somatic cell
True for alleles
The offspring of a cross between two heterozygous purple flowering plants results in
Purple flowered plants and white flowered plants
