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Std 7

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allele
one of two alternate forms of a gene that can have the same locus on homologous chromosomes and are responsible for alternative traits
chromosomes
threadlike structure within the nucleus containing the genetic information that is passed from one generation of cells to the next
condominance
A condition in which neither of two alleles of a gene is dominant or recessive.
color blindness
genetic inability to distinguish differences in hue
Cystic Fibrosis
A genetic disorder that occurs in people with two copies of a certain recessive allele; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.
dihybrid cross
a cross between individuals that have different alleles for the same gene
dominant allele
an allele whose trait always shows up in the organism when the allele is present
Down Syndrome
a congenital disorder caused by having an extra 21st chromosome
genes
sequence of DNA that codes for a protein and thus determines a trait
genetic code
the term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid
genetic variation
the number and frequency of alleles that are present in a particular population
genetics
the science of heredity and of the mechanisms by which traits are passed from parents to offspring
genotype
the genetic makeup of an organism
genotype ratio
the ratio of the genotypes that appear in offspring
heterozygous
term used to refer to an organism that has two different alleles for the same trait
homologous
corresponding or similar in position or structure or function or characteristics
homozygous
term used to refer to an organism that has two identical alleles for a particular trait
incomplete dominance
situation in which one allele is not completely dominant over another
karyotype
A picture of all the chromosomes in a cell arranged in pairs
Mendel's Laws
Unit character-traits controlled by factors (genes) which occur in pairs, Principle of Dominace, Principle of Segregation, and Principle Independent Assortment
monohybrid cross
a cross between individuals that involves one pair of contrasting traits
multiple alleles
three or more forms of a gene that code for a single trait
offspring
Product of reproduction, a new organism produced by one or more parents
pedigree
a diagram that shows the occurrence of a genetic trait in several generations of a family
phenotype
The physical traits that appear in an individual as a result of its gentic make up.
phenotypic ratio
a ratio that shows the varied outcomes that results from a genetic cross and is based on physical appearance alone
Phenylketouria
Absence of an enzyme, both recessive alleles must be inherited for the disorder to be displayed
polygenic trait
trait controlled by two or more genes
Punnett Square
a chart that shows all the possible combinations of alleles that can result from a genetic cross
recessive allele
An allele that will not determine the phenotype unless the genotype is homozygous in that allele
recombinant DNA
genetically engineered DNA made by recombining fragments of DNA from different organisms
sex-linked trait
a trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans
sickle cell anemia
a genetic disorder in which erythroctyes take on an abnormal curved or "sickle" shape
Tay-Sachs disease
recessive disorder that is of the nervous system and the child usually dies by the age of 4
traits
a characteristic that an organism can pass on to its offspring through its genes