Heredity Flashcards
Genotype
Genetic component of inheritance. Includes one copy from each parent
Phenotype
Physical trait displayed, arising from genotype
Gene
Basic unit or sequence of genetic material that encodes a trait
Locus
A gene’s location within a genome
Allele
variant form of a gene
Homologous chromosomes
Pair of chromosomes that contain the same genes in the same locations
Hemizygous
Having only one copy of a gene instead of two
Heterozygous
Carrying a copy of the recessive allele on one of the homologous chromosomes and a copy of the dominant allele on the other chromosome
Homozygous
Carrying the same alleles on each homologous chromosome
Homozygous dominant
Carries two copies of the dominant allele (BB)
Homozygous recessive
Carries two copies of the recessive allele (bb)
Law of Segregation
During Anaphase 1, homologous chromosomes segregate resulting in haploid gametes that contain only one allele per gene
Law of independent assortment
Lining up and seperation of one pair of homologous chromosomes does not influence that of a different pair of homologous chromosomes
Law of dominance
Dominant allele masks the expression of a recessive allele
Test cross
Genetic cross between homozygous recessive person and person in question to determine genetype of given trait
P1 generation
Parental generation
F1 generation
1st generation (offpsring)
F2 generation
2nd generation
Punnett squares
Diagram to observe probabilities of offspring genotypes using the parent genotypes
Epistasis
One gene’s expression masks the phenotypic expression of another
Epistasis example
Baldness gene over hair color gene
Pleiotropy
Single gene affects multiple phenotypic traits
Pleiotropy example
Single gene controls a plants height, color, texture
Multiple alleles
More than two possible alleles for a gene
multiple allele example
blood type, eye color
Polygenic Inheritance
Many genes determine one phenotyptic outcome
Polygenic inheritance example
Height, skin color
Incomplete dominance
More than one dominant allele. Heterozygote with two dominant alleles shows a blended phenotype
Codominance
Both inherited dominant allels are completely expressed. Heterozygote with two dominant alleles shows both phenotypes simultaneously
Sex linked genes
Reside on sex chromosome
Sex influenced genes
Expression is influenced by the sex of the individual
X- inactivation
Female phenomemnon in which one of the two X chromosomes (random) condenses down into an inactivated Barr body. Expressed gene come from the remaining X chromosome
Phenotype Variability
Penetrance
Probability that an organism with a specific genotype will express the corresponding phenotype
Phenotype Variability
Expressivity
Level of expression of a phenotype for a specific genotype
Human genetic defects
Aneuploidy
Organism or cell has an abnormal number of chromosomes
Monosomy
One copy of chromosome
Trisomy
Three copies of chormosome (Down syndrome)
Nondisjunction
Failure of chromosomes or chromatids to seperate during mitosis-meisosis. Reults in gametes with too many/few chromosomes
Autosomal dominant
Single copy of mutated gene is enough to express condition
Autosomal recessive
Two copies of mutated gene must be present to express the condition
X -linked dominant
Single copy of the mutation of a gene on the X chromosome is enough to cause the condition in both males and females
X-linked dominant fact
Affected fathers always have affected daughters
X-linked recessive
Two copies of mutated gene on the X chromosomes causes the condition in females; one copy will cause condition in males
X-linked recessive facts
Affected mothers always have affected sons
Common in males than females
Normal fathers never have affected daughters
Chromosomal aberrations
Inversions
Chromosome segement is rearranged in the reverse of its original orientation
Deletions
Chromosome segment is missing or deleted
Translocation
Chromosome segment is moved to another
Duplication
Chromosome segment is repeated on the same chromosome
