14 Mendel and the Gene Flashcards
Polymorphic
a species that has two or more distinct phenotypes in the same interbreeding population at the same time
Self-fertilization
the fusion of two gametes produced by the same individual to form offspring
Gene
a hereditary factor that influences a particular trait
Allele
a particular form of a gene
Genotype
combination of alleles of particular genes in an individual
Phenotype
an individual’s observable traits
Homozygous
having two of the same allele
Heterozygous
having two different alleles
Dominant allele
an allele that produces its phenotype in heterozygous and homozygous genotypes
Recessive allele
an allele that produces its phenotype only in homozygous genotypes
Pure line or pure breeding
individuals of the same phenotype that, when crossed, always produce offspring with the same phenotype; parents are homozygous for the gene in question
Hybrid
offspring from crosses between homozygous parents with different genotypes; heterogenous for one or more specific genes
Reciprocal cross
a cross in which the phenotypes of the male and female are reversed compared with a prior cross
Testcross
a cross of a homozygous recessive individual and an individual with the dominant phenotype but unknown genotype in order to infer the unknown genotype from phenotypes seen in the offspring
X-linked
referring to a gene located on the X chromosome
Y-linked
referring to a gene located on the Y chromosome
Autosomal
referring to a gene located on any non-sex chromosome (an autosome)
Chromosome theory of inheritance
the principle that genes are located on chromosomes and that patterns of inheritance are determined by the behavior of chromosomes during meiosis
Principle of segregation
each pair of hereditary elements (alleles on homologous chromosomes) separate from each other during the formation of offspring in anaphase of meiosis I
Principle of independent assortment
alleles of different genes separate into gametes independently because pairs of homologous chromosomes have two equally likely ways of lining up before segregating during metaphase of meiosis I
Linkage
tendency of alleles of particular genes to be inherited together (do not assort independently); seen when two or more genes are on the same chromosome
Multiple allelism
the existence of more than two alleles of the same gene
What does the physical distance between genes determine?
how frequently crossing over occurs between them
Recombination frequency
how often genes recombine due to crossover during meiosis
What is the relationship between the distance between a pair of genes and the probability that crossing over will take place?
the shorter the distance between a pair of genes, the lower the probability that crossing over will take place between them
Dihybrid cross
a mating between two individuals who are heterozygous for two traits
Dependent assortment
transmission of one particular allele would depend on the transmission of another
Wild type
the most common phenotype(s) seen in a wild population
Mutation
any permanent change in the hereditary material of an organism or the nucleotide sequence that is the only source of new alleles in populations
Mutant
an individual with a new or rare phenotype due to a mutation
Sex-linked inheritance
inheritance patterns observed in genes carried on sex chromosomes; females and males have different numbers of alleles of a gene, often creating situations where a trait appears more in one sex
Autosomal inheritance
inheritance patterns that occur when genes are located on autosomes
What is the difference between linkage and sex-linkage?
Linkage refers to two or more genes located on the same chromosome while sex-linkage can refer to a single gene located on a sex chromosome and says nothing about the relative location of genes
What are the three possible dominance relationships between different alleles?
complete, incomplete (heterozygotes have an intermediate phenotype), and codominance (heterozygotes have phenotypes of both alleles)
Mode of transmission
type of inheritance observed as a trait is passed from parent to offspring; describes a trait as autosomal or sex-linked and the type of dominance e.g. autosomal recessive, autosomal dominant, X-linked recessive
Pedigree
family tree of parents and offspring, showing inheritance of particular traits of interest
Carrier
a heterozygous individual carrying a normal allele and a recessive allele for an inherited trait who does not display the phenotype of the recessive trait but can pass the recessive allele to offspring
Autosomal recessive traits
(1) individuals with the trait must be homozygous (1) if the parents of the affected individual do not have the trait, both parents are heterozygous (3) trait often skips generations
Autosomal dominant trait
(1) individuals who are homozygous or heterozygous for it have the dominant phenotype (2) affected offspring have at least one affected parent and are heterozygous if only one parent is affected (3) trait does not skip generations
Why do males exhibit X-linked recessive traits more often than females do?
Males have only one copy of the X chromosome so any X-linked allele will determine the phenotype in a male
What causes mutations?
errors during dna replication and dna repair
What are the possible associations between genotype and phenotype?
(1) Many genes can influence one trait (2) Many traits can result from a single genotype (3) A single gene can influence more than one trait
What factors influence the expression of genetic traits?
epigenetic factors and environmental factors (e.g. cell type and diet); the same genotype could result in very different phenotypes depending on these factors
Epigenetic factors
heritable changes in gene function that do not involve changes to the DNA sequences
Are alleles inherently dominant or recessive?
No, dominance depends on the relative influence of each allele on a specific phenotype under specific environmental conditions
Non-dominance
either incomplete dominance or codominance; the heterozygotes show a different phenotype than either homozygote
Which of the sex chromosomes in humans is smaller?
Y chromosome
X chromosome
contains many genes that are essential for development, especially the development of intelligence and social cognition
Y chromosome
carries a few genes that are essential for the expression of male-specific traits
Gender
socially constructed roles, behaviors, expressions and identities of girls, women, boys, men, and gender diverse people (continuum)
Sex
set of biological attributes primarily associated with physical and physiological features including chromosomes, gene expression, hormone levels and function, and reproductive/sexual anatomy (continuum)
Sexual orientation
direction of romantic, sexual, and emotional feelings (continuum)
