Genetics Flashcards
What is Mendel’s Law of Segregation?
Alleles segregate randomly during gamete formation, and each gamete receives one copy of each gene.
What does “true breeding” mean?
True breeding plants exhibit the same characteristics generation after generation.
Define genotype and phenotype.
Genotype: The combination of alleles an organism has. Phenotype: The observable physical traits.
What is the difference between homozygous and heterozygous?
Homozygous: Two identical alleles for a trait. Heterozygous: Two different alleles for a trait.
What is a monohybrid cross?
A cross between two parents that differ in a single gene.
What is a Punnett square used for?
A tool used to predict the genotypic and phenotypic outcomes of genetic crosses.
What are linked genes?
Genes located close together on the same chromosome that tend to be inherited together.
What is crossing over, and when does it occur?
Exchange of genetic material between non-sister chromatids during prophase I of meiosis.
What is a recombinant type?
Offspring with a different combination of traits than the parents due to crossing over.
What is Mendel’s Law of Independent Assortment?
Alleles for different genes assort independently during gamete formation.
How are map units calculated?
Recombination frequency = Number of recombinant offspring ÷ Total offspring × 100%.
What is incomplete dominance?
A pattern where heterozygotes show an intermediate phenotype (e.g., pink flowers from red and white).
What is co-dominance?
Both alleles are fully expressed in the phenotype (e.g., roan cattle have red and white hairs).
Define polygenic traits.`
Traits controlled by multiple genes, such as human height.
What is a sex-linked trait?
A trait controlled by a gene located on a sex chromosome, often on the X chromosome.
What is a Barr body?
The inactivated X chromosome in female cells.
What is selective breeding?
The process of breeding plants or animals for specific traits.
What is a pedigree?
A chart showing the inheritance of traits over generations.
How do you distinguish autosomal dominant traits in pedigrees?
Affected individuals have at least one affected parent; the trait does not skip generations.
What are autosomal recessive traits?
Traits where individuals must inherit two recessive alleles to show the phenotype; unaffected parents can have affected children.
Give an example of a genetic condition caused by autosomal recessive inheritance.
Cystic fibrosis or phenylketonuria (PKU).
What is genetic screening?
The process of testing individuals for the presence of certain genes or genetic conditions.
What is the role of a genetic counselor?
To assess the risk of genetic conditions, provide information, and offer emotional support to families.
What is the chromosome Theory of Inheritance?
Genes are carried on chromosomes.
What is chromosome mapping?
The process of determining the relative positions of genes on a chromosome based on recombination frequencies.
What is a map unit?
A unit of measurement for genetic linkage; 1 map unit = 1% recombination frequency.
What are recombinant types?
Offspring with new combinations of traits resulting from crossing over during meiosis.
What are parental types?
Offspring whose traits match one of the parental genotypes without recombination.
Define recombination frequency.
The percentage of recombinant offspring produced in a genetic cross, used to measure the distance between genes.
What are sex-linked traits?
Traits controlled by genes located on sex chromosomes (X or Y chromosomes).
What does the term multiple alleles mean?
A situation where more than two alleles exist for a gene in a population.
What is meant by the order of dominance?
The hierarchy of dominance among multiple alleles, determining phenotype expression.
What are continuous traits?
Traits that exhibit a range of phenotypes due to polygenic inheritance.
Define polygenic traits.
Traits controlled by multiple genes, contributing to continuous variation in phenotype.
What is genetic screening?
Testing individuals to determine the presence of specific genes or genetic conditions.
What is a test cross?`
A cross between an individual of unknown genotype and a homozygous recessive individual to determine the unknown genotype.
What does the phenotypic ratio 9:3:3:1 in a dihybrid cross signify?
The ratio of offspring phenotypes when two heterozygotes for two independently assorting traits are crossed.
What is heterozygote advantage?
A condition where heterozygous individuals have a survival advantage, such as in sickle cell trait providing resistance to malaria.
How does polygenic inheritance affect phenotypes?
Polygenic traits show a range of phenotypes due to the additive effects of multiple genes (e.g., human height, skin color).
What does a recombination frequency of 50% indicate?
The genes are either on different chromosomes or very far apart on the same chromosome, assorting independently.
How do you determine the order of genes on a chromosome?
Use recombination frequencies to infer relative distances and construct a linear map.
What does a low recombination frequency between two genes suggest?
The genes are located close to each other on the same chromosome.
How can you identify an autosomal recessive trait in a pedigree?
Unaffected parents produce affected offspring; the trait may skip generations.
How can you identify an X-linked recessive trait?
Males are more frequently affected, and the trait is passed from carrier mothers to sons.
What evidence shows a dominant inheritance pattern in a pedigree?
The trait appears in every generation, and affected individuals usually have at least one affected parent.
Why is male-to-male inheritance impossible for X-linked traits?
Males inherit their X chromosome from their mother, not their father
How does epistasis affect inheritance?
One gene masks or modifies the expression of another gene.
