Biology Unit 2 SAC 3 Revision: The Nature of Genes and Patterns of Inheritance (Flashcards)

A comprehensive set of practice questions (Question and Answer format) covering genetics basics, chromosomal structure, meiosis, and patterns of inheritance to help review for the exam.

What is the difference between a gene, an allele, and a genome?

A gene is a unit of heredity at a specific locus; an allele is a variant form of a gene; a genome is the complete set of an organism’s genetic material.

What is a gene locus (loci)?

The fixed position of a gene on a chromosome.

What are homologous chromosomes?

A pair of chromosomes with the same gene loci, one inherited from each parent, which may carry different alleles.

What is the difference between autosomes and sex chromosomes?

Autosomes are non-sex chromosomes; sex chromosomes (X and Y in humans) determine sex and carry sex-linked genes.

How do chromosome size and number vary among organisms?

Chromosome number and size vary across species; some have many chromosomes and large genomes, others have fewer or smaller ones.

What is a karyotype?

A visual representation of an organism’s chromosomes used to identify abnormalities.

What happens in meiosis to produce haploid gametes?

Diploid cells undergo meiosis to produce haploid gametes through two divisions, with crossing over and independent assortment contributing to diversity.

Why is crossing over important for genetic diversity?

Crossing over exchanges chromatids between homologous chromosomes, creating new allele combinations.

What is independent assortment?

The random orientation of homologous chromosome pairs during meiosis I, producing diverse gamete genotypes.

What is a haploid cell?

A cell containing one complete set of chromosomes (n), such as gametes.

What is genotype?

The genetic makeup at a particular gene locus, represented by the alleles present.

What is phenotype?

The observable traits expressed by the genotype, influenced by environment and epigenetic factors.

What is a dominant allele?

An allele that masks the expression of the other allele in a heterozygote.

What is a recessive allele?

An allele whose effects are masked in the presence of a dominant allele and expressed only in homozygous recessive individuals.

What is codominance?

Both alleles in a heterozygote are fully expressed, producing a distinct phenotype (e.g., AB blood type).

What is incomplete dominance?

Heterozygotes show an intermediate phenotype between the two homozygotes.

How do genetic, environmental, and epigenetic factors influence phenotype?

Phenotype results from the interaction of genotype with the environment; epigenetic regulation also shapes gene expression.

What are Mendel's Laws of Segregation and Independent Assortment?

Law of Segregation: alleles separate during gamete formation; Law of Independent Assortment: alleles of different genes assort independently.

What is a Punnett square used for?

To predict possible genotypes and phenotypes of offspring from parental genotypes.

What is a test cross?

Crossing an individual with an unknown genotype with a homozygous recessive to determine if the unknown is homozygous or heterozygous.

What is a dihybrid cross and its typical outcome for unlinked genes?

A cross involving two genes; for unlinked autosomal genes, often yields a 9:3:3:1 phenotypic ratio.

What is autosomal dominant inheritance?

An inheritance pattern where a dominant allele on an autosome leads to the phenotype; affected individuals can be heterozygous or homozygous.

What is X-linked recessive inheritance?

Mutation on the X chromosome; more males are affected; daughters of affected males may be carriers.

What is X-linked dominant inheritance?

Dominant allele on the X chromosome; affected both sexes, often with affected mothers passing to both sons and daughters.

What is Y-linked inheritance?

Genes on the Y chromosome; passed from father to son; affects only males.

What is sex-limited inheritance?

Traits expressed in one sex due to hormonal or physiological differences (e.g., milk production in females).

What is a pedigree chart used for?

A family tree used to deduce inheritance patterns and identify carriers or affected individuals.

What does it mean that unlinked genes segregate independently?

Genes on different chromosomes (or far apart on the same chromosome) assort independently during meiosis.

What are recombinants and recombination?

Offspring with new combinations of alleles due to crossing over; recombination creates genetic diversity.

What is a chiasma?

The site where crossing over occurs between homologous chromosomes during meiosis.

What is gene linkage?

Genes located close together on the same chromosome tend to be inherited together; recombination can separate them.

What is a karyotype used to identify?

Chromosome abnormalities such as extra chromosomes, missing chromosomes, or structural changes.

What is epigenetics?

Heritable changes in gene expression not due to changes in the DNA sequence; can influence phenotype.