Biology From Chromosomes to Genomes Flashcards

Practice questions covering genes, alleles, chromosomes, karyotypes, inheritance patterns, and environmental influences on phenotype.

What is a gene?

A segment of DNA that contains instructions for making a specific protein.

What is an allele?

An alternative version of a gene.

What is a genome?

The complete set of DNA in an organism.

What is a chromosome?

A thread-like structure made of DNA wrapped around histone proteins.

What are histones and why are they important?

Histones are proteins around which DNA wraps to help it fit inside the nucleus.

What defines a homologous pair of chromosomes?

A pair of chromosomes that have the same genes and the same gene loci, with one coming from the mother and one from the father.

What is a gene locus?

The specific position of a gene on a chromosome.

What are autosomes?

All chromosomes except the sex chromosomes; humans have $22$ pairs.

What are the sex chromosomes for human males and females?

Female = $XX$, Male = $XY$.

Which parent determines the biological sex of the offspring?

The father.

Does having more chromosomes mean an organism is more complex?

No.

What is a karyotype?

A visual representation of chromosomes arranged into homologous pairs.

What is the cause and scientific name of Down Syndrome?

Cause: An extra copy of chromosome $21$; Scientific name: Trisomy $21$.

What is the cause and result of Klinefelter Syndrome?

Cause: $XXY$ chromosomes; Result: Male with an extra $X$ chromosome.

What is the cause of Turner Syndrome?

Only one $X$ chromosome ($XO$).

What are the human diploid and haploid numbers?

Diploid: $2n = 46$; Haploid: $n = 23$.

What is meiosis?

The process that produces haploid gametes from diploid cells.

What is crossing over?

The exchange of DNA between homologous chromosomes during meiosis that creates new allele combinations.

What is independent assortment?

The random separation of chromosome pairs into gametes to produce genetically unique gametes.

Define genotype and phenotype.

Genotype: The combination of alleles an organism possesses; Phenotype: The observable characteristics of an organism.

What is the difference between homozygous and heterozygous?

Homozygous: Having two identical alleles (e.g., $TT$ or $tt$); Heterozygous: Having two different alleles (e.g., $Tt$).

What is complete dominance?

One allele completely masks the other (e.g., in $Tt$, the $T$ trait is expressed).

What is incomplete dominance?

Neither allele is dominant, resulting in a heterozygous phenotype that is a blend (e.g., $RR = \text{red}$, $WW = \text{white}$, $RW = \text{pink}$).

What is codominance?

Both alleles are fully expressed, such as the $AB$ blood group where both $A$ and $B$ antigens are present.

What is polygenic inheritance?

A trait controlled by many genes, such as human skin colour or height.

What three factors influence an organism's phenotype?

Genotype, Environment, and Epigenetic factors.

How do hydrangeas demonstrate environmental influence?

Acidic soil results in blue flowers, while alkaline soil results in pink flowers.

What are epigenetic modifications?

Changes that affect gene expression without changing the DNA sequence.

What is histone modification?

Changes to histones that alter how tightly DNA is wrapped, which can turn genes on or off without changing the DNA sequence.

What are the two steps of gene expression?

1. Transcription (DNA is copied into mRNA) and 2. Translation (mRNA is used to build a protein).

Which genotypes give the dominant Rhesus phenotype?

$DD$ and $Dd$.