Science Chapter 1.6-9

What is a genotype?

The genetic makeup of an organism, determining inherited traits through specific gene combinations.

What is Homozygous?

Having two identical alleles for a specific gene, either both dominant or both recessive.

What is Heterozygous?

Having two different alleles for a specific gene, one dominant and one recessive.

What is a phenotype?

The observable physical or biochemical traits of an organism, shaped by genotype and environment.

What is a allele?

A different version of a gene that determines specific traits or characteristics.

What are dominant traits?

Characteristics expressed when at least one dominant allele is present in the genotype.

What are recessive traits?

Characteristics only expressed when two recessive alleles are present in the genotype.

What is a Punnett square?

A chart used to predict offspring’s possible genotypes from parental allele combinations.

What does it mean when something is co-dominant?

Both alleles in a gene pair are fully expressed, showing both traits equally.

What are sex chromosomes?

The pair of chromosomes (X and Y) that determine an organism’s biological sex.

What are Autosomes?

Chromosomes that do not determine sex; they carry genes for other traits.

What are Pedigrees?

Diagrams showing the inheritance of traits across multiple generations in a family.

What’s the difference between a dominant and recessive autosomal?

A dominant autosomal trait appears when at least one dominant allele is present, while a recessive autosomal trait appears only when both alleles are recessive.

What’s the difference between a dominant and recessive X- link?

Dominant X-linked appears with one affected X; recessive X-linked usually affects males only.

Explain communicating sex linkages:

Communicating sex linkages means showing how X or Y chromosome traits are inherited and passed.

How many sex chromosomes do people have?

2

What is Hemophilia?

A genetic disorder where blood doesn’t clot properly, causing excessive bleeding.

Explain how Hemophilia works in the body?

Occurs when the body lacks clotting proteins, so blood cannot form clots, causing excessive bleeding from injuries or spontaneously inside joints and muscles.

What are mutations?

Sudden, mostly permanent, changes in the nucleotide sequence of DNA

Where can mutations occur, and can they occur in somatic cells?

Mutations can occur anywhere in genes or non-coding DNA and may happen in somatic cells

Do mutations pass to offspring and how do they affect descendant cells?

Somatic mutations don't pass to offspring but affect descendant cells. Germline mutations can be inherited (may affect gametes)

What role do mutations play in populations?

They create genetic variation in populations, providing the raw material for evolution by natural selection.

What are natural causes of mutations?

Mistakes during DNA replication, chemical reactions inside cells, and environmental factors (e.g., radiation, toxins).

What environmental factors cause DNA mutations?

• Chemical — e.g., cigarette smoke, industrial chemicals, nitrosamines
• Physical — e.g., ultraviolet light, X-rays; they break DNA strands or create abnormal bonds.
• Biological — e.g., some viruses or transposons; they insert into or disrupt genes.

Since mutations from mutagens are random, how might they affect cell-control genes?

It can disrupt genes that control mitosis or apoptosis, potentially leading to uncontrolled cell growth (cancer).

How can certain chemicals cause mutations in DNA?

Some chemicals insert into DNA, disrupting replication. Examples: arsenic, asbestos, cigarette smoke, alcohol.

How does nuclear radiation damage cells?

It creates free radicals (unstable molecules with unpaired electrons) that damage DNA and proteins.

What does UV radiation cause in DNA?

Forms thymine dimers, causing replication and transcription errors.

What are the two main types of mutations?

Genetic mutations affect a single gene, while chromosomal mutations affect multiple genes with much greater impact.

What are the main types of genetic mutations?

Point substitution swaps one base for another, while frameshift mutations shift reading frame, altering entire gene.

What are possible effects of point mutations?

Point mutations may change DNA, mRNA, proteins, or traits, but splicing often makes them silent.

Why are most mutations harmless or neutral?

Most mutations are corrected or silent; many are neutral, while harmful or beneficial mutations are rare.

What causes sickle cell disease and what are its effects?

A single base substitution in hemoglobin gene causes sickled cells, anemia, organ damage, and malaria resistance.

What results from a base change in the beta globin gene?

Causes sickle cell disease, damaging hemoglobin and impairing oxygen transport.

What are examples of beneficial mutations?

Lactose tolerance, antibiotic resistance, German super boy muscle gene, and HIV resistance.

What is a frameshift mutation and its effect?

They insert or delete bases, shifting reading frame, producing faulty proteins with major consequences.

What diseases may result from frameshift mutations?

Tay-Sachs, cystic fibrosis, Crohn’s disease, Charcot-Marie-Tooth, and hypertrophic cardiomyopathy.

What can chromosomal mutations do and their types?

They can change whole chromosomes or parts; types are deletion, inversion, translocation, duplication, nondisjunction.

What is nondisjunction in meiosis?

Occurs when chromosomes fail to separate during meiosis, producing abnormal gametes with incorrect chromosome numbers.

For eye colour (B), what is the genotype and phenotype?

Genotype: Bb. Phenotype: Brown eyes.

Define loci.

The position of a gene along a chromosome.

Define chromosome.

A molecule of DNA coiled around histone proteins, containing many genes.

Define carrier.

A heterozygous individual showing a dominant phenotype but carrying a recessive allele.

What chance do two right-handed parents have of producing a left-handed child?

25% chance.

Why is it preferable for patients to receive the same blood group in transfusions?

Receiving unmatched proteins can cause dangerous blood clots, blocking vessels and potentially leading to death.

What percentage of individuals are rhesus negative?

20% are rhesus negative; 80% have rhesus markers on their red blood cells.

Name the term used to describe traits and genes that are carried on the sex chromosomes.

Sex-linked

Explain why there is a greater percentage of males than females that have red, green color blindness

Red, green color blindness is X-linked; males need one faulty allele, females need 2.

Suggest how a man and woman, both with normal sight, could have children that have red, green color blindness.

The woman must be a carrier with the genotype XcX. The male has normal sight so must have the genotype XY.