🧬 Genetics (Chapters 9–10)- Bio Exam 3

Q: Who is considered the father of genetics?

A: Gregor Mendel

Q: What organism did Mendel use in his experiments?

A: Pea plants

Q: Why did Mendel choose pea plants for his experiments?

A: They grow quickly, reproduce easily, and have visible traits with contrasting forms.

Q: What is a trait?

A: A characteristic that can vary from one individual to another.

Q: What is a gene?

A: A segment of DNA that codes for a specific trait.

Q: What are alleles?

A: Different versions or forms of a gene.

Q: What does it mean if an organism is homozygous for a trait?

A: It has two of the same alleles (like TT or tt).

Q: What does heterozygous mean?

A: It has two different alleles (like Tt).

Q: What is a genotype?

A: The genetic makeup of an organism (the alleles it has).

Q: What is a phenotype?

A: The physical expression or appearance of a trait.

Q: What is Mendel’s Law of Segregation?

A: Allele pairs separate during gamete formation; offspring receive one allele from each parent.

Q: What is Mendel’s Law of Independent Assortment?

A: Genes for different traits separate independently during gamete formation.

Q: What is a Punnett square used for?

A: To predict the possible genotypes and phenotypes of offspring.

Q: What is the difference between dominant and recessive alleles?

A: A dominant allele shows its trait if present; a recessive one only shows if both alleles are recessive.

Q: What is a monohybrid cross?

A: A genetic cross that tracks one trait.

Q: What is a dihybrid cross?

A: A genetic cross that tracks two traits at once.

Q: What is incomplete dominance?

A: When neither allele is completely dominant and the heterozygous phenotype is a blend (like red + white = pink).

Q: What is codominance?

A: When both alleles are fully expressed (like AB blood type).

Q: What are multiple alleles?

A: Traits controlled by more than two alleles (e.g., blood type).

Q: What are polygenic traits?

A: Traits controlled by two or more genes (e.g., height, skin color).

Q: What are sex-linked traits?

A: Traits carried on sex chromosomes (usually the X chromosome).

Q: Why are males more likely to express sex-linked disorders?

A: Males have only one X chromosome, so one recessive allele is enough to show the disorder.

Q: Give an example of a sex-linked disorder.

A: Color blindness or hemophilia.

Q: What are autosomes?

A: Chromosomes that are not sex chromosomes (in humans, pairs 1–22).

Q: What are sex chromosomes?

A: Chromosomes that determine biological sex (X and Y).

Q: What is a pedigree chart used for?

A: To trace inheritance of traits through generations of a family.

Q: What do circles and squares represent in a pedigree?

A: Circles = females, squares = males.

Q: What does a shaded shape in a pedigree mean?

A: The individual shows the trait being studied.

Q: What does meiosis produce?

A: Four genetically different haploid gametes (sex cells).

Q: What does haploid mean?

A: A cell with one set of chromosomes (n).

Q: What does diploid mean?

A: A cell with two sets of chromosomes (2n).

Q: How many chromosomes do humans have in somatic (body) cells?

A: 46 (23 pairs).

Q: How many chromosomes are in human gametes?

A: 23.

Q: What happens during crossing over?

A: Homologous chromosomes exchange pieces, creating new gene combinations.

Q: During what phase does crossing over occur?

A: Prophase I of meiosis.

Q: What is the main difference between mitosis and meiosis?

A: Mitosis makes identical diploid cells; meiosis makes unique haploid gametes.

Q: Why is meiosis important for genetic variation?

A: It mixes genes through crossing over and independent assortment.

Q: What is nondisjunction?

A: The failure of chromosomes to separate properly during meiosis.

Q: What can nondisjunction lead to?

A: Chromosome number disorders like Down syndrome (trisomy 21).

Q: What is fertilization?

A: The fusion of male and female gametes to form a zygote.

Q: What is a zygote?

A: The first cell of a new organism formed from fertilization.

Q: What is the relationship between genes, DNA, and chromosomes?

A: Genes are segments of DNA, and DNA coils into chromosomes.