Chromosomes

Chromosomes and Inheritance

Learning Objectives

• Define genes, chromosomes, and their link to DNA.

• Explain how parents pass chromosomes to offspring through sex cells.

• Describe homologous chromosomes, alleles, and their effect on traits.

• Learn to read pedigree charts to trace inherited traits.

• Explain crossing over and its role in genetic diversity.

• Genes are DNA segments with instructions for your traits.

• Chromosomes are coiled DNA, organizing many genes in the nucleus.

• Deoxyribonucleic Acid (DNA) holds the genetic code for life.

• DNA makes genes; genes are on chromosomes in the nucleus.

Genes, Chromosomes, & DNA: Life's Blueprint!

Multiple Choice

What are genes primarily made of?

• Proteins

• DNA

• RNA

• Carbohydrates

​​Body Cells (Somatic Cells)

• Sex cells (sperm/eggs) are for making babies!

• Half set: humans 23 (single), mallards 40.

• Fertilization? Boom! Full, paired set restored!

​​Sex Cells (Gametes)

Chromosome Numbers: Body Cells vs. Sex Cells

• Body cells pack chromosomes tightly in pairs!

• Humans have 46, mallards have 80 (full set).

• They build most of your body's tissues and organs!

Multiple Choice

If a mallard duck has 80 chromosomes in its body cells, how many chromosomes are in its sex cells?

• 20

• 40

• 80

• 160

• Genes are instructions for how your body grows and works.

• They determine your traits, like your unique hair and eye color.

• Humans have thousands of genes on 46 chromosomes.

• Larger chromosomes hold more genes; each gene has a specific spot.

Genes on Chromosomes: Your Body's Master Plan!

Multiple Choice

Approximately how many genes are found on the 46 human chromosomes?

• 1,000-5,000

• 5,000-10,000

• 10,000-15,000

• 20,000-25,000

• You get 23 chromosomes from mom and 23 from dad.

• These form pairs called homologous chromosomes, similar in size and gene order.

• Alleles are different gene versions, like 'purple' or 'white' for flower color.

• Two alleles (same or different) decide how traits show up (e.g., homozygous/heterozygous).

Homologous Chromosomes, Alleles, and Gene Expression

Multiple Choice

What are homologous chromosomes?

• Identical copies of a single chromosome before cell division

• Pairs of chromosomes, one inherited from each parent, that carry genes for the same traits

• Chromosomes that only carry recessive alleles for all traits

• Chromosomes that are exclusively found in sex cells

• Pedigrees are like family trees, mapping traits through generations.

• Symbols: squares are males, circles are females. Lines connect parents.

• Vertical lines show children. Generations use Roman numerals (I, II).

• Shaded symbols show traits. Helps predict future inheritance patterns.

Pedigrees: Charting Family Traits

Multiple Choice

In a standard pedigree chart, what does a circle symbol represent?

• A male

• A female

• An individual expressing the trait

• A deceased individual

• Special sex cells (sperm and eggs) carry genes for new offspring.

• Sex cells have half the chromosomes of an organism's body cells.

• Chromosome pairs separate, so each sex cell gets one from each pair.

• Sperm + egg unite, restoring full chromosomes (e.g., humans: 23+23=46).

Sex Cells: Halving Chromosomes for New Life!

Multiple Choice

What is a zygote?

• A mature sex cell ready for fertilization

• A cell with half the number of chromosomes as a body cell

• A fertilized egg cell, formed by the fusion of a sperm and an egg

• A type of body cell that undergoes rapid division

• Sex cells form; homologous chromosomes pair up and exchange genetic material.

• One chromosome part breaks and swaps with its partner's corresponding part.

• This shuffles genes, creating new allele combinations in sex cells.

• Crossing over boosts genetic diversity, aiding adaptation and evolution.

Crossing Over: Genetic Shuffling!

Multiple Choice

What best describes the process of crossing over?

• Chromosomes making identical copies of themselves

• Homologous chromosomes exchanging corresponding segments of genetic material

• The fusion of sperm and egg to form a zygote

• Genes spontaneously changing into new alleles

​Correction

• Chromosome number doesn't define complexity. Ferns can have more.

• Each chromosome carries hundreds to thousands of genes.

• You get genes from both parents. Allele combinations matter.

• Dominant means expressed if present. Not stronger or more common.
  

​Misconception

Common Misconceptions

• More chromosomes mean more complex.

• Chromosomes carry only a few genes.

• Traits come from parent you look like.

• Dominant alleles are stronger or common.
  

Summary

• Genes on chromosomes determine your traits; alleles are different gene versions.

• You inherit one set of chromosomes from each parent via sex cells.

• Meiosis creates sex cells with half the chromosomes, ensuring genetic diversity.

• Crossing over and chromosome sorting during meiosis create unique gene combinations.

Open Ended

In your own words, explain the relationship between a gene, a chromosome, and DNA.

Poll

If an organism's body cells have 30 chromosomes, how many chromosomes will its sex cells typically have?

• 10

• 15

• 30

• 60

Open Ended

Name one process that occurs during sex cell formation which contributes to genetic variation in offspring.

Poll

On a scale of 1 to 4, how well do you feel you understand the main concepts covered in this lesson? (1=Not at all, 4=Very well)

• 1

• 2

• 3

• 4

Open Ended

What is one concept from today"s lesson that you would like to learn more about or found particularly challenging?