Reproduction and Genetics

Chapter 16 Section 4

DNA and Genes• Parents pass their characteristics on to their offspring• Heredity- process in which characteristics pass from

parents to offspring• Genetics- scientific study of heredity• Traits- organism’s physical characteristics• Traits are controlled by the genetic materials in an

organisms chromosomes (rodlike structures located in the nucleus of the cell)

• Chromosomes also control an organism’s inherited characteristics

• Chromosomes are made partly of long-chain molecules called DNA

• DNA contains segments called genes• Gene- a segment of DNA molecule that contains

information that governs a specific trait

Sexual Reproduction

• Sexual reproduction- reproduction involving 2 parents whose combined genetic material produces a new organism

• Male sperm cell joins with a female egg cell to produce offspring

• Egg an sperm cells contain half the number of chromosomes that are in the other cells

Asexual Reproduction• Asexual reproduction- the reproductive process in

which the offspring have only one parent• Offspring of asexually reproducing organisms

inherit genes from only that parent; therefore they are genetically identical to the parent

• Sexual reproduction results in offspring that are not exactly like either parent.

• Offspring of sexually reproducing organisms are more diverse than the offspring of those that reproduce asexually

Alleles

• Traits are controlled by genes• Chromosomes exist in pairs• Both chromosomes in a pair have the same

genes• Allele- different forms of a gene• An organism has 2 alleles for each trait, one from

each parent

Dominant and Recessive Alleles

• Dominant allele- one whose trait always shows up in the organism

• Recessive allele- hidden, covered up trait in an organism

• Two dominant alleles express the dominant trait• Two recessive alleles express the recessive trait• One dominant and one recessive trait expresses

a dominant trait

Review• What is a gene?

• Why are offspring that result from asexual reproduction so much like their parents, while the offspring of sexually reproducing organisms are not exactly like their parents?

• What is the difference between a dominant and recessive allele? Give an example.

• What kind of alleles must an organism inherit in order for a recessive trait to show up?

• Baby Amanda Ortiz inherited one allele for attached earlobes and one for free earlobes. Predict the shape of her earlobes.