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Heredity and Evolution -

Essential Question: What processes are responsible for life’s unity and diversity?

8.2 — Reproduction is a characteristic of living systems and it is essential for the continuation of every species.

GRADE-LEVEL CONCEPT 8.2.a

Heredity is the passage of genetic information from one generation to another.

(Students should understand that ...)
1. Living organisms must reproduce to continue the existence of their species. Through reproduction new individuals which resemble their parents are formed. All the organisms alive today arose from preexisting organisms.
2. All the cells in a multicellular organism result from a single fertilized egg cell, through a process of continuous cell divisions (mitosis). Instructions for how an organism develops are stored in DNA molecules which are part of the chromosomes inside the cell nucleus.
3. The chromosomes occur in matching pairs, and each cell in a multicellular organism contains the number of chromosomes that are typical of that species. For example, cells in human beings contain 23 pairs of chromosomes; 46 in all.
4. Organisms grow by increasing the number of body cells. During mitosis, a body cell first duplicates the chromosomes and then divides into two identical daughter cells, each one with a complete set of chromosomes.
5. Most multicellular organisms reproduce by sexual reproduction, in which new cells are produced by the combination of two germ cells (gametes). During meiosis, matching chromosomes in each pair separate from each other so that each germ cell contains only half of the chromosomes of the original cell.
6. Mitosis and meiosis are similar processes in that they both result in the separation of existing cells into new ones. They differ in that the germ cells produced during meiosis have only one copy of each chromosome. When two germ cells unite during fertilization, the resulting zygote has two copies of each chromosome, one from each parent, ensuring maternal and paternal genetic contribution.
7. Meiosis and gamete formation takes place in the reproductive organs; testes in males produce the sperm and ovaries in females produce the eggs.
8. In humans, the reproductive organs are in place at birth, but are readied to perform their reproductive functions by hormones released during adolescence. Males produce millions of sperm over the course of their adult life. Females are born with a finite number of immature eggs in the ovaries that are released one at a time in a monthly cycle.
9. In humans, if an egg is fertilized by a sperm in the female’s fallopian tube, the resulting zygote may develop into a fetus in the female uterus. If the egg is not fertilized, it will leave the female’s body in a monthly discharge of the uterine lining (menstrual cycle).
10. A segment of DNA that holds the information for a specific trait is called a gene. Each chromosome in a pair carries the same genes in the same place, but there are different versions of each gene.
11. In sexual reproduction, offspring of the same parents will have different combinations of genes and traits, creating genetic variability within the species. Sexual reproduction is the basis for the evolution of living organisms.

C25. Explain the differences in cell division in somatic and germ cells.
C26. Describe the structure and function of the male and female human reproductive systems, including the process of egg and sperm development.

GRADE-LEVEL CONCEPT 8.2.b

Some of the characteristics of an organism are inherited and some result from interactions with the environment.

(Students should understand that ...)
1. Gender in humans is a trait determined by genes carried by a special pair of chromosomes identified as “X” and “Y”. Female gametes have only an “X” chromosome; male gametes can have either an “X” or a “Y”. The sperm that fertilizes the egg determines the sex of the offspring: a zygote containing two X chromosomes will develop into a female and a zygote containing X and Y chromosomes will develop into a male.
2. Most human traits are inherited from parents, but some are the result of environmental conditions. For example, eating and exercising habits may affect the body mass and shape of individuals in the same family.

C27. Describe how genetic information is organized in genes on chromosomes, and explain sex determination in humans.

Grade Level Expectations

(Students should be able to ...)

1. Relate the continued existence of any species to its successful reproduction and explain in writing the factors that contribute to successful reproduction.
2. Describe the structure, location and function of chromosomes, genes and DNA and how they relate to each other in the living cell.
3. Illustrate and chart the purpose, cell type (somatic and germ) and resulting chromosome count during cell division in mitosis and meiosis.
4. Identify the major structures in human male and female reproductive systems and explain where meiosis and gamete formation take place.
5. Investigate and report on the role of hormone production as it initiates and regulates the creation of male and female germ cells from birth through adolescence and into adulthood.
6. Compare and contrast the events and processes that occur when a human egg is fertilized or not fertilized.
7. Demonstrate the relationship of corresponding genes on pairs of chromosomes to traits inherited by offspring.
8. Describe in writing the role of the germ cells in the formation of the human zygote and its resulting 23 pairs of chromosomes, the 23rd of which determines gender and the other 22 of which determine the characteristics of that offspring.

SCIENTIFIC LITERACY TERMINOLOGY: multicellular organism, heredity, trait, chromosome, gene, DNA, species, mitosis, meiosis, gamete, adolescence, hormone, testes, sperm, ovary, egg, fallopian tube, uterus