Unit 6 Section 4: Chromosomes & Inheritance

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Unit 6 Section 4 Chromosomes & Inheritance

A genetic technologist studies the chromosomes in cells. They analyze the information on them and try to pinpoint the causes of many diseases, hoping to cure them

Multiple Choice

What does the notation TT mean to geneticists?

• Two dominant alleles

• heterozygous alleles

• at least one dominant allele

• one dominant and one recessive allele

Multiple Choice

What is the probability of producing a tall pea plant from a genetic cross between two hybrid tall pea plants?

• one in four

• two in four

• three in four

• four in four

Multiple Choice

What does a Punnett square show?

• all the possible outcomes of a genetic cross

• only the dominant alleles in a genetic cross

• only the recessive alleles in a genetic cross

• all of Mendel’s discoveries about genetic crosses

Lesson Objectives

• Describe the role chromosomes and genes play in inheritance

• Identify the events that occur during meiosis

What is A Chromosome?

• Chromosome: a Long DNA molecule that carries the genetic information of an organism

  • Different species have different numbers of Chromosomes

What is A Chromatid

• Chromatid: One-half of a chromosome

  • Two Chromatids are joined at a Centromere

The Clue in the Grasshoper's Cells

• Mendel proved that genes existed, but no one knew where they were in the body

• Early 1900's: Walter Sutton studied grasshoppers

  • He wanted to understand how the sex cells formed

    • Noticed how chromosomes moved in cells during their creation

  • Hypothesized that chromosomes are key to learning how genes pass from parents to offspring

Chromosomes and Inheritance

• When Sutton looked at grasshopper cells, he found that their sex cells had half as many chromosomes as their body cells

  • The combination of the two sex cells gave the offspring the total number of chromosomes

• He noticed that the chromosomes came in pairs just like alleles

  • Realized that Alleles were carried on chromosomes

Chromosomes Theory of Inheritance

• Chromosome Theory of Inheritance:

  • Genes pass from parents to offspring on their chromosomes

  • Each parent gives half of the chromosomes to their offspring

  • Mutations/damage to chromosomes affect how traits are shown

Chromosomes

• Humans have 23 pairs of chromosomes

  • A total of 46

• Each chromosome carries multiple genes in them

  • The human body contains between 20,000 and 25,000 genes

  • Each Gene is made up of two alleles

Multiple Choice

For Gene A, is the owner of this chromosome homozygous or heterozygous

• Homozygous

• Heterozygous

Multiple Choice

For Gene F, is the owner of this chromosome homozygous or heterozygous

• Homozygous

• Heterozygous

Multiple Choice

For Gene B, is the owner of this chromosome homozygous or heterozygous

• Homozygous

• Heterozygous

Dropdown

When two grasshopper sex cells join, the chromosome number in the new body cell has ​

Select answer

the number of chromosomes in the sex cells.

Meiosis

• Meiosis: The process by which the number of chromosomes is reduced by half as sex cells form.

  • Forms new sex cells, not body cells

  • A cell divides into two cells, which then divide again to form four cells

  • A key part of sexual reproduction

Meiosis stages

• There are two stages to meiosis

• Follow the same pattern of Mitosis, but does each one twice

  • Prophase

  • Metaphase

  • Anaphase

  • Telophase

Meiosis Stage 1

• Before Meiosis begins, each chromosome in a cell is copied

• The Chromosomes move to the center of the cell and separate

• Two cells are formed with half of the number of chromosomes

  • Each Chromosome has two Chromatids

Meiosis Stage 2

• The chromosomes in the two cells move to the center and split into separate chromatids

• The two cells then split into four cells, each with one chromatid

Multiple Choice

True or False: Body Cells of Humans contain 46 pairs of Chromosomes

• True

• False

Multiple Choice

True or False: Sex Cells have twice the number of chromosomes as body cells

• True

• False

Multiple Choice

True or False: Genes Pass from parents to offspring on chromosomes

• True

• False