Rendell/Walz

Period 2

Chapter 6 Introduction to Genetics

Key Words

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Notes

Heredity / Set of characteristics an organism receives from its parents.
Genetics / Study of heredity.
Gregor Mendel / Pioneer of genetics
Traits / Characteristic that distinguishes one individual from another.
Hybrid /
  • Offspring of parents with different characteristics.
  • F1 generation (F = filusson )

P generation /
Parentis  of the parent
F1 generation / First generation of offspring from the P generation
F2 generation / Second generation which is produced when the F1 generation are crossed among themselves.
Gene / Unit that determines traits.
Alleles / Different forms of a gene.
Dominant allele / Form of allele that is expressed.
Recessive allele / Form of allele that is not expressed.
Phenotype / Form of trait that it displays (physical appearance).
Genotype / Genetic composition of organism.
Homozygous / Organisms with identical pair of alleles, ex. TT or tt .
Heterozygous / Organisms with mixed pair of alleles, ex. Tt.
Segregation / Process that separates the two alleles of gene.
Independent assortment / Genes that segregate independently, ex. Genes for seed shape and color do not influence each other’s inheritance.

Key Words

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Notes

Gametes /
  • Reproductive cell
  • Contain half the number of chromosomes (one set)
  • Human cells  46 chromosomes
  • Human gametes (sperm and egg cells)  23 chromosomes

Haploid cell
Diploid cell /
  • Contains only one set of chromosomes (n).
  • Contains a double set of chromosomes (2n).

Meiosis
Meiosis I
Meiosis II /
  • Process of cell division.
  • Number of chromosomes in a diploid cell is reduced by half.
  • End products  Four haploid cells

Meiosis I /
  1. Each chromosome is replicated.
Duplicate chromatids are formed.
Chromatids are joined at centromeres.
  1. Prophase I - like prophase of mitosis.
  • Chromosomes uncoil.
  • Spindle apparatus forms.
  • Crossing over
  1. Metaphase I
  • homologous chromosomes (corresponding chromosomes) pair together.
  • Chromosomes line up in center of cell.
  • Paired chromosomes form structures called tetrads.
  • Independent Assortment occurs here
  1. Anaphase I
  • Homologous chromosomes are pulled toward opposite sides of cell.
  1. End products of meiosis I  two haploid (n) daughter cells.

Meiosis II /
  • Two daughter cells undergo a second round of cell division.
  1. Metaphase II
  • Chromosomes line up as in metaphase of mitosis.
  1. End products of meiosis II four haploid cells.

Crossing Over / Switches alleles from one chromosome to another.
Probability and Genetics / Probability applies to genetics because formation of gametes depends on random events.

Key Words

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Notes

Incomplete Dominance /
  • Heterozygote phenotype is somewhere between the two homozygous phenotypes.
  • Example: (RR) x (rr)  (Rr)
Red x white pink
Codominance /
  • Both alleles affect phenotype.
  • Example: roan horses have 2 colors in their coats.

Multiple Alleles /
  • Genes with more than two alleles.
  • Example: genes for blood group and eye color.

Polygenic Traits / Traits controlled by more than one gene.

Answer the Following

1._____ What type of allele is always expressed?

a. dominant alleleb. homologous allele

c. recessive alleled. incomplete allele

2._____In pea plants, the tallness or shortness is known as

a. genotypeb. phenotype

c. dominanced. gametes

3._____ The haploid number of chromosomes for a human is

a. 23b. 26c. 46d. 92

4._____ Cells that contain only a single set of chromosomes are

a. homologousb. haploid

c. diploidd. heterozygous

5._____ Which process reduces the number of chromosomes in a diploid cell by half to produce gametes?

a. mitosisb. codominancec. crossing-overd. meiosis

6. _____An identical pair of alleles for a trait(TT or tt) has what type of genotype?

a. homologousb. homozygousc. heterozygousd. segregation

7._____ Crossing different true-breeding(purebred) stocks produces offspring called

a. P generationb. F2 generationc. cross-oversd. hybrids

8._____ The different forms of a gene are called

a. traitsb. allelesc. gametesd. hybrids

9._____Crossing over is the exchange of genetic information between

a. reproductive cellsb. diploid cells

c. any 2 chromosomesd. homologous chromosomes

10. In a pea plant, axial flower position is dominant over terminal flower position. What genotype and phenotype ratios will result if a heterozygous axial pea plant is crossed with a pea plant with terminal flowers? (Show work)

11. During metaphase I of meiosis, homologous chromosomes line up at the equator of a cell.

A) Diagram this in a cell with four chromosomes.

B) Label: chromosome, chromatid, spindle fiber, pole, centromere, tetrad

C) Explain what happens next.

12.

13. A female horse that is pure black and a pure trotter is crossed with a male horse that is hybrid for both traits.

A) What are the genotypes of the parents?

B) What gametes are produced by each of the parents?

C) Draw a Punnet square representing this cross.

D) What are the genotypic and phenotypic ratios that result?

Genotype:

Phenotype:

During which phase(s), does following occur? Write the correct answer on the line provided. For some, there may be more than one answer.

S phase of Interphase Prophase I Prophase II Metaphase I

Metaphse IIAnaphase IAnaphase IITelophase I

Telophase II

1. ______The chromosomes line up as a tetrad at the equator.

2. ______The chromosomes move to the poles.

3. ______The spindle fiber shortens.

4.______DNA synthesis occurs.

5. ______Homologous chromosomes pair up at the equator.

6. ______The cell membrane pinches forward.

7. ______The sister chromatids divide and move apart.

8.______Chromosomes lined up at the equator is not in a tetrad.

9.______Homologous chromosomes BEGIN to pair up.

10.______Sister chromatids, still joined, move toward the poles.