Genetics

Warm Up Exercise: -Using your previous knowledge of genetics, determine what maternal genotype would most likely yield offspring with such characteristics. -Use the genotype that you came up with for the mother, to complete a punnett square.

Agenda •  Warm up exercise and discussion •  Lesson: inheritance, sexual and asexual

reproduction, karyotypes, and chromosomes. •  Meiosis inquiry activity •  Genetic disease projects •  Exit slip

Learner Outcome: I can differentiate between sexual and asexual reproduction. I can explain how chromosomes are inherited and explain the concept of homologous chromosomes.

Defining Key Terms

•  Heredity- the transmission of traits from one generation to the next.

•  Variation- differences between members of the same species.

•  Genetics- the scientific study of heredity and hereditary variation.

•  Meiosis- a modified type of cell division in sexually reproducing organism consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell.

•  Gene- a unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA in some viruses). –  A gene’s specific location along the chromosome is

called the gene’s locus. •  Gametes- reproductive cells that transmit genes

from one generation to the next.

Sexual vs. Asexual Reproduction

•  Asexual Reproduction- a single individual is the sole parent and passes copies of all its genes to its offspring. As a result, the offspring are an exact copy of themselves (a clone).

•  Sexual Reproduction- two parents give rise to offspring that have unique combinations of genes inherited from two parents. Offspring of sexual reproduction vary genetically to their siblings and both parents.

Karyotypes

•  Karyotype- a display of the chromosome pairs of a cell arranged by size and shape. –  22 pairs of autosomes –  1 pair of sex chromosomes

Sister chromatids

Pair of Homologous Replicated Chromosomes

Centromere

Fig.

Key Maternal set of chromosomes (n = 3) Paternal set of chromosomes (n = 3)

2n = 6

Centromere

Two sister chromatids of one replicated chromosome

Two nonsister chromatids in a homologous pair

Pair of homologous chromosomes (one from each set)

Exit Slip •  Provide the following information on a note card.

–  List two authentic examples of offspring that reproduce sexually and two that reproduce asexually.

–  How are homologs similar, and how are they different?

–  The fruit fly, Drosophila melanogaster has a chromosome number of 4. Draw a picture of this cell.

Homework: –  Finish reading chapter 13 and complete reading

guide- due Friday! –  Work on genetics disease project.

Agenda

•  Warm Up: Meiosis/Mitosis Compare and Contrast •  Lesson: Meiosis •  Lab 3: Mitosis/Meiosis •  Exit slip

Learner Outcome: I can compare and contrast between meiosis and mitosis. I can explain the causes of genetic variation.

The Human Life Cycle

•  Fertilization- the union of haploid gametes to produce a zygote. –  Meiosis- gametes (sex cells) reproduce by meiosis

Fig. 13-7-3 Interphase

Homologous pair of chromosomes in diploid parent cell

Chromosomes replicate

Homologous pair of replicated chromosomes

Sister chromatids Diploid cell with

replicated chromosomes

Meiosis I

Homologous chromosomes separate

1

Haploid cells with replicated chromosomes

Meiosis II

2 Sister chromatids separate

Haploid cells with unreplicated chromosomes

Metaphase I

Fig. 13-8a

Prophase I Anaphase I Telophase I and Cytokinesis

Centrosome (with centriole pair)

Sister chromatids Chiasmata

Spindle

Homologous chromosomes

Fragments of nuclear envelope

Centromere (with kinetochore)

Metaphase plate

Microtubule attached to kinetochore

Sister chromatids remain attached

Homologous chromosomes separate

Cleavage furrow

Fig. 13-8d

Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis

Sister chromatids separate Haploid daughter cells

forming

SUMMARY

Genetic Variation

•  Independent Assortment of Chromosomes- allele pairs separate independently during the formation of gametes.

Fig. 13-11-3

Possibility 1 Possibility 2

Two equally probable arrangements of chromosomes at

metaphase I

Metaphase II

Daughter cells

Combination 1 Combination 2 Combination 3 Combination 4

Genetic Variation

•  Crossing Over- the exchange of genetic material between nonsister chromatids during prophase I of meiosis.

Fig. 13-12-5 Prophase I of meiosis

Pair of homologs

Nonsister chromatids held together during synapsis

Chiasma

Centromere

Anaphase I

Anaphase II

Daughter cells

Recombinant chromosomes

TEM

Genetic Variation

•  Random Fertilization- there are over 70 trillion possible diploid combinations of a zygote during fertilization. This makes each individual truly unique.

•  Mutations

Exit Slip •  Meiosis II is similar to mitosis in that:

a)  Sister chromatids separate during anaphase. b)  DNA replicates before the division. c)  The daughter cells are diploid. d)  Homologous chromosomes synapse. e)  The chromosome number is reduced.

•  Homework:

–  Finish lab questions. –  Read chp. 14, section 1. Complete reading guide. –  Study for quiz (tomorrow). –  Genetics presentation research due next class.