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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.
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.
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
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.
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